Download iGCSE Biology Section 3 lesson 5

IGCSE BIOLOGY
SECTION 3 LESSON 5
Content
Section 3
Reproduction
and
Inheritance
a) Reproduction
- Flowering plants
- Humans
b) Inheritance
Content
Lesson 5
b) Inheritance
b) Inheritance
3.21 understand that the sex of a person is controlled by one pair of
chromosomes, XX in a female and XY in a male
3.22 describe the determination of the sex of offspring at fertilisation,
using a genetic diagram
3.23 understand that division of a diploid cell by mitosis produces two
cells which contain identical sets of chromosomes
3.24 understand that mitosis occurs during growth, repair, cloning and
asexual reproduction
3.25 understand that division of a cell by meiosis produces four cells,
each with half the number of chromosomes, and that this results in
the formation of genetically different haploid gametes
3.26 understand that random fertilisation produces genetic variation
of offspring
3.27 know that in human cells the diploid number of chromosomes is
46 and the haploid number is 23
3.28 understand that variation within a species can be genetic,
environmental, or a combination of both
3.29 understand that mutation is a rare, random change in genetic
material that can be inherited
3.30 describe the process of evolution by means of natural selection
3.31 understand that many mutations are harmful but some are
neutral and a few are beneficial
3.32 understand that resistance to antibiotics can increase in bacterial
populations, and appreciate how such an increase can lead to
infections being difficult to control
3.33 understand that the incidence of mutations can be increased by
exposure to ionising radiation (for example gamma rays, X-rays and
ultraviolet rays) and some chemical mutagens (for example
chemicals in tobacco).
“describe the
process of
evolution by
means of natural
selection”
In 1859 Charles Darwin
published ‘The Origin
of Species by Natural
Selection’.
In 1859 Charles Darwin
published ‘The Origin
of Species by Natural
Selection’.
As a 22 year old,
Darwin joined the crew
of HMS Beagle as a
naturalist
www.worldatlas.com
Alfred Russel Wallace
Observations and Conclusions
Observations and Conclusions
1. Organisms produce many
offspring
There must be a struggle
for survival and competition
for food, water, and a place
to live.
Observations and Conclusions
1. Organisms produce many
offspring
There must be a struggle
for survival and competition
for food, water, and a place
to live.
2. The size of a population
of one species in nature
tends to remain constant
Some organisms are better
adapted to survive in their
environment. So they breed
and produce offspring.
Observations and Conclusions
1. Organisms produce many
offspring
There must be a struggle
for survival and competition
for food, water, and a place
to live.
2. The size of a population
of one species in nature
tends to remain constant
Some organisms are better
adapted to survive in their
environment. So they breed
and produce offspring.
3. Members of a species
vary
The offspring inherit the
characteristics of the
organisms best fitted for
survival. So an improved
form is evolved by natural
selection.
Evolution by Natural Selection
4 key points to remember
Evolution by Natural Selection
4 key points to remember
1. Individuals within a population show variation
(i.e. differences due to their genes)
Evolution by Natural Selection
4 key points to remember
2. There is competition between individuals for
food and mates, etc., and also predation and
disease. This keeps the population sizes
constant in spite of production of many offspring
i.e. there is a ‘struggle for survival’ and many
individuals die.
Evolution by Natural Selection
4 key points to remember
3. Individuals which are better adapted to the
environment are more likely to survive, breed
successfully and produce offspring. This is
termed ‘survival of the fittest’.
Evolution by Natural Selection
4 key points to remember
4. These ‘survivors’ will therefore pass on their
genes to their offspring, resulting in an improved
organism being evolved through natural
selection.
Evolution in Action
Bacteria resistant to
penicillin
Evolution in Action
Penicillin is an antibiotic – it
kills or slows down the
growth of bacteria.
Bacteria resistant to
penicillin
Evolution in Action
Penicillin is an antibiotic – it
kills or slows down the
growth of bacteria.
Mutations have arisen
amongst certain strains of
bacteria that have resulted
in penicillin resistance.
Bacteria resistant to
penicillin
Evolution in Action
VARIATION
Bacteria mutated. Some
were resistant to the
antibiotic penicillin. Others
were not.
Bacteria resistant to
penicillin
Evolution in Action
VARIATION
Bacteria mutated. Some
were resistant to the
antibiotic penicillin. Others
were not.
COMPETITION
The non-resistant bacteria
were more likely to be killed
by the penicillin.
Bacteria resistant to
penicillin
Evolution in Action
BEST ADAPTED
The penicillin-resistant
bacteria survived and
reproduced more often.
Bacteria resistant to
penicillin
Evolution in Action
BEST ADAPTED
The penicillin-resistant
bacteria survived and
reproduced more often.
PASS ON THEIR GENES
More bacteria are becoming
resistant to penicillin. This
is a major health issue.
Bacteria resistant to
penicillin
Evolution in Action
Other examples:
Varieties
Selection by
Result
Gazelles, fast and slow
Lions
Only the fastest survive
to produce offspring
Peppered moth, light
and dark forms
Birds, selecting the
least camouflaged
Light forms in
unpolluted areas, dark
in smoky cities
Rats – some killed by
warfarin, others
resistant
Warfarin used by
farmers
New variety of warfarin
–resistant rats.
Rabbits – resistant to or
killed by myxomatosis
Virus introduced by
farmers
New myxomatosis –
resistant population
End of Section 3 Lesson 5
In this lesson we have covered:
Natural selection by evolution