EDIT: I\'m pretty sure I\'ve already solvedthese problems correctly. However, I
ID: 4715 • Letter: E
Question
EDIT: I'm pretty sure I've already solvedthese problems correctly. However, I am interested in knowing ifany shortcuts exit for #2. I was able to solve it but I had to drawout a Punnett Square for a Trihybrid Cross which was timeconsuming.I would still like to see what other people get for answers tocheck me own. Thanks a bunch!
1. For the purpose of this problem assume that in humans the genefor brown eyes is dominant to that for blue eyes.
a. What is the probability that the first child produced by parentswho are both heterozygous for brown eyes will be blue-eyed?
b. If the first child is a brown-eyed girl (same parents as in a),what is the probability that the second child will be a blue-eyedboy?
2. In peas, seeds can be round (R) or wrinkled (r) and eitheryellow (Y) or green (y). Stem length may result in a tall (T) ordwarf (t) plant.
a. In the cross (parent A) TTYyRr x TtYyRr (parent B), how manydifferent types of gametes can be produced by each parent and howmany different phenotypes are possible from the cross?
b. What proportion of the offspring from the cross in part a wouldbe tall with yellow, wrinkled seeds?
c. In the cross TtYYRr x ttYYrr what proportion of the offspringwould be expected to be tall plants with round, yellow seeds?
Explanation / Answer
If your looking for a way to shorten the paper work required in alarge Punnet Square you can make three single cross Punnet Squaresinstead of a larger version with more squares. When you do it this way, there will be less paper work but you willneed to do some math in order to arrive at the same conclusions thelonger version delivers. Since each single cross punnet square provides probabilities forevery combination of genotype possible you can multiplyprobabilities from each punnet square for the specific genotype youare interested in. If for instance with a TtRr ttrr cross you are asked how many ttrrresult first focus on the Tt tt cross and you will find there are1/4 tt and when you do a single cross for Rr rr you will note theyare 1/4 rr. Since 1/4 X 1/4 is 1/16, 1/16 of the offspringwill have a ttrr genotype. Hope this helps
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