7 Genetics, populations, evolution and ecosystems

Question 1

Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation. (2)

Answer 1

(Any 2 of these)

Crossing over.

Independent assortment/segregation of chromosomes.

Random fertilisation.

Question 2

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as expected ratios. Suggest two reasons why. (2)

Answer 2

(Any 2 of these)

1. Small sample size
2. Random fertilisation of gametes
   3.Linked genes
3. Epistasis

Question 3

If an organism carries two copies of the same allele it is said to be…(1)

Answer 3

homozygous at that locus

Question 5

What is meant by the term phenotype? (2)

Answer 5

Expression/appearance of alleles due to genetic constitution.

Question 6

A student wished to test her results with the ones she had expected. What statistical test should she use? (1)

Answer 6

Chi squared test

Question 7

What is meant by codominant alleles? (1)

Answer 7

When both alleles are expressed in the phenotype.

Question 8

What is meant by genotype? (1)

Answer 8

the genetic constitution of an organism.

Question 9

What is a gene pool? (1)

Answer 9

All of the alleles in a population.

Question 10

Succession occurs in natural ecosystems. Describe and explain how succession occurs. (4)

Answer 10

Pioneer species colonise and change the environment conditions. The new environment becomes more suitable for new species.

Question 11

What are two features of a climax community?

Answer 11

The same species is present over a long time.

Abiotic factors become more constant over time.