Transcript 24.3 The pattern of inheritance

24 Genetics
•
24.1 What is genetics?
•
24.2 Genes and inheritance
•
24.3 The pattern of inheritance
•
24.4 Variations
•
25.5 Inherited disorders in humans (Extension)
•
25.6 Genetic engineering
•
Mind Map
24.1 What is genetics?
24.1 What is genetics?
Heredity
Passing on characteristics from
one generation to the next
The differences between
individuals of the same species
Genetics
Variation
The study of how characters
are transferred or inherited
from one generation to the next
24.2 Genes and inheritance
24.2 Genes and inheritance
3
1
DNA
Nucleus
is composed
of
contains
2
Chromosome
24.2 Genes and inheritance
DNA (deoxyribonucleic acid)
consists of two chains
2
1
Each of them contains
sugar & phosphoric acid
3
Two chains twist together to
form a double helix
4 Connecting two chains are
thousands of pairs of organic bases
24.2 Genes and inheritance
A gene
forms part of a chromosome
24.2 Genes and inheritance
controls
Gene
control
Protein
Synthesis
produces
Protein
Chromosome
A specific
character
determines
Specific
reaction
catalyses
Enzyme
24.2 Genes and inheritance
controls
Gene
A specific
character
Gene is a short length of
DNA
can determine a specific
character of an organism
Chromosome
24.2 Genes and inheritance
Gene 1
Brown
eye
Allele 2
Gene 1
Control eye colour
Black
eye
Allele 1
Allele 1
Gene 1
Eye Color
Allele 2
Different color
Alleles = the alternative forms of a gene
24.2 Genes and inheritance
Human Genome Project (HGP)
Genome is ALL the
genes of an organism
Aim:
Mapping the base sequence
of the human genome
24.2 Genes and inheritance
Human Genome Project (HGP)
Applications
1
Improved diagnosis of disease
2
3
Gene therapy
New energy sources (biofuels)
4
Environmental monitoring to detect pollutants
24.2 Genes and inheritance
Human Genome Project (HGP)
5
Applications
Safe, efficient cleanup of toxic waste
6
Study of evolution and mutation
7 Develop disease-and-insect-resistant crops
8
Develop healthier, more productive and
disease-resistant farm animals
24.2 Genes and inheritance
Human Genome Project (HGP)
Drawbacks
1
Expensive &
time-consuming
2
Problem of ownership
24.3 The pattern of inheritance
24.3 The pattern of inheritance
Mendel is known as the
‘father of genetics’
He carried out a series of
breeding experiments on
garden pea
which were easily grown &
have easily identifiable
characteristics
Gregor Mendel
(1822-1884)
24.3 The pattern of inheritance
Mendel’s breeding experiment
2
anthers are removed
to prevent selfpollination
1 pea flower bud
5
enclosed the
flower with a bag
to prevent further
pollination
4
pollens from other plant
was taken & were dusted
onto the stigma, resulting
in cross-pollination
3
wait until the
stigma was ready
to receive pollen
24.3 The pattern of inheritance
Mendel studied the
inheritance of just ONE pair of
contrasting characteristics
(traits) of pea plants each time
Monohybrid
inheritance
Gregor Mendel
(1822-1884)
24.3 The pattern of inheritance
X
Parents
(pure-breeding)
short
tall
Why?
