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Bio 311 > Chapter 4 > Flashcards

Chapter 4 Flashcards

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Biology 101 flashcards
1
Q

Why is gene mapping important?

A
  • gene position is crucial info for building complex genotypes required for experimental purposes or commercial applications
  • knowing the position occupied by a gene provides a way pf discovering its structure and function
  • can deduce evolutionary genetic mechanisms where genomes diverged by comparing the genes present and the arrangement to closely related species
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2
Q

How is the arrangement of genes on chromosomes represented?

A
  • as a unidimensional chromosome map showing gene positions (loci) and the distance between the loci based on a scale
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3
Q

What are the 2 different types of chromosome maps?

A
  • recombination-based maps

- physical maps

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4
Q

What are recombination-based maps?

A
  • a map of the loci of genes that have been identified by mutant phenotypes showing single-gene inheritance
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5
Q

What are physical maps?

A
  • show the genes as segments arranged along the long DNA molecule that constitutes a chromosome
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6
Q

Why do genotypes deviate from Mendel’s 1:1:1:1 prediction in a dihybrid cross?

A
  • genes can be linked, so a pair of allele combinations can be similar numbers and make up the majority because they are the same genotypes as the parents
  • also recombinant genotypes will have similar numbers but make up the minority of the progeny
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7
Q

What genotypes typically make up the majority of the progeny genotypes and why?

A
  • the parental genotypes

- because they are typically linked

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8
Q

What is the general pattern for dihybrid crosses and the number and type of genotype?

A
  • 2 equally frequent nonrecombinant classes total >50% of the progeny
  • 2 equally frequent recombinant classes total <50% of the progeny
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9
Q

Why do allele combinations from the parental generations stay together?

A
  • the genes are physically attached by the segment of chromosome between them
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10
Q

Why do allele combinations from the recombinants occur?

A
  • when the homologous chromosomes pair in meiosis sometimes the chromosomes break and exchange parts in a process called crossing over
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11
Q

What are the rules for symbolizing linkage?

A

1) alleles on the same homolog have no punctuation between them
2) a slash symbolically separates the 2 homologs
3) alleles are always written in the same prder on eac homolog
4) genes known to be on different chromosomes (aka unlinked) are shown seperated by a semicolon
5) unknown linkages are seperated by a dot

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12
Q

What is the importance of the chiasmata?

A
  • they are the sites of exchange during crossing over
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13
Q

What is crossover the result from?

A
  • the breakage and union of DNA
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14
Q

What is has a direct correlation with the appearance of recombinants?

A
  • the chromosomal event of crossing over
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15
Q

What do crossovers occur between?

A
  • sister chromatids
  • if it occurred at the 2 chromosome stage then there would only be a maximum of 2 different genotypes in an individual tetrad, but there are 4
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16
Q

What are double crossovers?

A
  • 2 crossover events that occur in a meiocyte
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17
Q

Can double crossovers occur between sister chromatids?

A
  • it can happen, but it is very rare
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18
Q

How many chromatids are typically involved in a double crossover?

A
  • usually between 3 or 4 chromatids

- but in one meiocyte

19
Q

How many chromatids are involved in a single crossover?

A
  • only between 2 chromatids
20
Q

What is the key to chromosome mapping?

A
  • the frequency of recombinants produced by crossing over
21
Q

T/F: the further apart genes are the less likely a crossover will occur

A
  • false

- the further apart genes are the more likely they are to crossover and the higher number of recombinants there will be

22
Q

What is the range of recombinant frequency for linked genes?

A
  • 0-50%
23
Q

What’s the recombinant frequency for genes far apart from each other?

A
  • the further apart genes are the closer to 50% recombinant it will be
  • when it’s close to 50% we cannot decide if they’re linked or unlinked
24
Q

When is there a recombinant frequency greater than 50%?

A
  • this never happens
25
Q

Define genetic map unit (m.u.)

A
  • the distance between genes for which 1 product of meiosis in 100 is recombinant
  • ex. 10.7% recombinant = 10.7 mu
26
Q

How are genes arranged? What does this mean for map unit?

A
  • they are arranged in a some linear order

- this makes map units additive

27
Q

What are the 2 directions we can use recombinant frequencies?

A

1) recombinant frequencies can be used to make maps

2) when given a map with map units we can predict the frequencies of progeny in different classes

28
Q

What are recombinant hotspots?

A
  • places in the genome where crossing over takes place more frequently than usual
  • this causes proportional expansion in some regions of the map
29
Q

What are recombinant blocks?

A
  • places in the genome where crossing over occurs less frequently than usual
30
Q

How do we account for double crossovers when finding the distance between each gene?

A
  • add the double crossover progeny number twice
31
Q

T/F: you can use a chi squared test to test gene linkage

A
  • true
  • the expected value is from the 1:1:1:1
  • expect the genes to be unlinked
  • reject hypothesis = there is linkage
32
Q

Define chromosome map

A
  • a representation of all chromosomes in the genome as lines, marked with the positions of genes known from their mutant phenotypes, plus molecular markers
  • based on analysis of recombination frequency
33
Q

Define recombination map

A
  • a chromosome map in which the positions of loci shown are based on recombinant frequenices
34
Q

Define linked

A
  • the situation in which 2 genes are on the same chromosome as deduced by recombinant frequency less than 50 %
35
Q

Define gene locus (pl loci)

A
  • the specific place on a chromosome where a gene is located
36
Q

Define crossing over

A
  • the exchange of corresponding chromosome parts between homologs between breakage and union
37
Q

Define crossover products

A
  • the meiotic product cells with chromosomes that have engaged in a crossover
38
Q

Define trans conformation

A
  • in a heterozygote with 2 mutant sites within a gene or gene cluster, the arrangement is a1+/+a2
39
Q

Define cis conformation

A
  • in a heterozygote having 2 mutant sites within a gene or within a gene cluster, the arrangement is A1A2/a1a2
40
Q

Define linkage map/ genetic map

A
  • a chromosome map

- an abstract mao of chromosomal loci that is based on recombinant frequencies

41
Q

Define map unit

A
  • m.u.
  • the “distance” between 2 linked gene pairs where 1% of the products of meiosis are recombinant
  • a unit of distance in a linkage map
42
Q

Define centimorgan

A
  • unit for map unit

- named after person who discovered it

43
Q

Define three point testcross / three factor testcross

A
  • a testcross in which one parent has 3 heterozygous gene pairs

Bio 311 (6 decks)

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