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Genetics > Week 10 > Flashcards

Week 10 Flashcards

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Biology 101 flashcards
1
Q

Meiosis

A

two phases

meiosis I is a modified form of mitosis

alignment of two replicated homologous chromosome, synapsis

synaptomenal complex forms during prophase I of meiosis

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2
Q

Meiosis I

A

monopolar attachment of microtubules to the centromeres of homologous chromosomes to move chromosomes apart

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3
Q

Meiosis II

A

Splitting of the sister chromatids of the homologous chromosomes

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4
Q

Recombination

A

Occurs during the meiosis I at the tetrad

physical exchnage of genetic information

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5
Q

What processes give rise to recombinants

A

Recombination

Law of independent assorment (Mendel’s second law)

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6
Q

Law of independent assortment

A

Mendel’s 2nd law

random alignment of chromosomes at the metaphase plate

50% chance assortment

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7
Q

Recombination and gene mapping

A

the number of recombinations is proportional to the distance between two genes on the same chromosome

map the relative position of genes on the chromosome

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8
Q

Two point test cross

A

Cross a diploid heterozygous for alleles at two genes

cross back to a test strain homozygous for the recessive alleles in the two genes

follow what happened in the meiosis of the F1 heterozygotes in creating the gametes for the test cross

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9
Q

Three-point test cross

A

cross parents homozygous for 3 dominant alleles and recessive alleles to create a heterozygote

cross the heterozygote with a homozygote for 3 recessive alleles

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10
Q

Chance of a double crossover

A

product of two single crossovers

rare

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11
Q

Interference

A

A single crossover event supresses the occurence of a near by crossover event

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12
Q

Following meiosis in human and fruitflies

A

not possible due to the loss of genetic information, sperm swim away and oogenesis only produces 1 viable oocyte (genetic info is lost in 3 polar bodies)

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13
Q

Tetrad Analysis (purpose)

A

Allows you to conclude that recombination occurs after DNA replication and map the position of centromeres

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14
Q

Yeast life cycle

A

yeast have a viable haploid stage and they can fuse to give rise to a diploid, the diploid is an ascospore that undergoes meiosis and contains four haploid spores

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15
Q

Dissolve ascus cell wall to release spores

A

use a glass needle to pick and plate the four haploid spore

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16
Q

2:2 segregation

A

Mendel’s first law of segregation

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17
Q

Unlinked genes on different chromosomes

A

will assort independently of one another, mendel’s second law.

18
Q

Unlinked genes

A

PD = NPD (50/50) due to random alignment at the metaphase plate

19
Q

Tetratype

A

All four spores have different genotypes of which two have the same as parents and two do not

recombination during meiosis I leads to tetretypes

20
Q

Recombination before DNA replication

A

results in all non parental ditypes instead of tetratypes

NPD>T

This is not observed

21
Q

No crossing over events

A

Parental ditypes

22
Q

Linked genes

A

PD»NPD

23
Q

Single crossover event

A

tetratype

24
Q

Double crossover event (2-strands)

A

Parental ditype

25
Q

Double crossover (3-strand)

A

tetratype

26
Q

Double crossover (4-strand)

A

non parental ditype

27
Q

Calculating recombination frequency

A

NPD all four spores recombinant

T two of the four spores recombinant

RF = NPD + 1/2 T/Total tetrads x 100% mu

28
Q

Mapping centromeres

A

can only map when we have ordered tetrads

29
Q

During Meiosis

A

Centromeres are pulled to opposite poles

30
Q

Recombination between a gene and a centromere

A

RF= 1/2(# of tetrads with 2nd division events)/Total tetrads x 100% or mu

31
Q

Model for recombination

A

Double-strand break model

double stranded breaks a recombinant genic

homologous chromosomes differe at a few points

double stranded breaks are very dangerous, one mechanism of repair is to employ homologous recombination

32
Q

Recombination steps

A

Double stranded break

Resection of 5’ ends (Degredation)

One of the single stranded ends finds homologous sequence on another homologous chromosome and base pairs displacing the other strand

33
Q

Holliday Junction

A

Two strands binding to the other two strands of the homologous chromosome

mismatches can occur

34
Q

Heteroduplex

A

The section of the chromosome involved in binding with the other homologous chromosome

35
Q

When do you observe 3:1 segregation patterns in tetrad analysis

A

Gene conversion

Breaks mendel’s law of segregation

replacement of 1 piece of information with another

3:1 segregation in a tetrad analysis

first evidence of heteroduplex formation

36
Q

Mismatch in a heteroduplex

A

DNA sequence variation between homologous chromosomes resulting in mismatches in the heteroduplex, repairs will occur at random

mismatches are changed to the recessive allele 3 out of 4 of the time

repairing one allele to another 3 to 1 segregation

37
Q

Role of recombination

A

exchange of information between homologous chromosomes

do crossovers (chiasma) hold the tetrad together?

are crossovers important for segregation?

what does the synaptomenal complex do?

38
Q

Synaptomenal complex

A

structure holds the homologous chromosomes together during prophase of meiosis I

contains Zipper proteins

39
Q

Random Crossovers

A

If there was no interference small chromosomes will have less crossovers than large chromosomes regulating crossovers through interference will spread crossovers across the genome

40
Q

zip1 mutant phenotype

A

recombination. ZIP1 and SC not required for recombination

No interference. ZIP1 and SC required for negative interference

No interference and loss of small chromosomes (non-disjunction). Spreading X overs is required for segregation during meiosis

Genetics (16 decks)

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