Topic 3 - Voice of the Genome 🧫🍼🧬

What is Meiosis and what does it entail?

A type of cell division specialised for the production of gametes.

It’s when a diploid parent cell divides to produce 4 genetically different haploid daughter cells

Following Interphase, what are the names of all the following phases in order?

Meiosis I

• Prophase I

• Metaphase I

• Anaphase I

• Telophase I

• Cytokinesis I

Meiosis II

• Prophase II

• Metaphase II

• Anaphase II

• Telophase II

• Cytokinesis II

What is the Acrosome reaction?

When the acrosome on the head of a sperm swells and fuses with the CSM of the sperm cell as well as releasing digestive enzymes for the breakdown of the zona pellucida.

What is the cortical reaction?

What does it prevent?

When a sperm cell fuses with the ovum membrane, which initiates the release of chemicals by the ovum, that causes the thickening of the zona pellucida.

It prevents another sperm cell from penetrating the ovum.

How does meiosis create genetic variation?

1. Independent assortment

2. Crossing over

What is independent assortment?

The random combinations of homologous chromosomes that are inherited by gametes.

What is crossing over and when does it occur?

Crossing over is when non-sister chromatids of a homologous pair of chromosomes form a chiasma and exchange segments of their DNA at that point of contact.

It occurs during the first meiotic division.

What is linkage?

Linkage is when genes at different loci on the same chromosome get inherited together.

What is sex-linkage?

Sex linkage is when inheritable genes are found on the sex chromosomes, particularly the X-chromosome.

Name 3 adaptations of sperm cells.

• Streamlined heads to reduce drag when swimming

• Lots of mitochondria to generate enough energy for swimming

• Acrosome to breakdown the zona pellucida

Name 3 adaptations for egg cells.

• Large compared to sperm cells to m, make it easier to find

• Follicle cells act as protection for the egg cell

• Zona pellucida can thicken to stop additional sperm cells from getting in.

What are 4 key differences between Mitosis and Meiosis?

1. Mitosis = 2 genetically identical daughter cells

   Meiosis = 4 genetically different daughter cells

2. Mitosis produces diploid cells whereas Meiosis produces haploid gametes

3. Mitosis has 1 division, Meiosis has 2 divisions

4. Meiosis is needed for SEXUAL reproduction, Mitosis is needed for ASEXUAL reproduction.

What occurs during INTERPHASE?

• DNA replication

• Synthesis of new organelles

What occurs during PROPHASE?

The chromosomes condense and the centrioles move to opposite ends of the nuclear envelope that then breaks down. Spindle fibres also form.

What occurs during METAPHASE?

Chromosomes line up along the middle of the cell and the spindle fibres attach to the centromeres of each chromosome.

What occurs during ANAPHASE?

The spindle fibres shorten pulling sister chromatoids apart and towards opposite poles of the cell.

What occurs during TELOPHASE?

The chromosomes unravel and 2 new nuclear envelopes form around the sets of chromosomes resulting in 2 new nuclei.

What is different about Cytokinesis in plant and animal cells

- In plant cells: a new cell wall plate gets synthesised between the 2 new cells

- In animal cells: The CSM constricts around the middle of the 2 cells and protein filaments contract until the cytoplasm divides.

What happens during G1 of the cell cycle?

How long does G1 last?

• Growth

• production of new organelles

• protein synthesis

G1 lasts abt 10-11 hours

What happens during S of the cell cycle?

How long is this phase?

DNA replication

S phase lasts abt 8 hours

What happens during G2 of the cell cycle?

How long does G1 last?

• Growth

• Further preparation for mitosis

• Reorganisation of cytoplasmic components

G2 lasts abt 4 hours

What are Histones?

Histones are proteins that DNA wraps around.

What is a:

1. Multipotent

2. Pluripotent

3. Totipotent

   Stem cell?

1. Multi = stem cells that are limited in the number of cells they can turn into.

2. Pluri = stem cells that can turn into most cells the body is composed of.

3. Toti = stem cells that can turn into all & any type of human cell.

Where are Totipotent stem cells found vs Pluripotent stem cells

Both are found in embryos but Totipotent can only be found in very early embryos.

What is a blastocyst?

A hollow ball of cells formed 5-6 days following conception in the early development of mammals.

Pros / Cons:

Use of Embryonic stem cells

Embryonic stem cells:

Pros

• They can turn into most body cells.

• Scientists use cells left over from IVF.

• Genetic material can be changed to match the patient

Cons

• seen as unethical

• Rapid division gives rise to mutations, can lead to them behaving like cancer cells