2. Genes, gametes and chromosomes
Genes are found in
chromosomes in the
nuclei. Human body
cells have 46
chromosomes in each
nuclie(diploid
number) while
gametes have 23
( Haploid number).
During fertilization the
nuclei in each gamete
join to form 46.
done by Mr J Thomas 2
3. Mitosis & Meiosis
Mitosis occurs when the
daughter cells are the
same as the mother.
The chromosomes split in
to two chromatids
with each chromatid
going into each
daughter cell.
done by Mr J Thomas 3
4. Meiosis
Meiosis is the process by
which gametes are formed.
During meiosis, similar
gametes pair and exchange
genes in a process called
Crossing Over.
One chromosome in each
pair comes from the father
and the other for the
mother.
done by Mr J Thomas 4
5. Inheritance with dominance
Inheritance is the passing on of
genetic information from
one off spring to another.
GENOTYPE – the genes that an
individual has.
PHENOTYPE – the
characteristics that can be
seen in an individual, e.g.
Skin and eye colour.
Genes control all the
characters in an organism
from eye colour to height,
hair texture to tongue
rolling. done by Mr J Thomas 5
6. Alleles dominant and recessive
A dominant allele causes a
character to be expressed
A recessive allele does not
cause a character to be
expressed. If an individual
inherits a allele pair with
one dominant then the
character will be
expressed. If the pair of
allele is recessive, the
character will not be
expressed.
done by Mr J Thomas 6
7. Homozygous and heterozygous
Similar alleles are
homozygous, e.g. TT or tt.
Heterozygous alleles are
different, e.g. Tt.
A person who posses TT or Tt
are able to express the
trait where as those with tt
do not express the trait.
done by Mr J Thomas 7
8. If the albino child grow up
and have children with
a normal person, they
will be normal. If he/she
has kids with a carrier,
half the kids will be
carriers and half will be
albino.
done by Mr J Thomas 8
9. Down syndrome occurs when
the zygote receives an
extra chromosome. The
extra chromosome causes
the child to develop down
syndrome.
The extra chromosome
comes from the mother.
done by Mr J Thomas 9
10. Monohybrid inheritance
The ability to taste PTC ( a
bitter chemical) is
controlled by one pair of
genes. This is called
monohybrid inheritance.
An allele is the alternative
gene available to control
one character.
If a person can taste PTC, it
means that the allele that
controls the ability to taste
is dominant over the allele
that does not. done by Mr J Thomas 10
11. Monohybrid Recessive inheritance
This is cause by the
inheritance of two
recessive allele. A
dominant allele controls
the normal condition and
its absence results in the
condition. Albinism is cause
by the inheritance of two
recessive allele.
if A represents normal skin
pigment and a the albino
condition, A carrier will
appear normal but have
the recessive allele ( Aa).done by Mr J Thomas 11
12. Incomplete dominance
Incomplete dominance
describes when a character
in both parent is expressed
equally in an offspring.
When both alleles are
inherited by the off spring
the character they
expressed are shown
equally.
done by Mr J Thomas 12
13. Co-dominance and multiple alleles
• The gene for the ABO
blood groups is a good
example of co-dominance.
• Blood cells have proteins
on their surface called
antigens.
• Antigen A- controlled by
allele IA
• Antigen B –controlled by
allele IB
• Neither antigen A nor B –
controlled by allele Io
done by Mr J Thomas 13
14. Blood transfusion
• Its important to know
your blood type before
you receive blood. This
will ensure that your
body does not reject
the donation.
done by Mr J Thomas 14
15. Types of Inheritance
Sex is inherited due to different sex
chromosomes in the male and
female.
A male has an X and a Y chromosome,
while the female has two X
chromosomes.
There is 50% chance of producing a boy
or a girl. Statistic show that with
every 100 girl born there is 105 boys.
The Y chromosomes have a gene that
stimulate the body to produce a testis
and male hormones, absence of this
gene results in the formation of a girl.
done by Mr J Thomas 15
16. Red/green colour blindness
• This condition is Sex
linked, it is on the X
chromosome and it is a
recessive allele. There
are two X chromosomes
in females therefore the
dominant allele will
cause the character not
to show.
• Males have a X and a Y
chromosome, therefore
males will develop the
condition.
done by Mr J Thomas 16
17. Variation
Continuous variation is when
there are small differences
between individuals
arranged in order, e.g.
Height of students in a
class. There are short,
medium sized and tall
students.
Discontinuous variation
occurs when there are big
differences between
individuals, e.g. Number of
students who carry brown,
black or white bags.
done by Mr J Thomas 17
18. What are the sources of variation?
Crossing over at meiosis.
Random fusion of egg and
sperm.
Characters are inherited from
both parents.
Environmental factors such
as diet, education, health,
daily activities.
done by Mr J Thomas 18
20. Genetics and environmental
effects
Identical twins are produced when a
zygote splits in two to form separate
embryos.
Any difference between the two can be
contributed to their environment.
Your blood group is entirely inherited
and cannot be changed; also your eye
colour & natural hair colour.
Genes may control your height, but diet,
absence or presence of diseases and
your daily activities may change or
influence your growth, e.g. Athletes
grow taller. done by Mr J Thomas 20
21. Weight is genetically
controlled, but it is
influenced by the
environment. If you inherit
a large skeleton, you are
likely to weigh more. If
you eat a lot you are likely
to become fat.
Deaths through accidents are
controlled by the
environment, death by
famine and starvation are
also controlled by the
environment.
done by Mr J Thomas 21
22. Nature – nurture
If you smoke, your will damage your
lungs, if you do a lot of manual
labour, you will have big muscles. All
these characters are controlled by the
environment.
Nature- how you were born.
Nurture- your lifestyle- your
environment.
Characters developed by the
environment cannot be passed on to
your off spring. It doesn't matter how
hard you work, your child can still be
born lazy.
done by Mr J Thomas 22
23. DNA, RNA, protein synthesis.
Genes control the making of
protein that are the building
blocks of out body.
DNA is the chemical that forms
protein. DNA is short for
Deoxyribonucleic acid.
There are 20 different amino acids
that make the protein in our
bodies. This protein is made on
the ribosome in the cell. The
messenger RNA carry the code
from the nucleus to the
ribosome where the protein is
made. done by Mr J Thomas 23
24. How protein is made
• Protein is made up of
amino acids linked
together in a certain order.
Every protein has a
different arrangement of
amino acids.
• Protein is made by:
• Transcription – a copy of
the gene is made as RNA.
• Translation – the copy is
used to link the amino
acids together.
done by Mr J Thomas 24
25. A gene mutation is an abrupt
change in the DNA, e.g.
Albinism.
Sickle cell anaemia is caused
by a change in one part of
a DNA that controls
haemoglobin ( glutamine is
replaced by valine). This
cause the blood cells to
have a sickle shape which
reduces the blood’s ability
to carry oxygen.
done by Mr J Thomas 25
