Exam II will be made up of questions similar to the examples below and similar to questions you have received on the last 2 homeworks.

A generation of animals expected to differ from each other genetically (eg. The F₂ generation)

A psychiatric disorder characterized by long-term thought disorders, hallucinations and disorganized speech.

Twins who are genetically no more alike than ordinary brothers and sisters.

The process of deciding which type (either MZ or DZ) a pair of twins is.

A generation of animals not expected to differ from each other genetically.

An estimate of the additive genetic contribution to variation in a population.

Twins who are genetically identical.

An estimate of the total genetic contribution to variation in a population.

non-segregating generation            narrow heritability                        MZ twins

half-siblings                                   back cross                                  manic depression

zygosity determination                   selection differential                      schizophrenia

broad heritability                           DZ twins                                     dominance deviation

segregating generation                   correlation                                  allele-sharing method

concordance                                identical-by-descent method

The above section will be longer in your exam – make sure you have learnt and understood all the vocabulary used in the past weeks.

The following table gives the reported correlations for same-sex twins raised together for 4 traits. Assume that the sample sizes are large.

TRAIT                                MZ CORRELATION                   DZ CORRELATION

Body mass index (BMI)                     0.80                                             0.40

General cognitive ability                      0.86                                              0.60

Extraversion (EXT)                           0.50                                              0.13

Dust allergy (ALL)                            0.52                                              0.21

Basing your answers on these correlations and assuming the validity of twin study methods:

Which trait is the least influenced by non-shared environments?

Justify your answer.

Which trait is most influenced by the shared environment?

Justify your answer.

What is the narrow heritability of BMI?

Show how you arrived at this answer.

For which 2 traits might non-additive genetic influences (eg. dominance) be a factor?

Justify your answer.

Two inbred strains of fruit flies (Drosophila melanogaster), P₁ and P₂, were crossed to give the F₁ generation. Flies from the F₁ were bred to give the F₂ generation. Male flies were placed with a standard "target" female and the amount of time spent in courtship was recorded. The sample sizes, mean courtship time observed for the 4 generations, and the variance for each generation are given below:

GENERATION         SAMPLE SIZE        MEAN COURTSHIP                     VARIANCE IN

                                                                           TIME (%)                            COURTSHIP TIME

            P₁                           100                             74.0                                                344

            P₂                           100                             70.0                                                372

            F₁                                    100                             84.0                                                383

            F₂                           400                             74.9                                               621

Do the generation means give evidence of genetic influences on courtship activity?

Justify your answer.

Do the generation variances give evidence of genetic influences on courtship activity?

Justify your answer.

Given that genes seem to be important in determining courtship time, what do the generation means tell you about the nature of that genetic control?