INHERITANCE

Chapter 15

INHERITANCE

Q.1. Define genetics. What do you meant by traits?
Ans. Genetics is the branch of biology in which we study inheritance. Inheritance means the transmission of characteristics from parents to offspring. These characteristics are called the traits. For example; in man height, colour of the eyes, intelligence etc. are all inheritable traits.

Q.2. What are genes? What is the relationship between genes and chromosomes?
Ans. Parents pass characteristics to their young through gene transmission. Equal number of chromosomes from each parent are combined during fertilization. The chromosomes carry the units of inheritance called the genes.
Genes consist of DNA. They contain specific instruction for protein synthesis. In order to know the nature and working of genes, we will have to study chromosomes in detail. The body cells have a constant number of paired chromosomes. The two chromosomes of a pair are known as homologous chromosome. In human body cells, there are 23 pairs of homologous chromosomes for a total of 46 chromosomes. We may recall that during meiosis, the two members of each chromosome pair separate and each of-them enters onegarnete.
Chromosome are made of chromatin material (simply as chromatin). Chromatin is a complex material, jnade of ONA and proteins (mainly histpne proteins). DNA wraps around histone proteins and forms round structures, called nucleosomes. DNA is also present between nucleosomes. In this way, the nucleosomes and the DNA between them look like “beads on a string”. The fibres consisting of nucleosomes condense into compact form and get the structure of chromosomes. Figure 15.1
__. Nucleosome DNA between

Q.3. Describe the Watson-Crick . i—————i nucleosomes
model of DNA. DNA Ans. Watson-Crick Model of DNA
In 1953, James Watson and
Francis Crick proposed the
structure of DNA. According to
the Watson^Crick nodel, a
DNA molecule consists of two Proteins
polynucleotide strands. These (Histories)
strands are coiled around each
other in the form of a double Figure 15.1 Chemical composition of chromosome
helix. There is a phosphate-sugar backbone on the outside of double helix, and
the nitrogenous bases are on the inside. •
108
Q.4.In double helix, the nitrogenous bases of opposite nucleotides form pairs through hydrogen bonds. This pairing is very specific. The nitrogenous base adenine of one nucleotide forms pair with the thymine of opposing nucleotide, while cytosine forms pair with guanine.
There are two hydrogen bonds between adenine and thymine while there are three hydrogen bonds between cytosine and guanine. Figure 15.2
How DNA Replication occurs?
Polynucleotide strands
Phosphate-sugar backbone
Double helix
H bonds
-Nitrogenous bases
– Phosphate
-Sugar
Ans. DNA Replication „_
FigtireJ$2 The Watson and Crick model of DNA
Before a cell divides, its DNA -“*
is replicated (duplicated). It is done to make the copies of
the chromatids of chromosomes. During replication, the DNA double helix is unwound and the two strands are separated, much like the two sides of a zipper. Each strand acts as a template to produce another strand. Its N bases, (nitrogenous bases) make pairs with the N-bases of new nucleotides. In this way, both template strands make new
Double helix is unwound
Strands are separated
Template strands
2 strands of Parent DNA
New nucleotides

Figure 15.3 DNA replication.

New strands
New DNAs
polynucleotide strands in front of them. Each template and its new strand together then form a new DNA double helix, identical to the original. Figure 15.3

Q.5. How Does the DNA of Chromosome work?

Ans. DNA-Genetic Material
DNA is the genetic material i.e. it contains the instructions to direct all the functions of cells. It performs its role by giving instructions for the synthesis of
Chrbmatids
Centromere
The sequence of DNA nucleotides is copied in the ‘ i form of mRNA
Ribosome reads the mRNA
sequence of nucleotides and
Joins specific amino acids
DNA of chromosome
Specific.protein
: (structural protein or enzyme).
‘: makes the characteristic of the
cell and organism

