Exam 5: Linkage, Recombination, and the Mapping of Genes on Chromosomes

In Neurospora, the white-spore allele (ws) results in white spores rather than the wild-type black spores. Diploid ws / ws+ cells undergo meiosis followed by one round of mitosis to form ordered tetrads. Indicate if the pattern of spores seen in the tetrads are consistent with first-division or second-division segregation. -ws; ws; ws^{+; ws+; ws+; ws+; ws; ws}

A dihybrid testcross is made to determine if genes C and D are linked.The results are shown in the table. Parent genotypes: Cc nbsp;Dd\timesccdd Cc nbsp;Dd 222 Cc nbsp;dd 280 Progeny genotypes: cc nbsp;Dd 280 cc nbsp;dd 218 1000 -Using the chi-square test for goodness of fit, how many degrees of freedom are in this data set?

In Drosophila, singed bristles (sn)and carnation eyes (car)are both caused by recessive X-linked alleles.The wild-type alleles (sn⁺ and car⁺)are responsible for straight bristles and red eyes, respectively.A sn car female is mated to a sn⁺ car⁺ male and the F₁ progeny are interbred.The F₂ are distributed as follows: sn\nobreakspacecar 55 sn\nobreakspaceca 45 s 45 s 200 -What is the ?² value for a chi-square test for goodness of fit of the null hypothesis?

In humans, the genes for red-green color blindness (R = normal, r = color blind) and hemophilia A (H = normal, h = hemophilia) are both X-linked and only 3 map units apart. -A woman whose mother is color blind and whose father has hemophilia A is pregnant with a boy.If the alleles for color blindness and hemophilia A are rare in the population, what is the probability that the baby will have normal vision and normal blood clotting?

Genes that are not syntenic are not linked.

A dihybrid testcross is made to determine if genes C and D are linked.The results are shown in the table. Parent genotypes: Cc nbsp;Dd\timesccdd Cc nbsp;Dd 222 Cc nbsp;dd 280 Progeny genotypes: cc nbsp;Dd 280 cc nbsp;dd 218 1000 -What is a reasonable conclusion based on the chi-square analysis?

Sturtevant's detailed mapping studies of the X chromosome of Drosophila supported what genetic principle?

Chiasmata are structures that show where recombination occurred between sister chromatids.

A coefficient of coincidence of 0.5 in a region of three genes means that half as many double crossovers were observed as would have been expected if crossovers in the two intervals were independent.

Another name for a chromosome is a ________, because it contains alleles that are often inherited together.

Chiasmata can be seen through a light microscope and are sites of recombination.

In Neurospora, the white-spore allele (ws) results in white spores rather than the wild-type black spores. Diploid ws / ws+ cells undergo meiosis followed by one round of mitosis to form ordered tetrads. Indicate if the pattern of spores seen in the tetrads are consistent with first-division or second-division segregation. -ws^{+; ws+; ws+; ws+; ws; ws; ws; ws}

In Drosophila, the autosomal recessive pr and cn mutations cause brown and bright-red eyes, respectively (wild-type flies have brick-red eyes).Flies who are homozygous recessive at both pr and cn have orange eyes.A female who has wild-type eyes is crossed to an orange-eyed male.Their progeny have the following distribution of eye colors: wild-type 8 brown 241 briphit-red 239 orarnge 500 -Which phenotypes are parental?

In Drosophila, singed bristles (sn)and cut wings (ct)are both caused by recessive, X-linked alleles.The wild-type alleles (sn⁺ and ct⁺)are responsible for straight bristles and intact wings, respectively.A female homozygous for sn and ct⁺ is crossed to a sn^+ct male.The F₁ flies are interbred.The F₂ males are distributed as follows: sn ct 13 sn c 36 sct 39 sc 12 What is the map distance between sn and ct?

The pairwise map distances for four linked genes are as follows: A-B = 22 m.u. , B-C = 7 m.u. , C-D = 9 m.u. , B-D = 2 m.u. , A-D = 20 m.u. , A-C = 29 m.u.What is the order of these four genes?

The Q gene locus is 10 map units from the R gene locus which is 40 map units from the S gene locus: Q--10 m.u.--R--40 m.u.--S Which interval would likely show the higher ratio of double to single chiasmata?

Females heterozygous for the recessive second chromosome mutations px, sp, and cn are mated to a male homozygous for all three mutations.The offspring are as follows: \begin{array}{|l|r|}\hline p x  s p  c n & 1461 \\\hline p x  s p  c n^{+} & 3497 \\\hline p x  s p{+ c n} & 1\\\hline p x  s p^{+}  c n+ & 11 \\\hline p x^{+}  s p  c n & 9 \\\hline p x^{+}  s p  c n+ & 0 \\\hline p x^{+}  s p+ c n & 3483 \\\hline p x^{+}  s p+ c n+ & 1539 \\\hline & 10,000 \\\hline\end{array} -What is the coefficient of coincidence in this region?

The genetic distance from one end of a linkage group and the other may exceed 50 m.u.because the distances between many gene pairs are added together to make the map.

If the map distance between genes A and B is 20 map units and the map distance between genes B and C is 35 map units, what is the map distance between genes A and C?

Females heterozygous for the recessive second chromosome mutations px, sp, and cn are mated to a male homozygous for all three mutations.The offspring are as follows: \begin{array}{|l|r|}\hline p x  s p  c n & 1461 \\\hline p x  s p  c n^{+} & 3497 \\\hline p x  s p{+ c n} & 1\\\hline p x  s p^{+}  c n+ & 11 \\\hline p x^{+}  s p  c n & 9 \\\hline p x^{+}  s p  c n+ & 0 \\\hline p x^{+}  s p+ c n & 3483 \\\hline p x^{+}  s p+ c n+ & 1539 \\\hline & 10,000 \\\hline\end{array} -Which of the following linkage maps correctly shows the order and distance between the px, sp, and cn genes?