First filial (F1)
generation
all tall
self-pollination
Tall : Short
= 3:1
Second filial (F2)
generation
787 tall
277 short
24.3 The pattern of inheritance
Homologous chromosomes
controls the height
of the garden pea
pure-breeding
parent is tall
controls the height
of the garden pea
Gene 1
Gene 1
Tall allele
Tall allele
If pure-breeding parent is tall, it means
1
two alleles are identical
2
& control the same feature (tall)
24.3 The pattern of inheritance
Homologous chromosomes
controls the height
of the garden pea
pure-breeding
parent is tall
controls the height
of the garden pea
Gene 1
Gene 1
Tall allele
Tall allele
Let T be the allele for being tall
The alleles for pure-breeding
tall parent are TT
24.3 The pattern of inheritance
Homologous chromosomes
pure-breeding
parent is short
Let t be the allele for being short
pure-breeding
The alleles for pure-breeding
parent is tall
short parent are tt
Let T be the allele for being tall
The alleles for pure-breeding
tall parent are TT
24.3 The pattern of inheritance
Tall allele
Tall allele
Express
Tall Only
24.3 The pattern of inheritance
Short allele
Short allele
Express
Short Only
24.3 The pattern of inheritance
parents
P:
Tall
cross
Short
TT
x
tt
A pure-breeding tall plant
crosses with
a pure-breeding short plant
24.3 The pattern of inheritance
Short
Tall
P:
TT
G: T
T
x
tt
t
t
gametes
When gametes are formed by meiosis,
the homologous chromosomes separate
24.3 The pattern of inheritance
Short
Tall
P:
TT
G:
T
x
tt
t
gametes Just show the possible types of gametes produced
When gametes are formed by meiosis,
the homologous chromosomes separate
24.3 The pattern of inheritance
Short
Tall
P:
TT
G:
T
x
tt
t
Fertilisation
F1:
Tt
Tall
All F1 are tall (Tt)
24.3 The pattern of inheritance
Short allele
Tall allele
Express
Tall Only
∵ Allele for tall suppresses the
expression of allele for short
∴ Allele for tall is dominant &
allele for short is recessive
24.3 The pattern of inheritance
X
Parents
(pure-breeding)
short
tall
First filial (F1)
generation
all tall
self-pollination
Tall : Short
= 3:1
Second filial (F2)
generation
787 tall
277 short
24.3 The pattern of inheritance
Tall
Tall
F1:
G:
Tt x Tt
t
T
T t
F2:
TT Tt
Tt
tt
Genotypic ratio
Tall
Short
TT : Tt : tt = 1 : 2 : 1
Phenotypic ratio
Tall : Short = 3 : 1
24.3 The pattern of inheritance
Mendel’s first law
Short
Tall
P:
TT
G:
T
x
tt
t
gametes
Of a pair of contrasting characteristics, only one
can be represented in the gametes
24.3 The pattern of inheritance
The terms used in genetics
alleles
genes
heterozygous
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
The terms used in genetics
alleles
Gene
A gene is a short
length of DNA on a
chromosome which
determines the
expression of a trait.
genes
heterozygous
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
The terms used in genetics
alleles
Allele
Allele is the
alternative forms of
a gene.
genes
heterozygous
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
The terms used in genetics
alleles
Phenotype
Phenotype is the
observable
characteristic of an
organism, e.g. tall
plant or short plant.
genes
heterozygous
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
The terms used in genetics
alleles
Genotype
Genotype is the
genetic make-up of
an organism, e.g.
BB, Bb, or bb.
genes
heterozygous
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
The terms used in genetics
alleles
Homozygous
Homozygous is the
condition in which
an organism has two
identical alleles for a
certain characteristic,
e.g. tt, Tt.
genes
heterozygous
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
The terms used in genetics
alleles
Heterozygous
Heterozygous is the
conditions in which
an organism has two
different alleles for a
certain characteristic,
e.g. Tt.
genes
heterozygous
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
The terms used in genetics
alleles
Dominant allele
A dominant allele e.g.
(T) can express its
effect in both
homozygous (TT) and
heterozygous (Tt)
states. It is usually
represented by a
capital letter.
B
A
genes
R
T
heterozygous
V
homozygous
recessive
homozygous
dominant
V
24.3 The pattern of inheritance
The terms used in genetics
alleles
b
Recessive allele
A recessive allele
e.g. (t) only
expresses its effect
in homozygous
state (tt). It is
usually represented
by a small letter.
a
genes
r
heterozygous
d
d
homozygous
recessive
homozygous
dominant
24.3 The pattern of inheritance
How can you find out the
genotype of an organism?