Figure 15.4 Working of DNA-the central dogma

specific proteins. Some proteins perform structural roles while the others act as enzymes to control all biochemical reactions of cells. In this way, whatever a cell does, is actually controlled by its DNA. In other words, DNA makes the characteristic or trait of cell or organism. Figure 15.4
Transcription
Traits are made by specific proteins. Specific proteins have specific number and sequence of their amino acids. DNA controls this sequence of amino acids by the. sequence of its nucleotides. During protein synthesis, the sequence of DNA nucleotides decides that what will be the sequence of amino acids. For this purpose, the specific sequence of DNA nucleotides is copied in the form of messenger RNA (mRNA) nucleotides. This process is called transcription.
Translation
The mRNA carries the sequence of its nucleotides to rtbosoroe. The ribosome reads this sequence and joins specific amino acids, according to it, to form • protein. This step is known as translation.
Gene
The part of DNA (sequence of nucleotides) that contains the instructions for the synthesis of a particular protein is known as a gene. DNA of each chromosome contains thousands of genes. Like chromosomes, genes also occur in pairs, one on each homologous chromosome. The locations or positions of genes on chromosomes are known as loci. • ,
Each gene determines a particular trait in an organist. Each individual carries at least one pair of genes for each trait. For convenience, pairs of genes are represented by a letter or symbol. Both members of a gene pair may be the

same in some individuals (a condition which we may represent as AA or aa or BB) and different in others (Aa or Bb). It means that a gene exists in more than one alternate forms. In the above example, ‘A’ and ‘a’ are the two alternate forms of a gene and ‘fi’ and ‘b’ are the alternate forms of another gene.
Alleles
The alternate forms of a gene are called alleles. If an individual has Aa gene pair, ‘A is located on one of the two homologous chromosomes and the allele ‘a1 is on the other chromosome. When chromosomes separate during meiosis, alleles also separate and each gamete gets one of the two allelrs. When gametes of both parents .unite, tne zygote (and the offspring also) receives one allele from each parent. Figure 15.5
Figure 15.5 Location of alleles on chromosomes

Q.6. What is genotype? Define their types.

Ans. Genotype and its Types Genotype
The specific combination of genes in an individual is known as genotype.
Types
It is of two types, i.e. i) homozygous and ii) heterozygous.
Example
In order to understand the concept of genotype, let us consider an example trait i.e. albinism (a condition in which normal body pigments are absent). Like other traits, it is also controlled by one pair of genes. We can represent the two alleles of the pair as ‘A’ and ‘a’. Three combinations i.e. genotypes are possible for these two alleles i.e. AA, Aa, and aa. These genotypes can be grouped into two types.
The genotype in which the gene pair contains two identical alleles (AA or aa) is called homozygous genotype.
The genotype in which the gene pair contains two different alleles (Aa), is called heterozygous genotype.

Q.7. What do you mean by dominant and recessive alleles?
Ans. When in the heterozygous condition one allele masks or prevents the expression of the other, it is called the dominant allele. The allele whiqh is not expressed is called Recessive. A dominant allele only suppresses the expression of recessive allele. It does not affect its nature.
Presentation
The dominant alleles are represented by capital letters and recessive alleles b’ lower case letters.
Example
Albinism is a recessive trait i.e. it is produced when both alleles are recessive. In humans, allele ‘A’ produces normal body pigments while allele ‘a’ does not produce pigments, If genotype is AA or Aa, the individual will produce pigments. On the other.hand if genotype is aa, no pigments will be produced and the individual will be albino. In this example, we see that the allele ‘A’ dominates over ‘a’, because in Aa individual pigmepts are., produced and the effect of ‘a’ is suppressed by ‘A’.

Q.8. Define Phenotype. ‘
Ans. The expression of the genotype in the form of trait (in our example, being albino or having normal pigmentation) is known as the phenotypc.

Q.9. Who is Gregor Mendel? Why, he is famous for?
Ans. Gregor Mendel was a monk (priest) in Austria. He developed the fundamental principles of genetics. Mendel proposed that there are “special factors” in organisms, which control the expression of traits and their transmission to next generations. These factors”were eventually termed genes.

Q.10. Why Mendel selected pea plant as his experimental tool?
Ans. Mendel selected pea plant (Pisum sativum) to carry out a large number of experiments. In his writings, he gave reasons for this selection. He argued that an organism for genetic experiments should have the following features: ,
• There should be a number of different traits that can be studied. Figure 15.6
• The organism should have contrasting traits e.g. for the trait Of height there should ^ only two very different phenotypes i.e. tallness and dwarfness.
• The organism (if it is a plant) should be self-fertilizing but cross fertilization should also be possible.
» The organism should have a short but fast life cycle.
All these features are present in pea plant. Normally, the flowers of pea plant allow self-pollination. Cross pollination can also be done by transferring the pollen grains from the flower on one plant to the flower on another plant. Each trait studied in pea plant had two distinct forms. Mendel’s succeeded in his work not only because he selected the right organisms for his experiments but also because he analyzed the results by using the principles of statistics (ratios).
Q.11. Describe Mendel’s Law of Segregation.

