2. Mendel's Laws of Inheritance

Sex-Linked Genes

Open Question
While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses:brown females x vermilion males
Open Question
While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses:vermilion females x brown males
Open Question
In a cross in Drosophila involving the X-linked recessive eye mutation white and the autosomally linked recessive eye mutation sepia (resulting in a dark eye), predict the F₁ and F₂ results of crossing true-breeding parents of the following phenotypes:Note that white is epistatic to the expression of sepia.sepia females x white males
Open Question
In a cross in Drosophila involving the X-linked recessive eye mutation white and the autosomally linked recessive eye mutation sepia (resulting in a dark eye), predict the F₁ and F₂ results of crossing true-breeding parents of the following phenotypes:Note that white is epistatic to the expression of sepia.white females x sepia males
Open Question
Predict the F₁ and F₂ results of crossing a male fowl that is cock-feathered with a true-breeding hen-feathered female fowl. Recall that these traits are sex limited.
Open Question
Form a small discussion group and decide on the most likely genetic explanation for each of the following situations;

Cross A performed by Morgan and shown in Figure 3.18 is between a mutant male fruit fly with white eyes and a female fruit fly from a pure-breeding, red-eye stock. The figure shows that 1237 F₁ progeny were produced, all of them with red eyes. In reality, this isn't entirely true. Among the 1237 F₁ progeny were 3 male flies with white eyes. Give two possible explanations for the appearance of these white-eyed males.
Open Question
Form a small discussion group and decide on the most likely genetic explanation for each of the following situations;

A man who has red–green color blindness and a woman who has complete color vision have a son with red–green color blindness. What are the genotypes of these three people, and how do you explain the color blindness of the son?
Open Question
Duchenne muscular dystrophy (DMD; OMIM 310200) and Becker muscular dystrophy (BMD; OMIM 300376) are both X-linked recessive conditions that result from different mutations of the same gene, known as dystrophin, on the long arm of the chromosome. BMD and DMD are quite different clinically. DMD is a very severe disorder that first appears at a young age, progresses rapidly, and is often fatal in the late teens to 20s. BMD, on the other hand, is much milder. Often symptoms don't first appear until the 40s or 50s, the progression of the disease is slow, and fatalities due to BMD are infrequent. Go to https://www.ncbi.nlm.nih/omim and survey the information describing the gene mutations causing these two conditions. Discuss the information you find with a few others in a small group, and write a single summary explaining your findings.
Open Question
Red–green color blindness is a relatively common condition found in about 8% of males in the general population. From this, population, biologists estimate that 8% is the frequency of X chromosomes carrying a mutation of the gene encoding red and green color vision. Based on this frequency, determine the approximate frequency with which you would expect females to have red–green color blindness. Explain your reasoning.