Patterns of Inheritance

are variations of the DNA code responsible for a specific trait. They combine to create our own personal version of the trait.

• A dominant allele will always be expressed when present. • Individual only has to inherit one of that allele. (from any parent) (Ee, EE)

• Only expressed if the dominant is not expressed • An individual has to inherit two of that allele (one from each parent). (ee)

• Both alleles will be equally expressed

• Used to predict the offspring • work out the ratio of expected offspring genotypes

is the allele combination an individual carries for a trait. For example: Gg.

is the observable characteristics of a trait (what you can see). For example: Green or yellow.

means that the individual carries two of the same alleles for the trait. For example: AA or aa.

means that the individual is carrying two different alleles for then trait. For example: Aa

are those with a heterozygous genotype, but express the dominant allele.

• Every individual possesses two alleles, but only one is passed on to the offspring. When a monohybrid cross starts with one parent that is homozygous dominant and the other that is homozygous recessive: - The first generation of offspring will all have a heterozygous genotype. - They will carry one allele from each parent and will - present with the dominant phenotype. - They will also be carriers of the recessive gene.

• For non-sex chromosomes

• For traits on a sex chromosome (X or Y), the inheritance patterns and expression ratios are different.

Female offspring will express the trait as they usually would with dominant-recessive genes, as females receive two X alleles. Male offspring are hemizygous and will only receive one allele, therefore will express whichever one they receive.