If tall is dominant
How can your determine
the genotype of a tall plant?
24.3 The pattern of inheritance
Let T be the dominant allele for tall
The genotype of
the tall plant
TT
or
Tt
24.3 The pattern of inheritance
Carry out self-pollination
Case I :
P : TT
G: T
F1:
X
Case II :
TT
T
TT
All are tall
P:
G:
Tt
X Tt
T t
T t
F1:
TT Tt Tt tt
tall : short = 3: 1
24.3 The pattern of inheritance
Carry out self-pollination
Case I :
P : TT
G: T
F1:
X
TT
T
TT
All are tall
If all are tall, the
unknown tall plant
must be homozygous
(TT)
24.3 The pattern of inheritance
Carry out self-pollination
If a mixture of tall &
short is obtained in P :
a 3:1 ratio, then the
G:
unknown tall plant
must be
F1:
heterozygous (Tt)
Case II :
Tt
X Tt
T t
T t
TT Tt Tt tt
tall : short = 3: 1
24.3 The pattern of inheritance
However, some plants cannot
carry out self-pollination
and most animals cannot
carry out self fertilisation
If black is dominant
How can your determine the
genotype of a black mice?
24.3 The pattern of inheritance
Let B be the dominant allele for black colour
The genotype of
the black mice
BB
or
Bb
24.3 The pattern of inheritance
Carry out a test cross
i.e. cross it with a
homozygous recessive
individual
24.3 The pattern of inheritance
Carry out a test cross
Case I :
Case II :
P : BB X bb
P:
Bb
X
bb
G: B
G:
B
b
b
b
Bb
F1:
All are black
bb
Bb
F1:
black : brown = 1 : 1
24.3 The pattern of inheritance
Carry out a test cross
Case I :
P : BB X bb
G: B
b
Bb
F1:
All are black
If all are black,
the unknown black
mice must be
homozygous (BB)
24.3 The pattern of inheritance
Carry out a test cross
If a mixture of black
& brown is obtained
in a 1:1 ratio, then
the unknown black
mice must be
heterozygous (Bb)
Case II :
P:
Bb
X
bb
G:
B
b
b
bb
Bb
F1:
black : brown = 1 : 1
24.3 The pattern of inheritance
Summary
How can you find
out the genotype
of an organism?
Carry out selfpollination
Carry out a
test cross
Homozygous
Heterozygous
All offspring show
dominant
characteristic
dominant
characteristic:
recessive
characteristic
= 3:1
All offspring show
dominant
characteristic
dominant
characteristic:
recessive
characteristic
= 2:1
24.3 The pattern of inheritance
Experiment 24.1
Observation of maize cobs with grains of different colours
1. Your teacher will give you a maize cob with grains of
two different colours. Examine it carefully.
2. Count the numbers of dark-coloured grains and lightcoloured grains.
3. Record the results and calculate the ratio of the number
of dark-coloured to light-coloured grains.
4. Deduce the phenotypes and genotypes of the parent
plants.
24.3 The pattern of inheritance
How is sex determined in man?
The 23rd pair of
chromosome
determines sex
Sex chromosomes
24.3 The pattern of inheritance
How is sex determined in man?
mother XX
father XY
sperms X
50% XX
Y
ovum X
Girl
50% XY
Boy
24.3 The pattern of inheritance
What is pedigree?
A pedigree
is used for the analysis
of human inheritance
24.3 The pattern of inheritance
male tongue
roller
What is pedigree?
1
3
female
tongue roller
2
4
5
male nontongue roller
female nontongue roller
Individual 1 crosses
with individual 2
produce three
offspring
24.3 The pattern of inheritance
What is pedigree?
1
3
2
4
Individual 5 crosses with
individual 6 to produce
individual 10
5
10
6
24.3 The pattern of inheritance
What is pedigree?
1
3
7
8
2
9
4
Individual 3 crosses
with individual 7 to
produce two
offspring
5
10
6
24.3 The pattern of inheritance
What is pedigree?
