1. Human Inheritance & Exceptions to the Rule of Dominance & Recessiveness

2. Traits Controlled by Single Gene (Monohybrid) Many human traits are controlled by a single gene with one dominant allele and one recessive. Possess two very different phenotypes Ex. Widow’s Peak or Straight Hairline Dimples

3. Punnett Square for Single Gene with 2 Alleles

4. Multiple Alleles –A gene that has three or more alleles that code for a single trait. Human Blood Type –Controlled by three alleles –I A, I B, i –I A and I B are codominant

5. Codominance Both dominant and recessive alleles are expressed (multiple alleles) in heterozygous individuals. Ex. Human Blood Type Ex. #2 Erminette chicken feathers –Both black and white feathers

7. Human Blood Type Blood Types Blood TypeCombination of Alleles AI A I A or I A i BI B I B or I B i ABIAIBIAIB Oii

8. Codominance Problem Example:homozygous male Type B (I B I B ) x heterozygous female Type A (I A i) IAIBIAIB IAIBIAIB IBiIBiIBiIBi 1/2 = I A I B 1/2 = I B i IAIA IBIB IBIB i

9. Another Codominance Problem Example:Example: male Type O (ii) x female type AB (I A I B ) IAiIAiIBiIBi IAiIAiIBiIBi 1/2 = I A i 1/2 = I B i i IAIA IBIB i

10. Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (I A I B )

11. Codominance Answer: IAIBIAIB ii Parents: genotypes = I A i and I B i phenotypes = A and B IBIB IAIA i i

12. Incomplete Dominance Heterozygotes in between phenotypes Heterozygotes have an appearance somewhat in between the phenotypes of the dominant and the recessive. (Mix) Example:snapdragons (flower) Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower r r RR

13. Incomplete DominanceRrRrRrRr r rRR All Rr = pink (heterozygous pink )

14. Incomplete Dominance

15. Traits Controlled by Many Genes Large number of phenotypes –Usually indicates that the trait is controlled by many genes –Genes act together as a group to produce a single trait. Example –Height & Skin Color

16. Effect of the Environment Effects of genes are often altered by the organism’s surroundings. Ex. Since the late 1800’s, the average height in the U.S. has increased by almost 10 cm.

17. Male of Female? Sex Chromosomes –23 rd pair of chromosomes –XX genotype=Female, XY genotype=Male

18. Sex-Linked Genes Sex-Linked Traits –Traits (genes) located on the sex chromosomes –Many sex-linked traits carried on X chromosome –Many genes/alleles are not found on male Y chromosome –Because males have only one X chromosome, males are more likely than females to have a sex-linked trait that is controlled by a recessive allele. Carrier –A person who has one recessive allele for a trait and one dominant allele. Only females in sex-linked traits. –Does not have the trait but can pass the recessive (disease) allele to her offspring.

19. Red-Green Colorblindness Sex-linked trait A girl who receives only one recessive allele (written X C ) will not have the trait. A boy who receives only one recessive allele will be colorblind.

20. Sex-linked Traits Sex Chromosomes XX chromosome - femaleXy chromosome - male fruit fly eye color Example: Eye color in fruit flies

21. Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r X r Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed Xy = male XX = female X R X r X r y XrXr XRXR y XrXr 50% red eyed female 50% white eyed male

22. Pedigrees If you were a geneticist trying to study human inheritance patterns, how would you go about doing that? You couldn’t set up crosses with people as Mendel did with peas. Need to trace the inheritance of traits through many generations in a number of families. Pedigree –Tool used to trace the inheritance of traits in humans –A chart of “family tree” that tracks which members have a particular trait.

23. Reading a Pedigree A half-shaded circle or square indicates that a person is a carrier. A completely shaded circle or square indicates that a person has the trait. A circle or square that is not shaded in green indicates that a person neither has the trait nor is a carrier. A horizontal line connecting a male and female represents a marriage. A vertical line and a bracket connect the parents to their children. A circle represents a female. A square represents a male.

24. Female Carriers

25. Human Inheritance Summary such as controlled by Human traits Single genes Multiple alleles Many genes Sex-linked genes Widow’s peak Blood type Height Colorblindness

26. Summary Questions If a gene has multiple alleles, why can a person only have two of the alleles for the gene? Why to human traits such as height and skin color have many different phenotypes? Explain why red-green colorblindness is more common in males than in females. What is a pedigree? How are pedigrees used? Could two people with widow’s peak have a child with a straight hairline? Could two people with strait hairlines have a child with a widow’s peak? Explain.