1. 12.2 Complex patterns of inheritance

2. Complex patterns of inheritance Mendel’s experiments show simple inheritance with recessive and dominant alleles Some patterns of inheritance are more complex

3. Complex patterns of inheritance Incomplete dominance Codominance Multiple alleles Sex-linked inheritance Polygenic inheritance Environmental factors

4. 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

5. Codominance Phenotypes of both homozygotes are produced in heterozygote, both alleles are expressed equally BB=black feather WW= white feather BW= checkered

6. Multiple alleles Traits controlled by more than two alleles Each pigeon has two alleles for feather color, but there are many possible alleles

7. Sex-linked inheritance In humans have 46 chromosomes, 23 pairs 22 pairs autosomes one pair sex chromosomes, determine sex

8. 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

9. 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

10. 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

11. Environmental factors Internal  Males and females differ due to hormones  Age may change trait expression

12. Complex patterns of inheritance Mendel’s idea that heredity is a composite of many traits still holds Later researchers have filled in details