Cross 1 Progeny:38 two-lobed, red18 two-lobed, yellow38 multilobed, red18 multilobed, yellowCross 2 Progeny:14 two-lobed, red14 two-lobed, yellow14 multilobed, red14 multilobed, yellowIn tomato plants, the production of red fruit color is under the control of an allele R. Yellow tomatoes are rr. The dominant phenotype for fruit shape is under the control of an allele T, which produces two lobes. Multilobed fruit, the recessive phenotype, have the genotype tt. Two different crosses are made between parental plants of unknown genotype and phenotype. Use the progeny phenotype ratios to determine the genotypes and phenotypes of each parent.PART A: For cross 1, determine two appropriate genotypes for both parents.a) Rrtt × Rrttb) Rrtt × rrTtc) RrTt×Rrttd) Rrtt × RrTt OR rrTt × RrTtPart B: For cross 1, determine two appropriate phenotypes for both parents.a) yellow fruit, two lobes AND red fruit, multiple lobesb) red fruit, two lobes AND red fruit, two lobesc) red fruit, two lobes AND red fruit, multiple lobesd) red fruit, two lobes AND yellow fruit, two lobesPART C: For cross 2, determine two appropriate genotypes for both parents.a) RrTt × Rrttb) RrTt × rrttc) RrTt × rrTtd) RrTt × rrtt OR Rrtt × rrTt

Question

05-02-2020
Biology

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Cross 1 Progeny:38 two-lobed, red18 two-lobed, yellow38 multilobed, red18 multilobed, yellowCross 2 Progeny:14 two-lobed, red14 two-lobed, yellow14 multilobed, red14 multilobed, yellowIn tomato plants, the production of red fruit color is under the control of an allele R. Yellow tomatoes are rr. The dominant phenotype for fruit shape is under the control of an allele T, which produces two lobes. Multilobed fruit, the recessive phenotype, have the genotype tt. Two different crosses are made between parental plants of unknown genotype and phenotype. Use the progeny phenotype ratios to determine the genotypes and phenotypes of each parent.PART A: For cross 1, determine two appropriate genotypes for both parents.a) Rrtt × Rrttb) Rrtt × rrTtc) RrTt×Rrttd) Rrtt × RrTt OR rrTt × RrTtPart B: For cross 1, determine two appropriate phenotypes for both parents.a) yellow fruit, two lobes AND red fruit, multiple lobesb) red fruit, two lobes AND red fruit, two lobesc) red fruit, two lobes AND red fruit, multiple lobesd) red fruit, two lobes AND yellow fruit, two lobesPART C: For cross 2, determine two appropriate genotypes for both parents.a) RrTt × Rrttb) RrTt × rrttc) RrTt × rrTtd) RrTt × rrtt OR Rrtt × rrTt

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Question reformatted

In tomato plants, the production of red fruit color is under the control of an allele R. Yellow tomatoes are rr. The dominant phenotype for fruit shape is under the control of an allele T, which produces two lobes. Multilobed fruit, the recessive phenotype, have the genotype tt. Two different crosses are made between parental plants of unknown genotype and phenotype. Use the progeny phenotype ratios to determine the genotypes and phenotypes of each parent.

Cross 1 Progeny: 38 two-lobed red, 18 two-lobed yellow, 38 multilobed red, 18 multilobed yellow.

Cross 2 Progeny: 14 two-lobed, red 14 two-lobed, yellow 14 multilobed, red 14 multilobed, yellow

Part A

For cross 1, determine two appropriate genotypes for both parents.

a) Rrtt × Rrtt

b) Rrtt × rrTt

c) RrTt×Rrtt

d) Rrtt × RrTt OR rrTt × RrTt

Part B

For cross 1, determine two appropriate phenotypes for both parents.

a) yellow fruit, two lobes AND red fruit, multiple lobes

b) red fruit, two lobes AND red fruit, two lobes

c) red fruit, two lobes AND red fruit, multiple lobes

d) red fruit, two lobes AND yellow fruit, two lobes

Part C

For cross 2, determine two appropriate genotypes for both parents.

a) RrTt × Rrtt

b) RrTt × rrtt

c) RrTt × rrTt

d) RrTt × rrtt OR Rrtt × rrTt

Answer:

Part A - C

Part B - C

Part C - D

Explanation:

Part A

The genotype for two lobed red must be either RRTT, RrTT, RRTt or RrTt, as these are both dominant traits

The genotype for two lobed yellow must be rrTt or rrTT, as yellow is a recessive trait but two lobed is dominant.

The genotype for multilobed red must be Rrtt or RRtt, as multilobed is recessive but red is dominant

The genotype for multilobed yellow must be rrtt, as both these traits are recessive.

The answer cannot be a) as we have multilobed fruit which would require a T allele.

For a dihybrid cross between two heterozygous individuals (i.e. both RrTt) gives the expected ratio of 9:3:3:1, a classic Mendelian ratio for this type of cross. That is not the case for this cross, as there are double the amount of multilobed yellow than we would expected, and half the amount of two lobed red. This suggests one of the parents is homozygous for the t allele, but that they are both heterozygous for the R/r allele. Therefore, we can first check the ratios of RrTt x Rrtt (answer c) by a punnett square (see attached).

The possible gametes are RT, rT, Rt, rt for one parent (RrTt), and RT, Rt and rt for the other parent (Rrtt). This gives us the correct progeny.

If you ever struggle with these questions, just draw out all the possible punnett squares!

Part B

We have determined that the parental genotypes are RrTt x Rrtt. This means the parental phenotypes are Red two-lobed and red multi-lobed, corresponding to answer C.

Part C

The second cross has a ratio of 1:1:1:1. This gives the clue that the gametes are all present in equal numbers (i.e. each parent is heterozygous for one trait and homozygous for the other), OR that one parent is heterozygous for both and one is homozygous to both. This points to option d.