Ans. Mendel’s Law of Segregation
Mendel studied the inheritance of seed shape first. For this purpose, he crossed (reproduced) two plants having one contrasting trait i.e. seed shape, A cross in which only one trait is studied at a time, is called as a monohybrld cross.
Explanation .
Mendel crossed a true-breeding round-seeded plant with a true-breeding * wrinkled-seeded plant. All resulting seeds of the next generation were round. Mendel declared the trait “round*seeds” as dominant, while “wrinkled seeds” as recessive. The following year, Mendel planted these seeds and allowed the new plants to self-fertilize. As a result, he got 7324 seeds: 5474 round and 1850 wrinkled (3 round: 1 wrinkled). ”

Figure 15.6 The seven traits in pea plant studied by Mendel
P1 generation
The parental generation is denoted as P1 generation.
F1 generation
The offspring of P1 generation are F1 generation (first filial).
F2 generation
The cross in F1 generation produces F2 generation (second filial).
Similarly, when “true-breeding” tall plants were crossed with “true-breeding” short plants, all offspring of F1 were tall plants i.e. tallness was a dominant trait. When members of Ft generation were self-fertilized, Mendel got the ratio of tall to short plants in F2 as 3:1 Figure 15.7
Conclusion
Mendel concluded that the traits under study were controlled by discrete (separable) factors or genes. In each organism, the genes are present in pairs. During gamete formation, the genes (alleles) of each pair segregate from each other and each gamete receives one gene from the pair. When the gametes of male and female parents unite the resulting offspring again gets the genes in pairs. These conclusions were called the Law of Segregation.
Parental generation
F1 generation
Round Wrinkled
F1 XF1
F2 generation
Round
Round
75% 25% Round Wrinkled

Parental

RR rr
F1 Round
Rr
Rr
generation (Round X Winkled)

€> x<ity
r x
F1 Round
f>xf>

1

I 1
1
I
I

Gametes
o o|
Gametes
oo
OO

I

\s
«U* • •
1
1
/ \

F1
r
Rr /
F2

O
O

generation

$s

generation
o
1
Rr

All Round

Rr
rr

i

o

&

75 % Round : 25% Wrinkled

Figure 15.7 Illustration Law of segregation

Q.12. Describe Mendel’ Mendel’s Law of Independent Assortment

Ans. Mendel’s Law of Independent Assortment
Mendel studied two contrasting traits at a time. Such crosses are called dihybrid crosses. He performed experiments on two seed traits i.e.”Shape and colour
iv^ilSL k “i?! S!6dS (controlled &y a»ele R) was dominant over wrinkled (con rolled by allele r) seeds. Similarly yellow seed colour (controlled by Y) was dominant over green (controlled by y). * • Cross
Mendel crossed a true-breeding plant that had round yellow seeds (RRYY) with a true-breeding plant having wrinkled green seeds (rryy). All seeds in F1 generation were round yellow.
Result
When F1 seeds grew into plants, they were self-fertilized, This cross produced seeds with four phenotypes. There were 315 round yellow seeds, 108 round
generation
Gametes
generation
RRYY
rryy
Round, Yellow
Wrinkled, Green
RrYy
All Round, Yellow
F1 X F1
Gametes
F2° generation
RrYy
RrYy
Round, Yellow
Round, Yellow
Gametes from RrYy parent
cc
I
ro CD
• RRYY
* RRYy
RrYY
.* RrYy
RRYy
€>
Rryy
RrYy
Rryy rrYy
RrYY
RrYy
rrYY
RrYy
Rryy
rrYy
rryy
Punnett Square-
Figure 15.8 Illustration Law of Independent Assortment with the help of Punnett square
green seeds, 101 wrinkled yellow seeds and 32 wrinkled green seeds. The of these phenotypes was 9:3:3:1. Figure 15.8
Explanation
Mendel explained that the two traits i.e. seed shape and seed colour are not tied| with each other. The segregation of ‘R’ and V alleles happens independently of| the segregation of ‘Y and ‘/ alleles.
From this experiment, Mendel concluded that different traits are inherited I independently of one another. This principle is known as the Law Of I independent Assortment. It states as: “the alleles of a gene pair segregate (get; separated and distributed to gametes) independently from the alleles of other • gene pairs”. ‘ ,

Q.13. What is Punnett square?
Ans. The Punnett square is a diagram (in the form of a checker board) that is used to predict an outcome of a particular cross or breeding experiment. It is named after R. C. Punnett (an English mathematician). The gametes of both parents having all possible genetic set-ups are determined A checker board is used to cross all the possible gametes of one parent with all the gametes of other parent. In this way, a biologist can find all the possible genotypes of offsprings.

