Download Homework Assignment #5

Homework 5
1. A female has a mosaic, patchwork skin pigmentation phenotype. Describe her genotype and explain the mosaic
pigment pattern if:
a) the phenotype is due to an X-linked recessive allele (10 Points);
b) the phenotype is due to a mitochondrial mutation (10 Points);
c) If she mated with a normal, wild-type male, what is the probability that their first child would be a daughter with
mosaic skin pigmentation pattern if inheritance is as described in (part a)? If the probability cannot be determined with
certainty, please explain why not and describe what might happen with as much precession as possible (10 Points).
d) If she mated with a normal, wild-type male, what is the probability that their first child would be a daughter with
mosaic skin pigmentation pattern if inheritance is as described in (part b)? If the probability cannot be determined with
certainty, please explain why not and describe what might happen with as much precession as possible (10 Points).
2. Drug resistance in Chlamydomonas can be due to mitochondrial mutations, chloroplast mutations, or nuclear
mutation. You have two strains of Chlamydomonas. One is mt+ mating type and is resistant to Drugs A, B and C. The
other is mt- mating type and is sensitive to Drugs A, B and C. You crossed the two strains and analyzed 300 progeny. The
phenotypes of the progeny are shown below.
140 mt+ resistant to A sensitive to B and resistant to C
10 mt+ sensitive to A sensitive to B and resistant to C
10 mt- resistant to A sensitive to B and resistant to C
140 mt- sensitive to A sensitive to B and resistant to C
a) Which, if any, drug resistance phenotype is due to a mutation in a mitochondrial gene? Briefly explain your answer
using the information on the phenotypic proportion of progeny.
b) Which, if any, drug resistance phenotype is due to a mutation in a chloroplast gene? Briefly explain your answer using
the information on the phenotypic proportion of progeny.
c) Which, if any, drug resistance phenotype is due to a mutation in a nuclear gene? Briefly explain your answer using
the information on the phenotypic proportion of progeny.
d) For each drug resistance gene that is nuclear, indicate whether it is linked to the mating type gene (mt) or not. If it is
linked, what is the genetic distance separating mt and the drug resistance gene? (10 Points)
4. Human females who have 47,XXX or 48,XXXX karyotypes who are not homozygous for recessive, deleterious alleles
and do not contain dominant deleterious alleles are more or less phenotypically normal.
a) Explain why this should be true in terms of the levels of expression of most genes on X in 46,XX, 47,XXX and 48,XXXX
individuals. (10 Points)
b) Do you expect the levels of expression of all X genes in a woman who is 46,XX to be identical to that in one who is
48,XXXX? Explain.
c) You have mapped the location of two traits showing autosomal recessive inheritance. One is located on the human X
chromosome and the other is located on the human Y chromosome. How do you explain these results? (10 Points)
5. You are investigating the chromosomal basis of sex in three
new animal species. The primary sex ratio in each species is
approximately 1:1 regardless of environmental conditions. You
look at cells at metaphase of meiosis I from males and females
in all three species and see the images shown in the figure. Use
this information to answer the questions below.
a) Which species, if any, has XX XY sex determination? Label
the X and Y chromosomes in the figure. (10 Points)
b) Which species, if any, has ZZ ZW sex determination? Label
the Z and W chromosomes in the figure. (10 Points)
c) Which species, if any, has neither an XX XY nor a ZZ ZW sex
determination mechanism? How do you explain the 1:1
primary sex ratio in this species? (10 Points)