Inheritance I & II

Question 1

Define Locus.

Answer 1

The position of a gene on a chromosome is known as a locus (plural: Loci)

Question 2

Define gene.

Answer 2

Gene is a specific length of a DNA or a sequence of bases that codes for a polypeptide

Question 3

Define allele.

Answer 3

Alleles are alternative forms of a gene, each having a slightly different nucleotide sequence, which gives rise to a slightly different phenotype.
–> Alleles code for different forms of the same trait.

Question 4

Define codominance

Answer 4

The phenomenon in a heterozygote
in which both alleles of the pair under
consideration are expressed in the
phenotype.

Question 5

Define incomplete dominance

Answer 5

A case where neither allele is
completely dominant and the F1
offspring have a phenotype in between
that of the two parental varieties.

Question 6

Define homozygous.

Answer 6

The diploid condition where both the alleles for a particular gene are identical.

Question 7

Define heterozygous.

Answer 7

Diploid condition where different alleles of a gene are present.

Question 8

Define phenotype.

Answer 8

The phenotype refers to the characteristics of an individual that are expressed. The phenotype is dependent on the genotype of the organism (usually).

Question 9

Define Genotype.

Answer 9

A genotype is the genetic makeup of an organism, or a set of alleles of an organism.

Question 10

Define sex-linkage

Answer 10

genes that are found on the sex chromosomes and hence their expression will be affected by the sex (or gender) of the organism.

Question 11

What is meant by true bred?

Answer 11

Term used to denote that the organism is homozygous for a particular characteristic or trait and hence will give rise to offspring having the same characteristic as itself.

Question 12

What is the expected ratio from the crossing of two double heterozygotes?

Answer 12

9:3:3:1

Question 13

What is the expected ratio of crossing a double heterozygote with a double homozygous recessive individual?

Answer 13

1:1:1:1

Question 14

What are Mendel’s Laws?

Answer 14

The 2 laws are:
- Law of segregation -> An organism’s characters are determined by internal factors occurring in pairs. Only one of a pair can be represented in a single gamete.
- Law of independent assortment -> Any one pair of characteristics may combine with either one of another pair.

Question 15

Define autosomal linkage.

Answer 15

The linkage between two separate genes found on the same chromosome that do not assort independently but are inherited together (if there is no crossing over).

Question 16

Define epistasis.

Answer 16

Epistasis is one form of gene interaction, in which one gene (epistatic) masks or modifies the phenotypic expression of another gene (hypostatic).

[Number of phenotypic classes decreases from four classes in a typical dihybrid cross to three or even two.]

Question 17

What is polygenic inheritance?

Answer 17

A trait is the result of multiple genes, each of which perhaps have multiple alleles. The phenotypic outcome is due to the additive effect of these alleles of these different genes in an organism.

Question 18

What role does the environment play in the expression of phenotypes?

Answer 18

The expression of genes in an organism can be influenced by the environment in which the organism is located or develops, as well as the organism’s internal environment (such as hormones and metabolism).

Question 19

What effect does temperature have on the Himalayan rabbit fur colour?

Answer 19

> 33 degrees, color of fur is light/white
<33 degrees, color of fur is black

Question 20

What effect does the diet have on the differentiation of honey bees?

Answer 20

Though both queen and worker bees have same genotype, the larvae in queen cells are fed with royal jelly, which results in increased expression of queen-specific genes.

Question 21

What is a null hypothesis?

Answer 21

A null hypothesis is a hypothesis that there is no significant difference between observed and expected data. Any difference is due to chance.

Question 22

What is the chi-squared test used for?

Question 23

What are some sources of variation?

Answer 23

• Environment
• Gene reshuffling (genetic variation)
• Gene mutations
• Chromosomal aberrations

Question 24

What are the types of variation, and what do they mean?

Answer 24

• Discontinuous variation: The type of variation in which individuals show clear-cut differences (or fall into distinct classes) with no intermediates between them.
• Continuous variation: Individuals show a complete gradation from one extreme to another without a break. These characteristics are controlled by the additive effect of many genes (polygenes), as well as the environment.

Question 25

What is a test cross?

Answer 25

A cross between an organism with an unknown genotype with a homozygous recessive individual.

Question 26

What is a reciprocal cross?

Answer 26

A cross where 2 crosses are done where the same genetic features are used but the sexes are reversed for each cross.