1. 3/19 BR: Dihybrid Cross Do a Punnett Square for the following dihybrid cross: plants heterozygous for seed shape and color (RrYy) Write the genotype & phenotype ratios in the offspring

2. Dihybrid Cross KEY Genotype ratio = 1 RRYY : 2 RRYy : 2 RrYY : 4 RrYy : 1 RRyy : 2 Rryy : 1 rrYY : 2 rrYy : 1 rryy Phenotype ratio = 9 round & yellow : 3 round & green: 3 wrinkled & yellow : 1 wrinkled & green

3. The allele for colorblindness is recessive and on the X chromosome

4. Are YOU colorblind????

7. The ABO blood group is a case of multiple alleles AND codominance (FYI, +/- blood type is a different group)

8. 3/20: BR 1. Oh no! Some babies were separated from their parents in the hospital nursery. Help them out. Match the parents with the children in the problem below. Couple 1: blood types A & OBaby 1: Type AB Couple 2: blood type B for both Baby 2: Type A Couple 3: blood types A & BBaby 3: Type O 2. Why do you think there so many different shades of skin in the human population?

9. Date: 3/20 Other forms of inheritance Pleiotropy: When 1 gene has multiple effects (p.170) Ex. Sickle-cell disease – blood can’t carry oxygen well, but makes a person resistant to malaria Polygenic traits: traits controlled by >1 gene (p.172) ex. human skin tone & height have a continuous range of phenotypes

10. Other forms of inheritance Epistasis: 1 gene influences the expression of another ex. in mice, black (B) is dominant over brown (b) But another gene codes for the ability to produce ANY pigment (C = pigment, c = no pigment / albino) Bbcc = white (albino) BbCc = black bbcc = brown Environmental influence: phenotype can be influenced by environment ex. the color of the arctic fox changes from brown during the summer time to white during the winter

11. (3/23) BR: Pedigrees 1. The chart to the right is called a pedigree. What do pedigrees show? How are they used to study genetics?

12. Pedigrees = female = female carrier = male= male carrier = female with trait = male with trait

14. Pedigree Analysis #1 A.Draw the pedigree to the left B.Is this trait dominant or recessive?

15. Pedigree analysis… It is RECESSIVE, because if it was dominant the parents would have had the trait as well

16. Pedigree analysis #2 A.Draw the pedigree. B.Is this trait dominant or recessive? C.Write the genotypes next to each individual.

17. DOMINANT. Explanation: Tt Tt tt TT or Tt

18. #3: Is this trait Dominant or Recessive?

19. CAN’T TELL. Could be either dominant or recessive. Just because you are seeing a trait, doesn’t mean it is dominant.

20. Pedigree analysis # 4 A.Draw the pedigree. B.Is this trait dominant or recessive? C.Write the genotypes next to each individual

21. RECESSIVE Tt Tt TT or Tt tt

22. Pedigree Analysis # 5 What type of inheritance is this?

23. This is most likely a SEX-LINKED trait

24. Is this a sex-linked trait?

25. NO (at least not sex-linked recessive). Explanation: If the mother were X h X h, then each of her sons would have to be X h Y and show the trait. They do not, and so it cannot be sex-linked.

26. 3/24 BR: Genetic Disorders 1. You have studied chromosomal disorders. How do you think a genetic disorder is different? 2. What is a gene? 3. Why are genetic disorders usually caused by recessive alleles?

27. 3/24 BR: Answers Chromosomal disorders are the result of extra, missing, or damaged chromosomes & are usually not inherited. Genetic disorders are due to mutations in genes that are ON chromosomes. They can be passed from parents to offspring. A sequence of DNA that codes for a specific PROTEIN. Those proteins determine our traits. Genetic disorders result because a mutated gene codes for a dysfunctional protein. Because if a disorder decreases the chances of survival or reproduction, it will get passed on to offspring less frequently and eventually be eliminated from the population. But recessive alleles can remain in the population in heterozygotes who show a “normal” phenotype (they don’t have the disorder).

