Eduqas Biology A Level C2 - Mitosis and Meiosis

What is a chromosome?

A long, thin structure of DNA and protein carrying the genes

What is a chromatid?

One of two identical copies of a chromosome, joined at a centromere

What is a centromere?

Specialised region of a chromosome where two chromatids join and to where the microtubules of the spindle attach at cell division

Draw a chromosome prior to DNA replication

Draw a chromosome after it has gone through DNA replication

What is an organism's ploidy level?

The number of complete sets of chromosomes in an organism

Define haploid

Having one complete set of chromosomes

Define diploid

Having two complete sets of chromosomes

What is a homologous pair?

A pair of chromosomes, one from each parent, carrying genes for the same characteristics at corresponding loci, and therefore affecting the same features

How many pairs of chromosomes do humans have in a normal body cell?

23 pairs of chromosomes

How many chromosomes do humans have in a normal body cell?

46 chromosomes

How many pairs of chromosomes are there in a human gamete?

23 chromosomes

Define mitosis

A type of cell division in which the two daughter cells have the same number of chromosomes and are genetically identical to the parent cell

What are the three main stages in the cell cycle?

Interphase, mitosis and cytokinesis

Interphase is described as...

a period of synthesis and growth

Cytokinesis is described as...

the division of the cytoplasm to form two daughter cells

What events occur during interphase?

- DNA replication (s phase)

- Organelle replication

- Protein synthesis

- Respiration

The part of interphase in which DNA is replicated is called...

the S phase

The 'S' in S phase stands for...

synthesis

List the 4 stages of mitosis, in order

prophase, metaphase, anaphase, telophase

Describe prophase of mitosis

- Chromatin condenses into visible chromosomes

- Centrioles appear and begin to move towards the opposite ends (poles) of the cell

- Protein microtubules form, radiating from each centriole, making the spindle fibres which extend from pole to pole

- The nuclear envelope disintegrates

Draw a diagram to show prophase of mitosis

Describe metaphase of mitosis

- Chromosomes align at the equator

- Spindle fibres attach to the centromeres of the chromosomes

Draw a diagram to show metaphase of mitosis

Describe anaphase of mitosis

- The centromere splits, separating the two sister chromatids

- The spindle fibres contract and shorten, which pulls the chromatids apart

- The now separated chromatids move towards the poles, centromere first

Draw a diagram to show anaphase of mitosis

Describe telophase of mitosis

- The chromatids have reached the poles of the cell and are now called chromosomes again

- The chromosomes uncoil and lengthen

- The spindle fibres break down

- The nuclear envelope appears and the nucleolus reforms

Draw a diagram to show telophase of mitosis

Name the stage of mitosis where each of the following occur:

A. Chromosomes line up at the equator

B. Centromeres separate

C. Spindle fibres shorten

D. Chromosomes are first visible as a pair of chromatids

E. Nuclear envelope reforms

A = Metaphase

B = Anaphase

C = Anaphase

D = Prophase

E = Telophase

What are the differences between mitosis in plant and animal cells?

- Animal cells become rounded before mitosis, plant cells have no shape change

- Centrioles are present in animal cells, but not plant cells

- In cytokinesis of animal cells, the cleavage furrow develops from the outside inwards. In plant cells, the cell plate develops from the inside out

- In animals, the spindle fibres degrade at telophase. In plant cells, the spindle fibres remain

TRUE OR FALSE: Mitosis produces cells with the same number of chromosomes as the parent cell

True

Define oncogene

A gene with the potential to cause cancer

Define meiosis

A two-stage cell division that produces 4 genetically identical daughter cells, each with half the number of chromosomes of the parent cell

Define gamete

haploid sex cell

Define zygote

The result of the fusion of a sperm and an egg, diploid

What are the stages of meiosis?

Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

What are the stages of meiosis I?

Prophase I, Metaphase I, Anaphase I, Telophase I

What are the stages of meiosis II?

Prophase II, Metaphase II, Anaphase II, Telophase II

When does crossing over occur?

prophase I of meiosis