Chapter 15 - GENETICS CAN BE USED TO UNDERSTAND THE TRAITS OF INDIVIDUALS AND FAMILIES

phenotype

The phenotype is the physical appearance of a trait as determined by the genotype, the combination of alleles. If the alleles are the same, the genotype is homozygous; if the alleles are different, the genotype is heterozygous.

Gene

The factor that determines an inherited characteristic; located in the chromosomes

Allele

An alternative form of a gene (e.g. the gene for pod colour in peas has two alleles, green and yellow)

Dominant

An allele that masks the effect of another allele (e.g. a pea plant with alleles for green and yellow pods will produce green pods because green is dominant to yellow)

Recessive

An allele that is masked by the alternative, dominant allele (e.g. the allele for yellow pod colour is masked by the allele for green pod colour)

Homozygous

The situation where an individual has the same alleles for a particular characteristic; also called pure-breeding (e.g. a pea plant with two alleles for green pod colour is homozygous green)

Heterozygous

The situation where an individual possesses different alleles for a particular characteristic; also called hybrid (e.g. a pea plant with alleles for both green- and yellow-coloured pods is heterozygous)

Phenotype

The physical appearance of an individual as determined by the expression of the alleles for that characteristic (e.g. a pea plant with alleles for green-coloured and for yellow-coloured pods will have the phenotype green pods)

Genotype

The genetic make-up of an individual as determined by the alleles for the characteristic being considered (e.g. a pea plant with one allele for green-coloured pods and one for yellowcoloured pods will have the heterozygous genotype)

Hemizygous

Having no allelic counterpart; occurs with alleles in the X chromosome in males

Heterozygous

Possessing different alleles for a given characteristic

Homozygous

Possessing the same alleles for a given characteristic

Phenotype

The appearance of an individual as determined by their genetic constitution