The gene controlling the Xg blood group alleles \(\left(X g^{+} \text {and } X g^{-}\right)\) and the gene controlling a newly described form of inherited recessive muscle weakness called episodic muscle weakness \((E M W X)\) (Ryan et al., 1999 ) are closely linked on the X chromosome in humans at position \(\mathrm{Xp} 22.3\) (the tip of the short arm \() .\) A male with EMWX who is \(\mathrm{Xg}^{-}\) marries a woman who is \(\mathrm{Xg}^{+}\), and they have eight daughters and one son, all of whom are normal for muscle function, the male being \(\mathrm{Xg}^{+}\) and all the daughters being heterozygous at both the \(E M W X\) and \(X g\) loci. Following is a table that lists three of the daughters with the phenotypes of their husbands and children. (a) Create a pedigree that represents all data stated above and in the following table. (b) For each of the offspring, indicate whether or not a crossover was required to produce the phenotypes that are given.

Short Answer

Expert verified
Question: For each of the offspring in the given family, indicate whether a crossover was required to produce the phenotypes given. Answer: In the first daughter's offspring, no crossover was required. In the second daughter's offspring, a crossover was required. In the third daughter's offspring, no crossover was required.

Step by step solution

01

Draw a square for the father who is EMWX and Xg- (shaded square with Xg-), and a circle for the mother who is Xg+. Connect them with a horizontal line. #Step 2: Add the children#

Draw eight circles for the daughters and one square for the son. Label them all as Xg+, and connect them with vertical lines to their parents. Label the sons and daughters with their respective blood group alleles and EMWX status. #Step 3: Connect daughters to their husbands and children#
02

For each of the three daughters listed in the table, draw a circle for the daughter. Connect her with a horizontal line to a square, representing the husband, with their blood group and EMWX alleles. Connect the offspring with vertical lines, and draw circles/squares for each child, with their blood group and EMWX alleles. After completing these steps, you have a pedigree that represents all data provided. Now we can proceed with the second part of the exercise. #b) For each of the offspring, indicate whether a crossover was required to produce the phenotypes given.# To answer this question, we will compare each offspring's genotype with the genotypes of their parents and determine if a crossover event could have resulted in the given phenotypes. #Step 1: Determine whether a crossover has occurred in the first daughter's offspring#

Compare each of the offspring's genotypes with their mother, who is heterozygous for both EMWX and Xg loci. If at least one of the offspring has a genotype that could not have been produced by inheriting a single parental chromosome, then a crossover has occurred. In the first daughter's offspring, both children have inherited the Xg+ blood type, and one has inherited the EMWX gene. Since the mother is heterozygous for both EMWX and Xg, a crossover has not occurred in this case. #Step 2: Determine whether a crossover has occurred in the second daughter's offspring#
03

Follow the same logic for the second daughter. In this case, one of the children has inherited the Xg- blood type, and the other has inherited the Xg+ blood type. Both children have inherited the EMWX gene. Since the mother is heterozygous for both EMWX and Xg, a crossover has occurred in this case. #Step 3: Determine whether a crossover has occurred in the third daughter's offspring#

Apply the same logic to the third daughter's offspring. Here, both children have inherited the Xg+ blood type, and both have inherited the EMWX gene. Since the mother is heterozygous for both EMWX and Xg, a crossover has not occurred in this case. To summarize: - In the first daughter's offspring, no crossover was required. - In the second daughter's offspring, a crossover was required. - In the third daughter's offspring, no crossover was required.

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Most popular questions from this chapter

Why does more crossing over occur between two distantly linked genes than between two genes that are very close together on the same chromosome?

Another cross in Drosophila involved the recessive, X-linked genes yellow \((y),\) white \((w),\) and \(c u t(c t) .\) A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The \(\mathrm{F}_{1}\) females were wild type for all three traits, while the \(\mathrm{F}_{1}\) males expressed the yellow-body and white- eye traits. The cross was carried to an \(\mathrm{F}_{2}\) progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed. (a) Diagram the genotypes of the \(\mathrm{F}_{1}\) parents. (b) Construct a map, assuming that white is at locus 1.5 on the X chromosome. (c) Were any double-crossover offspring expected? (d) Could the \(\mathrm{F}_{2}\) female offspring be used to construct the map? Why or why not?

A homozygous \(A A B B\) mouse was crossed to a homozygous recessive aabb mouse. The \(\mathrm{F}_{1}\) were backcrossed to a homozygous recessive aabb mouse, and the offspring were analyzed for \(A\) and \(B\). The genetic distance between \(A\) and \(B\) was found to be \(10 \mathrm{cM}(\mathrm{mu})\). If 200 mice were analyzed, deduce the phenotypes observed in the offspring.

What possible conclusions can be drawn from the observations that in male Drosophila, no crossing over occurs, and that during meiosis, synaptonemal complexes are not seen in males but are observed in females where crossing over occurs?

An organism of the genotype \(A a B b C c\) was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table. (a) If these three genes were all assorting independently, how many genotypic and phenotypic classes would result in the offspring, and in what proportion, assuming simple dominance and recessiveness in each gene pair? (b) Answer part (a) again, assuming the three genes are so tightly linked on a single chromosome that no crossover gametes were recovered in the sample of offspring. (c) What can you conclude from the actual data about the location of the three genes in relation to one another?

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