Medelian Ratios, Chi-Squared And Probabilities

Question 1

When you work out an expected ratio from a genetic cross, the result you would get would be from a what sample? What if you use a small sample?

Answer 1

A large sample size as the smaller the sample size, the less likely for the ratios of the phenotypes to match.

Question 2

What are the 2 reasons why the expected ratios do not match?

Answer 2

1. A small sample size is used.
2. Random fertilisation.

Question 3

How does random fertilisation possible cause the expected ratio to be different?

Answer 3

Because it is due to chance.

Question 4

What are medelian ratios used to estimate?

Answer 4

The probability that certain genotypes and phenotypes will occur.

Question 5

What is the equation for the chi-squared test? Meanings?

Answer 5

x^2 = Z (O-E)^2 / E

• Z = sum of.
• O = observed.
• E - expected.

Question 6

What hypothesis should we always start with in chi-squared?

Answer 6

The null hypothesis = ‘there is no significant difference between observed and expected results.

Question 7

What is the probability level and DOF?

Answer 7

P = 0.05.
DOF = n-1.
n = number of phenotype categories.

Question 8

What is a conclusion for chi-squared test?

Answer 8

If our value is smaller than the table value, there is no significant difference between the observed and expected results at 5% probability level. So we accept the null hypothesis.
- vice versa.

Question 9

What does the Hardy-Weinberg principle state?

Answer 9

‘In a stable population with no disturbing factors, the allele frequency will remain constant from one generation to the next and there will be no evolution.

Question 10

What are the 4 things that the principle assumes?

Answer 10

1. No mutations occur.
2. No natural selection occurs.
3. No immigration or emigration to and from a population.
4. The population is large and mating is random.

Question 11

What are the 2 equations in this principle?

Answer 11

p = frequency of dominant allele.
q = frequency of recessive allele.

Question 12

What is the equation when trying to work out the allele frequencies?

Answer 12

p + q = 1.0.

Question 13

What is the equation for working out the genotype/phenotype frequencies? Meaning?

Answer 13

p^2 + 2pq + q^2 = 1.0.
- p^2 = frequency of dominant individual.
- 2pq = frequency of heterozygous individual.
- q^2 = frequency of recessive individual.

Question 14

What is a hint when answering Hardy-Weinberg questions?

Answer 14

Many questions already give you the q^2 value in the question.