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26 Jun 2018

Hi, could somebody explain me how the linked genes A/a and C/c affect the probability in the following problem?

You are running a dihybrid cross involving 4 different genes. Three different chromosomes are involved and only the A/a and C/c genes are linked. With diploid parents AaBbccDd x AaBbcCdd (Ac and aC are linked in the second parent) and no crossing over, what are the odds of progeny with genotypes (a) aaBbccdd, (b) aabbCcDd, (c) AABbccdd?

Here are the solutions but I do not understand how they obtiened the calculations for A/a and C/c

Answers: (a) Can’t happen (second parent provides gametes Ac and aC only; (b) ¼ (bb part) * ½ (Dd) * ¼ (aaCc) = 1/32; (c) ½ * ½ * ¼ (same order as with (b)) = 1/16

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Casey Durgan
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27 Jun 2018

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Males can inherit a gene for an X-linked trait from either parent but normally inherit it from their fathers.

Question:

If a female animal with genotype A/A. b/b (the back-slash indicates the chromosome) is crossed with a male that is genotypically a/a. B/B and the F1 is testcrossed, determine the percentage of the progeny from the testcross that will be a/a. b/b, if the two genes are:

a. Unlinked (Show your work).

Answer: AaBb X aabb AaBb – ¼ aabb - ¼ aaBb - ¼ Aabb - ¼ OK

b. Completely linked, i.e., no crossing over at all (Show your work).

Answer: With completely linked genes without crossing over, the only genes possible are AB and ab gametes.

Result:

Therefore the only possibility of having homozygous aabb is 50%.

No; a b is recombinant; please redo

c. 10 mp units apart (Show your work).

Answer: If the linked genes are 10 map units apart, 10% of the results would be recombinants. As F1 progeny ab is part of the parental class, only half of the total parental genotypes will be present. Therefore: 45%

No; a b is recombinant; please redo

d. 24 map units apart (Show your work).

Answer: Same rule applies for c. Therefore the percentage of progeny would be equal to 38%.

No; a b is recombinant; please redo

This is all the information given and need help. I've answered the question and my prof says the answers for b c and d are wrong. Could you please help me out? and also could you explain with the answers? Thank you.

ANSWER ALL the PARTS you can

PART1 Alleles are considered linked if recombination is less than 50% in:

a) a Px P Fl cross

b) an F1 x F1F2 cross

c) an F2 x F2F3 cross

d) an Fl x homozygous recessive cross

e) any F2 progeny x homozygous recessive cross 1.

PART2 If two loci A/a B/b are 9 map units apart, and an Ab/aB individual is testcrossed,

a) There will be 9% AB individuals

b)There will be 91% Ab individuals

c) There will be 4.5% ab individuals

d) There will be 91% recombination individuals

If two genes a and b show 50% recombination genes a and c show 35% recombination, and genes b and show 32% recombination, then

a) Genes a and b are on the same chromosome, and 50 m.u. apart

b) Genes a and b are on different chromosomes

c)Genes a and b are on the same chromosome, and 67 map units apart

d) One cannot tell if genes a and b are on the same or different chromosomes from given data.

PART4 If two genes a and b are 8.3 m.u. a part, one expects to find

a) 8.3% recombinant gametes from a double heterozygous parent

b) 91.7% recombinant gametes from a double heterozygous parent

c) A chiasma between the a and b loci in 8.3% of the meiosis

d) A chiasma between the a and b loci in 91.7% of the meiosis.

PART5 Map distances are most accurate when genes are closely linked because as genes become further apart,

a) They always show independent assortment

b)The chance of multiple crossovers increases

c) They no longer recombine

d) There is chiasma interference

PART6 In a three-point testcross, the most frequent classes of progeny were ABc and abC. The less frequent classes of progeny were AbC and aBc. Which gene is in the middle?

a) Aa

b) B/b

c)C/c

d) It is not possible to tell from just these data

PART7 In a three-point testcross with 100 progeny, there were 16 single crossovers between genes A and B, 29 single crossovers between genes B and C, and 4 double crossovers. The correct gene order was determined to be A-B-C. What is the map distance between A and B?

a) 20%

b) 0.2 m.u

c) 20 m.u.

d) 16 m.u.

e) 29 m.u.

f) 16%

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