Download iGCSE Biology Section 3 lesson 4

IGCSE BIOLOGY
SECTION 3 LESSON 4
Content
Section 3
Reproduction
and
Inheritance
a) Reproduction
- Flowering plants
- Humans
b) Inheritance
Content
Lesson 4
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).
Chromosomes
In human body cells there are 46 chromosomes,
arranged into 23 pairs.
Chromosomes
In human body cells there are 46 chromosomes,
arranged into 23 pairs.
This picture is
known as the
human karyotype.
Chromosomes
In human body cells there are 46 chromosomes,
arranged into 23 pairs.
This picture is
known as the
human karyotype.
The human diploid
number is 46.
Chromosomes
In human body cells there are 46 chromosomes,
arranged into 23 pairs.
This picture is
known as the
human karyotype.
The human diploid
number is 46.
The human haploid
number is 23.
Chromosomes
In human gametes (sex cells) there are 23
chromosomes, one from each pair.
Chromosomes
Other species have different numbers of
chromosomes – there is no relationship between
the size of an organism and the chromosome
number.
Chromosomes
Other species have different numbers of
chromosomes – there is no relationship between
the size of an organism and the chromosome
number.
Chromosomes
Other species have different numbers of
chromosomes – there is no relationship between
the size of an organism and the chromosome
number.
Organism
Diploid number of
chromosomes
Pigeon
Dog
Cat
Bean
Pea
Meerkat
Pig
Dolphin
80
78
38
22
14
36
38
44
Sex chromosomes
One pair of chromosomes are the sex
chromosomes – they determine the gender of an
individual (male or female)
The male has an X sex
chromosome and a Y
sex chromosome (shown
here)
Sex chromosomes
One pair of chromosomes are the sex
chromosomes – they determine the gender of an
individual (male or female)
The female has two X
sex chromosomes
Sex chromosomes
One pair of chromosomes are the sex
chromosomes – they determine the gender of an
individual (male or female)
Male = XY
Female = XX
Inheritance of sex
Sex chromosomes
=XX
Sex chromosomes
=XY
Inheritance of sex
Sex chromosomes
=XX
Sex chromosomes
=XY
X X
X Y
In gamete (sex cell)
formation, the sex
chromosomes separate
Inheritance of sex
sperm
egg
X
X
X
Y
Inheritance of sex
X
Y
X
XX
XY
X
XX
XY
sperm
egg
Inheritance of sex
sperm
egg
X
Y
BABY
GIRL
X
XX
XY
BABY
BOY
X
XX
XY
Inheritance of sex
sperm
egg
BABY
GIRL
X
BABY
BOY
X
X
Y
XX
XY
XX
XY
FERTILISATION is RANDOM
-There is an equal chance that
an X-sperm or a Y-sperm will
fertilise the egg.
Therefore, there is an equal
chance of having either a baby
girl or a baby boy.
Inheritance of sex
sperm
egg
BABY
GIRL
X
BABY
BOY
X
X
Y
XX
XY
XX
XY
SEXUAL REPRODUCTION
means loads of variation,
because the genetic material
from both parents is mixed
together when the sperm
fertilises the egg
“understand that
division of a diploid
cell by mitosis
produces two cells
which contain identical
sets of chromosomes”
“understand that
division of a cell by
meiosis produces four
cells, each with half
the number of
chromosomes”
“understand that
division of a diploid
cell by mitosis
produces two cells
which contain identical
sets of chromosomes”
MITOSIS
The method by
which all body
cells divide, to
maintain the
diploid number
(46)
“understand that
division of a cell by
meiosis produces four
cells, each with half
the number of
chromosomes”
MEIOSIS
The method by
which sex cells
are produced,
resulting in the
haploid number
(23)
“understand that
“understand that
division of a diploid
division of a cell by
WARNING! meiosis
Mitosis
and four
cell by mitosis
produces
produces two cellsMeiosis are both
cells, difficult
each with half
which contain identical
theso
number
of
concepts to grasp,
make
sets of chromosomes”
chromosomes”
sure you take this section
slowly and go over it again and
again until you’ve grasped all
the necessary facts.
