Red fruits (T-) is dominant to tangerine fruits (tt), and smooth leaf (H-) is dominant to hair leaf (hh). Suppose the recombination frequency between these genes is 16%. You take a pure-breeding plant with red fruits and smooth leaves and cross it with a pure-breeding plant with tangerine fruits and hairy leaves. You perform a test-cross with the F1 generation and produce 500 offspring. What is the approximate number of offspring for each possible phenotype?

Question

Briana Banks

Biology

14 January, 11:19

Red fruits (T-) is dominant to tangerine fruits (tt), and smooth leaf (H-) is dominant to hair leaf (hh). Suppose the recombination frequency between these genes is 16%. You take a pure-breeding plant with red fruits and smooth leaves and cross it with a pure-breeding plant with tangerine fruits and hairy leaves. You perform a test-cross with the F1 generation and produce 500 offspring. What is the approximate number of offspring for each possible phenotype?

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Nehemiah Saunders · Answer 1

210 Red fruits, smooth leaf

210 Tangerine fruits, hair leaf

40 Red fruits, hair leaf

40 Tangerine fruits, smooth leaf

Explanation:

1) Cross between pure-breeding plant with red fruits and smooth leaves with a pure-breeding plant with tangerine fruits and hairy leaves.

Pure breeding means that the individual is homozygous for all genes.

The genotypes of these plants, considering that the T/t and H/h genes are linked, can be written as:

TH/TH (same as TTHH) and th/th (same as tthh)

This cross will have a homogeneous F1 offspring: TH/th.

2) Test-cross of the F1

A test cross is a cross between any individual and a homozygous recessive individual.

The gametes produced by the parents are:

Homozygous recessive th/th: only th gametes (parental). F1 individual TH/th: TH (parental), th (parental), Th (recombinant), tH (recombinant).

The frequency of recombination between these genes is 16%, so the total percentage of recombinant gametes produced by the F1 individual is 16%. Because there are 2 possible recombinant gametes, each of them will appear in 8% of the total produced gametes (to add up to the total of 16%).

The other possible gametes are parental, which will appear in 84% of the cases (total 100% minus the recombinant 16%). Because there are 2 possible parental gametes, each of them will appear in 42% of the cases.

The th gamete will be inherited by all of the individuals of the offspring, so the phenotypes of the offspring will be determined by which gamete they inherited from the F1 parent.

The phenotypes of the offspring will be:

Red fruits, smooth leaf (TH/th) : 42% x 500 = 210 Tangerine fruits, hair leaf (th/th) : 42% x 500 = 210 Red fruits, hair leaf (Th/th) : 8% x 500 = 40 Tangerine fruits, smooth leaf (tH/th) : 8% x 500 = 40