Intro to genetics and punnet squares

genetics is the study of how, in all living things, the characteristics and qualities of parents are given to their children by their genes.

they receive two copies of each gene, one from each parent

alleles are alternative forms of genes

alleles control the contrasting characteristics of each trait

dominant or recessive

dominant alleles are symbolised by capital letters and they will always express/show themselves

recessive alleles are symbolised by lowercase letter and they only express/show themselves in the absence of dominant alleles

e genetic makeup (combination of alleles) of an organism

the physical features/appearance of an organism

phenotype is the expression of genotype eg: If the genotype is TT, the plant’s phenotype is tall If the genotype is tt, the plant’s phenotype is short

homozygous (pure bred) means that an organism has two identical alleles for a trait eg: BB, bb BB – both alleles are dominant, so homozygous dominant. bb – both alleles are recessive, so homozygous recessive.

heterozygous (hybrid) means that organism has two different alleles for a trait. eg: Bb In this case the recessive allele is hidden by the dominant allele and is not expressed.

Reginald Punnet