10.1 Meiosis

Question 1

Where do chromosomes replicate before meiosis?

Answer 1

Interphase

Question 2

What are the 3 cell cycle phases in interphase?

Answer 2

• G1
• S
• G2

Question 3

What happens in the S phase of interphase?

Answer 3

DNA is repilicated so that each chromosome consits of two chromatids

Question 4

At the start of meiosis, what do the chromosomes do?

Answer 4

They condense and are visible as two chromatids, called sister chromatids

Question 5

Where do pairing or synapsis occur in meiosis?

Answer 5

Occurs where homologous chromosomes come to align beside each other

Question 6

What a tetrad?

Answer 6

The combination of chromatids as it is composed of four chromatids
Also a homologous pair

Question 7

What is a tetrad also referred to as and why?

Answer 7

Bivalent - as it is composed of a homologous pair

Question 8

What is the protein-based structure that forms between the homologous chromosomes called?

Answer 8

Synaptonemal complex

Question 9

In what type of cells do synaptonemal complexes form?

Answer 9

Eukaryotic cells

Question 10

What is crossing over?

Answer 10

The exchange of DNA material between non-sister homologou chromatids

Question 11

When do breaks in the DNA occur in meiosis?

Answer 11

Prophase I

Question 12

What happens during crossing over?

Answer 12

Non-sister chromatids “invade” a homologous sequence on a non-sister chromatid and bind in the region of the break

Question 13

What are the connection points where crossing over occured called?

Answer 13

Chiasmata (P) or Chiasma (S)

Question 14

What does the chiasmata formation between non-sister chromatids in a bivalent result in?

Answer 14

An exchange of alleles

Question 15

What are the two consequences of chiasmata formation?

Answer 15

• Increased stability of bivalents at chiasmata
• Increase genetic variability if crossing over occurs

Question 16

What are the two consequences of chiasmata formation?

Answer 16

• Increased stability of bivalents at chiasmata
• Increase genetic variability if crossing over occurs

Question 17

What chromosomes are exchanged in crossing over?

Answer 17

The process of crossing over results in the exchange of DNA between the maternal and paternal chromosomes

Question 18

What leads to independent assortment?

Answer 18

Crossing over can decouple linked combinations of alleles and therefore lead to independent assortment

Question 19

How many times can crossing over occur?

Answer 19

Multiple times and between different chromatids within the same homologous pair.

Question 20

When does crossing over and independent assortment occur?

Answer 20

Crossing over - Prophase I
Independent assortment - Metaphase I

Question 21

What are the 3 methods by which meiosis creates genetic variation?

Answer 21

• Crossing over - Prophase I
• Independent assortment - Metaphase I
• Random Fusing of gametes

Question 21

What are the 3 methods by which meiosis creates genetic variation?

Answer 21

• Crossing over - Prophase I
• Independent assortment - Metaphase I
• Random Fusing of gametes

Question 22

How are recombinant chromatids fromed?

Answer 22

When exchange of alleles occurs due to crossing over

Question 23

Compared to before, what do recombinant chromatid still contain? Whats different?

Answer 23

Recombinant chromatids still contain the same genes but a different combination of alleles

Question 24

After crossing over, what are chromatids of each chromosome no longer?

Answer 24

They are no longer genetically identical

Question 25

What are the 3 features shared between homologous chromosomes?

Answer 25

* Same length * Same centromere position * Same gene content

Question 26

What is a difference between homologous chromosomes?

Answer 26

They will have different combinations of alleles

Question 27

What is a chiasma?

Answer 27

An X-shaped knot-like strcuture that forms where crossing over has occurred

Question 28

What do chiasmata do to homologous chromosomes?

Answer 28

They hold homologous chromosomes together for a while

Question 29

What do chiasmata do to homologous chromosomes?

Answer 29

They hold homologous chromosomes together for a while

Question 30

Which round of meiosis resembles mitosis?

Answer 30

The first meiotic division is unique while the second round resembles mitosis

Question 31

How does meiosis 1 differ from mitosis and meiosis 2?

Answer 31

1. Sister chromatids remain associated with each other 2. The homologous chromosomes behave in a coordinated fashion in prophase 3. Homologous chromosomes exchange DNA leading to genetic recombination 4. Meiosis I is a reduction division in that it reduces the chromosome number by half

Question 32

Which stage of meiosis initiates the processes that result in the creation of genetic variety of gametes?

Answer 32

Meiosis 1

Question 33

When does the segregation of homologous chromosomes occur?

Answer 33

During anaphase I, resulting in two haploid cells, each with only one copy of each homologous pair

Question 34

How does independent assortment occur?

Answer 34

independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I

Question 35

What is independent orientation?

Answer 35

The direction in which one pair is facing does not affect the direction in which any of the other pairs are facing. This is called independent orientation

Question 36

If an organism is heterozygous for a gene, how would you expect their chromosomes to be like in a cell?

Answer 36

In its cells, one chromosome in a pair will carry one allele of the gene and the other chromosome will carry the other allele

Question 37

How is it determined which allele moves to which pole in meiosis?

Answer 37

The orientation of the pair of chromosomes will determine which allele moves to which pole

Question 38

What is the chance of each allele moving to a particular pole?

Answer 38

50%

Question 39

By is there a 50% chance of an allele moving to a particular pole?

Answer 39

Because there is random orientation of chromosome pairs

Question 40

What are separated in meiosis II?

Answer 40

Sister chromatids

Question 41

What do daughter cells of meiosis I not do before entering meiosis II?

Answer 41

After meiosis I, the daughter cells enter meiosis II without passing through interphase

Question 42

How is meiosis II similar to mitosis?

Answer 42

The replicated chromosome is separated into chromatids

Question 43

Why are the sister chromatids separated in meiosis II likely to be non-identical?

Answer 43

Due to the occurrence of crossing over