Dihybrid cross

Question 1

Different forms of a gene.

Answer 1

Definition of Allele

Question 2

The alleles an organism has

Answer 2

Definition of Genotype

Question 3

What an organism looks like or can do.

Answer 3

Definition of Phenotype

Question 4

Genotypes of the gametes from an organism which is aabb

Answer 4

ab are the only gametes

Question 5

Genotypes of the gametes from an organism which is AaBb

Answer 5

AB, Ab, aB and ab gametes are produced

Question 6

Phenotype ratio from two heterozygous parents

Answer 6

Offspring ratio: 9: 3: 3: 1

Question 7

Phenotype ratio of offspring from a parent heterozygous for both alleles and a homozygous recessive parent.

Answer 7

Offspring ratio: 1: 1: 1: 1

Question 8

Reason why the expected and actual results of a genetic cross are often different.

Answer 8

Explained by “fertilisation being a random process”. The sample size is often small, as well.

Question 9

An organism with a genotype AaBb may produce only gametes AB and ab because ?

Answer 9

The genes are linked - on the same chromosome

Question 10

The reason for recombinant phenotypes appearing when the genes for the two characteristics are on the same chromosome.

Answer 10

Crossing over can produce these “new” phenotypes, separating linked genes.

Question 11

The process during meiosis that can separate linked genes, giving new combination of alleles.

Answer 11

Crossing over

Question 12

Structure where crossing over occurs during the first Meiosis division.

Answer 12

Chiasma (Chiasmata - pl )

Question 13

Why the crossing over frequency of linked genes R and T is greater than of linked genes R and S.

Answer 13

Gene R is further away from gene T, than from gene S

Question 14

Sex chromosomes of a human male

Answer 14

XY

Question 15

Sex chromosomes of a human female

Answer 15

XX

Question 16

There are no sex linked alleles on this human male sex chromosome

Answer 16

Y chromosome

Question 17

Parent who gives their son an allele for a sex linked condition (X^h), such as haemophilia.

Answer 17

Mother, as must get Y from father

Question 18

Genetic term for a parent with an X^R X^r genotype

Answer 18

The genotype for a carrier (female)

Question 19

Random change in a gene or chromosome

Answer 19

Definition of a Mutation

Question 20

The phenotype ratio of the F1 offspring of a dihybrid cross between a dominant and a recessive true beeding organism.

Answer 20

All dominant (heterozygous)

Question 21

The genotype of an organism that is heterozygous for both alleles (use B and G)

Answer 21

BbGg

Question 22

The genotype of an organism that is homozygous dominant for both alleles (use B and G)

Answer 22

BBGG

Question 23

The genotype of an organism that is homozygous recessive for both alleles (use B and G)

Answer 23

bbgg

Question 24

Genes which are present on the same chromosome

Answer 24

Definition of Linked genes