Q.14. What do you mean by co-dominance? Give an example.

Ans. Co-dominancen Co-dominance is the situation where two different alleles of a gene pair’express themselves completely, instead of showing a dominant-recessive relationship. As a result, the heterozygous organism shows a phenotype that is different from both homozygous parents
Genotype
Antigen produced
Phenotype
Relationship between alleles
.1*1*. or l*i Antigen A
Blood group A Allele IA is dominant over i
tB!Bor fr Antigen B
Blood group B Allele I8 is dominant over i
* B
No Antigen
Blood group O Allele-i is recessive
Antigen A & Antigen B Blood group AB Alleles IA and IB are co-dominant

Figure 15.9 Table Blood Groups

Example
An example of co-dominance is the expression of human blood group AB. The ABO ‘blood group system is controlled by the gene T. This gene has three alleles i.e. IA, IB and i. The allele I* produces antigen A in blood and the phenotype is blood group A. The allele I8 produces antigen B in blood and the phenotype is
inheritance*
blood group B. The allele I does not produce any antigen and the phenotype is blood group O. The alleles IA and IB are dominant over i. When there is a heterozygous genotype of IA IB, each of the two alleles produces the respective antigen and neither of them dominates over the other/Figure 15.9

Q.15. Explain the phenomenon of Incomplete dominance with the help of example.
Ans. Incomplete Dominance Incomplete dominance is the situation where, in heterozygous genotypes, both the alleles express as a blend (mixture) and neither allele is dominant over the other. As a result of this blending, an intermediate phenotype is expressed. Following is the familiar example of incomplete dominance: Figure 1510
Example Figure 1$.10 Illustration Incomplete dominance
In Four O’ clock plant, the trait of flower colour is controlled by two alleles (let us say them R and r). The true breeding plants RR and rr have red and white flowers, respectively. When a homozygous red flowered plant (RR) is crossed with homtozygous white flowered plant (rr), the heterozygous (Rr) plants of F1 generation produce pink flowers (pink is a blend of red and white colours). This result clearly indicates that neither of the red flower allele (R) and white flower i allele (r) is dominant. However, when two heterozygous plants with’ pink flowers (Rr) are crossed, F2 generation shows phenotypes of red, pink and white flowers in the ratio! :2:1.

Q.16. What I* the dominance relationship between blood group alleles I A and I B?

Ans. Go-dominance.ion genetically different children!

Q.17. What are the main sources of variations?
Ans. The main sources of variations in sexually reproducing populations are as follows;
• The genetic recombination produced through crossing over (recall that crossing over occurs during meiosis) results in gametes with variations.
• Mutations (changes in DNA) are important source of variations. Mutations also happen during gametes formation through meiosis.
• During fertilization, one of the millions of sperms combines with a single egg. The chance involved in this combination also act as the source of variations.
• Gene flow i.e. movement of genes from one population to another is also an important source of variations.
• Variations are also caused by different combjna|ops> of chromosomes in gametes and then in zygote. In the Mse of hurt^’ttsl possible number of ^romosdmal combinations at ffjgjjzajojfc is 70,3^»f4!4I177i,664. In other words, a’couple can produce

Q.18. Write down the types of variations.
Ans. Types of Variations:
The inheritable Variations are of two types i.e. discontinuous and continuous vans
ous Variations
Discontinuous variations show distinct phenotypes. The phenotypes of such variations cannot be measured. The indivjduw of a population either have •? <|teii^t jshenotypes, which can be easily distinguished from, each other. Blood groups are good example of such-variations. In a human population, an individual has one of the four distinct phenotypes (blood groups) and cannot have in between. Discontinuous variations are controlled by the alletes of a single gene pair. The environment has little effect on this type of variations.
(ii) Continuous Variations
In continuous variations, the phenotypes show a complete range of measurements fronj; one extreme to the other. Height, weight, feet size, intelligence etc. are example of continuous variations. In every human population, the individuate have a range of heights (from very small to tall). No population can show only two or three distinct heights. Continuous variations are controlled by many genes and are often affected by environmental factors.

