PSYCH 3102-001




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.

Possible answers

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.





Twin studies

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.













Cross-breeding studies of animal behavior.

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:


                                                                           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?