In an 1889 book titled Natural Inheritance (Macmillan, New York), Francis Galton, who investigated the inheritance of measurable (quantitative) traits, formulated a law of 'ancestral inheritance.' The law stated that individuals inherit approximately one-half of their genetic traits from each parent, about one-quarter of the traits from each grandparent, one-eighth from each great grandparent, and so on. In light of the chromosome theory of heredity, argue either in favor of Galton's law or against it.

Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.

If the first son of the woman described in (a) is affected, what is the probability that her second son is affected?

Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.

What is the probability that the first son of a man whose brother has Lesch–Nyhan syndrome will be affected?

In humans, SRY is located near a pseudoautosomal region (PAR) of the Y chromosome, a region of homology between the X and Y chromosomes that allows them to synapse during meiosis in males and is a region of crossover between the chromosomes. The diagram below shows SRY in relation to the pseudoautosomal region.

About 1 in every 25,000 newborn infants is born with sex reversal; the infant is either an apparent male but with two X chromosomes or an apparent female but with an X and a Y chromosome. Explain the origin of sex reversal in human males and females involving the SRY gene. (Hint: See Experimental Insight 3.1 for a clue about the mutational mechanism.) 

In Drosophila, the X-linked echinus eye phenotype disrupts formation of facets and is recessive to wild-type eye. Autosomal recessive traits vestigial wing and ebony body assort independently of one another. Examine the progeny from the three crosses shown below, and identify the genotype of parents in each cross.

A wild-type Drosophila male and female are crossed, producing 324 female progeny and 161 male progeny. All their progeny are wild type.

Propose a genetic hypothesis to explain these data.

A wild-type Drosophila male and female are crossed, producing 324 female progeny and 161 male progeny. All their progeny are wild type.

Design an experiment that will test your hypothesis, using the wild-type progeny identified above. Describe the results you expect if your hypothesis is true.