Q.19. How would you prove that variations lead to evolution?

Ans. Variations lead to Evolution Organic Evolution
Organic evolution (biological evolution) is the change in the characteristics of a population or species of organisms over the course of generations. The evolutionary changes are always inheritable. The changes in an individual are

not considered .as evolution, because evolution refers to populations and not to individuals. Organic evolution includes two major processes:
• Alteration in genetic characteristics (traits) of a type of organism over time; and
• Creation of new types of organisms from a single type.
Theory of Special Creation
The study of evolution determines the ancestry and relationships among different kinds of organisms. The anti-evolution ideas support that all living things had been created in their current form only a few thousand years ago. It is known as the “Theory of Special Creation”. But the scientific work in eighteenth century led to the idea that living things might change as well.
Theory of Natural Selection
Charles Darwin (1809-1882) proposed the mechanism of organic evolution in 1838. It was called as “The Theory of Natural Selection”. Darwin proposed this theory after his S-year voyage on the HMS (His Majesty’s Ship) Beagle. He also published a book “Orr theOrigin of Species by Means of Natural Selection” in 1859. •:’:•••-*-• fr
Darwin’s theory of evolution was not widely accepted because, of lack of sufficient evidence. Modem evolutionary theory began in the late 1920s and early 1930s. Some scientists proved that the theory of natural selection and Mendelian genetics are the same ideas just as Darwin had proposed.

Q.20. Who first proposed the mechanism of evolution?
Ans. J. de Lamarck (1744-1829) was the first to propose a mechanism of evolution. Lamarck’s ideas were soon rejected due to the vagueness of the mechanisms he proposed. •

Q.21. Write an account on natural selection.

Ans. Mechanism of Evolution-Natural Selection Almost every population contains several variations for the characteristics of its members. In other words, there are morphological and physiological variations in all populations.
Natural Selection
Natural selection is the process by which the better genetic variations become more common in successive generations of a population:
Explanation .
The central concept of natural selection is the evolutionary fitness of an organism. Fitness means an organism’s ability to survive and reproduce. Organisms produce more offspring than can survive and these offspring vary in fitness. These conditions produce struggle for-survival among the organisms of popufation. The organisms with favourable variations are able to reproduce and pass these variations to their next generations. Oh the other hand, the rate of the transmission of unfavourable variations to next generations is low. We can say

that the favourable variations are “selected for” their transmission to next generations, while the unfavourable variations are “selected against” their transmission to next generations. ,»
Examples
1) We can see a mouse population with variations in skin colour. Cat preys upon light and medium coloured mouse. In first generation, light coloured mouse is preyed upon by cat. Only medium and dark coloured mouse can make their next generations. In next generation, population again contains light, medium and dark coloured mouse. Cat preys upon the light and medium coloured mouse. Now only the dark coloured mouse make new generation. If this happens in many generations, we will see only the dark coloured (favourable variation) mouse in the population.
As a result of natural selection, the allele that gives more fitness of characteristics (favourable variations) than other alleles becomes more common within population. So, the individuals with favourable vanatton become a major part of population while the injiyj|uj^ wKft rfermful or unfavourable variations become rarer. . ,,.v…/••«?&»”-^–^
2) In England, the moths had two variations i.e. dark and white coloured moths. The moths used to rest on the light cotpwred tree trunks (on which white lichens had grown). In the 19th centtfrf when industries were established in England, the lichens on tree trunks died (due to polluted air) and the naked tree trunks turned dark. Now the white moth variation became harmful because a white moth resting on a dark tree trunk was easily visible to the predatory birds, the natural selection selected dark moths to reproduce. In this way dark coloured .moth became more common and aflasVthe white moths disappeared from population. In this case, the dark colour variation in moth may be considered an adaptation to environment.

Q.22. Write a note on artificial selection.

