12. Inheritance

Question 1

define gene

Answer 1

Gene is sequence of DNA nucleotides that stores information used to make a polypeptide, therefore gene is a unit of
inheritance passed from parents to offspring

Question 2

describe discontinuous variation (6)

1. phenotype
2. environmental influence
3. genes
4. additive effect
5. graph
6. examples

Answer 2

1. Few clear-cut phenotypes with no 
intermediate 
2. Rarely affected by environmental 
conditions
3. Controlled by one or few genes 
4. Not present
5. Discrete groups
6. Blood groups, eyelid, flower colour in pea plant

Question 3

describe continuous variation (6)

1. phenotype
2. environmental influence
3. genes
4. additive effect
5. graph
6. examples

Answer 3

1. Range of phenotypes
2. Greatly affected by environmental
   conditions
3. Controlled by many genes
4. The effect of many genes add together and contribute the
   phenotype
5. Normal distribution
6. Height, skin colour, weight, intelligence

Question 4

explain dominant

Answer 4

A dominant allele is the allele that is always expressed in the phenotype, no matter under homozygous or heterozygous
condition.

Question 5

explain recessive

Answer 5

A recessive allele is the allele that is only expressed under homozygous recessive condition.

Question 6

explain homozygous

Answer 6

Organisms having two identical alleles of a particular gene. Allele can be either both dominant or both recessive.

Question 7

explain heterozygous

Answer 7

Organisms having two different alleles of a particular gene

Question 8

explain phenotype (2)

Answer 8

• Phenotype refers to the expressed trait in an organism.

* The phenotype of an organism is the result of its genes and the effects of its environment

Question 9

explain genotype (2)

Answer 9

• A genotype is the genetic makeup of an organism.
• An organism’s genotype is homozygous for a trait if the two alleles controlling the trait are identical, heterozygous for a trait if
the alleles controlling the trait are different

Question 10

define inheritance

Answer 10

Inheritance is the process by which genetic information is passed on from parent to child

Question 11

State why observed ratios often differ from expected ratios, especially when there are small numbers of progeny (2)

Answer 11

1. the expected ratio are based on mathematical probability and fertilisation of gametes occurs in a random fashion/ is a random process
2. Hence, observed ratio often differ from expected ratios, even more so if the sample size is small

Question 12

predict results of simple crosses (4)

Answer 12

• The gene for flower colour of pea plant has two alleles: dominant
purple allele (P) and recessive white allele (p’)
• When a homozygous purple plants (PP) is crossed with a
homozygous white plant (p’p’), each organism inherits one allele
from the mother and one allele from the father during sexual
reproduction
• The offspring generation consisted of all purple-flowered plants
even though their genotype is heterozygous (Pp’) as the
dominant purple allele (P) is expressed over recessive white allele
• Self-pollination in the F1 generation produced a F2 generation
where the phenotypic ratio of purple-flowered to white-flowered
plants is 3:1

Question 13

what is variation

Answer 13

differences in traits between individuals of the same species