12.2 Complex patterns of inheritance. Complex patterns of inheritance Mendel’s experiments show simple inheritance with recessive and dominant alleles.

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<ul><li> Slide 1 </li> <li> 12.2 Complex patterns of inheritance </li> <li> Slide 2 </li> <li> Complex patterns of inheritance Mendels experiments show simple inheritance with recessive and dominant alleles Some patterns of inheritance are more complex </li> <li> Slide 3 </li> <li> Complex patterns of inheritance Incomplete dominance Codominance Multiple alleles Sex-linked inheritance Polygenic inheritance Environmental factors </li> <li> Slide 4 </li> <li> 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 </li> <li> Slide 5 </li> <li> Codominance Phenotypes of both homozygotes are produced in heterozygote, both alleles are expressed equally BB=black feather WW= white feather BW= checkered </li> <li> Slide 6 </li> <li> Multiple alleles Traits controlled by more than two alleles Each pigeon has two alleles for feather color, but there are many possible alleles </li> <li> Slide 7 </li> <li> Sex-linked inheritance In humans have 46 chromosomes, 23 pairs 22 pairs autosomes one pair sex chromosomes, determine sex </li> <li> Slide 8 </li> <li> 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 </li> <li> Slide 9 </li> <li> 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 </li> <li> Slide 10 </li> <li> 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 </li> <li> Slide 11 </li> <li> Environmental factors Internal Males and females differ due to hormones Age may change trait expression </li> <li> Slide 12 </li> <li> Complex patterns of inheritance Mendels idea that heredity is a composite of many traits still holds Later researchers have filled in details </li> </ul>


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