I1. Probability Pedigrees For pedigrees where you do not have all the informatio
ID: 190675 • Letter: I
Question
I1. Probability Pedigrees For pedigrees where you do not have all the information, you will need tohdifficult assumptions and calculate with probabilities. Here are some rules of thurn pedigrees rele vant i. Based on the pattern of inheritance and the affected individuals, fill in every genotype you can determine. ii. Starting at the top of the pedigree, write down the fraction of chanc relevant unknown individual is a carrier (in the problem below this sions) daughter of the filled in male) (You will use this fraction in your Then, for the next mating, assume that unknown individual is a carrier overall calculations) iii. For multi-generation pedigrees you then go to the next generation and determi iv. Then perform a Punnett squa v. Multiply together ALL the probabilities you have written down te down their probability that the next individual in question will also be a carrier, wr fraction chance, and continue until you reach the individual in question. re for the individuals you are crossing and calculate the to get the total chance that the offspring is affected. probability of the offspring inheriting the trait In addition, recall that unless there is evidence to the contrary, assume that the individuals that have married into each family do not carry a recessive allele for the trait in questions. Also assume 100% expressivity for the trait. 2. A man who suffers from a particular type of human deafness marries a phenotypically normal woman, and now, they are expecting a baby. They find out that they are distantly related, so they decide to go for genetic counseling to determine the probability that their child will be deaf. The genetic counselor asked about their family history and generates the pedigree shown below. Based upon the pedigree, what is the most likely mode of inheritance for this type of deafness? Explain your answer. (0.5) a.
Explanation / Answer
2 a). X-linked recessive. This is because if you look at the inheritance pattern, it will be observed that the trait skips generation, and affects the male members more, who carry only one X chromosome carry the disease and none of the female. This means that the disease is a recessive trait and only if present in the homozygous condition (XdXd or XdY) will it occur. Females in the family are therefore either normal or carriers for the deaf allelle. It cannot be Y-li nked because in that case the father of a deaf male would also be deaf, which is not the case.
b)
If the mother is heterozygous (XDXd)
XD
Xd
Xd
XD Xd
Xd Xd
Y
XDY
XdY
So the probability of deaf child is =2/4= 0.5
If the mother is homozygous (XDXD)
XD
XD
XD
XD XD
XDXD
Y
XDY
XDY
So the probability of deaf child is =0/4= 0
Following the pedigree aboce, the great grandparents (first generation) of the woman in question are both normal (grandmom XD Xd, and granddad XD Y). However among their children one son has the disease which means the greatgrandmother is heterozygous normal.
The granddad (second generation) of the woman in question is normal ( granddad XD Y) with grandmother being heterozygous (grandmom XD Xd as her father had the disease but she is normal).
Their childern i.e., the mother (third generation) of the woman in question is therefore normal but heterozygous (XD Xd). Now, when the heterozygous mother crosses with normal father in the third generation, the daughter can be either heterozygous or homozygous.
c) Just as in the above subpart b, the probability will be zero if the man's sister is homozygous and 0.5 if is sister is heterozygous.
XD
Xd
Xd
XD Xd
Xd Xd
Y
XDY
XdY