Genetics - basic terms

Question 1

Gene

Answer 1

Basic unit of inheritance, by which inherited characteristics are transferred from parents to offspring, consisting of a length of DNA on a chromosome

Question 2

Allele

Answer 2

One alternative form of a gene, occupying a specific position (locus) on a chromosome

Question 3

Loci

Answer 3

The positions along the chromosomes where genes occur, so alleles of the same genes occupy the same locus

Question 4

Genotype

Answer 4

The genetic constitution of an organism

Question 5

Phenotype

Answer 5

The characteristics displayed by an organism - the way I which the genotype is expressed

Question 6

Dominant allele

Answer 6

An allele that affects the phenotype of the organism, whether present in the heterozygous or homozygous condition

Question 7

Recessive allele

Answer 7

An allele that affects the phenotype of an organism only when the dominant allele is absent (in homozygous recessive individuals)

Question 8

Homozygous

Answer 8

A diploid organism that has inherited the same allele from both parents

Question 9

Heterozygous

Answer 9

A diploid organism that has inherited different alleles from each parent

Question 10

Test cross

Answer 10

Testing a suspected heterozygote by crossing it with a known homozygous recessive

Question 11

Codominant alleles

Answer 11

Pairs of alleles that both affect the phenotype when present in a heterozygote

Question 12

Carrier

Answer 12

An individual with a recessive allele of a gene that does not affect the phenotype - especially one responsible for a genetic disorder such a color blindness or hemophilia