P
1
2
F1
7
3
4
5
F2
8
10
9
There are 3 generations in this pedigree
6
24.4 Variations
24.4 Variations
What is variations?
Variations are the differences
from one another
Continuous
variation
Discontinuous
variation
24.4 Variations
Examples of
continuous variation
Hand
span
Height
Body
weight
Heart
beat
Intelligence
quotient
24.4 Variations
Continuous
variation
There is a continuous range of
intermediates
between two extremes
Result of interaction
of many gene pairs
Influenced by the
environment
Continuous
variation
A bell-shaped
normal distribution
curve can be
observed
Number of individuals
24.4 Variations
Intelligence quotient
24.4 Variations
Examples of
Discontinuous variation
Eye
colour
Tongue
rolling
Blood
group
Sex
Ear lobes
Pigmentation
24.4 Variations
Discontinuous
variation
The differences exist two extremes
but no intermediates
or the differences are clear-cut
Result of interaction of
small number of gene
Not influenced by
the environment
24.4 Variations
Experiment 24.2
Observation of variation in man;
e.g. tongue rolling and the length of the middle finger
A. To study variation in tongue rolling
1. Try to roll your tongue. If you can do this, you are a tongue
roller. Otherwise you are a non-tongue roller.
2. Count the number of tongue rollers and non-tongue rollers
in your class. Record the results.
24.4 Variations
Experiment 24.2
Observation of variation in man;
e.g. tongue rolling and the length of the middle finger
A. To study variation in tongue rolling
1. Measure the length of the middle finger of your left hand.
2. Divide the finger lengths into suitable categories, and
record the number in each category, like this
length/cm
7.1-7.5
7.6-8.0
8.1-8.5
number
2
4
3
3. Draw a histogram of your results.
24.4 Variations
Causes of variation
A. Heredity
1. Meiosis
2. Random
fertilisation
3. Mutation
B. Environmental
factors
24.4 Variations
A. Heredity
1. Meiosis
Since homologous
chromosomes
separate
independently &
pass into gametes
Different
gametes can
be produced
B
A
B
a
b
A
B
a
b
A
b
OR
a
b
A
b
a
B
A
b
a
B
A
B
a
24.4 Variations
A. Heredity
2. Random fertilisation
Fertilisation of an
ovum by a sperm
is a random
process
There are many
possible
combinations of
genes in a zygote
B
A
AABb
b
mother
x
father
a
AaBB
b
A
Aabb
B
a
aaBb
24.4 Variations
A. Heredity
3. Mutation
The suddenly change of the
genetic make-up of an organism
Change in a segment of DNA
in a chromosome
Gene
mutation
e.g. polydactyly and
sickle cell anaemia
24.4 Variations
A. Heredity
3. Mutation
Mutation arise from structural
changes in chromosomes
Missing of
chromosome
e.g. only have 45
chromosomes
Extra
chromosome
presents
e.g. 47 chromosomes
Turner
syndrome
Down
syndrome
24.4 Variations
Mutation may be caused by mutagens
Mutagens
Ionising radiations
Chemicals such as benzene
Ultraviolet (UV) light
24.4 Variations
B. Environmental
factors
It means that the environmental
factors can modify the phenotype
e.g.
Sunlight Nutrition
Temperature
24.4 Variations
B. Environmental
factors
A genotypically tall boy may become short
Why?
