Genetics Ch 4 Study Guide

Front 1

The phenomenon in which the products of a meiotic division in an Aa heterozygous genotype are in some ratio other than the expected 1A : 1a -- for example, 3A:1a, 1A:3a, 5A:3a, or 3A:5a.

Back 1

gene conversion

Front 2

An enzyme that catalyzes the breakage and rejoining of two DNA strands in a Holliday junction to generate two independent duplex molecules.

Back 2

holliday junction- resolving enzyme

Front 3

The proportion of gametes carrying combinations of alleles that are not present in either parental chromosome.

Back 3

frequency of recombination

Front 4

In meiosis, the effect that crossing-over between one pair of nonsister chromatids may have on the probability that a second crossing-over in the same chromosome will involve the same or different chromatids; chromatid interference does not generally occur.

Back 4

chromatid interference

Front 5

The region of the chromosome that is associated with spindle fibers and that participates in normal chromosome movement during mitosis and meiosis.

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centromere

Front 6

The arrangement of linked genes in a double heterozygote in which both mutations are present in the same chromosome -- fox example, a1a2/+ +; also called coupling.

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cis configuration

Front 7

The tendency for crossing-over to inhibit the formation of another crossover nearby.

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interference

Front 8

An ascus containing two pairs of nonrecombinant spores.

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parental ditype (PD)

Front 9

A nuclease that recognizes a short nucleotide sequence (restriction site) in a DNA molecule and cleaves the molecule at that site; also called a restriction endonuclease.

Back 9

restriction enzyme

Front 10

A diagram of the order of genes in a chromosome in which the distance between adjacent genes is proportional to the rate of recombination between them; also called a genetic map.

Back 10

linkage map

Front 11

The arrangement of linked genes in a double heterozygote in which both mutations are present in the same chromosome -- fox example, a1a2/+ +; also called cis-configuration, or cis-heterozygote.

Back 11

coupling configuration

Front 12

Cross in which three genes are segregating; used to obtain unambiguous evidence of gene order.

Back 12

three point crossing

Front 13

In fungi, the genetic analysis of spores collected at random rather than from individual tetrads.

Back 13

random spore analysis

Front 14

The arrangement in linked inheritance in which a genotype heterozygous for two mutant sites has received one of the mutant sites from each parent -- that is, a1+ / +a2.

Back 14

repulsion configuration

Front 15

A diagram of the order of genes in a chromosome in which the distance between adjacent genes is proportional to the rate of recombination between them; also called a genetic map.

Back 15

genetic map

Front 16

The set of genes present together in a chromosome.

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linkage group

Front 17

Separation of a pair of alleles into different nuclei in the first meiotic division; happens when there is no crossing-over between the gene and the centromere in a particular cell.

Back 17

first division segregation

Front 18

sac containing the spores (ascospores) produced by meiosis in certain groups of fungi, including Neurospora and yeast.

Back 18

ascus

Front 19

An ascus containing spores of four different genotypes -- one each of the four genotypes possible with two alleles of each of two genes.

Back 19

tetratype

Front 20

A site in the DNA occupied by a different nucleotide pair among a significant fration of the individuals in a population.

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single- nucleotide polymorphism (SNP)

Front 21

The spores produced by meiosis in certain groups of fungi; contained in the ascus

Back 21

ascopore

Front 22

The presence in a population of two or more relatively common forms of a gene, chromosome, or genetically determined trait.

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polymorphism

Front 23

All or part of a double-stranded nucleic acid molecule in which the two strands have different hereditary origins; produced either as an intermediate in recombination or by the in vitro annealing of single-stranded complementary molecules.

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heteroduplex

Front 24

Any pair of alleles whose inheritance can be traced through a mating or through a pedigree.

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genetic marker

Front 25

A chromosome that results from crossing-over and that carries a combination of alleles differing from that of either chromosome participating in the crossover; the cell or organism that contains a recombinant chromosome.

Back 25

recombinant

Front 26

The arrangement of linked genes in a double heterozygote in which both mutations are present in the same chromosome -- fox example, a1a2/+ +; also called coupling.

Back 26

cis- heterzygote

Front 27

Segregation of a pair of alleles into different nuclei in the second meiotic division, the result of crossing-over between the gene and the centromere of the pair of homologous chromosomes.

Back 27

second division segregation

Front 28

The site or position of a particular gene on a chromosome.

Back 28

locus

Front 29

Genetic variation in a population associated with the size of restriction fragments that contain sequences homologous to a particular probe DNA; the polymorphism results from the positions of restriction sites flanking the probe, and each variant is essentially a different allele.

Back 29

restriction fragment length polymorphism (RFLP)

Front 30

An experimental value obtained by dividing the observed number of double recombinants by the expected number calculated under the assumption that the two events take place independently.

