The gene causing Coffin–Lowry syndrome (OMIM 303600) was recently identified and mapped on the human X chromosome. Coffin–Lowry syndrome is a rare disorder affecting brain morphology and development. It also produces skeletal and growth abnormalities, as well as abnormalities of motor control. Coffin–Lowry syndrome affects males who inherit a mutation of the X-linked gene. Most carrier females show no symptoms of the disease but a few carriers do. These carrier females are always less severely affected than males. Offer an explanation for this finding.

Earlier, we described CC, the cat created by nuclear transfer cloning, whereby a diploid nucleus from one cell is injected into an enucleated egg cell to create an embryo. Cattle, sheep, rats, dogs, and several other species have been cloned using nuclei from somatic cells. Embryos and adults produced by this approach often show a number of different mitochondrial defects. Explain possible reasons for the prevalence of mitochondrial defects in embryos created by nuclear transfer cloning.

A wild-type male and a wild-type female Drosophila with red eyes and full wings are crossed. Their progeny are shown below.

What is/are the genotype(s) of females with purple eye? Of males with purple eye and miniature wing?

A wild-type male and a wild-type female Drosophila with red eyes and full wings are crossed. Their progeny are shown below.

Using clearly defined allele symbols of your choice, give the genotype of each parent.

If you knew that a devastating late-onset inherited disease runs in your family (in other words, a disease that does not appear until later in life) and you could be tested for it at the age of 20, would you want to know whether you are a carrier? Would your answer be likely to change when you reach age 40?

Four eye-color mutants in Drosophila—apricot, brown, carnation, and purple—are inherited as recessive traits. Red is the dominant wild-type color of fruit-fly eyes. Eight crosses (A through H) are made between parents from pure-breeding lines.

Predict F₂ phenotype ratios of crosses A, B, D, and G.

Four eye-color mutants in Drosophila—apricot, brown, carnation, and purple—are inherited as recessive traits. Red is the dominant wild-type color of fruit-fly eyes. Eight crosses (A through H) are made between parents from pure-breeding lines.

Which of these eye-color mutants are X-linked recessive and which are autosomal recessive? Explain how you distinguish X-linked from autosomal heredity.

For each pedigree shown,

Identify which simple pattern of hereditary transmission (autosomal dominant, autosomal recessive, X-linked dominant, or X-linked recessive) is most likely to have occurred. Give genotypes for individuals involved in transmitting the trait. 

The genes encoding the red- and green-color-detecting proteins of the human eye are located next to one another on the X chromosome and probably evolved from a common ancestral pigment gene. The two proteins demonstrate 76 percent homology in their amino acid sequences. A normal-visioned woman (with both genes present on each of her two X chromosomes) has a red-color-blind son who was shown to have one copy of the green-detecting gene and no copies of the red-detecting gene. Devise an explanation for these observations at the chromosomal level (involving meiosis).