Unit 6: Meiosis

Question 1

Events of prophase I (meiosis)

Answer 1

1. Homologous chromosomes join to form tetrads; 2. Crossing over occurs

Question 2

Define Crossing over

Answer 2

Genetic material is swapped between homologous chromosomes

Question 3

Define Chiasma (pl: chiasmata)

Answer 3

Sections of homologous chromosomes that have crossed over; physically form Xs

Question 4

Define Synapsis

Answer 4

The touching of homologous chromosomes, which is what allows for chiasmata and crossing over to occur

Question 5

Describe this

Answer 5

A and B are sister chromatids
C and D are sister chromatids
A/B and C/D are homologous
A, B, C, and D form a tetrad
E is a chiasma, where crossing over will occur
B and C will be recombinant chromosomes

Question 6

Events of metaphase I (meiosis)

Answer 6

Tetrads line up along metaphase plate

Question 7

What is important about metaphase I?

Answer 7

The tetrads line up randomly, which is why Mendel’s Law of Independent Assortment is correct.
The orientation of one tetrad doesn’t affect others

Question 8

How many unique arrangements are possible during metaphase I?

Answer 8

2ⁿ
n = number of unique chromosomes
In humans: 2²³, or 8.4 million combinations

Question 9

Events of anaphase I

Answer 9

Tetrads are pulled apart; each pair of sister chromatids goes toward opposite poles

Question 10

Events of telophase I

Answer 10

New nuclear membranes form around the two piles of chromosomes

Question 11

Results of meiosis I

Answer 11

Two cells, each of which contains n pairs of sister chromatids. The two daughter cells are distinct from each other.

Question 12

Events of prophase II

Answer 12

Sister chromatids are still joined; nuclear membrane disappaers

Question 13

Events of metaphase II

Answer 13

Sister chromatids line up on the metaphase plate at random; recombinant chromosomes don’t affect each other

Question 14

Events of anaphase II

Answer 14

Sister chromatids are separated

Question 15

Events of telophase II

Answer 15

New nuclear membranes form around each group of chromosomes

Question 16

Results of meiosis (overall)

Answer 16

One diploid cell divides to produce four haploid nuclei, each of which are genetically unique

Question 17

What is the purpose of meiosis?

Answer 17

To produce gametes (sex cells)

Question 18

Def Germ cell

Answer 18

Cells that can undergo meiosis

In humans: Spermatocytes (in testes) and oocytes (in females)

Question 19

Evolutionary purpose of sex

Answer 19

Increase genetic diversity

Question 20

How does sex lead to increased genetic diversity? (3 ways)

Answer 20

1. Crossing over
2. Independent assortment on the metaphase plate (in metaphase I, mainly)
3. Random fertilization

Question 21

Define Fertilization

Answer 21

The joining of two gametes to produce a single diploid cell

Question 22

What is the ultimate source of genetic variation?

Answer 22

Mutation

Question 23

Compare the processes of mitosis and meiosis

Answer 23

Mitosis: Prophase, metaphase, anaphase, telophase (once)
Meiosis: Prophase, metaphase, anaphase, telophase all happen twice