2. Beyond simple dominant and recessive alleles (other possibilities out there in the real world).
3. The real world of genetics Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.
4. Incomplete dominance Incomplete dominance – neither allele is completely dominant over the other. Therefore, in this case, the heterozygote’s phenotype is in between the two homozygous phenotypes (intermediate phenotype).
9. Incomplete dominance Make a Punnett square and give the genotypic and phenotypic ratios for a cross between two heterozygotes for a trait with incomplete dominance. (B allele for black fur, b allele for white fur)
10. Example: incomplete dominance in fur color BB = Black Fur Bb = Gray Fur Bb = White Fur Parents: Bb x Bb Both gray The heterozygous phenotype is in between the homozygous phenotypes. The alleles are incompletely dominant.
11. Codominance In codominance, both alleles contribute to the phenotype (neither allele is completely dominant nor completely hidden by the other-it’s a combination).
14. Codominance Make a Punnett square and give the genotypic and phenotypic ratios for a cross between two heterozygotes for a trait with Codominance. G allele for green leaves, g allele for yellow leaves)
15. Example: Codominance in leaf color Parents: Gg x Gg Both green and yellow leaves GG = Green Gg = BOTH green and yellow gg = yellow The heterozygous phenotype Expresses both the green and yellow leaf color of the homozygotes. The alleles are codominant.
16. Multiple Alleles When there are more than two alleles for a gene the trait is said to have multiple alleles.
17. Multiple Alleles Human blood type is controlled by multiple alleles. There are 3 alleles: IA IB i Two different things are going on—codominance and dominance. codominant Recessive to
18. What are the possible combinations of the three alleles and what blood types result from each combination? IA IB i
19. Genotypes and Phenotypes for ABO blood groups (alleles IA, IB, i) Genotypes Phenotypes IA IA IA i IB IB IB i IA IB ii Type A blood Type B blood Type AB blood Type O blood
20. Polygenic Traits Polygenic traits are those traits that are controlled by two or more genes (poly=many, genic=genes). Polygenic traits often show a wide range of phenotypes.
21. Multiple Gene (Polygenic) Inheritance of skin color Parent 1 genotype: AaBbCc Parent 2 genotype: AaBbCc Each capital letter represents an allele for dark skin, each lower-case letter represents an allele for light skin. Count the number of capital letters each possible child has to determine the how dark or light their skin would be.
22. Sex Chromosomes Two of the 46 chromosomes in humans are known as the sex chromosomes. The remaining 44 chromosomes (22 pairs) are known as autosomes.
