B1H REVISION NOTES

How characteristics are inherited

We inherit dominant or recessive genes from our parents
If there is a dominant gene in a pair that characteristic is
inherited
Recessive characteristics only show if there are two
recessive genes in a pair

Example of Dominant and Recessive genes

Brown hair allele is dominant ( B )
Blonde hair allele is recessive ( b )

If the male has brown hair and is homozygous ( BB ) and the
female has blond hair and is homozygous ( bb ) what colour hair
will…

Inherited disorders

Most inherited disorders are caused by faulty genes, most
of which are recessive

Example of Inherited disorders

Allele for no cystic fibrosis is dominant ( C )
allele for cystic fibrosis is recessive ( c )

A carries does not have cystic fibrosis because they are
heterozygous for the diseases ( Cc ), will their children have
cystic fibroses ?

C c
C…

Mutations

Mutations are caused by the miss ­ copying of the gene
sequence which DNA replicates, divides and copies

This can be caused be several factors :

Spontaneously at random
Diseases e.g. Rubella ( German measles )
Drugs
Nuclear radiation

Mutations are usually harmful but can sometimes be
beneficial
Beneficial…

Genetic Word and definitions

Chromosome
A chromosome is a long string of DNA containing genes

DNA
DNA contains genes ; made from 4 basis G, C, A and T

Gene
A gene is a section of DNA that makes a particular protein ;
determines character

Allele
An allele is a…