Define the Lyon hypothesis.

What is a Barr body, and where is it found in a cell?

Indicate the expected number of Barr bodies in interphase cells of individuals with Klinefelter syndrome, Turner syndrome, and karyotypes 47, XYY, 47, XXX, and 48, XXXX.

Drosophila may be monosomic for chromosome 4, yet remain fertile. Contrast the F₁ and F₂ results of the following crosses involving the recessive chromosome 4 trait, bent bristles:

monosomic IV, normal bristles x diploid, bent bristles.

Drosophila may be monosomic for chromosome 4, yet remain fertile. Contrast the F₁ and F₂ results of the following crosses involving the recessive chromosome 4 trait, bent bristles:

monosomic IV, bent bristles x diploid, normal bristles

Mendelian ratios are modified in crosses involving autotetraploids. Assume that one plant expresses the dominant trait green seeds and is homozygous (WWWW). This plant is crossed to one with white seeds that is also homozygous (wwww). If only one dominant allele is sufficient to produce green seeds, predict the F₁ and F₂ results of such a cross. Assume that synapsis between chromosome pairs is random during meiosis.

Can the Lyon hypothesis be tested in a human female who is homozygous for one allele of the X-linked G6PD gene? Why, or why not?

In humans that are XX/XO mosaics, the phenotype is highly variable, ranging from females who have classic Turner syndrome symptoms to females who are essentially normal. Likewise, XY/XO mosaics have phenotypes that range from Turner syndrome females to essentially normal males. How can the wide range of phenotypes be explained for these sex-chromosome mosaics?

A plant breeder would like to develop a seedless variety of cucumber from two existing lines. Line A is a tetraploid line, and line B is a diploid line. Describe the breeding strategy that will produce a seedless line, and support your strategy by describing the results of crosses.