genetic inheritance

what is an allele?

alleles are the different versions of a particular gene.

how many alleles of each gene does an individual have?

2

what does it mean to be ‘homozygous’ for a particular gene?

both alleles of that gene are identical.

what does it mean to be ‘heterozygous’ for a particular gene?

the two alleles of that gene are different.

what is a dominant allele?

a dominant allele is one which is always expressed, even if there is only one copy of that allele.

what is a recessive allele?

a recessive allele is one which is only expressed if there are two copies of it.

what does ‘genotype’ mean?

• one definition describes a genotype as: ‘an individual’s collection of genes’.

• but the more common definition in this course is: ‘the two alleles present for a particular gene’.

what does phenotype mean?

the characteristics an organism has as a result of their genotype (and environment).

are most characteristics determined by: a single gene, a combination of multiple genes, or the combination of multiple genes and the environment?

most characteristics are determined by the combination of multiple genes and the environment.

when writing genotypes, such as ‘Aa’, what does an upper case letter mean?

an upper case letter means that the alleles is dominant.

when writing genotypes, such as ‘Aa’, what does a lower case letter mean?

a lower case letter means that the allele is recessive.

what is a punnet square diagram?

a punnet square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment.

what does it mean for an individual to be ‘homozygous dominant’ for a gene?

they have two dominant alleles for that gene.

what does it mean for an individual to be ‘homozygous recessive’ for a gene?

they have two recessive alleles for that gene.