Genetic Crosses

Question 1

Alleles

Answer 1

Different forms of the same gene

Question 2

Locus

Answer 2

A genes position on a chromosome

Question 3

Dominant

Answer 3

The allele prevents the recessive allele from working

Question 4

Recessive

Answer 4

The allele is masked by the dominant gene

Question 5

Genotype

Answer 5

Genetic make-up of an organism

Question 6

Phenotype

Answer 6

Physical expression of a gene

Question 7

Progeny

Answer 7

Offspring

Question 8

Homozygous

Answer 8

The alleles present are identical

Question 9

Autosomes

Answer 9

Non-sex chromosomes

Question 10

Incomplete dominance

Answer 10

~ Neither allele is dominant or recessive
~ An intermediate phenotype is produced

Question 11

Pedigree studies

Answer 11

A pedigree is a diagram showing the genetic history of a group of related individuals

Question 12

Sex determination

Answer 12

~ Humans : XX=Female XY=Male
~ Other species (Birds, butterflies, moths) XY=Female XX=Male

Question 13

Gregor Mendel

Answer 13

Father of genetics

Question 14

Mendel’s first law - law of segregation

Answer 14

Inherited traits are controlled by pairs of factors. These factors separate during gamete formation. Each gamete contains one factor for each trait.

Question 15

Mendel’s second law - law of independent assortment

Answer 15

When gametes form, each member of one pair of alleles is equally likely to combine with either member of another pair of alleles.

Question 16

Linkage

Answer 16

~ Genes found on the same chromosomes
~ Leads to less variation

Question 17

Sex Linkage

Answer 17

Gene found on the X chromosome

Question 18

Non-nuclear inheritance

Answer 18

Non-nuclear or extra-nuclear genes are present in the mitochondria and chloroplasts

Question 19

Monohybrid cross - Example: In pea plants, green pods are dominant to yellow pods.
Show by means of diagrams the genotypes and phenotypes of the F1 progeny that result from crossing two heterozygous plants.

Answer 19

Key: GG=Green, Gg=Green, gg=Yellow

Parents: Gg x Gg
Gametes: G g G g
Genotype: G g
G GG Gg
g Gg gg
Phenotype: 3 Green
1 Yellow

Question 20

Dihybrid cross - Example : In guinea pigs, black coat is dominant to white coat . Also short hair is dominant to long hair.
Show the genotypes and phenotypes of a cross involving two black-coated, short-haired guinea pigs, heterozygous for both traits.

Answer 20

Key: BB=Black, Bb=Black,
bb=White, SS=Short, Ss=Short,
ss=Long

Parents: BbSs x BbSs
Gametes: BS Bs bS bs BS Bs bS bs
Genotype: BS Bs bS bs
BS BBSS BBSs BbSS BbSs
Bs BBSs BBss BbSs Bbss
bS BbSS BbSs bbSS bbSs
bs BbSs Bbss bbSs bbss
Phenotype: 9 Black and Short
3 Black and Long
3 White Short
1 White Long

Question 21

Sex-linked - Example: Outline the parents, gametes, genotype and phenotype for the following cross;
Normal male x Heterozygous female

Answer 21

Key: XNXN=Female Normal, XNXn=Female Normal, XnXn=Female Colour Blind, XNY- =Male Normal,
XnY- =Male Colour Blind

Parents: XNXn x XNY-
Gametes: XN Xn XN Y-
Genotype: XN Y-
XN XNXN XNY-
Xn XNXn XnY-
Phenotype: 2 Female Normal
1 Male Normal
1 Male Colour Blind