Chapter 7: Linkage and Chromosome Mapping in Eukaryotes Flashcards
True or False. In completely linked genes, only the parental chromosomes are produced upon segregation.
True
Determine what types of gametes are produced when two linked genes are far enough for recombination (crossing over) to occur.
- Two parental (non-crossover) gamete
2. Two recombinant (crossover) gamete
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.
True
Genes located on the same chromosome that show evidence of linkage to one another.
Linkage group
What is the linkage ratio?
1:2:1
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.
True
A phenomenon through which a crossover event in one region of the chromosome inhibits a second event in nearby region.
Interference
Defined as the disparities that result from interference
Coefficient of Coincidence (C) - Observed Double Cross Over/Expected Double Cross Over
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.
True
Happens when no double crossover occurred.
Complete interference
True or False. Observed frequency is often less than the expected frequency due to interference.
True
Fewer crossover is observed than expected.
Positive interference
More double crossovers are observed than expected.
Negative interference
Are short segments of DNA whose sequence and location are known, making them useful landmarks for mapping purposes.
DNA markers
Are polymorphic sites generated when specific DNA sequences are recognized and cut by restriction enzymes.
Restriction fragment length polymorphisms (RFLPs)
Are short repetitive sequences that are found throughout the genome, and they vary in the number of repeats at any given site.
Microsatellites
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.
Single-nucleotide polymorphisms (SNPs)
Provide the finest level of mapping detail because they pinpoint the nucleotide sequence of genes (and noncoding sequences) on a chromosome.
Sequence map
Map genes along a human chromosome in base-pair distances rather than recombination frequency.
Physical map of the genome
Maps the genome through recombination frequency
Genetic map
Chromatid reciprocal exchanges similar to crossing over occur between sister chromatids. This does not produce new allelic combinations.
Sister chromatid exchanges (SCEs)
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.
Bloom syndrome
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.
True
Sister chromatids exhibiting sister chromatid exchanges are called?
Harlequin chromosomes
