Linkage and Meiosis - Genetics 3

Question 1

Meiosis

Answer 1

type of cell division that occurs in sexually reproducing organisms to create gametes (haploid)

Question 2

Haploid

Answer 2

Cells with one set of chromosomes (23)

Question 3

Diploid

Answer 3

Cells with 2 sets of chromosomes that are copies of eachother

Question 4

Alleles in a zygote

Answer 4

2 alleles of each gene (one maternal and one paternal)

Question 5

How does meiosis produce 2 haploid daughter cells?

Answer 5

One round of DNA replication and two rounds of chromosome segregation

Question 6

Chromosome Segregation

Answer 6

Distribution of chromosomes/chromatids into daughter cells.

Question 7

First round of chromosome segregation in meiosis

Answer 7

Anaphase 1 - homologous chromosomes separate (pairs of chromosomes)

Question 8

Second round of chromosome segregation in meiosis

Answer 8

Anaphase II - sister chromatids separate (one chromosome into its 2 arms) by the centromere

Question 9

Haploid Daughter Cells

Answer 9

Cells with half the chromosome complement.

Question 10

Independent Assortment

Answer 10

Random distribution of chromosomes during meiosis depending on how the line up during metaphase I and II

Difference between number of segregations and if the daughter cells are genetically identical to the parent cell in mitosis vs meiosis

Question 11

Meiosis I

Answer 11

First meiotic division, specialized chromosome segregation.

Question 12

Difference between segregation in mitosis and meiosis 1

Answer 12

In mitosis kinetochores (proteins) pull apart sister chromotids by the centromere with spindle fibres whereas in meiosis one homologous pairs ar epulled apart

Question 13

Key steps for meiosis I to occur

Answer 13

• Pairing of homologous chromosomes
• Synapsis
• Crossing over
• Mono-orientation of kinetochore

Question 14

What needs to happen in meiosis I for the homologous chromosomes to be separated?

Answer 14

The cell needs to be able to recognise homologous chromosomes in order for pairing to occur. Once they pairs find each other they must stay together before division

Question 15

Synapsis

Answer 15

Pairing of homologous chromosomes during prophase I of meiosis.

Question 16

Crossing Over

Answer 16

Exchange of genetic material between homologous chromosomes.

Question 17

Synaptonemal Complex

Answer 17

Structure facilitating synapsis of homologous chromosomes. Made of highly conserved proteins that link together and is well orchestrated.

Electron micrograph of Synaptonemal Complex. The more dense fields (lateral elements on both sides) have homologous proteins wound around them

The crossing of colours (homologous chromosomes) shows strand break and repair from another chromosome = CROSSING OVER

Question 18

What holds sister chromatids together?

Answer 18

Chohesin. Most need to be lost in order for the chromatids to later be separated

Question 19

Separase

Answer 19

Enzyme that cleaves a part of the chromosome arms, so chohesin is no longer keeping them together. Some remains in the central part, keeping the sister chromatids together at the centrophere and next to the kinetochore.

Action of active separase in meiosis one

Question 20

Crossover Recombination

Answer 20

Creation of novel allele combinations in gametes during meiosis one (recombinanat chromatids)

Recombination of genes close to each other on the same chromosome is rare

Question 21

Meiosis products are parental types

Answer 21

A result of no crossing over between the genes (recombination). Results are in expected ratios

Question 22

Meiosis products are recombinant (and parental)

Answer 22

Crossing over breaks linkage of genes on chromosomes, creating recombinant genes where some are from paternal and some maternal.

Question 23

Recombination and linkage tells us that…

Answer 23

Genes are on the same chromosome. It doesn’t tell us how close they are

Question 24

Genetic Linkage

Answer 24

Tendency of genes on the same chromosome to be inherited together. Distorts mandelian ratios

Question 25

Phenotypes meet expected ratio

Answer 25

We can make the assertion that we are looking at unlinked genes (on different chromosomes)

Question 26

Recombinant Frequency

Answer 26

Percentage of recombinant offspring from a cross.

Question 27

Calculating recombination freqency

Answer 27

Add up amount of recombinant individuals and divide by the total number of individuals

Question 28

CentiMorgan (cM)

Answer 28

A distance. Map unit for measuring genetic linkage (distance between genes on a chromosome. It = recombination frequency as a %

Question 29

What would happen to recombination frequency and genetic map distance if there were 2 crossover events between the 2 genes?

Answer 29

A more diverse recombination frequency. Lots of different outcomes of phenotypes.

Question 30

Why is there a max recombination frequency?

Answer 30

More than 50 = the genes are on different chromosomes. Around 49 suggests the two genes are at either end of the chromosome. The genes are unlinked.

Question 31

What would happen to recombination frequency and genetic map distance if the 2 genes were closer together on the same chromosome?

Answer 31

Recombination frequency would decrease as crossing over separating the genes is less likely to occur (the genes are close together on the chromosome)

Question 32

Unlinked genes

Answer 32

Genes located on different chromosomes or very far apart on the same chromosome

Question 33

Mendelian Ratios

Answer 33

Expected ratios of offspring phenotypes from genetic crosses.

Question 34

Two Crossover Events

Answer 34

Can maintain parental genotype despite recombination.

Question 35

Linkage-Based Diagnostic Test

Answer 35

Test determining parental origin of chromosome regions for several embryones to know if offspring is affected, a carrier or unaffected.

Question 36

Monogenic Disease Screening

Answer 36

Testing for single-gene disorders using linkage.

Question 37

Gametes

Answer 37

Haploid cells involved in fertilization.

Question 38

Alleles

Answer 38

Different versions of a gene.

Question 39

Heterozygous

Answer 39

Having two different alleles for a gene.

Question 40

Homozygous

Answer 40

Having identical alleles for a gene.