Genetic Definitions

Question 1

Autosomal

Answer 1

Chromosomes 1-22, all the chromosomes apart from the sex chromosomes (XY).

Question 2

Locus

Answer 2

The position of a gene/DNA on the genetic map i.e. a fixed position on the chromosome.

Question 3

Genotype

Answer 3

The genetic constitution of an individual (which determines the phenotype).

Question 4

Phenotype

Answer 4

The appearance of an individual which results from the interaction of the environment and the genotype.

Question 5

Allele

Answer 5

One of the several alternate forms of a gene at a specific locus:

• A normal allele is A.K.A. wild type.
• Abnormal/mutant/disease alleles carry the (pathogenic) mutation.

Question 6

Polymorphism

Answer 6

Frequent hereditary variations at a locus- a gene is polymorphic if more than one allele occupies that gene’s locus within a population.

• Don’t cause problems i.e. mutations.
• Polymorphisms can make you more/less efficient or more/less susceptible to disease.

Question 7

Consanguinity

Answer 7

The reproductive union between 2 relatives.

Question 8

Autozygosity

Answer 8

Homozygous by descent i.e. the inheritance of the same mutant allele through the 2 branched of the same family.(high in endogamous populations).

Question 9

Homozygous

Answer 9

Both alleles are the same at a locus i.e. particular gene that has identical alleles on both homologous chromosomes.
N.B. It is referred to by two capital letters (XX) = dominant trait and two lowercase letters (xx) = recessive trait.

Question 10

Heterozygous

Answer 10

Alleles (for a gene) at a locus are different i.e. where an individual inherits different forms of a particular gene from each parent.

Question 11

Hemizygous

Answer 11

Describes genes that are carried on an unpaired chromosome.

Refers to a locus on an X chromosome in a male.

Question 12

Penetrance

Answer 12

The proportion of people with a gene/genotype who show the expected phenotype.

• Complete: the gene(s) for the trait are expressed in all the population.
• Incomplete: the genetic trait is only expressed in parts of the population.

Question 13

Variable expression

Answer 13

Variation in clinical features (type and severity) of a genetic disorder between individuals of with the same gene alteration.

Question 14

Sex limitation

Answer 14

Expression of a particular characteristic limited to one of the sexes.

Question 15

Multi-factorial conditions

Answer 15

Diseases due to a combination of genetic and environmental factors.
N.B. If the condition is more common in 1 sex:
- The relatives of the affected individual of the less frequently affected sex will be a higher risk than the relatives of an affected individual of the more frequently affected sex.
- i.e. if a boy has the condition, then the female relatives are more at risk (vice versa).

Question 16

Late-onset

Answer 16

The condition isn’t manifested at birth e.g. a classically adult onset condition= Huntington’s disease.

Question 17

Congenital

Answer 17

The condition is manifested at birth i.e. the disease or (physical) abnormality is present from birth.