HEREDITY

Question 1

Define heredity.

Answer 1

Passing of traits to offspring

Question 2

Define chromosome

Answer 2

Thread-like structure in the nucleus which is made up of DNA coiled around proteins

Question 3

Define gene

Answer 3

DNA segment located on a chromosome which codes for a single unit of inheritance (allows genetic information to be stored)

Question 4

Define gene locus

Answer 4

Position on the chromosome where the gene is located

Question 5

Define alleles

Answer 5

Different forms of the same gene located on the same gene locus on a pair of homologous chromosomes

Question 6

Define phenotype

Answer 6

Observable characteristics of an organism, depending on the genotype of the organism

Question 7

Define genotype

Answer 7

Genetic make-up of an organism that is determined by the existence of dominant and recessive alleles

Question 8

Define homozygote

Answer 8

Organism with two identical genes at a locus / containing two identical alleles for a specific trait (TT or tt)

Question 9

Define heterozygote

Answer 9

Organism with two different genes at a locus / containing two different alleles for a specific trait (Tt)

Question 10

Define dominant allele

Answer 10

Fully expressed allele in the phenotype under both homozygous and heterozygous conditions.

Question 11

Define recessive allele

Answer 11

Allele only expressed in the phenotype under the homozygous condition. Masked in the phenotype under heterozygous conditions

Question 12

Define complete dominance

Answer 12

When the heterozygote has the same phenotype as the dominant homozygote. The recessive allele present in the heterozygote is masked by the dominant allele

Question 13

Define co-dominance

Answer 13

When both alleles contribute equally to the phenotype

Question 14

Identify which alleles are recessive and dominant: Iᴼ, Iᴬ, Iᴮ

Answer 14

Iᴼ: Recessive
Iᴬ: Dominant (co-dominant with Iᴮ)
Iᴮ: Dominant (co-dominant with Iᴬ)

Question 15

Define incomplete dominance

Answer 15

When heterozygous individuals show an intermediate phenotype. This comes because neither allele is completely dominant over the other.

Question 16

Define karyotype

Answer 16

Picture of a set of chromosomes in a cell. It will show 22 pairs of homologous chromosomes (autosomes) and 1 pair of sex chromosomes (XY)

Question 17

What genotypes do males and females have?

Answer 17

M: XY
F: XX

Question 18

Define mutation

Answer 18

Change in gene or chromosomal structure that typically occur during the replication of genes or chromosomes

Question 19

How do mutations occur?

Answer 19

1. Spontaneous mutations during the replication or repair of DNA
2. Exposure to mutagens

Question 20

Define mutagens

Answer 20

Physical or chemical agents that increase the rate of mutation.

(e.g. ultraviolet radiation, certain chemicals)

Question 21

Define gene mutations

Answer 21

Mutation in genes typically linked to the X chromosomes

Question 22

Define chromosome mutations

Answer 22

Mutations involving a change in the number/structure of chromosomes, occurring during meiosis or mitosis

Question 23

What kind of mutation is albinism, and what is it?

Answer 23

Gene mutation.

Lack of pigmentation in skin, hair and eyes. It is caused by a mutation in a recessive allele which is involved in the production of pigments.

Question 24

What kind of mutation is sickle-cell anaemia, and what is it?

Answer 24

Gene mutation.

Blood disorder where red blood cells possess a rigid, sickle shape when oxygen concentration in the blood is low.
1. Sickle cells are not flexible -> block blood vessels -> blood unable to deliver oxygen to tissues -> tissue damage

It is caused by a mutation in the gene that codes for a protein required for haemoglobin production.

Question 25

What kind of mutation is down syndrome, and what is it?

Answer 25

Chromosome mutation.

Condition caused during meiosis, resulting in mental retardation, heart defects and respiratory defects.

Question 26

How does down syndrome happen?

Answer 26

1. Zygote inherits 3 copies of chromosome 21 instead of 2 -> mutation is present in all body cells due to mitosis during zygote development
2. HENCE, each body cell contains 47 chromosomes instead of 46

Question 27

Define genetic variations

Answer 27

Differences in phenotypes between individuals of the same species

Question 28

Define discontinuous variation

Answer 28

When individuals possess distinct and separate phenotypes with no intermediates. This is controlled by alleles of a single gene or a small number of genes.

e.g. human blood group

Question 29

Define continuous variation

Answer 29

When an unbroken range of phenotypes exists in the population (no distinct difference). This is controlled by the effect of many genes, and often affected by environmental factors.

e.g. intelligence, height, skin colour

Question 30

Define evolution

Answer 30

Change in genetic material of a population from one generation to the next

Question 31

Define natural selection

Answer 31

Major mechanism by which evolution takes place, causing helpful genes to become more common and deleterious genes to become rarer

Question 32

What are some environmental factors that act as forces of natural selection?

Answer 32

1. Disease (disease-resistant phenotypes would be selected)
2. Prey (characteristics conductive to obtaining more food are selected)
3. Predators (methods for evading predators are selected)
4. Mating (features more attractive to females of the same species are selected)

Question 33

Define artificial selection

Answer 33

Intentional breeding for particular genetic traits to produce several economically important crops and animals.

Question 34

What is hybridisation?

Answer 34

1. Two parents are selected, each of which possesses either one of two desirable traits
2. Crossing these parents will create new hybrids with the preferred combination of genes
3. Propagating these hybrids

Question 35

What is inbreeding?

Answer 35

1. Two parents are selected, each of which possesses either one of two desirable traits
2. Crossing these parents will create new hybrids with the preferred combination of genes
3. Breeding among closely related individuals