Understand the terms allele, dominant, recessive, genotype, phenotype, heterozygous, homozygous, sex linkage, carrier, affected/sufferer, non-affected/non-sufferer

Allele: Different forms of a gene. Often, one allele is inherited from each parent to make an individual’s DNA.
Dominant: An allele that is expressed in the phenotype, even if only one copy is present. Dominant alleles trump the expression of recessive ones.
Recessive: An allele that is only expressed in the phenotype when two copies are present (one from each parent). This is because dominant alleles mask them.

Genotype: The genetic makeup of an organism, concerning specific characteristics. It’s the combination of alleles that an organism inherits from its parents.
Phenotype: The physical expression of the genotype. The phenotype includes observable characteristics, influenced by the specific combination of the individual’s genotype and its environment.
Heterozygous: Describes a genotype consisting of two different alleles for a single trait (one dominant and one recessive).
Homozygous: Describes a genotype consisting of two identical alleles for a particular trait (either both dominant or both recessive).

Sex linkage: A term referring to genes that are present on either of the sex chromosomes, X or Y. The traits linked to these categories show different patterns of inheritance in males and females.
Carrier: An individual who has inherited a genetic trait or mutation but displays no symptoms of that trait. They however, can pass the trait to their offspring.
Affected/Sufferer: In terms of genetic disorders, this refers to an individual who has a gene mutation and exhibits signs of that disorder (also known as a patient).
Non-affected/Non-sufferer: Conversely, a non-affected/non-sufferer describes an individual who does not have the gene mutation and does not exhibit signs of the disorder.