Exam 4: Mapping Eukaryote Chromosomes by Recombination

In humans,the allele N causes an abnormal shape of the patella in the knee (n is the normal allele).A separate gene is concerned with finger length,and the allele B causes abnormally short fingers,whereas b gives normal length.A study focused on people who have both abnormal patellae and short fingers (they were most likely N/n ^. B/b in genotype),having inherited the N allele from one parent and the B allele from the other parent.These N/n ^. B/b people mated with normal spouses,producing 40 progeny classified as follows: Normal 3 Abnomal knees and fingers 2 Abromal knees only 17 Abnomal fingers only 18 a)Draw the chromosomes of the N/n ^. B/b individuals,their parents,and their four types of children,showing the positions of the alleles. b)Explain why the four types of children were in the proportions shown.

In the fungus Neurospora,a strain that was auxotrophic for thiamine (mutant allele t)was crossed to a strain that was auxotrophic for methionine (mutant allele m).Linear asci were isolated,and they were classified in the following groups: a)Determine the linkage relationships of these two genes to their centromere(s)and to each other.Specify distances in map units. b)If 1000 randomly selected ascospores are plated on a plate of minimal medium,how many are expected to grow into colonies?

The F,G,and H loci are linked in the order written.There are 30 map units between F and G,and 30 map units between G and H.If a plant F G H/f g h is testcrossed,what proportion of progeny plants will be f g h/f g h if there is no interference?

Two albino strains of Neurospora are crossed.Of 200 progeny,195 are albino and 5 are wild type (orange).Each parent,when mated with wild type,gives 1/2 wild-type and 1/2 albino progeny. a)How can you tell that the two mutations involved here represent different genes? b)What is your best estimate of map distance between the two mutations and how did you calculate it?

In the following cross,the genes are inherited independently except for C and D,which are tightly linked and show zero recombination: A/A ;b/b ;c/c ;D/D ;e/e ;F/F - a/a ;B/B ;C/C ;d/d ;E/E ;f/f.In the F₂,what proportion of individuals will be: a)pure breeding? b)heterozygous for all loci? c)homozygous recessive for all loci? d)A/a;B/B;c/c;D/D;E/e;f/f? e)phenotypically like either parent? f)phenotypically unlike either parent? g)genotypically like either parent? h)genotypically unlike either parent?

In a cross in which there is a mean crossover frequency of 0.9 between two marker loci,the recombinant frequency for those loci will be:

The linkage relationships among the four mouse genes,A,B,C,and D,are shown in the map below. What proportion of the eggs produced by a female mouse with genotype Ab/aB;CD/cd will carry all the recessive alleles?

An SSLP is located 2 map units away from the X-linked locus responsible for red-green color blindness.Three alleles of this SSLP are known: "4 repeats," "5 repeats," and "7 repeats." A woman with normal color vision,but whose father is color blind,marries a man with normal vision,and they have a son. Family member SSLP genotype Family member SSLP genotype Woman's father "5 repeats" Woman's husband "3 repeats" Woman "5 repeats"/"7 repeats" Couple's child "5 repeats" Given the SSLP genotypes of the family members shown above,what is the probability that the couple's son is color blind?

A male mouse of genotype A/a ^. B/b is testcrossed multiple times.Overall,these testcrosses produce 11 mice of phenotype A B,81 A b,77 a B,and 14 a b.Based on these data,the genotypes of the male mouse's parents are most likely:

In a diploid invertebrate,genes D and E are closely linked.Single crossovers between these two genes occurs only in 1 out of 40 meioses,and multiple crossovers are never observed.If an individual has the genotype D e/d E,what percentage of its gametes are expected to be recombinant (either DE or de)?

Which of the following is one of the steps that occurs during the process of crossing over?

A diploid plant is a trihybrid for flower color (gene "F"),leaf size (gene "L")and seed weight (gene "S");its phenotype includes red flowers,large leaves,and heavy seeds.This plant is crossed to a tester plant (which has white flowers,small leaves,and light seeds).The progeny is as follows: 23 Red, heavy, large 232 White, heavy, large 25, heavy, small 228 White, heavy, small 230 , light, large 25 White, light, large 235 , light, small 26 White, light, small What can be concluded about the linkage relationships of the three genes in question?

In a cross between an arginine-requiring,acetate-requiring strain of Neurospora and a wild-type strain (arg ac * + +)the following ordered tetrads of asci were found,with the numbers of each type indicated below the particular tetrad: a)Calculate the map distance between arg and its centromere. b)Calculate the map distance between ac and its centromere. c)What is the most likely map of the two genes in relation to each other and to the position of their respective centromere(s)?

Dominant alleles at two different loci affect the tail of mice.These genes are linked and both are lethal in the embryo when homozygous.One of the tail genes is called brachyury (T),and these mice have short tails.A third gene,histocompatibility-2 (H-2),is linked to the tail genes and is concerned with tissue transplantation.Mice that are H-2/+ will accept tissue grafts,unlike +/+.A cross was carried out between male T H-2/ + + and female + +/+ + mice,and produced the following baby mice. Brachy tail, accepts graft 105 Narmal tail, rejects graft 115 Brachy tail, rejects graft 14 Narmal tail, accepts graft 250 Determine if the linkage between H-2 and T is significant using the chi-square test.

Neurospora loci d and f are located on the same chromosome.The d locus always segregates at M_I,while the e locus segregates at M_II at a frequency of 10%.Assuming complete interference,the distance between loci d and f is:

In an experimental plant,the genes t and q are linked.A pure breeding t/t individual is crossed to a pure breeding q/q individual to obtain a dihybrid F₁.Genotypically,the F₁ individuals can be described as:

In a dihybrid female fruit fly with genotype AaBb,88% of the meiosis there are no chiasmata between the A and B loci,and in 12% there is one.What is the expected frequency of recombinant gametes produced by this fly?

Using data from a testcross of a dihybrid,a $\chi$ ² value of 6.5 was obtained,with 3 degrees of freedom.What is the correct interpretation of this result?

The mouse autosomal genes B and S are linked and 38 map units apart.Genotypes B S/B S and b s/b s are intercrossed,and the F₁ is testcrossed to b s/b s.The proportion of B-S- progeny will be:

In Neurospora,a,b,and c are auxotrophic mutants (require particular compounds for growth).The mating a b⁺ *a⁺b gives 5% prototrophs (grown on unsupplemented medium).The mating b⁺c * b c⁺ gives 2.5% prototrophs,and the mating a⁺c * a c⁺ gives 2.5% prototrophs.Assuming complete interference prevails in the chromosome segment in question,what percent of prototrophs would you expect in the mating a⁺b c⁺ * a b⁺c? (The order of mutations is not necessarily a,b,c: It can be determined on the basis of the two-point crosses above.)