Here are some practice questions from your textbook to work on during the week.

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Here are some practice questions from your textbook to work on during the week. We will take them up Friday so please put forth an effort and come with some answers. There are 5 questions in total (you may have to scroll to the right to see the rest) so please try them all 3.29. The following is a pedigree of a family in which a rare form of colour blindness is found (filled-in symbols) Indicate as much as you can about the genotypes of all the individuals in the pedigree. HINT Chapter 2 pg. 59 goes through a similar example 2.22. The self-fertilization of an F1 pea plant produced from a parent plant homorygous for yellow and wrinkled seeds and a parent homozygous for green and round seeds resulted in a pod containing seven F2 peas. (Yellow and round are dominant). What is the probability that all seven peas in the pod are yellow and round? 2.10. In humans, a dimple in the chin is a dominant characteristic a. A man who does not have a chin dimple 2.40. In the fruit fly Drosophila 3.36 In Drosophila, the autosomal recessive melanogaster, very dark (ebony) body brown eye colour mutation displays interactions with both the X-linked recessive allele produces the normal wild-type, vermilion mutation and the autosomal colour is determined by the e allele. The e has children with a woman with a chin the two alleles, a dark marking called the trident can be seen on the thorax, but otherwise the body is honey coloured. The e" allele is thus considered to be incompletely dominant to the e allele. have white eyes. Flies simultaneously homozygous for both the brown and scarietWhen female ee flies are crossed to mutations also have white eyes. Predict the F1 and F2 progeny of crossing the following b. A man with a chin dimple and a woman who lacks a dimple. What is the man's male ete files, what is the probability that progeny will have the dark trident A man with a chin dimple and a nondimpled woman produce 8 children, all having the chin dimple. Can you be certain of the man's genotype? Why or c. b. Animals with the trident marking mate a. vermilion females X brown males b. c. d. brown females X vermilion males scarlet females X brown males brown females X scarlet males how many would be expected to have a trident, how many ebony bodies, and how many bodies?

Explanation / Answer

3.29

THe given pedigree chart is of color blindess in a family which is a X-linked recessive trait. Let X- represent the recessive allele for colorblindness and X+ represent the normal domiant allele.

Therefore,

In F1 generation

1 - is a healthy carrier female with the genotype X+X-

2 - is a Healthy male with X+Y

In F2 generation

1 - is a healthy female with X+X+ genotype

2 - is a colorblind male with X-Y genotype

3 - is a healthy carier female with X+X- genotype

4 - is a healthy male with X+Y genotype

In F3 generation

1 - is a healthy carier female with X+X- genotype

2 - is a healthy female with X+X+ genotype

3 - is a colorblind male with X-Y genotype

4 - is a healthy male with X+Y genotype

2.10

Dimple in the chin is a dominant characterisrtic. So let the dominant allele be D where as the recessive allele be d

(A) Man lacks dimple. Hence he carriers recessive alleles i.e. dd

Woman on the other hand is heterzygous as her mother did not have dimple in the chin. Hence she has a genotype Dd.

dd X Dd

Dd Dd dd dd

Therefore 50% of their kids will have dimples in the chin.

(B) Woman and her child lacks dimple in the chin. Hence their genotype is dd.

This can be possible only if the father is heterozygous i.e. has a genotype Dd.

Mother. Father

dd X Dd

Dd Dd dd dd

(C)A man with chin dimple can have the genotype Dd or DD.

If the genotype Dd father has kids with non dimpled woman (genotype dd), the probability of each kid being dimples is 1/2.

However, if the genotype DD father has kids with non dimpled woman (genotype dd), the probability of each kid being dimples is 1, as all kids have the genotype Dd.

Therfore , we cannot be certain of the genotype of the father as more information is required about his genotype.

However its more likely that his genotype is DD, any kids will have will surely have dimples.

2.22

In a pea pland yellow and round are dominat characters.

Therefore let the genotype of Yellow and rounds seeds be YYRR and genotype of green and wrinkled seeds be yyrr.

The pods obtained by mating of these genotypes follow the dihybrid cross ratio of

9 (yellow and round) : 3 (Yellow and wrinkled) : 3 (green and round) : 1 (green and wrinkled)

Hence the probability of any seed being yellow and round is 9/16

Therefore for all 7 peas in a pod to be yellow and round, the probability id 9/16 * 9/16 * 9/16 * 9/16 * 9/16 * 9/16 * 9/16 = (9/16)^7

2.40

ee - dark body color

e+e+ - honey colored body

ee+ - trident containing honey colored body (incomplete dominance)

(A). e+e+ X ee+

F1 ee+ ee+ e+e+ e+e+

Therefore 50% have trident containing honey colored bodies.

(B). ee+ X ee+

F1. ee ee+ ee+ e+e+

Therefore, probability of ebony colored body = 1/4

trident containing honey colored body = 1/2

honey colored body = 1/4

Therefore of the 300 progeny,

ebony colored body = 1/4 * 300 = 75

trident containing honey colored body = 1/2 * 300 = 150

honey colored body = 1/4 * 300 = 75

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