Week 10

Question 1

Meiosis

Answer 1

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

Question 2

Meiosis I

Answer 2

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

Question 3

Meiosis II

Answer 3

Splitting of the sister chromatids of the homologous chromosomes

Question 4

Recombination

Answer 4

Occurs during the meiosis I at the tetrad

physical exchnage of genetic information

Question 5

What processes give rise to recombinants

Answer 5

Recombination

Law of independent assorment (Mendel’s second law)

Question 6

Law of independent assortment

Answer 6

Mendel’s 2nd law

random alignment of chromosomes at the metaphase plate

50% chance assortment

Question 7

Recombination and gene mapping

Answer 7

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

Question 8

Two point test cross

Answer 8

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

Question 9

Three-point test cross

Answer 9

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

cross the heterozygote with a homozygote for 3 recessive alleles

Question 10

Chance of a double crossover

Answer 10

product of two single crossovers

rare

Question 11

Interference

Answer 11

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

Question 12

Following meiosis in human and fruitflies

Answer 12

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)

Question 13

Tetrad Analysis (purpose)

Answer 13

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

Question 14

Yeast life cycle

Answer 14

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

Question 15

Dissolve ascus cell wall to release spores

Answer 15

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

Question 16

2:2 segregation

Answer 16

Mendel’s first law of segregation

Question 17

Unlinked genes on different chromosomes

Answer 17

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

Question 18

Unlinked genes

Answer 18

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

Question 19

Tetratype

Answer 19

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

Question 20

Recombination before DNA replication

Answer 20

results in all non parental ditypes instead of tetratypes

NPD>T

This is not observed

Question 21

No crossing over events

Answer 21

Parental ditypes

Question 22

Linked genes

Answer 22

PD»NPD

Question 23

Single crossover event

Answer 23

tetratype

Question 24

Double crossover event (2-strands)

Answer 24

Parental ditype

Question 25

Double crossover (3-strand)

Answer 25

tetratype

Question 26

Double crossover (4-strand)

Answer 26

non parental ditype

Question 27

Calculating recombination frequency

Answer 27

NPD all four spores recombinant T two of the four spores recombinant RF = NPD + 1/2 T/Total tetrads x 100% mu

Question 28

Mapping centromeres

Answer 28

can only map when we have ordered tetrads

Question 29

During Meiosis

Answer 29

Centromeres are pulled to opposite poles

Question 30

Recombination between a gene and a centromere

Answer 30

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

Question 31

Model for recombination

Answer 31

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

Question 32

Recombination steps

Answer 32

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

Question 33

Holliday Junction

Answer 33

Two strands binding to the other two strands of the homologous chromosome mismatches can occur

Question 34

Heteroduplex

Answer 34

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

Question 35

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

Answer 35

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

Question 36

Mismatch in a heteroduplex

Answer 36

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

Question 37

Role of recombination

Answer 37

exchange of information between homologous chromosomes do crossovers (chiasma) hold the tetrad together? are crossovers important for segregation? what does the synaptomenal complex do?

Question 38

Synaptomenal complex

Answer 38

structure holds the homologous chromosomes together during prophase of meiosis I contains Zipper proteins

Question 39

Random Crossovers

Answer 39

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

Question 40

zip1 mutant phenotype

Answer 40

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