A3 - Genes, Alleles + Inheritance

Section of DNA that codes for a protein of functional RNA

Position of an allele on a chromosome

All alleles in an organism
Only altered by mutation

Observable characteristics of an organism
Genotype + environment

Different versions of the same gene

Same alleles at a particular gene locus on homologous chromosomes

Different alleles at a particular gene locus on homologous chromosomes

Only 1 of these alleles needed to be expressed

2 identical alleles needed for it to be expressed

Both heterozygous alleles are equally expressed

More than 2 alleles available at a locus

Traits on x chromosome
Females need 2 copies of recessive allele for expression
Males only need 1

For some genes to be seen other genes need to be expressed
Eg. black stripes only in phenotype if coat colour isn't also black

Genes close together on same chromosome tend to be inherited together
Further apart = more likely to be separated in crossing over and ercombination