Genetic vocabulary and alleles

What is an allele?

An alternative version of a gene.

Why do inherited characteristics differ between individuals?

Individuals can inherit different alleles of genes from their parents.

What is a dominant allele?

An allele expressed in the phenotype when at least one copy is present.

What is a recessive allele?

An allele expressed in the phenotype only when two recessive copies are present in a simple dominant-recessive inheritance pattern.

What does homozygous mean?

Having two identical alleles for a particular gene.

What does heterozygous mean?

Having two different alleles for a particular gene.

What is a genotype?

The combination of alleles an organism possesses for a gene or characteristic.

What is a phenotype?

The observable characteristics of an organism, influenced by its genotype and environment.

What is a zygote?

The cell formed when the nuclei of two gametes fuse at fertilisation.

What is the difference between genotype and phenotype?

Genotype is the alleles an organism has; phenotype is its observable characteristics.

What is the difference between a gene and an allele?

A gene is a section of DNA coding for a protein; an allele is a version of that gene.

What symbol is commonly used for a dominant allele?

A capital letter, such as A.

What symbol is commonly used for a recessive allele?

The corresponding lowercase letter, such as a.

If A is dominant and a is recessive, what is the phenotype of AA?

The dominant phenotype.

If A is dominant and a is recessive, what is the phenotype of Aa?

The dominant phenotype.

If A is dominant and a is recessive, what is the phenotype of aa?

The recessive phenotype.