Back 30

coefficient of coincidence

Front 31

The genetic distance between two marker genes expressed as the sum of the length in map units across of a set of small, nonoverlapping intervals between the marker genes; corresponds to one-half of the average number of chiasmata between the genes multiplied by 100.

Back 31

map distance

Front 32

The cytological manifestation of crossing-over; the cross-shaped exchange configuration between nonsister chromatids of homologous chromosomes that is visible in prophase I of meiosis. The plural can be either chiasmata or (chiasmas.

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chiasma

Front 33

An ascus containing two pairs of recombinant spores.

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nonparental ditype (NPD)

Front 34

Any mechanism that arrests the cell cycle until one or more essential processes are completed.

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checkpoint

Front 35

A cross-shaped configuration of two DNA duplexes formed as an intermediate in recombination.

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holliday junction

Front 36

Exchange of parts between DNA molecules or chromosomes; recombination in eukaryotes usually entails a reciprocal exchange of parts, but in prokaryotes it is often nonreciprocal.

Back 36

recombination

Front 37

A unit of distance in the genetic map equal to 1 percent recombination; also called a map unit.

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centimorgan

Front 38

The tendency of genes located in the same chromosome to be associated in inheritance more frequently than expected from their independent assortment in meiosis.

Back 38

linkage

Front 39

The tendency of genes located in the same chromosome to be associated in inheritance more frequently than expected from their independent assortment in meiosis.

Back 39

map unit

Front 40

The arrangement in linked inheritance in which a genotype heterozygous for two mutant sites has received one of the mutant sites from each parent -- that is, a1+ +a2.

Back 40

trans configuration

Front 41

A diagram showing the locations and relative spacing of genes along a chromosome.

Back 41

chromosome map

Front 42

Alleles present in an offspring chromosome in the same combination as that found in one of the parental chromosomes.

Back 42

parental combination

Front 43

If recombination frequency between two genes is 3 percent, what is the distance between the genes in map units on the linkage map__

Back 43

3

Front 44

On a chromosomal map, 2 map units are equal to __

Back 44

2% of recombination

Front 45

The maximum recombination frequency between two genes is___

Back 45

50%

Front 46

A coefficient of coincidence of 0.5 means that___

Back 46

The frequency of double crossovers is 0.5 of the number expected if there were no interference

Front 47

The physical exchange of segments between homologous chromosomes is called ___

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crossing over

Front 48

In the absence of recombination, what ratio of phenotypes is expected in the progeny of the cross AB/ab x aB/Ab?

Back 48

1 aaB- : 2 A-B- : 1A-bb

Front 49

In tetrad analysis 3-strand double crossing-over between two linked genes results in___

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TT tetrad

Front 50

The tendency for crossing-over to inhibit the formation of another crossover nearby is called ___

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interference

Front 51

Gene conversion results from a normal DNA repair process in the cell known as ___

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excision repair

Front 52

Genes a and b are 10.0 map units apart, and genes b and c are 20 map units apart (gene order is a ? b ? c). In the absence of interference, what is the probability of a double crossover in these regions?

Back 52

2%

Front 53

Two genes that undergo independent assortment, indicated by a recombination frequency equal to ____, either are in non-homologous chromosomes or are located far apart in a single chromosome.

Back 53

50%

Front 54

facts about gene mapping are__

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1) distance measured by probability of recombination between 2 genes (2) distance is measured by map units and centimorgans. (3) independent assortment is indicated by a recombination frequency of 50% (4) genes with recombination frequencies of less than 50% are likely on the same chromosome

Front 55

___equals 1/2 of the average number of crossovers that take place in the region per meiotic cell.

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map distance

Front 56

___ is how much recombination is actually abserved in a particular experiment

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recombination frequency

Front 57

all known genes in a chromosome are the ___

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linkage group

Front 58

crossover in one region of a chromosome reduces probability of a second crossover in a nearby region

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chromosome interference

Front 59

Bivalents that lack chiasmata to help hold them together are prone to undergo nondisjunction. true of false?

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true

Front 60

In Genetics, a Holiday junction is ___

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(1) is resolved by the Holliday junction-resolving enzyme.
(2) A structure wear pairing partners are switched in a crossover pathway

Front 61

____demonstrate that crossing-over takes place at the four-strand stage of meiosis and is reciprical.

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tetratype tetrads

Front 62

these are true concerning polymorphic DNA sequences and genetic mapping___

Back 62

(1) some are detected by a restriction endonuclease and cleaves the double stranded DNA molecule wherever a particular short sequence of bases is present (2) different DNA fragment lengths are created based on the cleavage sites and are known as restriction fragment length polmorphisms