Inheritance

Question 1

Gene locus

Answer 1

Exact location of a gene in a chromosome

Question 2

Homologous chromosomes

Answer 2

• A pair of chromosomes of the similar size and shape
• One chromosome from male parent and one from female parent
• Humans have 23 pairs of homologous chromosomes

*Male have X and Y chromosomes while female of two X chromosomes

Question 3

Allele

Answer 3

• Different forms of gene that occupy the same relative position in a pair of homologous chromosomes
• They code for different polypeptides that lead to different traits

Question 4

Dominant allele

Answer 4

Allele that will always express itself

Question 5

Recessive allele

Answer 5

Allele that will only express itself when both copies are present

Question 6

Phenotype

Answer 6

The observable traits of an organism

Question 7

Genotype

Answer 7

The genetic make-up of an organism inherited from its parents
eg. RR, Rr, rr

Question 8

Homozygous

Answer 8

Same allele present (can be dominant or recessive)

Question 9

Heterozygous

Answer 9

Different allele present

Question 10

Human chromosomes

Answer 10

• Humans have 23 pairs of chromosomes
• Two types of chromosomes
  1. Autosome (22 pairs)
  2. Sex chromosomes (XY or XX)

Question 11

Gametes (1)

Answer 11

• Gametes are sex cells
• Male: Sperm while Female: Egg
• Gametes have half the number of chromosomes as compared to body cells

Question 12

Gametes (2)

Answer 12

Eggs contain an X chromosome while sperms may contain an X or Y chromosome

Question 13

Codominance

Answer 13

Occurs when two alleles express themselves in the heterozygote as neither is dominant over the other

Question 14

Genetic mutation

Answer 14

The change in the structure of a gene or in the number of chromosomes

Question 15

Causes of mutation

Answer 15

1. Exposure to radiation such as X-rays or uv-rays

Question 16

Advantageous mutations

Answer 16

When a mutation gives an organism a survival advantage over other organism, causing the mutation to be more likely to be passed down to future generations

Question 17

Disadvantageous mutations

Answer 17

When the mutation des not allow the organism to survive, the mutation is less likely to be passed down to future generations

Question 18

Natural selection

Answer 18

A process that ensures the best adapted organisms in a population survive to reproduce and pass their genes to future generations

Question 19

Process of natural selection

Answer 19

1. There is variation among individuals in a species
2. Environmental factors causes competition and better adapted individuals survive
   - Biotic factors (organisms):
   Predators or diseases
   - Abiotic factors (environment):
   Water supply or temperature
3. Individuals that survive then reproduce and pass their traits to the next generation
4. Over time present complex forms of living organism have emerged from simpler ancestral forms, this is known as evolution

Question 20

Two types of variation

Answer 20

1. Discontinuous variation
2. Continuous variation

Question 21

Discontinuous variation

Answer 21

• Distinctive phenotypes
• Controlled by a few genes
• Genes do not show additive effect
• Not affected by environmental factors
• Example: Ability to roll tongue and blood type

Question 22

Continuous variation

Answer 22

• A range of phenotypes
• Controlled by many genes
• Genes show additive effect
• Affected by environmental factors
• Example: Height and skin colour