(Problem 12c) In tomatoes, tall (D) is dominant over dwarf (d) and smooth fruit
ID: 93846 • Letter: #
Question
(Problem 12c) In tomatoes, tall (D) is dominant over dwarf (d) and smooth fruit (P) is dominant over pubescent fruit (p), which is covered with fine hairs. A farmer has two tall and smooth tomato plants, which we will call plant A and plant B. The farmer crosses plants A and B with the same dwarf and pubescent plant and obtains the following numbers of progeny:
!!!Please help. I do not know how to tell if this is coupling or repulsion to help me start the problem. please be detailed in your explanation. Thanks in advance.
Explain why different proportions of progeny are produced when plant A and plant B are crossed with the same dwarf pubescent plant.
A. The differences are due to sampling error and are statistically insignificant.
B. Plant A has the two loci in coupling configuration; Plant B has the two loci in repulsion.
C. Plant A has the two loci in repulsion; Plant B has the two loci in coupling configuration.
D. The two plants have different linkage maps for the two genes. E. The two loci are located on a region of the chromosome that has undergone a deletion in plant B compared to plant A.
Porgeny of Plant A Pant B Dd Pp 122 2 Dd pp 6 82 dd Pp 4 82 dd pp 124 4Explanation / Answer
In genetics, when the dominant alleles are present on the same homologous chromosome and recessive alleles are present in the other homologous chromosome, it is known as coupling. Coupling is also known as cis configuration. Here, the parental gametes are either AB and ab.
When each homologous chromosome has one dominant allele and one recessive allele, it is called repulsion. Repulsion is also known as trans configuration. Here, the parental gametes are Ab and Ab.
Plants A and b are crossed with dwarf and pubescent plant (dd pp). From the number of offsprings given in the table, it is easy to understand that the plant A must have two loci in coupling because the number of offsprings with genotype Dd Pp and dd pp are more. Similarly, plant B must have two loci in repulsion bacause the number of offsprings with genotypes Dd pp and dd Pp are more.
Therefore, the answer for this question is option (B) Plant A has the two loci in coupling configuration; Plant B has the two loci in repulsion.
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