Download Document

Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
You will see lots of
cats
monohybrid
The coat colour of cats shows a large amount of
discontinuous variation.
This suggests that each cat’s coat colour is likely to be
produced by the alleles of a large number of genes.
Despite the complexity that this large number of genes
causes, each one is inherited in the same way.
parental
phenotypes
this
that
parental
genotypes
AA
Aa
gamete
genotypes
A
A
dominance
sex linkage
multiple alleles
dihybrid
offspring
genotypes
offspring
phenotypes
a
A
a
A
AA
Aa
A
AA
Aa
½ are this (AA) and ½ are that (Aa),
the probability that it will be this is 0.5
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
Monohybrid inheritance
This is when a small number of phenotypes (usually only 2
or 3) are the result of one gene.
The gene has more than one allele (often 2 but it can be
more).
One allele is usually dominant. This means that it is
expressed whenever it is present in an individual.
The other allele is recessive. It is only expressed if it is the
only allele present in an individual.
monohybrid
dominance
sex linkage
multiple alleles
dihybrid
MM or Mm
mm
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
Incomplete or Co-dominance
Sometimes the dominance of one allele isn’t complete.
This usually results in three phenotypes produced by two
alleles instead of two.
Two phenotypes are produced by homozygous genotypes,
the third phenotype is produced when an individual is
heterozygous.
The third condition is often intermediate between the other
two phenotypes.
ss
monohybrid
dominance
sex linkage
multiple alleles
dihybrid
SS
Ss
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
Sex linkage
The locus of some genes is on the sex chromosome.
The gene is only present on the X chromosome because the
Y chromosome has a different structure.
Females have 2 copies of these genes but males only have
one since females have two X chromosomes.
The ratio of males and females with particular phenotypes
in a set of offspring can be unequal.
monohybrid
dominance
sex linkage
multiple alleles
dihybrid
XOXO or XOXo or
XOY
XoXo or XoY
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
Multiple alleles
Each gene locus can have more than 2 alleles.
An allele may be dominant to some alleles but recessive to
others.
This situation produces more than 2 different phenotypes.
Each individual has 2 alleles present in their cells at any
one time.
BB or Bb or Bbl
monohybrid
dominance
sex linkage
multiple alleles
bb or bbl
dihybrid
blbl
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
monohybrid
dominance
sex linkage
multiple alleles
dihybrid
Dihybrid inheritance
A phenotype can be produced by the action of two (or
more) genes, each with several alleles.
The expression of the two pairs of alleles can interact
directly or indirectly to produce the phenotype.
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
monohybrid
dominance
sex linkage
multiple alleles
dihybrid
Dihybrid inheritance
A phenotype could be produced by the action of two (or
more) genes, each with several alleles.
The expression of the two pairs of alleles can interact
directly or indirectly to produce the phenotype.
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
monohybrid
dominance
sex linkage
multiple alleles
dihybrid
Guess the
parents!
Lesson Aims
You will see
examples of the main
ways by which
features are
inherited.
You will record an
example of each
inheritance pattern
including a genetic
diagram.
monohybrid
dominance
sex linkage
multiple alleles
dihybrid
Multiple gene inheritance
Cat coat colour is the result of the inheritance of a large
number of different genes.