Genes control the inheritance of characteristics (or traits) through a process known as genetic inheritance, which is governed by the transfer of genetic material (DNA) from parents to offspring. Here’s how genes control this inheritance:
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Genes and Alleles:
- Genes are segments of DNA that carry the instructions for making proteins, which influence the traits of an organism.
- Each gene has different forms called alleles. For example, a gene for flower color may have an allele for red flowers and another allele for white flowers. An individual inherits two alleles for each gene, one from each parent.
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Dominant and Recessive Alleles:
- Some alleles are dominant, meaning they will express their traits over other alleles. For example, a dominant allele for flower color might result in red flowers even if the other allele is for white flowers.
- Recessive alleles only express their trait if both alleles are recessive (i.e., the organism inherits the recessive allele from both parents). For example, white flowers will only appear if both alleles for color are the white allele.
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Homozygous and Heterozygous:
- An individual is homozygous for a gene if they inherit the same allele from both parents (e.g., two red alleles or two white alleles).
- An individual is heterozygous if they inherit two different alleles for a gene (e.g., one red and one white allele). In this case, the dominant allele typically determines the trait (like red flowers in the red/white example).
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Genotype and Phenotype:
- The genotype refers to the actual genetic makeup of an organism (the alleles it carries), while the phenotype is the observable trait (such as the color of flowers).
- The genotype controls the phenotype, but environmental factors can also influence how some traits are expressed.
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Mendel’s Laws:
- Law of Segregation: Each individual has two alleles for each gene (one from each parent), and these alleles segregate, or separate, during the formation of reproductive cells (gametes like sperm and eggs). This ensures that offspring inherit one allele from each parent.
- Law of Independent Assortment: Genes for different traits are inherited independently of one another, as long as the genes are located on different chromosomes. This leads to genetic diversity in offspring.
In short, genes control inheritance by providing instructions for traits, with dominant and recessive alleles determining how those traits are expressed. Mendel’s principles of segregation and independent assortment further explain how traits are passed down from one generation to the next.