Ans. Artificial Selection
The term “Artificial Selection” was expressed by the Persian scientist Abu ^Rayhan Biruni in the 11th century. Charles Darwin also used this term in his work on natural selection. He noted that many domesticated animals and plants had special properties that were developed by:
• Intentional breeding among individuals with desirable characteristics; and
• Discouraging the breeding of individuals with less desirable characteristics
Artificial selection (or selective breeding) means intentional breeding between individuals for certain traits, or combination of traits. Selective breeding has revolutionized agricultural and livestock production throughout the world.
Animals or plants having desirable characteristics are selected for breeding. In this way, many new generations with desirable characteristics are produced.
Breeds
In artificial selection, the bred animals are known as breeds.

Inheritance
Numerous breeds of sheep, goat, cow, hen etc., have been produced by artificial selection to increase the production of wool, meat, milk, eggs etc.
Varieties or Cultivars
In artificial selection, bred plants are known as varieties or cultivate.
Many plant varieties (cultivars) have been produced for better quantity and quality of cereals, fruits and vegetables.
In artificial selection, humans favour specific variations for selection while in natural selection the environment selects or rejects variations. For example, many varieties of cauliflower (phool gobhi). cabbage, broccoli, kale, Kohlrabi have been obtained through artificial selection in wild mustard.
Encircle or tick (S) the correct Option for the statements from the MCQs given below:

1.Many answers to the questions about 5. the mechanism of how offspring get the characteristics from their parents came from the
(a) Lamarck’s work
(b) Mendel’s work • •• 6-
(c) Watson-Crick’s work
(d) Darwin’s work
2.Branch of biology that deals with the 7-study of inheritance is known as
(a) genetics
(b) embryology biotechnology
(c)
(d) molecular biology
3.Inheritance means the transmission of characteristics from parents to offspring and these characteristics are called
(a) genes
(b) traits
(c) chromosomes
(d) chromatin
4. The chromosomes carry the units, of inheritance called

(a) chromatids (b) centromeres (c) genes (d) traits
8.
Equal number of chromosomes from each parent are combined during
(a) mitosis (b) meiosis
(c) fertilization (d) DNA replication
Genes consist of
(a) RNA (b) DNA
(c) proteins (d) all these
DNA contain specific instructions for
(a) RNA replication
(b) protein synthesis ,(c) gamete formation (d) all these
Chromatin is the complex combination of DNA and (a) proteins (b) RNA (c) lipids (d) glucose
The structure of chromosome shows that DNA wraps around hlstone proteins forming (a) chromoplast (B) nucleosomes
(c) central dogma
(d) nucleotldes

