Chapter 16 Mendelian Genetics

Question 1

Why were peas used as Mendels experimental organism?

Answer 1

1. They were easy to grow.
2. They were available in many distinguishable varieties.
3. Strict control over mating was possible to ensure the parentage of new seeds.

Question 2

Define true breeding.

Answer 2

The physical appearance of the offspring in each successive generation is identical the to previous one.

Question 3

What were the results of Mendels first experiment involving a cross between two true breeding pea plants that varied in colour?

Answer 3

F1 generation was all purple.

F2 generation had 3/4 purple plants and 1/4 white plants.

Question 4

Define monohybrid cross.

Answer 4

A cross between teo individuals differing in a single character.

Question 5

How are round and wrinkled peas formed?

Answer 5

The dominant allele (round) codes for an enzyme that makes seeds round, while the recessive allele (wrinkled) codes for a defective enzyme resulting in wrinkled seeds.

Question 6

What is the Law of Segregation?

Answer 6

The Law of Segregation states that the two alleles for a heritable character separate during gamete formation and end up in different gametes.

Question 7

Differentiate between phenotype and genotype.

Answer 7

Phenotype is the physical appearance (purple) and genotype is the genetic makeup (Pp).

Question 8

What is happens in a testcross and what does it determine?

Answer 8

A testcross determines the genotype of an individual.
Breed the mystery individuals with a homozygous recessive individual. If any offsprings display recessive phenotype, the individual must be heterozygous.

Question 9

What is the Law of Independent Assortment?

Answer 9

The Law of Independent Assortment states that the two copies of each gene segregate into gamete independently of the two copies of another gene.

Question 10

What is a dihybrid cross?

Answer 10

A cross between F1 dihybrids. Crossing two true-breeding parents differing in 2 characters produces dihybrids (i.e. Heterozygous for both characters) in the F1 generation.
E.g. AaBb x AaBb

Question 11

What phenotypic ratio does a dihybrid cross give?

Answer 11

Phenotypic ration 9:3:3:1.

Question 12

How many genotypes are produced in a dihybrid cross?

Answer 12

9 different genotypes.

Question 13

What is a dihybrid cross equivalent to?

Answer 13

Two monohybrid crosses.

Question 14

When do you use the multiplication rule?

Answer 14

In calculating the chances for various genotyopes, each character is considered separately and then the individual probablities are multiplied together.

Question 15

What is incomplete dominance?

Answer 15

The phenotype of F1 hybrids is somewhere between the ohenotyoes of the two parental variaties.

Question 16

What is epistasis?

Answer 16

Genes that modify the phenotypic expression of other genes.

If the phenotypic ratio in the F2 generation from a dihybrid cross is 9:3:4 its most likely Epistasis.

Question 17

What are the 4 indicators for a dominant allele?

Answer 17

1. Affected individuals are equally likely to be females or males.
2. Most matings that produce affected offsprings only have one affected parent.
3. Among mating in which one parent is affected, half the offsprings are affected.
4. Two affected parents can produce an unaffected child.

Question 18

What are the indicators of a recessive trait.

Answer 18

1. The trait may skip one or generations.
2. Females and males are equally likely to be affected.
3. Affected individuals often result from mating between relatives, typically first cousins.
4. Two unaffected parents can produce an affected child.