Chapter 10 Human Biology

Cell cycle

is a series of events that occur as one cell grows and divides into new cells

Why do cells need to reproduce

-for organisms to grow               -to replace old, dead, or damaged cells

What are the 5 stages of the cell cycles

• G1 – growth • S – syntheses • G2 – growth • M – meiotic • G0 – functioning

What happens in each stage of the cell cycle

G1 – cell grows, produces new proteins and carries out normal functions S – DNA is duplicated so each new cell can receive a copy G2 – short growth phase where the cell prepares for division M – the cell divides into two daughter cells G0 – some cells leave the cycle and stops dividing for days, years, or permanently

Mitosis

is the cell division that produces two daughter cells containing the same genetic information as the parent cell

What happens before mitosis

DNA is copied during interphase

What is interphase

is the stage in the cell cycle when it is not dividing

What happens during interphase

G1 - the cell grows S – DNA molecules make exact copies of themselves G2 – cell grows

What are the stages of mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

5. Cytokinesis

What happens during prophase (mitosis) • Centrioles move towards opposite poles of the cell • Microtubules begin forming the spindle • The nuclear membrane begins forming the spindle • DNA becomes tightly coiled into visible chromosomes • Each chromosome consists of two chromatids joined at the centromere

What happens during metaphase (mitosis) • Chromosome pairs line up along the equator of the cell • Spindle fibres attach to the centromeres

What happens during anaphase (mitosis) • The two chromatids separate at the centromere • Each chromatid is now considered an individual chromosome • Chromosomes are pulled towards opposite poles of the cell

What happens during telophase (mitosis) • Chromosomes from two groups at opposite poles • A new nuclear membrane forms around each group • Tow nuclei develop • The spindle fibres disappear • Chromosomes gradually uncoil back into chromatin

What is cytokinesis

is the division of the cytoplasm

What happens during cytokinesis (mitosis)

• A furrow develops between the two nuclei • The furrow deepens and divides the cytoplasm • Two daughter cells are formed • Each daughter cell receives the same genetic information as the parent cell

What is differentiation

is the process by which cells become specialised to perform functions

What are stem cells

cells that can differentiate into specialised cell types.

Types of stem cells

totipotent, pluripotent, and multipotent

Totipotent stem cells

stem cells that can create any of the types of cells necessary for embryonic development.

Pluripotent stem cells

stem cells that can give rise to many, but not all, of the cell types necessary for foetal development.

Multipotent stem cells

stem cells that can give rise to a limited number of other cell types e.g. Blood stem cells will give rise to red and white blood cells and platelets.

What are gametes

reproductive cells – sperm and ova

What is diploid (2n)

two copies of each type of chromosome

What is haploid (n)

one copy of each type of chromosome

What are homologous chromosomes

chromosome pairs that are similar in shape and carry genes influencing the same characteristics

Meiosis

produces daughter cells containing half the chromosome number of the original cell

Before meiosis what happens during interphase

• The cell grows • DNA is replicated

First meiotic division

• Homologous chromosome pairs separate • Two daughter cell are formed • Each has chromosomes consisting of two chromatids

Second meiotic division

• Chromatids separate • Four daughter cells are produced • Each daughter cell is haploid

What are the stages of the first meiotic division

1. Prophase I

2. Metaphase I

3. Anaphase I

4. Telophase I a. Cytokinesis

Prophase I

during which the chromosomes become visible, the nuclear membrane breaks down and the spindle forms

Metaphase I

during which the homologous chromosomes line up on the equator

Anaphase I

during which the homologous chromosomes move to opposite ends of the cell

Telophase I and cytokinesis

during which the new nuclear membrane forms, producing two cells.

What are the stages of the second minority division

1. Prophase II

2. Metaphase II

3. Anaphase II

4. Telophase II a. cytokinesis

Prophase II

during which the nuclear membrane disappears and the spindles form

Metaphase II

which the chromosomes line up on the equator

Anaphase II

during which the daughter chromosomes move towards opposite ends of the cell

Telophase II and cytokinesis

during which the nuclear membrane forms producing 4 new cells.

Differences between mitosis and meiosis

Mitosis Meiosis 1 duplication of chromosomes and 1 nuclear division 1 duplication of chromosomes and 2 nuclear divisions Produces 2 diploid cells Produces 4 diploid cells Chromosomes do not change their genetic make-up Chromosomes genetic make-up may be changed through crossing over Produces new cells for growth and repair Produces haploid gametes for reproduction

Genetic variation through

• crossing over • non – disjunction • random/independent assortment

Crossing over

the interchange of the parts of the chromatids of a homologous pair of chromosomes during the first stage of meiosis

Chiasma

the point at which crossing over occurs between chromatids

Recombination

A changing of the order of alleles along a chromosome

Non-disjunction

when one or more of the chromosome pairs fail to separate properly during meiosis

Conditions caused by non-disjunction

• trisomy

The random/independent assortment

the random combinations of the alleles due to allele pairs separating independently of one another