1. Exceptions to Mendelian Inheritance

2. Mendelian Inheritance means…
one gene = one trait
2 different alleles (versions) for a gene
one dominant and one recessive allele (heterozygous = dominant phenotype)
segregation
independent assortment
genotype determines phenotype

3. Exceptions to Mendel Linkage ✓ Incomplete dominance Codominance
Multiple Alleles
Polygenic Traits
X-linked traits ✓
Environmental Influences

4. Incomplete Dominance Neither allele is dominant
Heterozygous phenotype is intermediate
Example:
Flower color in snapdragons

5. CWCW=white
CRCR=red
CRCW=pink

7. Codominance Both alleles are dominant
Heterozygous phenotype displays both traits
Example:
Coat color in horses

8. HRHW=roan (red and white)
HRHR=red
HWHW=white
HRHW=roan (red and white)

10. Multiple Alleles More than 2 alleles (versions) for a gene
Example: Human Blood Types

11. Multiple Alleles – Blood Types
Alleles: IA (dominant), IB (dominant), i (O, recessive)
Genotypes:
IA IA, IA i, IB IB, IB i, IAIB, ii
What phenotype is produced by each of these genotypes?

12. X-Linked Traits
Genes on X chromosome produce a different inheritance pattern in males vs. females
Example: Eye color in fruit flies

13. X-Linked Traits Alleles: XRXR – red eye female XRXr – red eye female
XR – red eyes (dominant)
Xr – white eyes (recessive)
Genotypes:
XRXR – red eye female
XRXr – red eye female
XrXr – white eye female
XRY – red eye male
XrY – white eye male

15. Polygenic Traits
Traits that are determined by multiple genes produce a range of phenotypes on a bell-shaped continuum.
Example: Human Skin Color

17. Modes of Selection

18. Environmental Influences
Environmental factors can influence an individual’s phenotype (without changing the genotype).

19. IQ Score Correlations: Genes vs. Environment
Genetic similarity: % % % % %

20. 1. In humans, straight and curly hair textures demonstrate incomplete dominance. The heterozygous individuals have wavy hair. The alleles are HC and HS. A woman and her husband who both have wavy hair desire a child with curly hair. What are the chances that their first child will have curly hair? Show the Punnett square.
In cats, the trait for calico (multicolored) cats demonstrates codominance and X-linkage. Females that receive a XB and an XR gene have black and orange splotches on white coats. Males can only be black or orange, but never calico. A female black cat is crossed with a male orange cat. What percentage off the offspring will be calico? What color would the males be? Show the Punnett square.
4. A man is suing his wife for divorce on grounds of infidelity (he thinks she is having an affair). Their 1st and 2nd children, whom they both claim, have blood types O and AB, respectively. The 3rd child, whom the father disclaims, is blood type B. Could he be the father of the third child? Show the Punnett square.