A Drosophila embryo dies during early embryogenesis due to arecessive maternal effect allele called bicoid−. The wild-type alleleis designated bicoid+. What are the genotypes and phenotypes ofthe embryo’s mother and maternal grandparents?

Another gene in Drosophila determines wing length. The dominant wild-type allele of this gene produces long wings; a recessive allele produces vestigial (short) wings. A female that is true- breeding for red eyes and long wings is mated with a male that has purple eyes and vestigial wings. F1 females are then crossed with purple-eyed, vestigial-winged males. From this second cross, a total of 600 offspring are obtained with the following combinations of traits: 252 with red eyes and long wings 276 with purple eyes and vestigial wings 42 with red eyes and vestigial wings 30 with purple eyes and long wings Are the genes linked, unlinked, or sex-linked? If they are linked, how many map units separate them on the chromosome?

The gene controlling ABO blood type and the gene underlying nail-patella syndrome are said to show linkage. What does that mean in terms of their relative locations in the genome? What does it mean in terms of how the two traits are inherited with respect to each other?

Assume that a meiotic-nondisjunction event causes trisomy 8 in a newborn. If two of the three copies of chromosome 8 are absolutely identical, at what point during meiosis did the nondisjunction event take place?

A geneticist discovers that a girl with Down syndrome has a Robertsonian translocation involving chromosomes 14 and 21. If she has an older brother who is phenotypically normal, what are the chances that he is a translocation carrier?

Variations in Phenotype Expression Define penetrance and expressivity.

Human females have two X chromosomes XX; males have one X and one Y chromosome XY. a. With respect to X-linked alleles, how many different types of gametes can a male produce? b. A female homozygous for an X-linked allele can produce how many types of gametes with respect to that allele? c. A female heterozygous for an X-linked allele can produce how many types of gametes with respect to that allele?

a. If an individual who is homozygous for the mutation found in individual 2 and heterozygous for the mutation found in individual 4 marries an individual who is homozygous for the mutation found in individual 4 and heterozygous for the mutation found in individual 2, what will be the phenotype of their children? b. List the intermediate that would build up in each of the types of children who could not produce protein E.

Human sex chromosomes are XX for females and XY for males. a. With respect to an X-linked gene, how many different types of gametes can a male produce? b. If a female is homozygous for an X-linked allele, how many different types of gametes can she produce with respect to this allele? c. If a female is heterozygous for an X-linked allele, how many different types of gametes can she produce with respect to this allele?

Almost all calico cats (one is pictured in FIGURE 10.7B) are female. Why? B When this calico cat was an embryo, one of the two X chromosomes was inactivated in each of her cells. The descendants of the cells formed her adult body, which is a mosaic for expression of X chromosome genes. Black fur arises in patches where genes on the X chromosome inherited from one parent are expressed; orange fur arises in patches where genes on the X chromosome inherited from the other parent are expressed. FIGURE 10.7 Animated X chromosome inactivation.