Genetic Inheritance & Key Terminology

What is genetic inheritance?

The transmission of genetic information from parents to offspring.

What is a genotype?

The combination of alleles an organism possesses for a particular gene.

What is a phenotype?

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

What is a dominant allele?

An allele that is expressed in the phenotype when only one copy is present.

What is a recessive allele?

An allele expressed in the phenotype only when two copies are present, in simple dominant–recessive inheritance.

What is homozygous?

Having two identical alleles for a gene.

What is heterozygous?

Having two different alleles for a gene.

What is homozygous dominant?

Having two copies of a dominant allele, such as AA.

What is homozygous recessive?

Having two copies of a recessive allele, such as aa.

What is heterozygous genotype?

Having one dominant and one recessive allele, such as Aa.

How are dominant alleles usually represented in genetic diagrams?

With capital letters.

How are recessive alleles usually represented in genetic diagrams?

With lowercase letters.

What is a carrier of a recessive genetic disorder?

A heterozygous individual who carries the recessive allele but does not show the disorder.

Why can two parents without a recessive disorder have an affected child?

Both may be carriers, allowing the child to inherit two recessive alleles.

What is a genetic cross?

A diagram showing the possible allele combinations inherited by offspring.

What is a Punnett square?

A diagram used to predict possible offspring genotypes and their probabilities.

Why are genetic cross outcomes expressed as probabilities?

Fertilisation is random, so each offspring outcome is uncertain.

Does a 25% probability mean exactly one in every four children will have a trait?

No, it means each child independently has a one-in-four chance.

What is a monohybrid cross?

A genetic cross involving one gene or inherited characteristic.

Why can phenotype differ between organisms with the same genotype?

Environmental factors can influence gene expression and development.