This document summarizes heredity and variation. It discusses genes and chromosomes, which carry genetic information from parents to offspring. It describes two types of cell division: mitosis, which produces identical body cells, and meiosis, which produces gametes with half the number of chromosomes. Meiosis allows for genetic variation between offspring. The document also covers sex determination, dominant and recessive traits, and mutations that can cause genetic disorders like Down syndrome, hemophilia, and albinism.

1. CHAPTER 3
HEREDITY AND
VARIATION

2. 3.1 CELL DIVISION

3. Genes
Genes are the basic units of
inheritance that determine the
characteristics of the individual.
Genes carry genetic information
from one generation to another.
Genes are located in long
molecules known as
deoxyribonucleic acid (DNA)

5. CHROMOSOMES
Are located in the nucleus
Carrying information that
determines our characteristic
Each chromosome is made up
from DNA

7. Relationship between gene,
chromosome, and DNA.

8. Type of Cell Division.
the processes of reproduction
and growth of any organism
involve cell division
there are two types, which is :
mitosis
meiosis

9. Mitosis

11. Is a type of cell division
which occurs in somatic cell.
Each cell divides into two part
identical daughter cells
Only occurs in somatic cell
but not in reproductive cells

12. Genetic content of the new
cells is the same as that the
parent cell.
The new cells have the same
number of chromosomes as
the parent cell

13. the importance of mitosis :
Increases the number of cells
during growth
Replace dead or damaged cells
Repairs injured cells

14. Meiosis

17. the process of cell division
to produce gametes
Contain half of the number
of chromosomes of the
parent cell.
occurs only in the
reproductive organs.

18. occurs in the testis of a
male and the ovary of
female who have attained
sexual maturity.
meiosis also occurs in the
anther and ovary of
plants.

19. the importance of meiosis :
The daughter cell have the same
number of chromosomes as parent cell
after fertilization has taken place
Genetic variation between the offspring
increases because of crossing-over
between the chromatids
The offspring produces will have
different characteristic because of
variation

20. Comparison between meiosis and
mitosis
Similarities
chromosome
replication
takes place
call division
occurs
new cells
are
produced

22. 3.2: The principles and
mechanism inheritance
Genes
Dominant Recessive

23. Dominant genes
are represented
by the letter ‘T’

24. are genes which show the
characteristics that they control
when paired with a dominant gene
or a recessive gene.
the characteristics determined
by this genes are called
dominant traits.
dominant traits are shown if
one or both dominant genes
which control the particular
characteristics are present.

25. human traits controlled
by this genes
tall, curly hair, free ear lobe,
black hair, able to roll the tongue,
dimples, long eye lashes, right-
handed, pigments in skin, black
or brown iris, normal eyesight

26. Recessive genes
are represented by the
letter ‘t’.

27. are genes which only
show the characteristics
that they control when
these genes are paired
with another recessive
gene.
the characteristics
determined by this
genes are called
recessive traits.
recessive traits are only
shown if the recessive
genes are not paired
with dominant genes.
short, straight hair,
attached ear lobe, blond
hair, unable to roll the
tongue, no dimples,
short eye lashes, left-
handed, albino, blue iris,
colour-blindness

28. The dominant and recessive characteristic in
human
Dominant traits Recessive traits
Black hair Brown hair
Curly hair Straight hair
Free ear lobes Attached ear lobes
Able to roll the tongue Unable to roll the tongue
Tall Short
Black/ brown eyes Blue eyes
Cheeks with dimples No dimples on the cheeks

29. The mechanism of trait inheritance
Gregor Mendel (1822-1884)
was an Austrian scientist known
as the father of genetics
because he discovered the
principle of inheritance.

30. Genotype refers to the genetic
information found in the genes of
an organism
Phenotype refers to the physical
properties which can be seen in
organism.
The genotype of an organism
determines the phenotype of the
organism

31. PLEASE SEE VIDEO

32. combination of gametes at the first filial
generation, F1, can be shown in the
Punnett Square.
Gen T t
T TT Tt
t Tt tt

34. 3.3 Sex Determination and the
occurrences of twins in human being
*a human somatic cell has 23
pairs of chromosomes (46
chromosomes).
*from the 23 pairs of
chromosomes, 22 pairs are
autosomes and one pair is sex
chromosomes.
*sex chromosome determine
the sex of a person
SexChromosomes

35. • male sex chromosomes
are XY
• male somatic cell contains
22 pairs of autosomes
with one X chromosome
and one Y chromosome.
44 + XY
• in meiosis, a male
produces two types of
gamete which :
carries 22 autosomes and
one X chromosome. 22+X
carries 22 autosomes and
one Y chromosome. 22+Y
Male sex
chromosome

36. Female sex
chromosome
female sex chromosome is XX
female somatic cell contains
22 pairs of autosomes and
two X chromosomes. 44 + XX
in meiosis, a female gamete
only carries 22 autosomes
and one X chromosome. 22+X

37. Sex Determination.
the sex of child is determined by the
father according to the type of sperm
that fertilises the ovum.
if a sperm that carries
the x chromosomes fertilises an ovum, a
baby girl is born.
the y chromosomes fertilises an ovum, a
baby boy is born.
the probability of having a male child or
female child is the same> 50 : 50

