Name:
Summary sheets: Inheritance
Variation
Write out definitions for the following terms:
Species: _______________________________________________________
_____________________________________________________________
Continuous variation: _____________________________________________
_____________________________________________________________
Discontinuous variation: ___________________________________________
_____________________________________________________________
Give two plant and two examples of variation which can occur within a species
Organism
E.gs. of Continuous variation E.gs. of discontinuous variation
Plant
Animal
What is inheritance?
Certain characteristics are determined by genetic information (contained in
chromosomes) received from the individual’s parents. Write down some examples
of inherited characteristics.
Genetic information is passed on to offspring by sex cells produced by the
parents. Sex cells are also called gametes. State the difference in
chromosome sets between a gamete and a ‘normal’ body cell.
Gamete=____ set(s)
‘Normal’ body cell _____ set(s)
Draw what happens at fertilisation in terms of sets of chromosomes
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The parts of chromosomes which determine certain inherited characteristics
are called genes. There are how many forms of a gene? _________________
Where do each of the forms of the gene come from? _____________________
What is the name for different forms of the same gene? _________________
These forms of a gene can be described as recessive or dominant. What do
these terms mean?
Dominant: ___________________________________________________
____________________________________________________________
Recessive: _____________________________________________________
____________________________________________________________
What the organism will look like (the phenotype) will depend on the forms of
the gene that are passed on from each parent. Possible combinations can be
DD
Dd
dd
(two dominant forms)
(dominant and recessive form)
(two recessive forms)
True breeding organisms have two of the same forms of a gene e.g. DD or dd
Monohybrid crosses
Write down definitions for the following terms/symbols
Monohybrid cross: ______________________________________
_____________________________________________________________
Phenotype:_____________________________________________________
_____________________________________________________________
Phenotypic ratio: _______________________________________________
____________________________________________________________
Genotype:______________________________________________________
____________________________________________________________
P: __________________________________________________________
F1: __________________________________________________________
F2: __________________________________________________________
2
Example of a monohybrid cross.
What is the phenotypic ratio of the F2 when two true breeding rabbits one
with blonde hair and one with brown hair (dominant) are crossed.
P:
F1:
F2
phenotype=
Genotype
brown
BB
Phenotype
Genotype
Brown
Bb
Genotype
Phenotypes
Phenotypic ratio
B
b
B
BB
Bb
b
Bb
bb
blonde
bb
BB, Bb, Bb, bb
brown, brown, brown, blonde
3brown: 1blond
True breeding
so they have
the same
alleles.
Brown is
dominant so it
is in capitals.
Offspring
receive one B
allele from
father and one b
allele from
mother
Punnet
square used
to calculate
genotypes of
offspring
Question: What is the phenotypic ratio of the F2 offspring when two true
breeding plants, one dwarf and one tall (dominant) are bred together?
(show working as above)
3
Observed vs predicted figures. Predicted figures are what we calculate, using
punnet squares, that the offspring will look like. However often what is produced,
the observed figures, are different. List possible reasons for the differences.
Sex determination
In each cell there are two sex determining chromosomes which determine if
the individual will be female or male. What sex chromosomes are present in the
different sexes and draw a diagram showing which they look like
Male: __________________________
Male
Female
Female: ________________________
While there are two sex chromosomes in each body cell of a human how many are
present in each sex cell? ___________
Explain how the sex of a child is determined you can include a diagram. ______
_____________________________________________________________
_____________________________________________________________
___________________________________________________________
Genetics and society
Selective breeding has been done by farmers and gardeners for years. It is a
way of bettering crops and herds of animals. Explain about how selective
breeding is done.
________________________________________________________
_____________________________________________________________
_____________________________________________________________
Make of list of ways plants and animals have been improved by selective breeding.
Plants
Animals
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Mutations
Mutations can occur in chromosomes during gamete production. If this happens
then the offspring can be affected.
Give an example of a human condition which is caused by a chromosome
mutation. _____________________________________________________
Mutations can be discovered before birth if doctors do a certain procedure.
State the name of the procedure and explain how it works.
Procedure: ____________________________________________________
How it works: ___________________________________________________
_____________________________________________________________
_____________________________________________________________
Mutations can be beneficial to man. Give an example of a mutation which is
advantageous to man.
_____________________________________________________________
_____________________________________________________________
List substances which can increase the rate of mutations:
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