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Published byNancy Jessica Atkins Modified over 9 years ago
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12.2 Complex patterns of inheritance
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Complex patterns of inheritance Mendel’s experiments show simple inheritance with recessive and dominant alleles Some patterns of inheritance are more complex
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Complex patterns of inheritance Incomplete dominance Codominance Multiple alleles Sex-linked inheritance Polygenic inheritance Environmental factors
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Incomplete dominance Phenotype of the heterozygote is in between the phenotypes of the homozygotes RR=red pigment R 1 R 1 =white, no pigment RR 1 =pink
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Codominance Phenotypes of both homozygotes are produced in heterozygote, both alleles are expressed equally BB=black feather WW= white feather BW= checkered
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Multiple alleles Traits controlled by more than two alleles Each pigeon has two alleles for feather color, but there are many possible alleles
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Sex-linked inheritance In humans have 46 chromosomes, 23 pairs 22 pairs autosomes one pair sex chromosomes, determine sex
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Sex-linked inheritance Sex-linked traits are controlled by genes located on the sex chromosomes Alleles are carried on the X chromosome, not the Y chromosome
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Polygenic inheritance A trait that is controlled by more than one gene Genes may be on different chromosomes Each gene may have more than one allele Trait usually expressed in a continuous range of variability
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Environmental factors External Gene may not be expressed due to temperature, nutrition, light, chemicals, infection For example, this bacteria is different color when grown at different temperature
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Environmental factors Internal Males and females differ due to hormones Age may change trait expression
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Complex patterns of inheritance Mendel’s idea that heredity is a composite of many traits still holds Later researchers have filled in details
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