Chapter 7: Linkage and Chromosome Mapping in Eukaryotes

Question 1

True or False. In completely linked genes, only the parental chromosomes are produced upon segregation.

Answer 1

True

Question 2

Determine what types of gametes are produced when two linked genes are far enough for recombination (crossing over) to occur.

Answer 2

1. Two parental (non-crossover) gamete

2. Two recombinant (crossover) gamete

Question 3

True or False. Frequency with which crossing over occurs between any two linked genes is generally proportional to the distance separating the respective loci along the chromosome such that the farther two genes are from one another, the higher the frequency of crossingover.

Answer 3

True

Question 4

Genes located on the same chromosome that show evidence of linkage to one another.

Answer 4

Linkage group

Question 5

What is the linkage ratio?

Answer 5

1:2:1

Question 6

True or False. If a single crossover occurs 100 percent of the time (when two genes are far from one another), recombination is subsequently observed in only 50 percent of the potential gametes formed.

Answer 6

True

Question 7

A phenomenon through which a crossover event in one region of the chromosome inhibits a second event in nearby region.

Answer 7

Interference

Question 8

Defined as the disparities that result from interference

Answer 8

Coefficient of Coincidence (C) - Observed Double Cross Over/Expected Double Cross Over

Question 9

True or False. If two single crossovers that make up a double crossover occur independently of one another, we can calculate the expected frequency of double crossovers by multiplying each individual frequency.

Answer 9

True

Question 10

Happens when no double crossover occurred.

Answer 10

Complete interference

Question 11

True or False. Observed frequency is often less than the expected frequency due to interference.

Answer 11

True

Question 12

Fewer crossover is observed than expected.

Answer 12

Positive interference

Question 13

More double crossovers are observed than expected.

Answer 13

Negative interference

Question 14

Are short segments of DNA whose sequence and location are known, making them useful landmarks for mapping purposes.

Answer 14

DNA markers

Question 15

Are polymorphic sites generated when specific DNA sequences are recognized and cut by restriction enzymes.

Answer 15

Restriction fragment length polymorphisms (RFLPs)

Question 16

Are short repetitive sequences that are found throughout the genome, and they vary in the number of repeats at any given site.

Answer 16

Microsatellites

Question 17

Found throughout the genome, up to several million of these variations may be screened for an association with a disease or trait of interest, thus providing geneticists with a means to identify and locate related genes.

Answer 17

Single-nucleotide polymorphisms (SNPs)

Question 18

Provide the finest level of mapping detail because they pinpoint the nucleotide sequence of genes (and noncoding sequences) on a chromosome.

Answer 18

Sequence map

Question 19

Map genes along a human chromosome in base-pair distances rather than recombination frequency.

Answer 19

Physical map of the genome

Question 20

Maps the genome through recombination frequency

Answer 20

Genetic map

Question 21

Chromatid reciprocal exchanges similar to crossing over occur between sister chromatids. This does not produce new allelic combinations.

Answer 21

Sister chromatid exchanges (SCEs)

Question 22

A human disorder caused by a mutation in the BLM gene on chromosome 15. A recessive disease characterized by prenatal and postnatal retardation of growth, great sensitivity of the facial skin to the sun, immune deficiency, a predisposition to malignant and benign tumors, and abnormal behavior patterns.

Answer 22

Bloom syndrome

Question 23

True or False. Chromosomes from cultured leukocytes, bone marrow cells, and fibroblasts derived from Bloom syndrome homozygotes are very fragile and unstable compared to those of homozygous and heterozygous normal individuals.

Answer 23

True

Question 24

Sister chromatids exhibiting sister chromatid exchanges are called?

Answer 24

Harlequin chromosomes

Question 25

A thymidine analog used to label one member of the sister chromatids to find possible sister chromatid exchanges.

Answer 25

bromodeoxyuridine (BrdU)