Inheritance 1- Variation
1- (G)State what is meant by “species”
2- (G) State the name of changes
which can observed between members
of a same species
3-(C) Explain what is meant by
continuous and discontinuous
variation. (G) Give examples of
continuous and discontinuous variation
How is discontinuous variation usually
represented?
How is continuous variation usually
represented?
Organisms who could interbreed to produce fertile
offspring.
These changes are known as “variation”
Discontinuous:
- clear-cut differences in features
- can be put in distinct groups separated by “or” .
E.g. Tongue rolling, handedness, blood groups, ear
lobe types.
→ bar-chart.
Continuous:
- no distinct groups
- gradual changes in features (range of values spanning
from one extreme to another with most organisms in the
middle).
E.g. Height, weight.
→ histogram: bell shaped line graph can be drawn from
histogram: normal distribution curve.
Inheritance 2- What is inheritance?
1- (G) State from where organisms’
characteristics come from.
Give examples for animals and plants.
Some are inherited from our parents.
Humans:
Tongue rolling, eye colour, hair colour.
Other animals:
Fur colour, eye colour.
Plants:
Flower colour, leaf shape, seed shape.
Remainder of our characteristics determined by our
environment and life style (e.g. weight).
2- (G) State what genes are.
3- (G) State what controls a
characteristic (e.g. type of ear lobe,
blood group, height)
4- (C) State the name given to the
different forms of a gene
5- (G) State how many matching sets of
chromosomes are found in a body cell
6- (G) State from where the two forms
of a genes come from
7- (G) State the meaning of homozygote
(1) and heterozygote (2).
Genes are parts of chromosomes
Inherited characteristics are controlled by the two
forms of a gene.
Alleles
Two
Each parent contributes one of the two forms.
(1) Organism with 2 identical alleles for one gene
(2) Organism with 2 different alleles for one gene
1
8- (G) What sex cells called?
9- (G) State how many forms of a
gene is carried by individual sex cell.
10- (G) State how many sets of
chromosomes are found in a sex cell.
11- (G) State when this reduction
from two sets to one set takes place.
12- (G) Describe how a complete set
of chromosomes is achieved at
fertilisation.
Monohybrid cross
1- Explain what is meant by
phenotype.
(G) Identify examples of phenotypes
of the same characteristic.
Explain what is meant by genotype.
2- (G) Explain what true breeding is.
3- (G) Explain what a dominant allele
is.
4- (G) Explain what a recessive
phenotype is.
Gametes.
Male gamete: sperm cell, pollen grain in plants
Female gamete: egg cell or ovum.
One
One set of chromosome
During gamete formation
Male gamete fuses with female gamete forming a
zygote with 2 sets of chromosomes.
Phenotype: the external expression of a feature
controlled by one or more genes.
Examples of phenotypes for the same
characteristic:
Hair colour: blond, brown, red
Ability to roll tongue: roller, non-roller
Seed shape: round, wrinkled
Genotype: the two alleles of a gene carried by an
organism. Often presented as a pair of alleles.
Organism has identical alleles for a particular
feature: it is a homozygous for this feature
An allele which phenotype shows, i.e. a stronger
allele.
An allele which phenotype does not show when the
other allele is dominant.
5- (G) Identify examples of truebreeding, dominant and recessive
characteristics from the number and
phenotypes of given crosses.
See other resources
6- (C) Explain what is meant by a
monohybrid cross.
7- (G) Identify using letters the
successive generations of a cross.
8- (G) State what is the phenotype
of the first generation of a
monohybrid cross.
9- (C) Predict the proportion of the
phenotypes of the second generation
of a monohybrid cross.
True-breeding parents for different phenotypes
produce offspring.
Parents: P
First generation: F1
Second generation: F2
All F1 organisms have the same phenotype; They are
said to be uniform.
A ratio of 3:1
3 showing dominant phenotype.
1 showing recessive phenotype.
2
10- (C) Explain monohybrid crosses
in terms of the genotype
E.g. Pea plant height: T: tall
Parent (P)
TT
F1
F1 cross
F2
11- (C) Explain differences
between observed and predicted
figures in monohybrid crosses.
12- (G) State what determines the
sex of a child.
13- (G) State the difference in
chromosomes between boy and
girls.
14- (G) Explain how the sex of a
child is determined with reference
to the X and Y chromosome.
Tt
X
Tt
T
t
TT
Tt
tt
and t: dwarf
X
Tt
T
Tt
t
T t
T TT Tt
t Tt tt
tt
- random nature of fertilisation
- death of embryo – death of seedlings
Sex chromosomes: X and Y chromosomes
Boy: one X and one Y chromosome
Girl: two X chromosome
The female gamete can only contribute with an X
chromosome. Therefore, it is the gamete from the father
(X or Y) which will determine the child’s sex.
Inheritance 3- Genetics and society
1- (G&C) Describe two examples, one
plant (1), one animal (2), of the
enhancement of a characteristic
through selective breeding.
3- (G) Describe an example of a human
condition caused by a chromosome
mutation e.g. Down’s syndrome.
4- (C) Give an example of a
chromosome mutation advantageous to
humans, in a plant or animal of
economic importance.
5- (C) What is a mutagenic agent? Give
an example.
6- (G) State what can be used to
detect chromosome mutations
(1) Crop yield per acre in cereals
(2) Race horse, Milk yield, Bacon Weight
Down’s Syndrome is a condition caused by one pair
of chromosome which fails to separate during
gamete formation. As the result, after fertilisation,
the zygote has 3 copies of chromosomes 21.
In bacteria: digest oil → used to clean oil spills.
In a plant: agricultural wheat has more
chromosomes than wild wheat. The mutated wheat
has higher yield.
A mutagenic agent or mutagen is a factor which can
change the structure of a chromosome.
Mutagens are for example: X-rays, ultra-violet,
radiations from radioactive material.
Amniocentesis: a sample is taken from the amniotic
fluid. Cells allowed to divide and photographed.
Chromosomes arranged in pairs and compared to
other pictures to detect anomaly in chromosome
number.
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