What is a genotype?
The set of alleles present in the DNA of an organism.
Where do alleles of a gene occur on homologous chromosomes?
At the same locus.
What does it mean if an organism is heterozygous?
It has two different alleles for a trait.
Examples: Gg, Rr, Tt.
What is a phenotype?
The physical characteristics of an organism, influenced by gene expression and the environment.
What does it mean if an organism is homozygous?
It has two identical alleles for a trait.
Examples: TT, tt, GG.
What is a carrier?
An organism that has inherited one recessive allele but does not show the trait because it is masked by a dominant allele.
What is complete dominance?
A dominance pattern where only the dominant allele is expressed in a heterozygous individual’s phenotype.
Example: HH or Hh → dominant phenotype.
What does a genotype represent in terms of alleles?
The combination of alleles using letters, usually related to the trait.
Example: Hh, Bb, GG.
Where are sex-linked traits located?
On the sex chromosomes (usually the X chromosome).
How are autosomal genotypes represented?
Two alleles are present (one from each parent) on chromosomes 1–22.
Examples: DD, FF, Gg.
Why can females be homozygous or heterozygous for sex-linked traits?
Females have two X chromosomes → can carry two alleles.
Example:
Black female cats = XᴮXᴮ
Orange females = XᴼXᴼ
Tortoiseshell females = XᴮXᴼ.
Why are males hemizygous for X-linked traits?
Males have only one X chromosome → only one allele for X-linked traits.
Example:
Black male cats = XᴮY
Orange males = XᴼY.
What are multiple allele genotypes?
Traits controlled by more than two alleles at the same gene locus, creating more genotype combinations.
What is a phenotype?
The observable traits of an organism, resulting from its genotype and the environment.
What is monogenic inheritance?
Traits controlled by a single gene with a few alleles → results in discrete variation.
eg. blood type
How can the environment affect phenotypes?
The same genotype can produce different phenotypes depending on environmental conditions.
What is polygenic inheritance?
Traits controlled by many genes (polygenes), producing a continuous range of phenotypes.
eg. hair and eye colour
What two factors determine an organism’s phenotype?
Genotype → inherited alleles
Environment → external influences