28. 3/24 Genetic Disorders (p.164) Genes code for proteins w/ a specific fxn Many genes have only 1 allele Any ∆ in that allele is a mutation that can be passed Usually harmful

29. Genetic Disorders Disorders may be caused by recessive, dominant, or codominant mutations Recessive… why are most genetic disorders caused by recessive alleles? Cystic fibrosis: gene mutation causes improper folding of membrane protein CFTR  absence of CFTR in cell’s membrane chloride ions (Cl - ) unable to cross cell membranes  mucus in lungs, digestive tract Common in people of northern European descent

30. Recessive Phenylketonuria (PKU): mutation in gene coding for an enzyme that breaks down the AA phenylalanine  phenyl. accumulation in tissues may cause mental retardation  early detection can allow for survival w/ dietary restrictions Tay-Sachs disease: mutation in gene that codes for enzyme that breaks down ganglioside lipids in neurons  results in nervous system break down & death Common in Ashkenazi Jews

31. Genetic Disorders Dominant Huntington disease: loss of muscle control & mental function  starts in 30s or older Achondroplasia: form of dwarfism

32. Genetic Disorders Codominant Sickle-cell disease –mutation ∆’s 1 AA in hemoglobin must be homozygous to have disease heterozygotes are resistant to malaria abnormal hemoglobin protein causes sickle-shaped RBCs  get caught in capillaries & block blood flow, starving tissues of oxygen and damaging organs like the brain, liver, &spleen Common in people living in tropical areas like western Africa where malaria kills millions (very common in African-Americans)

33. Recessive Disorders Disorders are often distributed among certain ethnicities much more frequently than others. Why do you think that is? Genetic disorders are inherited and due to mutations in genes. Mutations happen naturally and frequently. The average person has 60 in his/her DNA! But they are usually recessive if we survive with them. The smaller a population is, the more likely two people who breed will share the same random mutation in their DNA (this is why incest is risky!) Races/ethnicities exist because different populations of people were isolated from others for many generations, and any changes in their genes stayed within each population. This is how evolution works!

34. 3/25 BR: Construct a pedigree Construct a pedigree examining hemophilia inheritance and list the genotypes of each person: A woman is a carrier for hemophilia and marries a man who does not have hemophilia. This couple has 2 sons and 1 daughter. One son has hemophilia, the other does not. The daughter marries a man with hemophilia. They have 2 sons and 2 daughters. One of their sons has hemophilia, the other does not. One daughter has hemophilia, the other does not. List the genotypes of everyone in the pedigree.

35. KEY XHXhXHXh XHYXHY XHXhXHXh XHXhXHXh XHYXHY XhYXhY XhYXhY XhYXhY XHYXHY XhXhXhXh

36. 3/26 BR: Dihybrid Cross About 70% of Americans perceive a bitter taste from the chemical phenylthiocarbamide (PTC). The ability to taste this chemical results from a dominant allele (T) and not being able to taste PTC is the result of having two recessive alleles (t). Albinism is also a single locus trait (i.e., controlled by 2 alleles) with normal pigment being dominant (A) and the lack of pigment being recessive (a). Gloria is a normally-pigmented woman who cannot taste PTC. Her father is an albino who can taste PTC. Gloria marries Jay, who is a homozygous, normally-pigmented man who can taste PTC but whose mother cannot taste PTC. a. Identify the genotypes of Gloria and Jay and the possible allele combinations in their gametes (to use in a Punnett Square). b. What are the genotype and phenotype ratios of Jay and Gloria’s potential children? c. What can you definitively conclude about Jay and Gloria’s parents?

37. KEY a. Gloria: Aatt, Jay: AATt and the possible allele combinations in their gametes: Gloria: At, at Jay: AT, At b. Offspring genotype ratio = 1 AATt : 1 AaTt : 1 AAtt : 1 Aatt Phenotype ratio= 1 normally-pigmented who can taste PTC : 1 normally-pigmented who cannot taste PTC

38. KEY c. Gloria’s mom is A__t__ (normal pigment) Gloria’s dad is aaTt (albino & can taste PTC) Jay’s mom is aatt (albino & cannot taste PTC) Jay’s dad is aaT__ (albino & can taste PTC)