39. Occurrence of twins
in humans, normally one ovum fertilised
by one sperm to form one zygote which
will develop to form an embryo.
sometimes more than one embryo is
produced in a pregnancy.
twins - two babies born to a mother in a
pregnancy and generally at the
same time.
there are two types of twins  identical
twins non-identical twins

40. Comparison between identical and
non-identical twins
Similarities
two babies born in a
pregnancy

41. Differences Identical Twins Non-identical twins
Formation
Formed when an
ovum fertilised by
a sperm divides
into two to form
two similar
embryos.
Formed when two
ova are released
by the ovary at the
same time and
fertilised
separately by two
sperms to form
two different
embryos.
Placenta
The two embryos
formed will grow in
one shared
placenta in the
mother’s uterus.
The two embryos
formed when grow
in separate
placentas in the
mother’s uterus

42. Genetic
make-up
Same genetic
make-up.
Therefore,
identical twins
have the same
appearance and
the same sex.
Different
genetic make-
up since they
originate from
two different
ova and sperms.
Therefore, non-
identical twins
have different
appearances.
Sex
The sex of
identical twins
are the same.
The sex of non-
identical twins
may be the
same or
different.

43. sometimes the division of the embryo is
not complete, therefore Siamese twins
are formed.
Siamese twins may share certain organs
like brain, stomach, or heart and maybe
joined to one another at the head,
abdomen, breast, or buttocks.
they can be separated by surgery if they
do not share important organs like
brain, heart, kidneys, or lungs.

44. 3.4 Mutation
is the spontaneous change to the
structure of genes or chromosomes of an
organism.
causes change of characteristics in a child.
occurs in somatic cells or in gametes.
the effect of mutation will be inherited by
one generation to another.
there are two types of mutation
gene mutations
chromosome mutations

45. Gene Mutations
involve changes in the structure of
gene.
gene mutations change or produce
the new genes to replace normal
genes.
genes that have undergone
mutation are called mutants.

46. Heredity disease
caused by gene
mutation
Brief explanation
Albinism  albinisms is caused by the change in
the gene that controls skin colour.
 the newly produced genes are unable
to produce skin pigment.
 the skin and hair of albinos are white
and their eyes are pink.

47. Albinism

48. Sickle cell
anaemia
 sickle cell anaemia is a type of disease
caused by the change in the genes
that produce haemoglobin.
 haemoglobin that has undergone
mutation is not efficient in
transporting oxygen.

49. Sickle cell anaemia

50. Colour-blindness  is a sex-linked disease determined by
a recessive gene on the X
chromosome.
 a colour-blind person cannot see or
differentiate the colours red and
green.

51. Colour-blindness

52. Haemophilia  caused by the deficiency if a type of
protein in the blood required for blood
clotting.
 haemophilia is caused by the
deficiency of a type of protein in the
blood required for blood clotting.
 haemophilia is a sex-linked disease
determined by a recessive gene on the
X chromosome.
 a patient who has wound will
experience continuous bleeding or will
take a long time for the blood to clot
thus this condition way lead to death.

53. Haemophilia

54. Chromosome Mutations
 involve changes in the number of chromosomes or
arrangement of genes in chromosomes.
 sometimes, a portion of a chromosome may break
away and go missing, or become attached itself to
other chromosomes.
 this causes the arrangement of a chromosome to
change and differ from normal.
 the number of chromosomes can be increased or
decreased
 chromosome mutations can cause hereditary
diseases like Down’s syndrome, Klinefelter’s
syndrome, and Turner’s syndrome

55. Down’s syndrome
this heredity disease is caused by
the presence of one extra
chromosome at chromosomes 21 in
the somatic cells.
incomplete separation of
chromosomes during meiosis
causes the zygote to have an extra
chromosome : 47 in total.

57. characteristics of a down’s
syndrome patient :
slanting eyes
metal retardation
short fingers
wide distance between eyes
small mouth but big tongue
protruding tongue causing the
mouth to remain partially open

58. Klinefelter’s syndrome
a person who suffers from this
hereditary diseases has one extra
X chromosome : XXY

59. Turner’s syndrome
a person who suffers from this
hereditary lacks one X chromosome.
people with Turner;s syndrome have
only one sex chromosome which is XO.

60. Factors that cause mutation.
mutation can occur naturally, caused by
substances found in food or
environment.
agents causes mutations are called
mutagens.
chemical substances like pesticides,
nicotine in cigarettes, drugs, nitrous acid
and some preservatives, colouring and
artificial sweetener can cause mutation.

61. radiation
radioactive radiation can cause
mutation
gamma ray can affect growth and cell
division
ultraviolet rays and X-ray rays can
cause skin cells to mutate and this may
cause cancer
 temperatures which are too high or
too low can also cause mutation.

62. Advantages and disadvantages
of mutation.
not all occurrences of mutation bring
adverse effects to organisms.
advantages of mutation
mutation causes variations in organisms which
allow them to adapt to the environment.
species that are more resistant to disease,
weather, and polluted environment can be
produced.

63. disadvantages of mutation
some mutations cause diseases like
colour-blindness and haemophilia
cannot be cured.
sometimes, disease like haemophilia
and sickle cell anaemia can cause
death.
Klinefelter’s syndrome causes
infertility.
mutation causes physical, mental, or
foestus retardation.