Mitosis/Meiosis

Question 1

How many pairs of chromosomes do human cells contain?

Answer 1

23

Question 2

Diploid cells

Answer 2

Cells which contain chromosomes in pairs.

Question 3

In most organisms including humans are cells diploid/haploid?

Answer 3

Diploid

Question 4

What does mitosis start with and result in?

Answer 4

One diploid cell to two identical diploid cells.

Question 5

How is mitosis used?

Answer 5

For growth and repair. Also asexual reproduction.

Question 6

Things that occur during interphase

Answer 6

• Energy stores increase
• Cells grow in size
• Organelles are replicated
• DNA is copied

Question 7

Two main processes that occur in the mitotic phase.

Answer 7

Mitosis and cytokinesis

Question 8

Mitosis

Answer 8

Division of the cell’s nucleus.

Question 9

Cytokinesis

Answer 9

Division of the cell.

Question 10

Chromosomes in interphase

Answer 10

Cannot be seen but are there, in the form of a dark material called chromatin.

Question 11

What happens to chromosomes during interphase?

Answer 11

Replicated and become sister chromatids and are joined at the centromere.

Question 12

Stages of Mitosis

Answer 12

Prophase, metaphase, anaphase and telophase.

Question 13

What happens during prophase?

Answer 13

• Chromosomes condense and become visible.
• The nuclear membrane starts to break down.
• A pair of centrioles move to both poles of the cell.
• Proteins begin to form spindle fibres which attach to the centromere of each chromosome.

Question 14

What happens during metaphase?

Answer 14

• The spindle apparatus completely forms.
• The chromosomes line up at the centre.

Question 15

What happens in anaphase?

Answer 15

• The centromeres divide into two and spindle fibres begin to shorten. This pulls sister chromatids to opposite sides of the cell.

Question 16

What happens in telophase?

Answer 16

• Spindle apparatus breaks down and nuclear membranes reform.
• Chromosomes uncoil back to their chromatin state.

Question 17

How does cytokinesis work?

Answer 17

Central cell membrane is pulled inwards by the cytoskeleton. Eventually the membranes fuse to form two independent cells.

Question 18

Why do centrioles not play a role in forming spindle fibres in plant cells?

Answer 18

They do not contain them.

Question 19

Why and where does meiosis occur?

Answer 19

To produce gametes in sexual organs.

Question 20

What does meiosis start and result with?

Answer 20

A diploid cell to four haploid cells.

Question 21

Why are gametes still useful despite being haploid?

Answer 21

During fertilisation, they fuse together to form a zygote, combining chromosomes.

Question 22

Gametes are genetically…?

Answer 22

Different

Question 23

Both chromosomes in a homologous pair have exactly the same…?

Answer 23

Genes

Question 24

If both chromosomes in a homologous pair have the same genes how is genetic variation created?

Answer 24

Different alleles can be inherited from each parent.

Question 25

What do the chromatids do in the early stages of mitosis?

Answer 25

Cross over to form an attached pair of chromosomes (bivalent)

Question 26

Bivalent

Answer 26

Attached pair of chromosomes.

Question 27

Chiasmata

Answer 27

Points where the attached pair of chromosomes are joined.

Question 28

How do the chromatids cause generic variation in meiosis?

Answer 28

They break off and exchange dna, becoming recombinant chromosomes therefore exchanging alleles.

Question 29

Key difference in stages of mitosis/meiosis

Answer 29

The stages repeat in meiosis i.e prophase metaphase etc happen twice so 4 haploid cells are produced.

Question 30

Independent Assortment

Answer 30

You cannot predict whether the paternal/maternal chromosome will end up in which gamete when the pairs line up on the spindle.

Question 31

Whats independent assortment an example of ?

Answer 31

Genetic variation

Question 32

What about fertilisation causes genetic variation?

Answer 32

The fact male/female gametes fuse randomly.