Question
Problems 5and 6
Recitation Problem Set - Probability and Chi square Name Date Section Probability Questions. For each question: a. List how many genes are involved b. List how many alleles are involved Identify symbols and genotypes/ phenotypes d. c. Write the genotypes of the parents in the cross e. Write out the equations to determine probability. You can check your work by drawing a punnett square, but Iwant to see that you can calculate the answer using probabilities If two people who are both carriers for a genetically inherited fatal recessive disease decide to become parents, what will be the odds that their children will have the disease? (Don't just usea punnet square!) 1. 2. One of the most promising treatments for Leukemia is a bone marrow transplant from a matching donor. An ideal donor is hard to find because he or she must have the same two alleles as the patient at all of six different genes. In the human population, there are hundreds of alleles for each of these genes. A 10-year-old girl is diagnosed with leukemia. After a year of testing voluntary donors, no match has been found. Desperate to help their daughter, her parents decide to have another child to be a bone marrow match for their daughter. They plan to use in vitro fertilization (IVF) with genetic screening of fertilized embryos. All embryos are genotyped for all six genes affecting recognition of bone marrow Assume that: All eggs are successfully fertilized. Mother and Father are both heterozygous for different alleles of all six genes. Genotype frequencies predicted by Mendel's laws are observed Mother: A'A B'B cc D'DEE FF Father: A A B'B 'C D'DE'E FF Daughter: A A BB c'CD FF What fraction of embryos is expected to have the desired genotype? (don't need to write part c or here, since it is essentially done for you using the same information from question #2, if doctors could identify and collect sperm with the genotype A B'cDEF, and used only these sperm to fertilize a random collection of the mother's eggs, what fraction of the resulting embryos would be a perfect bone marrow match for their daughter? Again, don't need to define alleles or write out cross here 3, 4. If two people who are both heterozygous for Huntington's disease (an autosomal dominant trait) have a child, what is the probability that they will have three normal children? Human skin pigmentation is controlled by more than 30 genes. Let's consider 3 genes, with a dark skin allele for each gene being dominant (A, B, and C). If both parents are heterozygous for each gene (AaBbCc), use the rule of multiplication to calculate the probability that their baby would hav the darkest skin color of AABBCC. (Don't need to do part C here 5. In certain reptiles, eyes can be black (dominant) or yellow; and tails can be long (dominant or short If a lizard that is heterozygous black with a short tail is crossed with a yellow lizard heterozygous fo long tails, what is the probability that their first "baby" lizard will be a yellow short tailed lizard? 6.
Explanation / Answer
5. We know for a cross between heterozygotes for the same gene, the probability to get a homozygous dominant genotype in the offspring is 1/4. For a cross between parents heterozygotic for three genes, the probability to get an offspring homozygous for all three genes is 1/4 x 1/4 x 1/4 = 1/64
6. Let's assume the alleles B and b for black and yellow eyes, and T and t for long and short tails respectively.
The cross mentioned in the question is Bbtt (heterozygous black, short tail) x bbTt (yellow, heterozygous long tail)
Gametes produced by Bbtt - BT, bt
Gametes produced by bbTt - bT, bt
From the above, we can see that there is a one in four chance of the offspring being born with yellow eyes and a short tail.
BT bt bT BbTT (black, long) bbTt (yellow, long) bt BbTt (black, long) bbtt (yellow, short)
