What is an allele?

Alleles are the different versions of a particular gene.

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How many alleles of each gene does an individual have?

2

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What does it mean to be 'homozygous' for a particular gene?

Both alleles of that gene are identical. 

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What does it mean to be 'heterozygous' for a particular gene?

The two alleles of that gene are different.

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What is a dominant allele?

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

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What is a recessive allele?

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

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What does 'genotype' mean?

The term 'genotype' can be difficult to understand because it has multiple meanings.


  1. One definition describes a genotype as: 'an individual's collection of genes'.
  2. But the more common definition in this course is: 'the two alleles present for a particular gene'. 


In either case, the term genotype refers to the specific genes or alleles that an individual has.

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What does phenotype mean?

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

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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.

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