Deck 9: The Locations of Genes on Chromosomes: Linkage and Genetic Maps

Question 1

Match the missing words in the following phrase. Genes are [A] if they are on the same chromosome and are [B] if they are on different chromosomes. Genes that are on different chromosomes segregate [C] at meiosis whereas genes on the same chromosome are more frequently inherited [D].

Answer 1

a. A = linked
b. B = unlinked
c. C = independently
d. D = together

Question 2

Which structure that forms during meiosis leads directly to the formation of recombinant chromosomes?

A) microtubule
B) centromere
C) sister chromatid
D) crossover

Answer 2

crossover

Question 3

Fill in the blank. In a cross between parents with the genotypes A/a;B/b and a/a;b/b, where the A and B loci are unlinked, __% of the offspring will have a phenotype that differs from the phenotype of both parents.

Answer 3

50

Question 4

A cross between two true-breeding strains (P₀ generation) with genotypes A/A;b/b and a/a;B/B results in an F₁ genotype of A/a;B/b. If this is test-crossed to a/a;b/b, which of the following offspring have parental phenotypes?
Please select all that apply.

A) A/a;B/b
B) A/a;b/b
C) a/a;B/b
D) a/a;b/b

Question 5

A series of crosses to test whether two genes in Drosophila flies are sex-linked and on the same chromosome, and which alleles are dominant, are described below. Match each conclusion with the piece of evidence supporting it.
A cross between a true-breeding black, apterous (no wings) female parent and a true-breeding wild-type male parent produced 100% F₁ offspring with wild-type phenotype in both sexes. A test cross of an F₁ male with the female parent produced 45% wild-type flies, 45% black, apterous flies, 5% flies with a black body and normal wings, and 5% apterous flies with a normal colored body.
a. The two genes are autosomal
b. Normal wings is dominant
c. The two genes are on the same chromosome

Question 6

What does 10 centiMorgans (cM) represent?

A) 1% recombination between two genes on the same chromosome
B) 10% recombination between two genes on the same chromosome
C) 1% recombination between two genes on different chromosomes
D) 10% recombination between two genes on different chromosomes

Question 7

In an experiment, two homologous chromosomes with alleles as shown below (original homologous chromosomes) underwent meiosis and to product four chromosomes (resultant chromosomes). How many crossovers appear to have occurred during meiosis?

Question 8

Genes that are located close together on a homologous chromosome are more likely to be inherited together than genes that are further apart.

Question 9

Which of the following are necessary characteristics of balancer chromosomes? Please select all that apply.

A) Suppression of crossing over
B) No centromere
C) Easily distinguished heterozygote
D) Haploidy

Question 10

An experiment was conducted with Drosophila flies carrying recessive white-eye and yellow-body alleles. The white and yellow genes are on the X-chromosome. The parental (P₀) individuals were homozygous white-eye, normal body female and red-eye, yellow-body male. F₁ females had a wild-type phenotype and F₁ males had normal bodies and white eyes. F₁ individuals were then mated. What phenotypes are expected in the F₂ generation? Please select all that apply.

A) 100% of females have a normal body
B) There are very few wild-type males
C) ~25% of males have white eyes
D) ~25% of females have white eyes

Question 11

When genes are on the same chromosome, the alleles on one of the two homologous chromosomes are considered to be in trans.

Question 12

The maximum map distance that can be observed in a cross concerning two loci is ___ map units.

Question 13

What is a tetrad

A) The cellular structure that contains the four products of meiosis
B) The structure that joins chromosomes to microtubules
C) Four paired homologous chromosomes
D) Two pairs of sister chromatids

Question 14

Two genes can be syntenic and unlinked.

Question 15

Syntenic blocks are sections of chromosomes that have remained largely intact during evolution. For example, human chromosome 4 corresponds to syntenic blocks on mouse chromosomes 3, 5, and 8. Which of the following statements about synteny are true? Please select all that apply.

A) No crossovers occur in syntenic blocks
B) The ancestor of humans and mouse probably had similar syntenic blocks to those currently seen in mouse and human
C) X chromosomes are largely syntenic between placental mammals
D) The ancestor of humans and mouse had syntenic blocks as in human and these were rearranged to make different chromosomes in mouse

Question 16

Which of the following statements about double-crossovers are true? Please select all that apply.

