Genetics and Key Science Skills

Question 1

Genome

Answer 1

All of the genetic material in an individual or cell

Question 2

Allele

Answer 2

A variation of a gene at a particular gene locus

Question 3

Gene

Answer 3

The hereditary unit, which is a section of DNA occupying a specific location on a chromosome. It determines a characteristic of an organism by directing the formation of a protein.

Question 4

Genotype

Answer 4

The allele combination of an individual

Question 5

Phenotype

Answer 5

The physical, behavioural or physiological characteristics of an organism which are a result of the combination of the genotype and environment.

Question 6

Homozygous

Answer 6

Having identical alleles at the same gene locus on homologous chromosomes. Sometimes referred to as ‘purebred’.

Question 7

Heterozygous

Answer 7

Having different alleles at the same gene locus on homologous chromosomes. Sometimes referred to as ‘hybrid’.

Question 8

Carrier

Answer 8

An individual that has inherited a copy of a recessive allele for a particular trait, but does not display the trait due to the presence of a dominant allele.

Question 9

Dominant (allele)

Answer 9

An allele that is expressed in the heterozygous genotype

Question 10

Recessive (allele)

Answer 10

An allele that is only expressed when the genotype is homozygous for that allele

Question 11

Punnett Square

Answer 11

A table that shows the possible genotypes of offspring given the genotypes of the two parents

Question 12

F1 generation

Answer 12

The offspring of the parent generation

Question 13

F2 generation

Answer 13

The offspring of the F1 generation

Question 14

Monohybrid Cross

Answer 14

Determination of the possible genotypes and phenotypes of offspring at a particular gene locus

Question 15

Dihybrid Cross

Answer 15

Determination of the possible genotypes and phenotypes of offspring at two gene loci

Question 16

Co-dominance

Answer 16

Two alleles from the genotype are both fully expressed in the phenotype of a heterozygote

Question 17

Polygenic

Answer 17

The observed phenotype is the result of contributions from two or more genes, and does not follow Mendelian genetics

Question 18

Multifactorial

Answer 18

The observed phenotype is the result of contributions from one or more genes plus environmental factors.

Question 19

Sex-linked trait

Answer 19

A trait that occurs as a result of a gene on a sex chromosome. This may be on the X-chromosome (X-linked) or the Y-chromosome (Y-linked)

Question 20

Test cross

Answer 20

A cross performed between an individual showing a dominant phenotype with a homozygous recessive individual, to determine the genotype of the individual with the dominant phenotype

Question 21

Pedigree

Answer 21

A chart showing the relationship between family members and whether they show an inherited trait

Question 22

Gene linkage

Answer 22

When two genes are located on the same chromosome. This will result in ‘parental’ combinations of alleles which are inherited more often than ‘recombinant’ combinations

Question 23

Phenotype ratio of a monohybrid cross when both parents are heterozygous

Answer 23

3:1

Question 24

Phenotype ratio of a monohybrid test cross if the individual with the dominant trait is heterozygous

Answer 24

1:1

Question 25

Phenotype ratio of a dihybrid cross where both parents are double heterozygotes

Answer 25

9:3:3:1

Question 26

Phenotype ratio of a dihybrid test cross if the parent with dominant phenotypes is a double heterozygote (no gene linkage)

Answer 26

1:1:1:1

Question 27

Phenotype ratio of a dihybrid test cross where the parent with dominant phenotypes is a double heterozygote and there is gene linkage (assume crossing over occurs)

Answer 27

many:many:few:few

Question 28

Evidence for a recessive inheritance pattern

Answer 28

An affected individual has two unaffected parents, for example….

Question 29

Evidence that shows a dominant inheritance pattern is likely (but not definitive)

Answer 29

All affected individuals have an affected parent

Question 30

Evidence that shows a recessive trait is X-linked

Answer 30

An affected mother passes the trait onto all sons

Question 31

Evidence that a dominant trait is X-linked

Answer 31

An affected father passes the trait onto all daughters

Question 32

Evidence that a recessive trait is autosomal

Answer 32

An affected mother has an unaffected son

Question 33

Evidence that a dominant trait is autosomal

Answer 33

An affected father has an unaffected daughter