Inheritance 122
10. Who proposed the structure of DNA?
(a) James Watson
(b) Francis Crick
(c) McMillan James
(d) Both a and b
11 According to the Watson-Crick model, a DNA molecule consists of how many strands? (a) single (b) two-(c) three (d) four
12. The DNA strands are held together by
(a) carbon bonding
(b) hydrogen boding
(c) nitrogen pairing
(d) sugar-phosphate .back bone
13. In DNA, the nucleotide adenine pairs with
(a) thymine (b) cytosine , (c) uracil (d) guanine
14. In DNA, the nucleotide cytosine forms pair with
(a) thymine (b) adenine (c) guanine (d) uracil
15. DNA performs its role by giving instructions for the synthesis of (a) mRNA (b) rRNA (c) tRNA (d) proteins
16. The specific sequence of DNA nucleotides is copied in the form of sequence of
. (a) mRNA (b) rRNA (c) tRNA (d) proteins
17. The part of DNA that contains the instructions for the synthesis of a particular protein is known as a
(a) genetic code
(b) gene
(c) genome
(d) loci
18. The locations or positions of genes on chromosomes are known as (a) genetic code (b) chromatid (c) loci (d) genome
19. The specific sequence of DNA nucleotides is copied in the form of sequence of nucleotides in mRNA. This process in called
(a) transcription
(b) translation
(c) translocation
(d) genes li
20 The alternative form of gene is called (a) genome (b) loci (c) allele (d) genotype
21. The specific combination of genes in an individual is known as
(a) genome
(b) genotype *
(c) genetic recombination
(d) phenotype
22 A condition in which normal body pigments are absent is known as (a) albinism (b) haemophilia 9(c) scurvey (d) psoriasis
23. The genotype in which gene pair contains two identical alleles, is called
(a) homozygous genotype
(b) heterozygous genotype
(c) genome
(d) allotropic genotype
24. The allele which is not expressed is called
(a) dominant (b) recessive (c) phenotype (d) genotype
25. The expression of genotype in the form of trait is known as
(a) genome
(b) phenotype
(c) dominant trait
(d) recessive trait
Inheritance 123
26. How many pea plants Mendel used in his experiments?
(a) 12,000 (b) 18,000 (c) 24,000 (d) 28,000
27. Gregor Mendel was a monk (priest) in (a) Austria (b) Holland (c) Hungary (d) Philippine
28. The proteins are made in the cells under the instructions of (a) genes (b) tRNA (c) RNA (d) ribosomes
29 Decoding of mRNA information into a sequence of amino acid in a protein is
(a) transcription
(b) translation
(c) translocation
(d) replication
30. Which one of the following organisms did Mendel used as experimental tool/ (a) Drosophila (b) four o clock (c) garden pea (d) all these
31. A cross in which only -‘one trait is studied is called as
(a) monohybrid cross
(b) dihybfid,,cross
(c) contrasting cross
(d) true breeding cross
32 Mendel formulated Law of Independent Assortment with the help of
(a) monohybrid cross
(b) dihybrid cross
(c) test cross
(d) all these
33, The shape of pea seed may be rounded or
(a) inflated ‘ (b) wrinkled (c) pinched (d) wavy
34; The offspring of a true breeding tall male plant and a true breeding short female plant is called .
(a) parental generation
(b) a hybrid
(c) first filial generation
(d) a true breeding plant
35. The trait that appears in F1 after a cross is made between two true breeding plants is called (a) dominant (b) recessive (c) monohybrid (d) dihybrid
36. Mendel self-fertilized F1 tall plants and obtained tall and short plants in the ratio of
(a) 1:1 (b) 1:2:1 (c) 3:1 (d). 9:3:3:1
37. Mendel selected garden pea for his
experiments because . (a) the pea plant has contrasting traits
(b) the plant should have a short but fast life cycle
(c) there should be a number of different traits that can be studied
(d) all these
38 The paired genes are separated during gamete formation with each gamete receiving one or the other gene, but not both this is called
(a) Law of Inheritance
(b) Law of Independent Assortment
(c) Law of Segregation
(d) Law of Dominance
39. When both the-alletes of a gene pair in an organism are same the organism would be for that gene pair
(a) homozygote
(b) heterozygote
(c) homozygous
(d) heterozygous

Inheritance 124
40. If a homozygous tall (TT) is crossed with a homozygous short (tt), the F1 plants would be
(a) all tall
(b) 50% tall and 50% short
(c) all short
(d) 75% tall and 25% short
41. If a tall heterozygote (Tt) is crossed with a short homozygote (tt), the F1 offspring would comprise of
(a) all tall
(b) 50%.iall and 50 short
(c) all short
(d) 75% tall and 25% short
42. A phenotype ratio of 9:3:3:1 Ipsttqates which of the following crosses
(a) monohybrid cross
(b) dihybrid cross
(c) test cross
(d) back cross
43. A possible method used to predict an outcome of a particular cross or breeding experiment is
(a) Punnett square
(b) monohybrid cross
(c) dihybrid cross
(d) test cross
44. The situation where two alleles of a gene pair express their traits independently instead of showing a dominant recessive relationship is known as
(a) dominancy
(b) co-dominance
(c) incomplete dominance
(d) non-disjunctions ”
45. What is the dominance relationship between blood group alleles lAand IB?
(a) co-dominance
(b) in complete dominance
(c) complete dominance
(d) non-disjunction .
46. The pink coloured flowers in Four O’ clock is an example of
(a) co-dominance
(b) complete dominance
(c) in-complete dominance
(d) Law of Independent Assortment
47. The situation in which heterozygous genotypes both the alleles express as a blend and neither allele is dominant over the other is called
(a)’ in-complete dominance
(b) co-dominance
(c) non-disjunction
(d) miss-match crosses
48. Which one of the following is a major source of variations
(a) crossing over
(b) mutations
(c) gene flow
(d) all these
49. The movement of genes from one population to other is known as (a) mutations (b) crossing over (c) gene flow (d) fertilization
50. How many types of inheritable variations are presents? (a) two (b) three (c) four (d) five
51. No two individuals are phenotypically identical because of
(a), variations
(b) evolution
(c) natural selection
(d) artificial selection
52. When there is a complete range of measurements from one extreme to the other, it is called
(a) continuous variations
(b) discontinuous variations
(c) mutations
(d) independent assortment

