genetics lect 3 2011 colour 2 slides per page.pdf

8/13/2019 Genetics Lect 3 2011 colour 2 slides per page.pdf

1/11


2/11

Lecture3

Reproduction is when an entity undergoes division that

results in the production of two entities of the same

1. Reproduction of eukaryotic

somatic cells

BIOSCI101Essential

.

In biology this process is based on the reproduction of

cells and the cells genetic material.

Cell division plays several important roles in the life of

iology

. .

an entire individual, in multicellular organisms allows

growth and repair.

Mitotic cell division results in the production two

genetically identical daughter cells.

Lecture3

The cell cycle

BIOSCI101Essential

iology

Cell cycle = an ordered sequence of events in the life of a

cell. Mitotic (M) phase - division & interphase - non dividing


3/11

Lecture3

a) Interphase

~ 90% of cycle

Phases of the cell cycle

BIOSCI101Essential

intense biochemical activity

3 phases

G1 - 1st gap phase

S - DNA synthesis

G2 - 2nd gap phase

iology

b) M phase

mitosis = division of nucleus

cytokinesis = division of cytoplasm

Lecture3

c) DNA in cells during cell division

BIOSCI101Essential

iology


4/11

Lecture3

Overview of mitosis

BIOSCI101Essential

iology

Lecture3

Mitosis - division of an animal cell

BIOSCI101Essential

iology


5/11

Lecture3

BIOSCI101Essential

iology

Lecture3

2. Comparison of asexual & sexualreproduction

BIOSCI101Essential

sexua exua

One parent Two parents

Single parent

contributes all the

genes

Each parent

contributes half their

genes

iology Clones (copies) Vary genetically

The asexual reproduction of the hydra chip off the old

block or a clone


6/11

Lecture3

3. Ferti lization and meiosis alternate in

the sexual l ife cycles

Life cycle = sequence of stages in an organisms

reproductive history conception to production of aBIOSCI101Essential

new o spr ng.

Fertilization = the fusion of two haploid gamete nuclei to

form diploid zygote nucleus.

Haploid = a single set of chromosomes (1n).

iology

Diploid = the condition in which each autosome is

represented twice (2n).

Meiosis = the two successive nuclear divisions in which

a single diploid (2n) cell forms four haploid (1n) nuclei.

Lecture3

The human life cycle

BIOSCI101Essential

iology

The only cells that are are not produced by mitosis

are the gametes.


7/11

Lecture3

Overview of meiosis

BIOSCI101Essential

iology

Lecture3

4. Meiosis & independent assortment

BIOSCI101Essential

iology

A cell in G2 of interphase, following chromosome

replication


8/11

Lecture3

BIOSCI101Essential

iology

Lecture3

BIOSCI101Essential

iology


9/11

Lecture3

Independent assortment

BIOSCI101Essential

iology

Lecture3

Independent assortment of chromosomes

generates variation among offspring

At metaphase I, homologous pair, each consisting ofBIOSCI101Essential

one ma erna an one pa erna c romosome, a gn n a

random orientation.

Therefore each homologue assorts independently of

other chromosomes.

iology

The number of possible combinations for n = 2 is 4 -(2n), however when n = 23 as in humans, 8 million

combinations of chromosomes inherited from your

mother and father (223) are possible.


10/11

Lecture3

Crossing over occurs during prophase I.

5. Crossing over during meiosis &

random fertilisation

BIOSCI101Essential

,

individual chromosomes carrying genes derived from

two different parents.

Crossing over is the exchange of genetic material

between non-sister chromatids.

iology

In humans 1-3 crossover events occur per chromosome

pair.

Shuffles the genes within the chromosomes.

Lecture3

BIOSCI101Essential

iology


11/11

Lecture3

The random nature of fertilization adds to the genetic

Random fertilization

BIOSCI101Essential

.

Even without crossing over in humans each male and

female gamete represents 8 million possible chromosome

combinations.

The fusion of a sin le male amete with a sin le femaleiology

gamete will produce a zygote with any of about 64 trillion

(8 million x 8 million) diploid combinations.

Lecture3

Mechanism Description of mechanism

Origin of genetic variation in sexually

reproducing organisms

BIOSCI101Essential

MutationMutation is the original source of all variation and

is very rare

Crossing overShuffles genes within a chromosome, individuals

carrying genes derived from two different parents.

iology

assortment

independently during gamete formation.

Random

fertilization

At fertilization any male gamete can fuse with any

other female gamete and produce a zygote with

any of a possible ~ 64 trillion diploid combinations

of parental chromosomes.

genetics lect 3 2011 colour 2 slides per page.pdf

Documents