An allele is one of two or more versions of a gene. Humans inherit two forms, or alleles, for every gene, one from each parent. These alleles are located at the same position on each of two chromosomes. You can either inherit two of the same alleles, or you can inherit two different alleles. If the two alleles are the same, the individual is homozygous for that gene. If the alleles are different, the individual is heterozygous.
An autosome is any chromosome that is not a sex chromosome. Humans have 22 pairs of autosomes and one pair of sex chromosomes (either, XX in a female or XY in a male).
A carrier is a person who carries and is capable of passing on a genetic mutation associated with a disease. This person may or may not show symptoms. Carriers are associated with diseases inherited as recessive traits such as sickle cell anaemia or cystic fibrosis.
In plant and animal cells, DNA is tightly packaged into thread-like structures called chromosomes. Chromosomes carry genetic information that is passed from parents to offspring. We inherit 23 chromosomes from our mothers and 23 chromosomes from our fathers, giving a total of 46 chromosomes.
Descending from the same ancestor or kinship as another person; in other words blood relations who are relatively closely related such as first cousins.
A limitation or restriction.
When part of the genetic material is missing.
DNA is a molecule, found in all cells, that carries all the instructions for proper functioning and development of organisms. An individual’s DNA is unique to that individual, with the exception of identical twins.
When one allele has a dominant (‘stronger’) effect over the other, that trait will appear in the child. An example is dark hair, which is a dominant trait. If one parent contributes a gene for dark hair and the other contributes a gene for light hair, the child will have dark hair.
The loss of genetic variation that occurs when a small group of individuals migrate (move) from a larger group to form a new population. The Afrikaners are an example of a founder population.
Gametes are cells that produce a new individual organism during sexual reproduction, such as the male sperm and the female egg.
Information that is stored in DNA to facilitate the normal functioning and regulation of cells.
Genes encode the information that determines your traits, which are features or characteristics that are inherited from your parents.
genotype The genetic makeup of an individual that results in the specific characteristic (phenotype) of that individual.
Having different alleles of a gene for any hereditary or inherited characteristic. Sometimes one allele is dominant over the other.
When an individual has two of the same allele, whether dominant or recessive, they are homozygous.
A karyotype is the complete set of chromosomes in a species, or an individual organism.
The position/location of a specific gene on a chromosome. Example: the locus for the albinism gene, OCA2, is found on chromosome 15.
A specific type of cell division that produces sperm and egg cells with only 23 chromosomes in each cell. Each sperm or egg cell is unique compared to any other sperm or egg cell.
The process of cell division, whereby two identical daughter cells are produced from the parent cell. This is important for growth and differentiation of cells in the body.
Chemical agents that induce or increase the frequency of mutations in the DNA of an organism.
A mutation is any change in a gene that will alter the message that is carried by the gene. It may result in medical problems.
Failure of paired chromosomes to separate correctly during meiosis, resulting in an abnormal number of chromosomes in the gamete. This process is the underlying cause of trisomy 13, or Down Syndrome.
The specific part of a human cell which houses the genetic material.
The outward, physical appearance or traits of an organism which are determined by genetic and environmental factors.
Polygenes refers to two or more genes influencing one trait.
A trait (phenotype) that will only be seen when there are two copies of the same allele present. Otherwise its effects are covered up by a dominant allele.
Type of chromosome that contains genetic material for sex determination and sex-specific characteristics. In Humans there are two sex chromosomes, the X and Y chromosomes. Females have two X chromosomes and males have an X and a Y chromosome.
A gene or a trait that is carried by a sex chromosome. Sex-linked diseases affect males and females differently. These diseases are usually caused by mutations on the sex chromosomes, X and Y. Males have 1 X and 1 Y chromosome (XY) and females have 2 X chromosomes (XX). Example: The gene for haemophilia A (a bleeding disorder) is carried on the X chromosome. A male with a mutation in the haemophilia gene is affected with the disease but a female with the mutation is an unaffected carrier of the disease.
Traits and diseases that are affected by only one gene. For example, a change that occurs in one, single gene can be sufficient enough to bring about a change in the trait, or can lead to disease.
Any drug, chemical agent or infection, consumed or contracted during pregnancy, which interferes with normal foetal growth and causes birth defects. Examples are alcohol, cigarette smoke, mercury and various medications like warfarin.
A condition where there are three copies of a particular chromosome in a cell, instead of the normal two.
Refers to traits found on the X-chromosome so the features can be tracked through the inheritance of the X-chromosome.
A zygote is a cell that is formed when the father’s sperm cell joins and fertilizes the mother’s egg cell. It will divide and grow into a person.