Inheritance 125
53. A human couple can produce how many genetically different children?
(a) 30 trillion
(b) 40 trillion
(c) 50 trillion
(d) more than 70 million
54. Blood group is an example of
(a) discontinuous variations
(b) continuous variations
(c) natural selection
(d) gene flow
55. The modification of living organisms during their descent, generation by generation, from common ancestors this is called
(a) Lamarckism
(b) Darwinism
(c) organic evolution
(d) natural selection
56. Which one of the following is the major process of organic evolution?
(a) alteration in genetic properties of a type organism over time
(b) creation of new types of organisms from a single type
(c) genetic recombination
(d) both a and b –
57. Who proposed the theory of natural selection?
(a) Charles Darwin
(b) Gregor Mendel
(c) J. de Lamarck
(d) C. de Buffon
58. Name the ship on which Charles Darwin went for a voyage? (a) Trtamc (b) HMS Beagle (c) LMH Beagle (d) HMS Google
59. Who was the first to hint at the mechanism of evolution?
(a) J.de Lamarck
(b) Charles Darwin
(c) Gregor Mendel
(d) C.de Buffon
60. Who first proposed a mechanism of evolution?
(a) Charles Darwin
(b) Jole Lamarck
(c) Jabar bin Hayan
(d) C.de Buffon
61. In artificial selection breed plants are known as
(a) cultivars (b) breed (c) layers (d) broilers
62. Many different vegetables such as Broccoli, Kale, Cabbage, etc., have been derived from wild mustard by the process of
(a) natural selection
(b) artificial selection
(c) genetic engineering
(d) cloning ,
ANSWER

1. b
2. a
3.
b
4.
c
5.
c
6. b
7.
b
8. a

9. b
10. d
11.
b
12.
b
13.
a
14. c
15.
d
16. a

17. b
18.” c
19.
a
20.
c
21.
b
22. a
23.
a
24. b

25. b
26. d
27.
a
28.
a
29.
b
30. c
31.
a
32. b

33. b
34. c
35.
a
36.
c
37.
d
38. c
39.
c
40. a

41. b
42. b
43.
a
44.
b
46.
a
46. c
^47.
a
48. d

49. c
50. a
51.
a
52.
a
53.
d
54. a
55.
c
56. d

57. a
58. b
59.
d
60.
b
61.
a
62. b

Inheritance 126
REVIEW QUESTIONS
1. An organism’s expressed physical trait such as seed colour or pod shape, is called it’s; (a) genotype (b) phenotype (c) karyotype (d) physical type
2. An organism has two different alleles for a single trait. Its genotype is said to be;
(a) homozygous (b) heterozygous (c) hemizygous (d) homologous
3. In the cross-pollination between a true-breeding yellow pod plant and a true-breeding green pod plant,, where green pod colour is dominant, the resulting offsprings (F1 generation) will be;
(a) % green, % yellow (b) all yellow (c) % yellow, % green (d) all green
4. How many genetically different kinds of gametes an individual with genotype Aabb can produce? (a) 1 (b) 2 (c) 4 (d) 8
5. Which of the following statement regarding genes is false?
(a) genes are located on chromosomes
(b) genes consist of a long sequence of DNA
(c) a gene contains information for the production of a protein
(d) each cell contains a single copy of every gene •
Mendel’s primary contribution to our understanding of inheritance was;
(a) the idea that genes are found on chromosomes
(b) explanation of the patterns of inheritance
(c) the discovery of alleles
(d) determining that informations contained in DNA are for protein synthesis
A purple-flowered pea plant has the genotype PP. Which of the following statements about this plant is FALSE?
(a) its phenotype will be white flowers
(b) it has a homozygous dominant genotype
(c) when bred to a white-flowered plant, all offspring will be purple flowered
(d) all the gametes produced will have the same flower colour allele
Chartes Darwin proposed that organisms produce many more offspring than can possibly survive on the limited amount of resources available to them. According to Darwin, the offspring that are most likely to survive are those that;
(a) are born first and grow fastest
(b) are largest and most aggressive
(c) have no natural predators
(d) are best adapted to the environment
1. b
2. b
3. d
ANSWER
4. b 5, d
6. b
7. a
8. d

Please follow and like us:
error