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Genetics - BI 312 > Chapter 5: Linkage Recombination and Eukaryotic Gene Mapping > Flashcards

Chapter 5: Linkage Recombination and Eukaryotic Gene Mapping Flashcards

1
Q

What information about recombination frequencies enables scientists to create linkage maps?

A) The recombination frequency between two genes reveals the nucleotide sequence of the two genes

B) The lower the recombination frequency, the farther apart two genes are on a chromosome

C) The recombination frequency is proportional to the distance between the two genes

D) The recombination frequency between two genes is equal to the distance in nanometers between the two genes

A

C

C) The recombination frequency is proportional to the distance between the two genes

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2
Q

A researcher crosses and F1 heterozygous progeny (BbTt x BbTt) and the F2 progeny is shown below:

BBtt = 24
BbTt or BBTT = 55
bbTT = 26
bbtt = 2

What is the most likely explanation for why homozygous recessive progeny (bbtt) are in this cross?

A) Recombination
B) Random mutagenesis
C) Horizontal gene transfer
D) Independent assortment

A

A

A) Recombination

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3
Q

In German cockroaches, bulging eyes (bu) are recessive to normal eyes (bu+). Curved wings (cw) are recessive to straight wings (cw+). Both traits are encoded by autosomal genes that are linked.

A cockroach has genotype bu+ bucw+ cw and the genes are in repulsion. (the spacing in the genotype matters)

Which set of genes will be found in the most common gametes produced by this cockroach?

A) bu cw+
B) bu+ bu
C) cw+ cw
D) bu+ cw+
E) bu cw

A

A)

A) bu cw+

This is because these genes are nonrecombinant and will appear more commonly than recombinant genes.

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4
Q

Two heterozygous individuals procreate. Predict the amount of possible phenotypes of the progeny if…

R is completely dominant to r

A

Only 2 possible phenotypes.

Explanation: If R is completely dominant to r then RR and Rr have the same phenotype, leaving rr to be the second possible phenotype

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5
Q

Two heterozygous individuals procreate. Predict the amount of possible phenotypes of the progeny if…

R is codominant with r

A

3 possible phenotypes

Explanation: Since R is not completely dominant over r, RR will be its own phenotype, rr will be its own phenotype, and Rr will be its own phenotype between the two opposites, leading to a total of three phenotypes.

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6
Q

Two heterozygous individuals procreate. Predict the amount of possible phenotypes of the progeny if…

R and S are completely dominant to r and s. R and S are linked by 20 m.u. and do not interact with each other.

A

Four possible phenotypes

Explanation: In the Rr x Ss cross, you get 4 results. RRSS, RRss, rrSS, and rrss. This results in 4 different phenotypes.

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7
Q

What is Mendel’s first law?

A

Equal segregation of gametes

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8
Q

What is Mendel’s Second Law?

A

Independent assortment of gene pairs

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9
Q

What products are made in prophase I when NO CROSSING OVER takes place?

A

Each gametes receives a nonrecombinant chromosome with an original combination of alleles.

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10
Q

What products are made if crossing over DOES take place in prophase I?

A

Half of the resulting gametes will have an unchanged chromosome (nonrecombinant) and half will have a recombinant chromosome

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11
Q

Define coupling

A

When wild-type alleles are together on one chromosome

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12
Q

Define repulsion

A

When wild type alleles are on different chromosomes

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13
Q

Define genetic map unit (m. u)

A

The percent chance of a recombination between two locations on a chromosome (also called a centimorgan)

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14
Q

How many map units are there if you have a recombinant frequency of 0.01%?

A

1 m. u

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15
Q

How does a genetic map differ from a physical map?

A

Genetic maps are based on rates or recombination while physical maps are based on physical distances (bases)

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16
Q

Which gene in a double crossover is the recombinant gene?

A

The middle gene

17
Q

When looking at the amount of gamates per phenotype. How do you determine which gene is in the middle?

A

Whichever has the lowest number

18
Q

What is the equation for Coefficient of coincidence?

A

COC = Observed # of double recombinants / Expected # of double recombinants

19
Q

How to calculate interference?

A

Interference = 1 - Coefficient of coincidence

I = 1 - COC

20
Q

Define locus

A

The chromosomal site where a specific gene is located

21
Q

Define interterferance

A

The occurrence of one crossing- over interferes with the occurrence of another crossing- over in the same pair of chromosomes

22
Q

Define linkage

A

The tendency for genes located close on the same chromosome to be inherited together

23
Q

Define recombination

A

The process by which a new pattern of alleles on a chromosome is generated

24
Q

T/F: Linkage mapping can be used to determine the relative distance between genes found on the same chromosome

A

True

25
Q

What do both Whole-genome sequencing and Marker-based sequencing have in common?

A

Both identify genes that contribute to uncharacterized diseases, and both can work with a biochemical pathway that remains unknown.

26
Q

How does Whole-genome sequencing differ from marker-based sequencing

A

Whole genome can identify DNA elements that flank a variant.

27
Q

How does marker-based sequencing differ from whole-genome sequencing?

A

Marker-based sequencing allows for a large sample size with a limited budget

28
Q

2 groups have their SNPs (single-nucleotide polymorphisms) tested for a heritable disease. One group is a control group that does not have the disease, and the experimental group does. The disease locus is later determined to be in linkage disequilibrium with one SNP in particular…

At what frequency are the disease allele and a particular nucleotide variant of the SNP found together, compared to the frequency expected by chance?

A) Consistent
B) Lower
C) Higher

A

C) Higher

29
Q

2 groups have their SNPs (single-nucleotide polymorphisms) tested for a heritable disease. One group is a control group that does not have the disease, and the experimental group does. The disease locus is later determined to be in linkage disequilibrium with one SNP in particular…

When did the mutation responsible for the disease arise on the chromosome, compared to the SNP?

A) Before
B) Concurrently
C) After

A

C) After

30
Q

Define haplotype

A

A group of alleles closely associated within a chromosome that are likely to be inherited together.

31
Q

Define SNP (single-nucleotide polymorphism)

A

When the nucleotide at a particular genomic position differs between two individuals

32
Q

How would a geneticist classify a progeny resulting from a double crossover event between two adjacent marker genes during a three-point cross?

A

The individual would be in the nonrecombinant class.

33
Q

What gene position can be determined by examining the double-crossover class of a three-point cross?

A

The second locus (middle gene)

34
Q

Why are linked genes often inherited together?

A

Linked genes are close together on the same chromosome- they can’t be separated.

35
Q

Which of the statements best describes interference?

A) Results in an increased relative proportion of double-crossover progeny in a three-point cross
B) The difference between map unit positions of a physical map and a genetic map
C) One crossover that interferes with the formation of additional crossovers in the same region
D) the difference between the expected and observed progeny number in a chi-square test

A

C) One crossover that interferes with the formation of additional crossovers in the same region

36
Q

A genetic cross with 2 genes produces 400 offspring, and 20 of them have recombinant phenotypes. What is the recombination frequency for this cross?

A

5%

37
Q

When two genes are linked but quite far apart, their estimated map distance, based on recombination frequencies, often underestimates their true map distance. What is the best explanation for this underestimation?

A

Some double cross-over events go undetected since they do not lead to recombinant progeny.

38
Q

Three-point test crosses are often used to map genes. The two least frequent classes from such crosses usually represent which type of progeny?

A

Double-crossover progeny

Genetics - BI 312 (11 decks)

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