A) The chance of double crossovers occurring between two loci increases with the distance between the loci
B) Double-crossovers result in the rate of recombination between two loci being overestimated
C) Double crossovers result in the estimated map distance between two loci being underestimated
D) The probability of a double crossover occurring between two loci is higher than the probability that a single crossover will occur between the same loci.

Question 17

Ascomycete fungi are valuable models for studying recombination. Which of the following are advantages of these systems? Please select all that apply.

A) Haploid progeny can be analyzed directly
B) The four products of meiosis remain together
C) Test crossing is not always needed
D) Haploids can undergo meiosis

Question 18

A Drosophila parent fly heterozygous for alleles for black body, dumpy wings, and purple eyes was test-crossed to a fly that was homozygous recessive for all three genes. The genes are all on the same chromosome. The offspring had the following phenotypes in the following numbers:
$\begin{array}{|l|c|}\hline \text { Phenotype } & \text { Number of offspring } \\\hline \text { wild type } & 225 \\\hline \text { black body, purple eyes, dumpy wings } & 238 \\\hline \text { dumpy wings } & 122 \\\hline \text { black body, purple eyes } & 135 \\\hline \text { black body, dumpy wings } & 15 \\\hline \text { purple eyes } & 19 \\\hline \text { purple eyes, dumpy wings } & 6 \\\hline \text { black body } & 5 \\\hline\end{array}$ What were the genotypes of the chromosomes in the parent? Please select all that apply.

A) b⁺ p⁺ d⁺
B) b p d
C) b⁺ p d⁺
D) b p⁺ d
E) b⁺ p⁺ d
F) b p⁺ d⁺

Question 19

A Drosophila fly heterozygous for alleles for black body, dumpy wings, and purple eyes was test-crossed to a fly that was homozygous recessive for all three genes. The genes are all on the same chromosome. The offspring had the following phenotypes in the following numbers:
$$\begin{array} { | l | c | } \hline \text { Phenotype } & \text { Number of offspring } \\\hline \text { wild type } & 225 \\\hline \text { black body, purple eyes, dumpy wings } & 238 \\\hline \text { dumpy wings } & 122 \\\hline \text { black body, purple eyes } & 135 \\\hline \text { black body, dumpy wings } & 15 \\\hline \text { purple eyes } & 19 \\\hline \text { purple eyes, dumpy wings } & 6 \\\hline \text { black body } & 5 \\\hline\end{array}$$ What is the order of the genes on the chromosome?

A) black - purple - dumpy
B) black - dumpy - purple
C) purple - black - dumpy
D) dumpy - purple - black

Question 20

Alleles for hairy body, curled wings, and glass eyes are on the same Drosophila chromosome. There are 23.5 map units between hairy and curled and 13 map units between curled and glass. One percent of offspring from a test cross had double crossovers. Was crossover interference observed?

A) Yes. Interference is 67%
B) Yes. Interference is 33%
C) No. Interference is 0%
D) No. Interference is 100%

Question 21

Match the missing words in the following phrase. Genomes in [A] could be mapped even though, unlike [B], they do not undergo meiotic [C]. Genes can be transferred between bacteria by [D] and bacterial genomes can be mapped according to [E]. Currently, bacterial genomes are almost always mapped by assessing the [F].

Question 22

Which of the following statements about genetic and physical maps are true? Please select all that apply.

A) The order of genes is the same in physical and genetic maps
B) A physical map shows the location of genes on the DNA molecule
C) A genetic map unit always corresponds to the same amount of DNA for a particular species
D) Physical maps give the probability that alleles of two genes will be inherited together

Question 23

Physical (top) and genetic (bottom) maps are shown for C. elegans chromosome I
Physical and genetic maps can be used to determine the physical length of a map unit. Put the following intervals in C. elegans chromosome I in ascending order, from shortest physical length per map unit to longest (i.e., A = shortest, C = longest).

Question 24

If recombination rate is high, then a particular combination of alleles is likely to be transferred to the next generation intact.

Question 25

What are cytological maps used for?

A) To examine whether cells are undergoing meiosis
B) To determine the recombination rate between loci
C) To determine the gene responsible for a trait
D) To examine changes in chromosomal structure