Inheritance

Question 1

What is a gene?

Answer 1

A length of DNA which codes for one polypeptide

Question 2

What is an allele?

Answer 2

Alternative forms of a gene occupying a similar position/locus on homologous chromosomes

Question 3

What is meant by a:

a) genotype
b) phenotype

Answer 3

a) The combination of alleles found in an individual

b) The appearance of an organism, determined by the genotype

Question 4

What is the difference between a dominant allele and a recessive allele?

Answer 4

› A dominant allele is always expressed in the phenotype

› A recessive allele is only expressed in the phenotype in the absence of a dominant allele

Question 5

What is Mendel’s first law?

Answer 5

The characteristics of an organism are determined by alleles which occur in pairs. Only one member of each pair of alleles can be represented in a single gamete

Question 6

What is a test cross used for? And how are they carried out?

Answer 6

› Used to find out whether an organism showing a dominant characteristic is heterozygous or homozygous
› By crossing the organism with homozygous recessive
› If homozygous recessive offspring are produced the original organism would have to be heterozygous

Question 7

What is co-dominance?

Answer 7

When the heterozygous organism expresses both characteristics individually (e.g. chickens with black feathers and white feathers producing speckled offspring)

Question 8

What is incomplete dominance?

Answer 8

When the heterozygous organism expresses a mixture of both characteristics (e.g. red flowers and white flowers giving rise to pink flowers)

Question 9

What is the typical ratio expected in a dihybrid cross?

Answer 9

9:3:3:1

Question 10

What is linkage?

Answer 10

› When two alleles are on the same chromosome
› Without crossing over, only two types of gametes can be produced
› Crossing over allows for a small about of recombinant gametes to be produced

Question 11

What is the null hypothesis is the χ^2 test?

Answer 11

There is no significant difference between the observed and expected results of a cross

Question 12

What number of degrees of freedom is used when carrying out a χ^2 test?

Answer 12

One less than the number of classes of data

Question 13

What does the value obtained for χ^2 mean?

Answer 13

› If lower than the value in the table (the critical value), the null hypothesis is accepted, as there is sufficient evidence that the difference is due to chance
› If higher than the critical value, the null hypothesis is rejected, as there is insufficient evidence that the difference is due to chance