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List the stages of the cell cycle

1) Interphase - G0, G1, S, G2

2) Mitosis

3) Cytokinesis


What happens in the G1 phase of the cell cycle?

Metabolic changes prepare the cell for division. At a certain point - the restriction point - the cell is committed to division and moves into the S phase


What happens in the S phase of the cell cycle?

DNA synthesis replicates the genetic material. Each chromosome now consists of two sister chromatids


What happens in the G2 phase of the cell cycle?

Metabolic changes assemble the cytoplasm materials necessary for mitosis and cytokinesis


What happens in the mitosis phase of the cell cycle?

A nuclear division (mitosis) followed by a cell division (cytokinesis)


What are the 5 stages mitosis is conventionally split into?

1) Prophase

2) Prometaphase

3) Metaphase

4) Anaphase

5) Telophase


What occurs during Prophase?

- The nuclear membrane breaks down to form a number of small vesicles and the nucleolus disintegrates

- The centrosome duplicates itself to form two daughter centrosomes that migrate to opposite ends of the cell

- The centrosomes organise the production of microtubules that form the spindle fibres that constitute the mitotic spindle

- The chromosomes condense into compact structures

- Each replicated chromosome can now be seen to consist of two identical chromatids (sister chromatids) held together by a centromere


What occurs during prometaphase?

- The chromosomes , led by their centromeres, migrate to the equatorial plane in the mid-line of the cell, at right angles to the axis formed by the centrosomes

- The region of the mitotic spindle is known as the metaphase plate

- The spindle fibre bind to a structure associated with the centromere of each chromosome called a kinetochore

- Individual spindle fibres bind to a kinetochore structure on each side of the centromere

- The chromosomes continue to condense


What occurs during metaphase?

The chromosomes align themselves along the metaphase plate of the spindle apparatus


What occurs during anaphase?

The shortest stage of mitosis

- The centromeres divide, and the sister chromatids of each chromosomes are pulled apart and move to opposite ends of the cell, pulled by spindle fibres attached to the kinetochores regions

- The separated sister chromatids now referred to as daughter chromosomes note

- It is the alignment and separation in metaphase and anaphase that is important in ensuring that each daughter cell receives a copy of every chromosome


What happens during telophase?

The final stage of mitosis, and a reversal of many of the processes observed during prophase

- The nuclear membrane reforms around the chromosomes grouped at either pole of the cell

- The chromosomes uncoil and become diffuse, and the spindle fibres disappear


What happens during cytokinesis?

The final cellular division to form two new cells

- There is a constriction of the cytoplasm

- The cell then enters interphase

- The interval between mitotic division


Define meiosis

A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes


What two processes creates genetic diversity during meiosis?

1) Crossing-over

2) Independent assortment of chromosomes


Define crossing-over

The exchange of genetic material between homologous chromosomes that occurs during meiosis and contributes to genetic variability


Define independent assortment

The principle of how different genes independently separate from one another when reproductive cells develop giving different traits an equal opportunity of occurring together


When does independent assortment occur?

Metaphase I


Define genotype

The genetic make-up of an individual


Define phenotype

All observable characteristics of an individual or the expressed trait as a result of the genetic make-up of one (or more) specific genetic locus (loci)


What environmental factors have an influence on both genotype and phenotype?

- Radiation

- Mutagens

- Chemicals that can affect cell growth

- Diet

- Life-style


Define gene

A unit of hereditary; a length of DNA on a chromosome that contains the code for a protein


Define allele

An alternative form of a gene; each individual has two alleles for every gene, which can either be the same or different


What is autosomal inheritance?

When the gene inherited is located on an autosome (not a sex chromosome)


What is sex linked inheritance?

When the gene in question is located on a sex chromosome


An example of an X-linked dominant disease?

Hypophosphatemic rickets


An example of an X-linked recessive disease?

Haemophilia, Duchenne muscular dystrophy


What is the inheritance pattern of Y-linked inheritance?

Quite rare, when the gene in question is located on the Y-chromosomes and inherited directly from father to son


What is dominant trait (genetics)?

A phenotypic trait is dominant when it occurs in both homo and heterozygotes


What is a recessive trait (genetics)?

A phenotypic trait is recessive when it occurs only in the homozygote


What is co-dominance?

When both alleles are expressed in the phenotype of a heterozygote Eg AB blood type