Inheritance

Question 1

Why is the expected ratio of offspring slightly different from observed ratio?

Answer 1

• The chance of each offspring receiving a certain allele from their
parents is independent of other offspring (random fertilisation)
-The offspring have equal chances of survival
-The observed ratio will become closer to the expected ratio as
the number of offspring increases

Question 2

What is codominance?

Answer 2

Codominance occurs when both alleles are equally expressed in the heterozygous condition.

Question 3

Describe the types of mutation

Answer 3

Chromosome mutation:

• Change in structure/number of chromosomes
• e.g. Down’s Syndrome (extra copy of chromosome 21)

Gene mutation:

• Permanent change in the sequence of nucleotides in DNA
• Produces variation between individuals as it results in new alleles of genes
  e. g. albinism, sickle cell anaemia, haemopholia

Question 4

What are some factors that increase the chance of mutation?

Answer 4

Radiation: UV Ray, X-Rays, Gammar rays
Chemicals: Benzene, bromine
Infectious agents: Viruses

Question 5

Describe continuous and discontinuous variation.

Answer 5

Continuous:
Traits brought about by combined effect of many genes
No distinct categories, many intermediates
Greatly influenced by environment

Discontinuous:
Controlled by a single/few genes
Distinct phenotypes, no intermediate forms
Rarely/not influenced by environment

Question 6

What is selection pressure?

Answer 6

Selection pressure refers to biotic and abiotic factors that act upon the survival and reproductive success of individuals

Natural selection is driven by selective pressures in the environment