MITOSIS
The method by
which all body
cells divide, to
maintain the
diploid number
(46)
MEIOSIS
The method by
which sex cells
are produced,
resulting in the
haploid number
(23)
Mitosis
This occurs for growth and repair
(and also in asexual reproduction)
and before each cell division a copy
of each chromosome is made so that
each body cell has exactly the same
genetic information. The
chromosome number is maintained.
DIPLOID  DIPLOID
Mitosis
Parental cell with two
pairs of chromosomes
Mitosis
Each chromosome
replicates itself
Parental cell with two
pairs of chromosomes
Mitosis
Each chromosome
replicates itself
Parental cell with two
pairs of chromosomes
The ‘copies’ are
pulled apart. Cell
now divides for the
only time.
Mitosis
Each chromosome
replicates itself
Parental cell with two
pairs of chromosomes
Each ‘daughter’ cell
has the same
number of
chromosomes as
the parental cell
and contains the
same genes as the
parental cell
The ‘copies’ are
pulled apart. Cell
now divides for the
only time.
Meiosis
Meiosis
Diploid number
Haploid number
Meiosis
Diploid number
Meiosis occurs in the
testes and ovaries to
produce the gametes
(eggs and sperm) for
sexual reproduction.
Haploid number
Meiosis
Parental cell with two pairs
of chromosomes
Meiosis
Parental cell with two pairs
of chromosomes
Each chromosome replicates
itself.
Meiosis
Parental cell with two pairs
of chromosomes
Each chromosome replicates
itself.
Chromosomes part company and move
to opposite sides with their copies.
Cell divides for the first time.
Meiosis
Parental cell with two pairs
of chromosomes
Each chromosome replicates
itself.
Chromosomes part company and move
to opposite sides with their copies.
Cell divides for the first time.
Copies now separate and the
second cell division takes place
Meiosis
Parental cell with two pairs
of chromosomes
Each chromosome replicates
itself.
Chromosomes part company and move
to opposite sides with their copies.
Cell divides for the first time.
Copies now separate and the
second cell division takes place
Four gametes now formed, each
with half the chromosome
number of the original parental
cell.
Why sexual reproduction
promotes variation
Why sexual reproduction
promotes variation
1. The gametes are produced by meiosis,
which ‘shuffles’ the genes.
Why sexual reproduction
promotes variation
1. The gametes are produced by meiosis,
which ‘shuffles’ the genes.
2. Gametes fuse randomly, with one of
each pair of alleles coming from each
parent.
Why sexual reproduction
promotes variation
1. The gametes are produced by meiosis,
which ‘shuffles’ the genes.
2. Gametes fuse randomly, with one of
each pair of alleles coming from each
parent.
3. The alleles in a pair may be different
and so produce different
characteristics.
understand that
variation within a
species can be
genetic,
environmental, or a
combination of both
Variation
Two possible
causes
Variation
Two possible
causes
Genetic
Variation
Two possible
causes
Genetic
As a result of the
different genes
inherited
Variation
Two possible
causes
Genetic
As a result of the
different genes
inherited
Variation
Two possible
causes
Genetic
As a result of the
different genes
inherited
Environment
Variation
Two possible
causes
Genetic
As a result of the
different genes
inherited
Environment
As a result of the
conditions in which
they develop
Variation
Two possible
causes
Genetic
As a result of the
different genes
inherited
Environment
As a result of the
conditions in which
they develop
Variation
Two possible
causes
Genetic
Environment
As a result of the
different genes
inherited
As a result of the
conditions in which
they develop
Usually, variation is
due to a combination
of genetic and
environmental causes
“understand that
mutation is a rare,
random change in
genetic material that
can be inherited”
“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)”
Genetic mutations
Every time a cell divides, all
the DNA in the nucleus must
be copied exactly.
Genetic mutations
Every time a cell divides, all
the DNA in the nucleus must
be copied exactly.
