a heritable factor that controls a specific characteristic.
Gene
one specific form of a gene, differing from other alleles by one or a few bases only
Allele
the whole of the genetic information of an organism.
Genome
a change to the base sequence of a gene.
Gene Mutation
Two Chromosomes which have the same structure and the same sequence of genes
Homologous chromosomes
where 2 homologous chromosomes stick together instead of separating during anaphase.
Non-disjunction
chromosomes are arranged in pairs according to their size and structure.
In Karyotyping
a small sample of amniotic fluid is drawn out of the uterus through a needle
Amniocentesis
The alleles of an organism.
Genotype
The physical characteristics of an organism.
Phenotype
The particular position of a gene on homologous chromosomes.
Locus
pairs of alleles that both affect the phenotype when present in a heterozygote.
Codominant alleles
an allele that has the same effect on the phenotype - in homozygous or heterozygous genotypes.
Dominant allele
an allele that only has an effect on the phenotype when in homozygous genotypes.
Recessive allele
Having two identical alleles of a gene.
Homozygous
Having two different alleles of a gene.
Heterozygous
the crossing of an individual of unknown genotype with a homozygous recessive individual to find out its genotype.
Test Cross
When a gene is located on the X or Y chromosomes (ie. on a sex-chromosome).
Sex linkage
A body of condensed DNA, with a centromere and one or two chromatids
Chromosome