BIO_SC 2200 Study Guide - Midterm Guide: Hfr Cell, Sister Chromatids, Genetic Recombination

Which of these statements is incorrect?

What is the relative genetic distance between two linked genesif the recombination frequency is 0.49?

What statement best explains the distortion in Mendelian ratiosobserved by Bateson & Punnett in 1905? (Reminder: they found anoverrepresentation of F2 offspring showing both dominant orrecessive phenotypes, and an underrepresentation of offspringdisplaying one dominant and one recessive phenotype)

When determining the relative genetic distance between twogenes, why is dihybrid back-cross preferable over traditionaldihybrid cross?

Why do we map genes?

Please show detailed work. Thanks in advance.

16. Syntenic genes can assort independently when

A) they are very close together on a chromosome.

B) they are located on different chromosomes.

C) crossing over occurs rarely between the genes.

D) they are far apart on a chromosome and crossing over occurs frequently between the genes.

E) they are far apart on a chromosome and crossing over occurs very rarely between the genes.

17. The alleles of linked genes tend to

A) segregate together more often than expected by random assortment

B) assort independently.

C) be mutated more often than unlinked genes.

D) experience a higher rate of crossing over.

E) assort independently and show a higher rate of crossing over.

18. If you know that the frequency of recombination between genes X and Y is 34% and between X and Z is 25%, can you predict the order of the three genes?

A) Yes; the order is X-Z-Y.

B) Yes; the order is X-Y-Z.

C) Yes; the order is Z-X-Y.

D) No; based on this data alone, the order could be Z-Y-X or X-Y-Z.

E) No; based on this data alone, the order could be X-Z-Y or Z-X-Y.

Question 19 - 20. You have performed the following dihybrid cross in Drosophila using the black body color (b) and vestigial wing (vg) mutations. The b+ (grey body) and vg+ (normal wing) are dominant wild type alleles. These genes are autosomal.

Female ♀ b+ vg+/b vg × male ♂ b vg/b vg

Progeny:

Phenotype # of Progeny

Grey body normal wing 965

Black body vestigial wing 944

Grey body vestigial wing 208

Black body normal wing 195

19. Assuming linkage between black and vestigial, the estimated recombination frequency would be:

0.17

0.09

0.82

1.00

0.50

20. What key test could you use to determine whether the observed offspring frequencies deviate from those expected by chance alone?

A) Pascal's triangle

B) The product rule

C) The Chi-square (χ²) test

D) The law of random assortment

E) The sum rule

21. In a genome wide association study (GWAS) designed to map the gene(s) that control height you divide subjects into a group of 1000 who are all more than seven feet tall and a control group of 1000 people of average height. You find the following associations between two genetic markers and the height trait:

What is your best guess for which marker is more closely linked to a gene that influences height?

A) Marker 1

B) Marker 2

22. Two pure breeding parents produce red and white flowers. They are crossed and the F1 produces pink flowers. When the F1 are selfed to produce the F2, nine distinct classes of pigmentation are present among F2 individuals. What is your best guess of the minimum number of genes that underlie flower pigmentation in this species?

A. 2

B. 3

C. 4

D. 5

E. 6

23. In a quantitative genetic experiment you identify two genes that confer bands of color on the back of a fly. At each gene, a dominant allele causes one band of color. If flies that are heterozygous at both loci are crossed, what ratio of offspring do you expect in each phenotype (i.e., number of color bands) class? (answer options are given from lowest to highest band number)

A) 1:1:1:1:1

B) 1:2:2:2:1

C) 1:4:6:4:1

D) 4:4:4:4:4

Canaries: Green (wild-type) Pied phenotype Yellow type

Canaries are popular pets and easy to breed in captivity. Additionally, they display great phenotypic diversity, which allows you to do some interesting genetic investigations with them.

When you take a canary from a true-breeding green strain and cross it with a canary from a true-breeding yellow strain, all offspring display the pied phenotype. Based on this you suspect that this color variation is inherited by a gene with a co-dominant inheritance pattern (showing both phenotypic traits in hybrid phenotypes).

You decide to test this hypothesis. To do so, you take pairs of your hybrid F1 individuals (of pied phenotype), and cross them to produce an F2 generation.

After many dozens of crosses and hundreds of offspring, you arrive at the peculiar ratio of:

3/16 green : 6/16 pied : 7/16 yellow

Which of the following hypotheses are consistent with these data? (Note that not all of these hypotheses are mutually exclusive. Assume that the two genes are independently assorting)

Hint: This problem is very hard to work from the given ratios to what is happening genetically. It is easier to "work backwards" and start with each choice below, and see if you can obtain all or important aspects of the results of your cross when making the assumption that the answer choice is correct.

Select all that apply:

Select one or more:

a. At least one of the genes involved is sex linked.

b. One gene controls production of darker pigment (melanin which appears green when mixed with yellow). A second gene acts as a patterning gene with one allele causing expression and the other non-expression of melanin and when in the heterozygous condition each allele controls melanin expression on different parts of the body so long as the bird's genotype of the first gene allows for the production of melanin.

c. this is a single-gene trait with co-dominance

d. one of the two genes involved displays complete dominance, while the other displays co-dominance.

e. the genes involved are epistatically interacting

f. more than one gene is involved