Patterns of
inheritance
Phenotypic variation Genetic variation
Phenotype=expression of an organism’s genetic Meiosis produces genetically different cells;
constitution genetic variation is achieved through:
Crossing over of chromatids- where
Phenotypic variation: pairs of homologous chromosomes line
There are two types of variation continuous and up and exchange some of their genetic
discontinuous. Variation can be influenced by material
both environmental and genetic factors. Independent assortment of
chromosomes- there are various
Continuous variation= type of variation where combinations of chromosome
the differences between phenotypes is arrangement.
quantitative Random fertilisation : gametes are haploid
Discontinuous variation= type of variation cells (only contain half of a person’s DNA)
where it involves assigning to a particular every gamete contains different DNA. The
category. same two individuals can produce genetically
different offspring.
Which characteristics are expressed?
Dominant- only a single allele is required for
the characteristic to be expressed, that allele
is always expressed in the phenotype.
Recessive- both alleles are required for the
characteristic to be expressed, only expressed
Types of inheritance in the phenotype if there is no dominant allele
present.
Monogenic inheritance Homozygous= two identical alleles
Where one phenotypic characteristic is Heterozygous= two different alleles
controlled by a single gene. Multiple alleles- a gene with more than two
alleles.
- Homozygous monogenic crosses Codominance- when both alleles are
always produce 100% heterozygous offspring expressed in a heterozygote so both alleles of
B B BB x one gene are dominant and expressed in the
bb phenotype (e.g. blood type).
b Bb Bb
b Bb Bb
- Heterozygous monogenic crosses
Patterns of
Always produce 25% homozygous dominant,
50% heterozygous and 25% homozygous
recessive
Linkage B b
inheritance Performing a genetic cross diagram
Bb x
Sex linkage
B BB Bb Bb
Where anballeleBbis located
bb on one of the sex 1) State the phenotype of both parents
chromosomes meaning its expression depends on 2) State the genotype of both parents by using
the sex of the individual letters to represent alleles (lower case for
Dihybrid
Determining sex inheritance recessive/ UPPER CASE FOR DOMINANT)
Humans have two
Where 23 pairs of chromosomes
phenotypic of varying
characteristics are 3) State the gametes of each parent by circling
shapescontrolled
and sizes by two different genes on two the letters
22/23 of the pairs,
different both members of the pair are the
chromosomes. 4) Use a punnet square to show the results of
same the random fusion in fertilisation
However the remaining 23rd pair, the members are
inheritance
Phenotypic variation Genetic variation
Phenotype=expression of an organism’s genetic Meiosis produces genetically different cells;
constitution genetic variation is achieved through:
Crossing over of chromatids- where
Phenotypic variation: pairs of homologous chromosomes line
There are two types of variation continuous and up and exchange some of their genetic
discontinuous. Variation can be influenced by material
both environmental and genetic factors. Independent assortment of
chromosomes- there are various
Continuous variation= type of variation where combinations of chromosome
the differences between phenotypes is arrangement.
quantitative Random fertilisation : gametes are haploid
Discontinuous variation= type of variation cells (only contain half of a person’s DNA)
where it involves assigning to a particular every gamete contains different DNA. The
category. same two individuals can produce genetically
different offspring.
Which characteristics are expressed?
Dominant- only a single allele is required for
the characteristic to be expressed, that allele
is always expressed in the phenotype.
Recessive- both alleles are required for the
characteristic to be expressed, only expressed
Types of inheritance in the phenotype if there is no dominant allele
present.
Monogenic inheritance Homozygous= two identical alleles
Where one phenotypic characteristic is Heterozygous= two different alleles
controlled by a single gene. Multiple alleles- a gene with more than two
alleles.
- Homozygous monogenic crosses Codominance- when both alleles are
always produce 100% heterozygous offspring expressed in a heterozygote so both alleles of
B B BB x one gene are dominant and expressed in the
bb phenotype (e.g. blood type).
b Bb Bb
b Bb Bb
- Heterozygous monogenic crosses
Patterns of
Always produce 25% homozygous dominant,
50% heterozygous and 25% homozygous
recessive
Linkage B b
inheritance Performing a genetic cross diagram
Bb x
Sex linkage
B BB Bb Bb
Where anballeleBbis located
bb on one of the sex 1) State the phenotype of both parents
chromosomes meaning its expression depends on 2) State the genotype of both parents by using
the sex of the individual letters to represent alleles (lower case for
Dihybrid
Determining sex inheritance recessive/ UPPER CASE FOR DOMINANT)
Humans have two
Where 23 pairs of chromosomes
phenotypic of varying
characteristics are 3) State the gametes of each parent by circling
shapescontrolled
and sizes by two different genes on two the letters
22/23 of the pairs,
different both members of the pair are the
chromosomes. 4) Use a punnet square to show the results of
same the random fusion in fertilisation
However the remaining 23rd pair, the members are
