DIHYBRID INHERITANCE

Question 1

Dihybrid inheritance

Answer 1

• inheritance of two unlinked genes

- i,e colour and shape RRYY

Question 2

dihybrid punnet square

Answer 2

ADD PICTURE

Question 3

dihybrid mendelian ratios

Answer 3

9:3:3:1 (unlinked)

Question 4

what is a dihybrid test cross for?

Answer 4

• to work out whether unknown is heterozygous or homozygous

Question 5

linkage

Answer 5

two genes are on the same chromosome therefore they are inherited together

Question 6

recombinants (2)

Answer 6

• produced by crossing over during meiosis prophase I
• genes are swapped producing new linked combinations
• i.e AB could become aB

Question 7

how to recognise linkage

Answer 7

when it doesn’t follow a mendelian ratio

Question 8

crossover value

Answer 8

(number of recombinants/number of progeny) x 100

Question 9

what does a chi^2 (x^2) test do? (2)

Answer 9

• it ascertains whether results slightly off of a mendelian ratio are due to chance or biological factors
• it tests the null hypothesis

Question 10

null hypothesis

Answer 10

there is no significant difference between the observed and expected results, and any deviation is due to chance

Question 11

Mendelian ratios assume there is no difference in… (3)

Answer 11

• number of different types of gametes
• probability of each gamete type fusing with another
• viability of the embryos regardless of genotype

Question 12

how to draw chi^2 table (ADD NO OF STEPS)

Answer 12

ADD PICTURE

Question 13

degrees of freedom

Answer 13

• in crosses degree of freedom = number of classes - 1

- i.e 4 phenotypes? so 3 degrees of freedom

Question 14

probability (2)

Answer 14

• use 5% or 0.05

- if predicted results occur 5% or more, any deviation is chance based

Question 15

critical value

Answer 15

found by using degrees of freedom and probability in table

Question 16

conclusion (if chi^2 > critical value)

Answer 16

• the value of x is > critical value
• the probability of chance is <5%
• the null hypothesis is rejected
• there is a significant difference between the observed and expected results
• inheritance isn’t mendelian and there must be another biological factor (such as linkage) as it is not due to chance

Question 17

conclusion (if chi^2 < critical value) (5)

Answer 17

• The value of x is < critical value
• the probability of chance is > 5%
• the null hypothesis is accepted
• there is no significant difference between the observed and expected results
• inheritance is mendelian and any variance is due to chance