1. Which diagram most accurately shows the arrangement of homologous chromosomes during the first metaphase of meiosis? Please explain why and how does this arrangement determine the law of "equal segregation"?
2. Which diagram most accurately shows the arrangement of homologous chromosomes during the first metaphase of mitosis? Please explain if this arrangement is important for the "independent assortment" of genetic factors, and why?
3. The following pedigree was obtained for a rare genetic disorder.
a) What is the inheritance of this condition, and why?
b) If persons 1 and 2 marry, what is the probability for their child to have the kidney disease?
4. Tritanopia (a rare form of inherited blue-yellow color blindness) is caused by mutations in a single gene. A woman with tritanopia marries a man who also has tritanopia. Their first daughter has normal color vision.?a) Based on this information, what is the most likely mode of inheritance of tritanopia, why?
b) Write the genotypes of the two parents and of their daughter.
c) The daughter married to a man with normal color vision. What is the probability of their first child to have tritanopia?
5. In a diploid organism (2n = 6) that is a trihybrid (A/a; B/b; D/d), there are two long, two intermediate, and two short chromosomes. The three genes are on different chromosomes.
a) Which is the accurate representation of a gamete resulting from meiosis in this organism?
b) How many different genotypes AND phenotypes can this organism produce after selfing?
c) What proportion of the progeny phenotypically resembles the trihybrid itself after selfing?
6. Draw linkage maps consistent with the following recombination frequencies. Please make sure to label genetic distances between the linked gene loci.
a) A-B 30%, A-C 50%, B-C 20%, B-D 35%, A-D 50%, C-D 15%
b) A-B 30%, A-C 50%, B-C 50%, B-D 50%, A-D 50%, C-D 15%
7. Three testcrosses involving three linked genes were performed, with the resulting phenotypes:
RT/rtX rt/rt: 43%RT, 43%rt, 7%Rt, 7%rT RS/rsX rs/rs: 45%RS, 45%rs, 4.5%Rs, 4.5%rS TS/tsX ts/ts: 47.5%TS, 47.5%ts, 2.5%tS, 2.5%Ts
(NOTE: Dominant alleles of the three genes are linked on one chromesome, while the recessive alleles are linked on another chromosome in all hybrid parents.)
a) Draw linkage maps consistent with the following recombination frequencies Please make sure to label genetic distances between the linked gene loci
b) You performed a testcross of a trihybridR T S / r t s. Which two phenotypes do you predict to be the least frequent among all progeny, and why?
9. Six haploid fungal mutants that require compound G for growth were isolated. Each mutant contains a recessive allele in a single gene. A total of five compounds (A to E) in the biosynthetic pathway to G are known, but their order in the pathway is not known. Each compound is tested for its ability to support the growth of each of the six mutants (1 to 5). Phenotypes of all of the six mutants are shown in the following table (a plus sign indicates growth and a minus sign indicates no growth).
|
Mutants
|
Compound tested
|
|
A
|
B
|
C
|
D
|
E
|
G
|
|
Mutant 1
|
-
|
-
|
-
|
+
|
-
|
+
|
|
Mutant 2
|
-
|
+
|
-
|
+
|
-
|
+
|
|
Mutant 3
|
-
|
-
|
-
|
-
|
-
|
+
|
|
Mutant 4
|
-
|
+
|
+
|
+
|
-
|
+
|
|
Mutant 5
|
+
|
+
|
+
|
+
|
-
|
+
|
|
Mutant 6
|
+
|
+
|
+
|
+
|
-
|
+
|
a) What is the order of compounds A to E in the pathway? At which point in the pathway is each mutant blocked?
b) What would be the phenotype of the diploid after crossing mutant 1 and 2?
c) What would be the phenotype of the diploid after crossing mutant 5 and 6?
d) What is your prediction of the haploid progeny's phenotype after inducing meiosis of the diploid formed by crossing mutant 1 and 2? (Please describe phenotype and their corresponding ratios, assume independent assortment).