Mitosis and Fertilisation

Question 1

What happens in Interphase?

Answer 1

• DNA is unravelled and replicated (as well as organelles), to double its genetic content
• ATP is increased

Question 2

What happens in Prophase?

Answer 2

• The chromosomes condense, getting shorter and fatter
• Tiny bundles of proteins called centrioles start moving to opposite ends of the cell, this forms a network of protein fibres called spindles
• The nuclear envelope breaks down

Question 3

What happens in Metaphase?

Answer 3

• The chromosomes line up along the middle of the cell and becomes attached to the spindle by their centromere

Question 4

What happens in Anaphase?

Answer 4

• The centromeres divide, separating each pair of sister chromatids
• The spindles contract, pulling chromatids to opposite ends of the spindle

Question 5

What happens in Telophase?

Answer 5

• Chromatids uncoil and become long and thin, they are now called chromosomes again
• A nuclear envelope forms

Question 6

What happens in Cytokinesis?

Answer 6

• The cytoplasm divides and there are now 2 daughter cells that are genetically identical

Question 7

What does the cell cycle consist of?

Answer 7

• Cell growth
• DNA replication
• Cell division

Question 8

What are the 2 checkpoints of the cell cycle called and what do they do?

Answer 8

• M and S
• Prevents uncontrolled cell division
• Detect and repair damage to DNA by prevent reversal of cell cycle and making sure DNA is only duplicated once

Question 9

Other than being a checkpoint what else does M phase do?

Answer 9

• Cell growth stops
• Nuclear division occurs

Question 10

Other than being a checkpoint what does S phase do?

Answer 10

• DNA replicates
• Once the cell enters this stage it is committed to the cell cycle

Question 11

What happens in G2 phase of the cell cycle?

Answer 11

• Cell keeps growing
• Proteins needed for cell division are made

Question 12

What happens in G1 phase of the cell cycle?

Answer 12

• Cell grows and duplicates
• P53 tumour supressed gene triggers and controls checkpoints
• Transcription

Question 13

What are telomeres and where are they found?

Answer 13

• Telomeres are ‘protective tips’ found on the ends of chromosomes
• Each time DNA replicates the telomere becomes shorter and eventually will become so short that they cannot carry out their function anymore

Question 14

What happens to telomeres in cancer cells?

Answer 14

In cancer cell the enzyme telomerase which ordinarily prompts the shortening, the enzyme will maintain telomere length and the cell has infinite replicative potential

Question 15

What is Hayflick’s constant?

Answer 15

The number of times that DNA can replicate before telomeres break down (around 50 times)

Question 16

Describe the process of fertilisation?

Answer 16

1. Acrosome reaction = enzymes in acrosome digest the zona pellucida, sperm nucleus enters egg cell
2. Cortical reaction = cortical granules are released by the egg membrane that causes the zona pellucida to harden, preventing polyspermy
3. Nucleic fusion = restoring full set of chromosomes, diploid zygote

Question 17

How are mammalian eggs adapted to its function?

Answer 17

• Zona pellucida (protective coating) to prevent polyspermy
• Haploid nucleus to restore full set of chromomes
• Has nutrients in cytoplasm for embryo

Question 18

How are sperm adapted to its functions?

Answer 18

• Hydrodynamic shape for reduced resistance
• Haploid chromosomes
• Mitochondria to provide energy
• Acrosome to provide digest zona pellucida
• Flagellum for motility
• Membrane has receptors

Question 19

What is a locus?

Answer 19

The position on a chromosome occupied by a gene

Question 20

What is meant by autosomal linkage?

Answer 20

Two or more genes are located on the same (non-sex) chromosome

Question 21

What is meant by sex-linkage?

Answer 21

Where an allele is located on one of the sex chromosomes

Question 22

What is meant by polygenic inheritance?

Answer 22

The kind of inheritance in which the trait is produced from the cumulative effects of many genes

Question 23

Describe 2 types of phenotypic variation?

Answer 23

Continuous = variation exists as gradual changes
Discontinuous = variation exists as distinct categories

Question 24

In which ways does meiosis ensure genetic variation?

Answer 24

1. Crossing-over alleles between chromatids
2. Independent assortment of chromosomes

Question 25

At the start of fertilisation, many sperm cells will surround the ovum.
i) Describe the events of fertilisation that occur after the acrosome reaction.

Answer 25

• Sperm cell fuses with membrane
• Exocytosis of cortical granules
• Zona pellucida hardens to avoid polyspermy

Question 26

Animals produce haploid gametes by meiosis.
i) Explain how meiosis gives rise to genetic variation in gametes.

Answer 26

• Independent assortment gives rise to new combinations of chromosomes
• Crossing over involves swapping sections of chromosomes

Question 27

Explain what is meant by the term polygenic inheritance.

Answer 27

• More than one gene for a single characteristic
• Different loci

Question 28

What is the process of protein trafficking?

Answer 28

• The ribosomes on the rER make proteins that are excreted
• New proteins are folded and processed in the rER
• They’re transported from the rER to the Golgi in vesicles
• At the Golgi they are modified
• They are transported to the cell surface where they are excreted