He is reared with a poor nutrition
e.g. lack of calcium, during the period
of active growth
24.5 Inherited disorders in humans
24.5 Inherited disorders in humans
Down syndrome
A normal person
Two 21st
chromosomes
A person with Down syndrome
Three 21st
chromosomes
24.5 Inherited disorders in humans
Down syndrome
Some degree of
learning difficulty
A retarded physical
development
Distinctive facial
appearance
24.5 Inherited disorders in humans
The caused is
not yet known
But evidence shows
that women aged 30
or older have a
higher chance of
giving birth to a child
with Down syndrome
infants with Down syndrome
(per 1,000 births)
Down syndrome
age of mother
24.5 Inherited disorders in humans
Colour blindness
is a genetic disorder inherited by a gene on the
sex chromosome called X chromosome
Males are more likely to be
colour blind than females
The most common type is
red-green colour blindness
24.5 Inherited disorders in humans
G6PD deficiency
Glucose-6-phosphate
dehydrogenase deficiency
Inherited by a gene on the
X chromosome
People with this deficiency cannot
produce an enzyme called
glucose-6-phosphate
dehydrogenase (G6PD)
24.5 Inherited disorders in humans
Effect of G6PD deficiency
G6PD is an enzyme for protecting
red blood cells against certain
poisonous chemicals
Patient’s red blood cells are
destroyed faster than those
produced in the bone marrow
This results in anaemia
24.4 Genetic engineering
24.4 Genetic engineering
What is genetic engineering?
It is a technique that
modifies an organism’s
own genes
OR introduces new genes from
another unrelated organism
24.4 Genetic engineering
Aim of genetic engineering
Modifying the hereditary
properties of organisms
Thus, it causes variations
among species by the human
24.4 Genetic engineering
Genetic engineering
can by applied on
Food production
Medical research
e.g. production of
genetically
modified foods
(GM foods)
e.g. production of
human insulin
from bacteria
24.4 Genetic engineering
Genetically modified foods (GM foods)
With the help of biotechnology
Genes can be transferred
from one organism to another
to produce genetically
modified organisms (GMO)
The food produced from
GM organisms is called
GM food
24.4 Genetic engineering
How to make a pest resistant GM plant?
A bacterium produces a toxic
protein which kills caterpillars
The gene coded for the toxin
which kills caterpillars is isolate
The gene for the toxin is introduced
into a bacterium vector
24.4 Genetic engineering
How to make a pest resistant GM plant?
The vector is transferred into
another bacterium
The bacterium divides repeatedly
and the gene in the vector is
replicated
24.4 Genetic engineering
How to make a pest resistant GM plant?
The vector will be transferred
from the bacterial cells to the
plant cells
The plant cells develop
to a plantlet
The plantlet develops to a
plant which carries the gene
for making the toxin
24.4 Genetic engineering
Soybean
Examples of GM foods
Potato
Corn
24.4 Genetic engineering
Potential benefits of GM foods
Providing resistance
to pests
Increasing tolerance
to poor environmental
conditions
24.4 Genetic engineering
Potential benefits of GM foods
GM tomatoes
Expiry date
Oct 2005
Improving nutritional
content of crops
Ordinary tomatoes
Expiry date
Oct 2003
Reducing wastage
and costs
24.4 Genetic engineering
Potential benefits of GM foods
Increasing crop
yields
GM tomato Ordinary tomato
Eliminating allergy-causing
properties in some foods
24.4 Genetic engineering
Criticisms against GM foods
Potential human
health impact
Development of
“super germs”
Disturbing the balance
of ecosystems
Ethical problems
Domination of world market
for good products by a few
large countries
24.4 Genetic engineering
Production of human insulin from bacteria
Insulin gene cut
out of DNA from
human cell
Vector taken out
of bacterium
Insulin gene
inserted into
the vector
Bacterium
multiplies
rapidly to
produce
insulin
Vector with
insulin gene
in it taken up
by bacterium
insulin
Mind Map
Genetics
is the study of
heredity
examples of
genetic diseases
chromosomes
1. Down syndrome
contain
DNA
includes
1. continuous
variation
2. color blindness
genes
consist of
variation
a pair of genes
is called
3. G6PD deficiency
the cure methods
may be found in
alleles
2. discontinuous
variation
caused by
Human Genome
Project
combinations
include
human manipulation of genes 1. heredity
homozygous
heterozygous
2 types of expression
dominant
recessive
genetic
engineering
products
factors determine
phenotype
genotype
2. environmental
factors
includes
1. meiosis
1. GM foods
2. random
fertilisation
2. human insulin
3. mutation