Occasionally a mistake may
occur, and bases may be put
in the wrong order.
Genetic mutations
Every time a cell divides, all
the DNA in the nucleus must
be copied exactly.
Occasionally a mistake may
occur, and bases may be put
in the wrong order.
As a result, there will be a
different sequence of amino
acids, and therefore a
different protein will be
made.
Genetic mutations
Every time a cell divides, all
the DNA in the nucleus must
be copied exactly.
Occasionally a mistake may
occur, and bases may be put
in the wrong order.
As a result, there will be a
different sequence of amino
acids, and therefore a
different protein will be
made.
This change in the order
of the bases is called a
MUTATION
Genetic mutations
Causes
Effects
Mutations occur naturally
but ……
• there is an increased risk
if
• individuals are exposed to
mutagenic agents
• such as ionising radiation
(UV, X-rays)
• radioactive substances and
certain chemicals (eg. in
cigarette smoke)
• the greater the dose, the
greater the risk.
Most mutations are harmful
and in …
• Reproductive cells can
cause death or abnormality
• in body cells they may
cause cancer
• some mutations are neutral
and some may increase the
survival chances of an
organism
• and its offspring who
inherit the gene
Types of gene mutations
Types of gene mutations
Duplication – the nucleotide (an individual base unit) is
inserted twice instead of once
Eg:
Normal
AAT CCG GCA TTC TAT
Duplicated
AAA TCC GGC ATT CTA
duplication here
Types of gene mutations
Deletion – the nucleotide is completely missed out
Eg:
Normal
AAT CCG GCA TTC TAT
Deletion
AAC CGC ATT CTA TTC
deletion here
Types of gene mutations
Substitution – a different nucleotide is inserted
Eg:
Normal
AAT CCG GCA TTC TAT
Substitution
AAG CCG GCA TTC TAT
substitution here
Types of gene mutations
Inversion – the sequence of bases is reversed
Eg:
Normal
AAT CCG GCA TTC TAT
Inversion
AAT CCG ACG TTC TAT
inversion here
Chromosome mutations
Rather than changes in individual bases, whole
chromosomes may be inserted or lost, or bits may be
broken off.
Chromosome mutations
Rather than changes in individual bases, whole
chromosomes may be inserted or lost, or bits may be
broken off. A relatively common chromosome mutation can
be found when the female ova may contain two copies of
chromosome 21.
Chromosome mutations
Rather than changes in individual bases, whole
chromosomes may be inserted or lost, or bits may be
broken off. A relatively common chromosome mutation can
be found when the female ova may contain two copies of
chromosome 21.
When fertilised by a normal
sperm, the offspring will
have three copies of
chromosome 21. This is
called trisomy 21 and the
resulting condition is known
as Down’s syndrome.
understand that resistance
to antibiotics can increase
in bacterial populations,
and appreciate how such an
increase can lead to
infections being difficult
to control
Resistance in bacteria
Scientists try to control the
spread of bacteria using
antibiotics .
Resistance in bacteria
Scientists try to control the
spread of bacteria using
antibiotics .
Gene mutations can result
in bacteria becoming
resistant to the use of
antibiotics.
Resistance in bacteria
Scientists try to control the
spread of bacteria using
antibiotics .
Gene mutations can result
in bacteria becoming
resistant to the use of
antibiotics.
Resistant bacteria have an
advantage over nonresistant bacteria and so
spread through the
population.
Resistance in bacteria
Scientists try to control the
spread of bacteria using
antibiotics .
Gene mutations can result
in bacteria becoming
resistant to the use of
antibiotics.
Resistant bacteria have an
advantage over nonresistant bacteria and so
spread through the
population.
This is an example of natural selection in action.
“describe the
process of
evolution by
means of natural
selection”
“describe the
process of
evolution by
means of natural
selection”
“describe the
process of
evolution by
means of natural
selection”
End of Section 3 Lesson 4
In this lesson we have covered:
Chromosomes
Inheritance of Sex
Mitosis
Meiosis
Variation
Mutations