Genetic Diagrams

What are alleles?

Different variations of the same gene

What do genes control?

What genes you inherit control what characteristics you develop. Some characteristics are controlled by a single gene. However most characteristics are controlled by several genes interacting.

How many genes do you usually have?

Two copies of each gene (two alleles) - one from each parent

How do alleles work?

If the alleles are different, you have instructions for two different versions of a characteristic (e.g. blue eyes or brown eyes) but you only show one version of the two (e.g. brown eyes). The version of the characteristic that appears is caused by the dominant allele. The other allele is said to be recessive. The characteristic caused by the recessive allele only appears if both alleles are recessive.

What are your genotype and phenotype?

Your genotype is the alleles that you have. Your phenotype is the characteristics the alleles produce.

How are genes represented in genetic diagrams?

Dominant alleles are always show with a capital letter (e.g. ‘C’) and recessive alleles with a small letter (e.g. ‘c’)

What do homozygous and heterozygous mean?

Homozygous for a trait you have two alleles the same for that particular gene e.g. CC or cc

Heterozygous for a trait you have two different alleles for that particular gene, e.g. Cc

What do genetic diagrams show?

The possible alleles in the offspring

What is the inheritance of a single characteristic called?

Monohybrid inheritance. You can use a monohybrid cross to show how recessive and dominant traits for a single characteristic are inherited

Hamster example of how alleles work

How does a Punnett square work?

1. Put the possible gametes from one parent down the side, and those from the other parent along the top

2. In each middle square, fill in the letters from the top and side that lineup with that square. The pairs of letters in the middle show the possible combinations of the gametes