1. A testcross includes a. one parent who is homozygous recessive for one gene p

Question

1. A testcross includes a. one parent who is homozygous recessive for one gene pair and a second parent one parent who is homozygous dominant for one or more genes and a second parent who is homozygous recessive for these same genes two parents who are both heterozygous for two or more genes. one parent who shows the dominant phenotype for one or more genes and a second parent who is homozygous recessive for these genes one parent who shows the recessive phenotype for one or more genes and a second parent who is homozy gous dominant for these genes. is homozygous recessive for a second gene pair. c. d. e. 2. Recombination frequencies can be calculated by counting the number of recombinant and parental offspring when an individual a. who is heterozygous for two genes is testcrossed. performing a chi-square test on the F2 progeny when an individual who is homozygous recessive for these two genes. when a heterozygous individual for two genes is testcrossed. homozygous for two genes is initially crossed to an individual who is c. counting the number of offspring who are expressing the dominant phenotype d, performing a chi-square test of the progeny of a cross between parents who are both heterozygous for the same two genes. counting the number of offspring that are found in the cross of an individual who is heterozygous for two genes with another parent who is homozygous dominant e. for one of these genes and homozygous recessive for the other gene. 3. Assume that an individual of AB/ab genotype is testcrossed and four classes of testcross progeny are found in equal frequencies. Which of the following statements is TRUE? a. The genes A and B are on the same chromosome and closely linked. b. The genes A and B are on the same chromosome and very far apart. The genes A and B are probably between 10 and 20 map units apart on the same c. chromosome. d· The genes A and B are likely located on different chromosomes. e. Either b or d could be correct. 4. Dr. Disney has been raising exotic fruit flies for decades. Recently, he discovered a designates as bb. He also has another it flies that in the recessive condition have baby blue eyes that he strain of fruit flies that in the recessive

Explanation / Answer

1. The correct answer is option (d)

A testcross is done to identify the zygosity of an organism, i.e., whether an organism exhibiting a dominant trait is homozygous or heterozygous. It is performed between a dominant phenotypic parent and a recessive parent.

2. The correct answer is option (a)

The recombination frequencies can be calculated by performing a testcross. In this testcross, a cross is performed between an individual that is heterozygous for both genes and an individual that is homozygous recessive. Homozygous recessive means the individual has only recessive alleles for both the genes and heterozygous means the individual has one dominant and one recessive allele for each of the two genes. Then, count the number of recombinant and parental offsprings. Now, to obtain recombination frequency, add the number of recombinant offsprings and divide it by the total number of offsprings (i.e., the sum of both recombinant and parental offsprings).

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