Lecture 6 - genetic hypothesis design & testing

Question 1

What do Punnett squares show?

Answer 1

gamete combinations

Question 2

What is an alternative to a Punnett square?

Answer 2

a probability tree

Question 3

What is a dihybrid cross?

Answer 3

a cross that considers 2 genes - e.g. RRMM & rrmm

Question 4

What are the 2 ways to form a genetic hypothesis?

Answer 4

• predict the number of progeny of different types that you expect before the experiment start
• look at the data and then come up with some ratios that fit fairly closely

Question 5

How do you test a genetic hypothesis?

Answer 5

• start with a biological hypothesis that allow us to predict the numbers we expect
• e.g. hypothesis = round is dominant and the ‘true’ ratio at F2 is 3 round: 1 wrinkled peas
• if our hypothesis is correct, we expect that numbers of observed and expected will not differ significantly
• statistical analysis - probably chi-squared test

Question 6

What is the expected outcome of cross pure-breeding dominant parental lines?

Answer 6

with each of the genotypes - we predict that 100% of the F1 offspring will have the dominant phenotype

Question 7

What is the expected outcome of self-fertilising the F1 generation (dominant allele)?

Answer 7

we predict that 75% of F2 generation will have the dominant phenotype

Question 8

What is the expected outcome when cross-fertilising the F1 generation with a homozygous recessive plant?

Answer 8

50% of F2 generation will have the dominant phenotype

Question 9

What can we use to create a cross of alleles?

Answer 9

a testcross

Question 10

What is the Chi-squared test used for?

Answer 10

Chi-squared gives us the probability, assuming our hypothesis is correct, that we would get, by chance, a deviation from the expected result as big as the one we have observed (or even bigger)?

Question 11

How do we use the Chi-squared test?

Answer 11

1. calculate observed and expected values
2. calculate chi-squared using the formula
3. use the table to get a p-value
4. interpret p-value with care

Question 12

What is the formula of the chi-squared test?

Answer 12

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

Question 13

What is meant as degrees of freedom?

Answer 13

the number of parameters that can vary independently

Question 14

How do we calculate the degrees of freedom?

Answer 14

number of classes minus 1

Question 15

What is the perfect match between observed and expected?

Answer 15

X^2 = 0