A mutation is a permanent change in the base sequence of DNA
Mutations can be: 1. silent, 2. harmful, 3. beneficial
Somatic mutations can't enter gene pool
Mutations can occur during DNA replication or from mutagens
Independent Assortment
When homologous pairs of chromosomes line up during meiosis, they do so randomly
This means it is completely random
which combination of alleles ends up
in a particular gamete
Segregation
Pairs of alleles are segregated when the homologous
chromosomes split so that each gamete receives one allele
Segregation results in all daughter cells being unique
Crossing Over
Occurs when homologous pairs of chromosomes line up on cell
equator and parts of neighbouring chromosomes cross over
These sections are then exchanged and each gamete
produced has a different combination of alleles
Dihybrid Inheritance
Dihybrid crosses involve two genes, and four alleles
These genes are linked if they are on the same chromosome,
and the closer together they are on the chromosome, the
less likely they will be separated during crossing over
They will therefore be inherited together and reduce the
number of possible combinations of alleles in gametes
Where there is no linkage
expected phenotype ratio is 9:3:3:1
Where this is not the case the genes are most likely linked
Monohybrid Inheritance
Co-dominance
Where a single gene has more
than one dominant allele
An organism heterozygous for both dominant alleles
with have both expressed in the phenotype (MIXTURE)
Multiple Alleles
Multiple alleles exist due to mutations in a
single gene resulting in more than two
alleles for that gene e.g. human blood type
Lethal Alleles
Lethal alleles code for a phenotype
that causes the death of an organism
Changes expected phenotype ratio
It usually arises as a result of a mutation in an
essential gene cauusing the gene to no longer
produce a functioning version of an essential protein
Incomplete Dominance
Where in a single gene the two alleles
are not dominant over each other
The resulting phenotype is a BLEND of the two alleles