Term 2:

Question 1

What does the term ‘heritable’ refer to?

Answer 1

Features determined by genes (rather than the environment) and therefore passed on to offspring

Heritable traits are typically influenced by genetic factors.

Question 2

Define ‘homologous chromosomes’.

Answer 2

A pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features

They are not necessarily identical as they may have different alleles.

Question 3

What is a ‘ratio’ in genetic terms?

Answer 3

A measure of the relative size of two classes that is expressed as a proportion

Question 4

What are ‘sex-linked’ genes?

Answer 4

Any gene that is carried on either the X or Y chromosome

Question 5

What does ‘linkage’ refer to in genetics?

Answer 5

The situation where two or more genes are carried on the same autosome

Question 6

Define ‘autosome’.

Answer 6

A chromosome which is not a sex chromosome

Question 7

What is ‘epistasis’?

Answer 7

This arises when the allele of one gene affects or masks the expression of another in the phenotype

Question 8

What does the Hardy-Weinberg Principle predict?

Answer 8

The proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to next provided five conditions:
* No mutations
* Population is isolated
* No natural selection (alleles are equally likely to be passed on)
* Large population
* Mating is random

Question 9

What is a ‘gene pool’?

Answer 9

All the different alleles of all the genes of all the individuals in a population at any one time

Question 10

Define ‘allelic frequency’.

Answer 10

The number of times an allele occurs within the gene pool in a population, relative to all others at the same locus

Question 11

What is ‘discontinuous variation’?

Answer 11

Distinct forms with no intermediate types

Question 12

What is ‘continuous variation’?

Answer 12

No distinct categories - likely to obtain a bell-shaped curve known as a normal distribution curve

Question 13

What is a gene?

Answer 13

Section of DNA on a chromosome that controls a feature by coding for formation of one or more specific polypeptides or a functional RNA (including rRNA and tRNA).

Question 14

What is a locus?

Answer 14

The specific linear position of a particular gene on a certain chromosome.

Question 15

What are alleles?

Answer 15

Alternative forms of a particular gene with different base sequences, and therefore different codes.

Question 16

What does homozygous mean?

Answer 16

Situation or organism in which paired alleles are the same.

Question 17

What does heterozygous mean?

Answer 17

Situation of organism in which paired alleles are different.

Question 18

What is a dominant allele?

Answer 18

An allele that expresses itself in the phenotype in heterozygous organisms.

Question 19

What is a recessive allele?

Answer 19

An allele that does not express itself in the phenotype in heterozygous organisms.

Question 20

What is co-dominance?

Answer 20

Alleles which both contribute to the phenotype (i.e. produce a blended effect) in the heterozygous condition.

Question 21

What are multiple alleles?

Answer 21

If there are more than two alleles for each gene in the gene pool.

Only 2 chromosomes in a homologous pair so only 2 of the three or more alleles can be present in a single organism.

Question 22

What is a pure-breeding strain?

Answer 22

Group of organisms in which a certain characteristic is unaltered for generations, indicating that organisms are homozygous for that feature.

Question 23

What is monohybrid inheritance?

Answer 23

Inheritance of a single pair of alleles.

Question 24

What is dihybrid inheritance?

Answer 24

Inheritance of two pairs of alleles.

Question 25

What is a haploid cell?

Answer 25

Cell or nucleus containing single, unpaired chromosomes.

Question 26

What is a diploid cell?

Answer 26

Cell or nucleus containing pairs of homologous chromosomes.

Question 27

What is phenotype?

Answer 27

The observable or biochemical characteristics of an organism, resulting from both its genotype and the effects of the environment.

Question 28

What is genotype?

Answer 28

The combination of alleles present within the cells of an organism.

Question 31

What is a population?

Answer 31

A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed. ## Footnote This definition emphasizes the potential for interbreeding among organisms of the same species within a defined area.

Question 32

Define community in an ecological context.

Answer 32

The organisms of all species that live in the same area. ## Footnote A community includes multiple species interacting within a shared environment.

Question 33

What is a habitat?

Answer 33

The place where an organism normally lives. ## Footnote A habitat provides the necessary resources and conditions for an organism's survival.

Question 34

What is meiosis?

Answer 34

A type of nuclear division in which the number of chromosomes is halved. ## Footnote Meiosis is essential for sexual reproduction, producing gametes with half the genetic material.

Question 35

What is a gamete?

Answer 35

Reproductive (sex) cell that fuses with another gamete during fertilisation. ## Footnote Examples of gametes include sperm and egg cells.

Question 36

Define diploid.

Answer 36

Cell or nucleus containing pairs of homologous chromosomes (two sets of chromosomes). ## Footnote Diploid organisms have two complete sets of chromosomes, one from each parent.

Question 37

Define haploid.

Answer 37

Cell or nucleus containing single, unpaired chromosomes (a single copy of each chromosome). ## Footnote Haploid cells are typically gametes, which have only one set of chromosomes.

Question 38

What are homologous chromosomes?

Answer 38

A pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features. ## Footnote Homologous chromosomes may have different alleles for the same gene.

Question 39

What is crossing over?

Answer 39

The process whereby a chromatid breaks during meiosis and rejoins to the chromatid of its homologous chromosome so that their alleles are exchanged. ## Footnote Crossing over increases genetic diversity in gametes.

Question 40

What are chiasmata?

Answer 40

A point at which paired chromosomes remain in contact during the first metaphase of meiosis and at which crossing over and exchange of genetic material occur between the strands. ## Footnote Chiasmata are crucial for genetic recombination during meiosis.

Question 41

Define recombination.

Answer 41

The rearrangement of genetic material, especially by crossing over in chromosomes. ## Footnote Recombination contributes to genetic variation in offspring.

Question 42

What is independent assortment?

Answer 42

The alleles of two (or more) different genes get sorted into gametes independently of one another. ## Footnote This process occurs during metaphase in meiosis, leading to genetic variation.

Question 43

Fill in the blank: During the formation of gametes, each gamete receives just one gene copy, which is selected _______.

Answer 43

randomly. ## Footnote Random selection of gene copies contributes to genetic diversity in gametes.

Question 44

What is independent segregation?

Answer 44

Each pair of alleles segregates independently of the other pairs and all possible combinations of alleles can occur in the resulting gametes. ## Footnote This principle is a fundamental aspect of Mendelian genetics.