Module 5 problem-solving worksheet PDF

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Module 5 problem-solving worksheet (Penetrance and multiple alleles) NO answers SP2021 1. As discussed in class, Lynch syndrome is an autosomal dominant disease with incomplete penetrance. Is there anyone in this pedigree that has the gene for Lynch syndrome but doesn't express it? If so, state which person it is?

2 ii

2. A gene is associated with a rare cancer, and it is inherited as a dominant trait with incomplete penetrance. The penetrance of this gene is 80%. If 40 people gave this gene, how many would be expected to get the cancer? 32 people 3. Assume that long fingers are inherited as a recessive trait with 60% penetrance. Two people heterozygous for long fingers get married. What is the probability that their first child will have long fingers? 0.15 = 15%

4. A cross between two green corn plants yields 2/3 progeny that are green and 1/3 progeny that are white. G = allele for green corn plants g = allele for white corn plants a. Why did this occur? The phenotype at the survival level, G is a recessive lethal allele because death requires two of them (GG). b. What is the genotype(s) of the green progeny? Gg c. What is the genotype(s) of the white progeny?

gg 5. An allelic series determines coat color in rabbits: C (full color), cch (chinchilla, gray color), ch (Himalayan, white with black extremities), and c (albino, all white). This dominance hierarchy can be summarized as C > cch > ch > c.    

The C allele is dominant over all others cch is dominant over ch and c ch is dominant over c c is recessive to all other alleles.

The rabbits in the table are crossed and produce the progeny shown.

Match the parental genotypes to the letter corresponding to the appropriate cross listed in the table. Answer bank: Cc x cc chch x cc chc x ccCch x cc h CC x cc Cc x c c Cc x Cc

A= Cc x cc B= chc x cc C= Ccch x cc D= Cc x chc E= Cc x Cc

6. You learned in this that wing pattern in pigeons is determined by 4 alleles that follow a hierarchy of dominance, as shown in those slides and here: The phenotypes are as follows.

For each of the genotypes below, write what you think the phenotype would be  (the first one is filled in for you)

Genotype

Phenotype

a. _____1________

b. ________3_____

c. ________1_____

d. ________3_____

e. _______2______

f. ______1_______

6. Mutations in a gene named RPE65 are responsible for an inherited form of blindness called Leber congenital amaurosis (LCA). Pedigrees have revealed that this form of blindness has an autosomal recessive pattern of inheritance: individuals with the disease have two mutated alleles. The tables below show the amino acid sequence show:  On the top line: the amino acid sequence of a portion of the normal RPE65 protein  On the 2nd and 3rd lines: and the sequence of the same region of RPE65 in two alleles of a single individual. o The “…” indicate amino acids in the full protein sequences that are not included in the tables. a. For the first set of sequences shown (starting with START-Ser-Leu-Leu), the same amino acid is changed in both alleles 1 and allele 2, due to a mutation RPE65. State what amino acid in the normal protein that is changed, and what changed into. The normal protein “Arg” is changed into “Gln” b. What is the correct term for this individual: Homozygous recessive, heterozygous, or compound heterozygous? Heterozygous

c. LCA caused by mutations in RPE65 is fully penetrant, and the amino acid changes shown result in a non-functional protein for both alleles. Does this individual have LCA? The individual is a carrier of LCA but not necessarily affected by it.

d. For the second set of sequences shown below (starting with START-Phe-Asp-Gly), for both in allele 1 and allele 2, circle the amino acid that is changed due to the mutation in the RPE65 allele. State what amino acid in the normal protein that is changed, and what changed into.  For Allele 1: “His” is changed into “Tyr”



For Allele 2: “Lys-Arg-Lys-Lys-Tyr-Leu” is deleted from the sequence

e. What is the correct term for this individual: Homozygous recessive, heterozygous, or compound heterozygous? Homozygous recessive f. LCA caused by mutations in RPE65 is fully penetrant, and the amino acid changes shown result in a non-functional protein for both alleles. Does this individual have LCA? Yes g. Based on what you learned in Module 1, what kind of mutation does allele 2 have: point, missense, nonsense or frameshift)? frameshift

7. You learned in this Module that blood types in humans is controlled by multiple alleles at a single gene, and that the A allele (IA) and B allele (IB) are codominant, and the O allele (i) is recessive. Assume a man with AB blood marries a woman with B blood with the genotype IBi. Fill in the Punnett square below, then answer these questions

A

B

B

AB

BB

O

AO

BO

a. What are the possible phenotypes of their children? AB, BB, AO, BO b. What percentage would be AB?

25% 8. The early film Charlie Chaplin was sued in a paternity suit in 1943. His long-term mistress Joan Barry, who was blood type A, claimed that Chaplin (blood type O) was the father of her daughter (blood type B). Is this possible? (assuming that there are no interactions with other genes)

It is possible

9.In chickens, comb shape is determined by genes at two loci (R, r and P, p). A figure from the original paper describing this is shown below.

  

  A walnut comb (shown in D) occur when at least one dominant allele (R) is present at both the 1st locus and the 2nd locus (genotype R_ P_). A rose comb (shown in B) occurs when at least one dominant gene is present at the 1st locus and two recessive genes are present at the 2nd locus (genotype R_ pp). A pea comb (shown in C) occurs when two recessive genes are present at the 1st locus and at least one dominant gene is present at the 2nd locus (genotype rr P_). A single comb (shown in A) occurs when both the 1st locus and the 2nd locus have two recessive genes (genotype rr pp).

a. A chicken with a walnut comb is crossed with a chicken with a single comb. Their offspring are 1 walnut, 1 rose, 1 pea, and 1 single offspring. Which of the following are the genotypes of the parents?

a. b. c. d. e.

RR PP × rr pp RR Pp × rr pp Rr PP × rr pp Rr Pp × rr pp Rr pp × rr pp

b. A chicken with a rose comb crossed with a chicken with a pea comb. All of the offspring have walnut combs. Which of the following are the genotypes of the parents? a. RR pp × rr PP b. Rr pp × rr Pp c. Rr pp × rr PP d. RR pp × rr Pp e. Rr pp × Rr Pp

10. Match the terms from the answer bank with the definition of concepts from this Module. a. ____Genetic maternal effect___ is the influence of the genotype of the female parent on the phenotype of her offspring. b. ____Pleiotropy_____ is when a gene affects more than one phenotype c. __Penetrance_____ is the percentage if individuals with a particular genotype that express the expected phenotype. d. __Sex-influenced trait___ is a trait determined by a gene on an autosome that is more often expressed in one sex e.

__Sex-limited trait_______ is a trait determined by a gene on an autosome that is only expressed in one sex

f.

A _polygenic trait____ determined by genes at many different loci

Answer Bank: Genetic maternal effect Sex-influenced trait Sex-limited trait Penetrance Pleiotropy Polygenic trait...