Meiosis

Question 1

What is meiosis?

Answer 1

Meiosis is a form of nuclear division that results in the production of haploid cells from diploid cells

Question 2

What does meiosis produce?

Answer 2

Meiosis produces:

1. Daughter cells that are genetically different from each other, introducing variation
2. Gametes are produced, in plants and animals, which are used in sexual reproduction

Question 3

Explain the process involved in meiosis

Answer 3

Meiosis involves two nuclear divisions, which create four haploid daughter cells

Question 4

What is meant by a “haploid” cell?

Answer 4

A cell being referred to as haploid means the cell contains a single set of chromosomes

Question 5

Where are the haploid cells formed from?

Answer 5

Haploid cells are formed from a single diploid parent cell

Question 6

What are diploid cells?

Answer 6

Diploid cells contain two complete sets of chromosomes

Question 7

How many stages of meiosis are there?

Answer 7

There are five stages

Question 8

What are the five stages of meiosis, in order?

Answer 8

Interphase
Prophase
Metaphase
Anaphase
Telophase

Question 9

There are two mechanisms used in meiosis to introduce variation.
What are they both called?
What part of meiosis involves the two mechanisms?

Answer 9

The two mechanisms used in meiosis are the independent segregation of homologous chromosomes and crossing over between homologous chromosomes.

These two mechanisms occur during meiosis I (the first round of division

Question 10

What are homologous pairs?

Answer 10

Homologous pairs are chromosomes that have the same genes, but different alleles

Question 11

Independent segregation is a mechanism used in meiosis. When does it occur?

Answer 11

Independent segregation occurs when homologous pair of the chromosomes line up opposite each other in the middle of the cell, in meiosis I

Question 12

When independent segregation occurs, what happens to the chromosomes during this process?

Answer 12

The maternal and paternal chromosomes randomly go to either side of the equator when lining up in the middle of the cell

Question 13

What occurs after independent segregation?

Answer 13

The paternal and maternal chromosome pairs are then separated, so one of each homologous pairs ends up in the daughter cell

Question 14

What is an advantage of independent segregation?

Answer 14

An advantage of independent segregation is a large number of possible combinations can be created from the chromosomes in the daughter cells produced

Question 15

When does crossing over occur?

Answer 15

Crossing over occurs when homologous pairs line up opposite each other at the equator in meiosis I

Question 16

What causes crossing over occur?

Answer 16

Crossing over occurs when homologous pairs line up opposite each other in meiosis I, parts of the chromatids can become twisted around each other

Question 17

What occurs during crossing over?

Answer 17

Parts of chromatids become twisted around each other. Tension is then placed on the chromatids, causing parts of the chromatid to break

Question 18

What happens to the broken parts of the chromatids after crossing over?

Answer 18

The broken parts of the chromatids recombine with another chromatid, resulting in new combinations of alleles

Question 19

How can the amount of possible combinations of chromosomes be calculated?

Answer 19

By using the calculation: 2 to the power of n (2^n)

Question 20

What does the n in the calculation stand for?

Answer 20

N stands for the number of homologous pairs

Question 21

How many combinations of chromosomes are possible for humans?

Answer 21

As humans, we have 23 chromosomes.
So 2 to the power of 23
There are 8,388,608 combinations

Question 22

What are the differences between meiosis and mitosis?

Answer 22

1. Meiosis has two nuclear divisions, whereas mitosis has one nuclear division
2. Meiosis forms haploid cells but mitosis forms diploid cells
3. Meiosis introduces genetic variation compared to mitosis that creates genetically identical cells

Question 23

How can you identify meiosis in a life cycle?

Answer 23

You can identify meiosis as it involves a diploid parent cell cell dividing to become a haploid cell

Question 24

What is random fertilisation?

Answer 24

Random fertilisation means during sexual reproduction the male and female gamete that fuse to produce an offspring are randomly selected from the pool of male and female gametes

Question 25

When considering random fertilisation, how many possible combinations of chromosomes are there?

Answer 25

There are actually (2^n)^2 possible combinations of chromosomes

Question 26

Considering there ar (2^n)^2 possible combinations of chromosomes, how many combinations do humans have?

Answer 26

There are (2^23)^2 = 7.04 x 10^13

Question 27

Why do you not get genetically identical humans unless they are twins?

Answer 27

You do not get genetically identical humans unless they are twins. This is because there are 7.04 x 10^13 possible combinations of chromosomes allowing a lot of variation