INTRODUCTION TO BEHAVIOR GENETICS

PSYCH 3102

DR HEWITT

PRACTICE EXAM 1 Answer Key

SECTION A

Match the following definitions to the terms they define:

1. Any chromosome other than the X or Y chromosomes                     autosome

2. Structure composed of chromatin, found in the nucleus of a cell        chromosome

3. An allele that produces a particular phenotype even when present in

the heterozygous state                                                                          dominant

4. The genetic constitution of an individual, or the combination of

alleles at a particular locus.                                                                  genotype

5. The presence of the same allele at a locus on both members of a

homologous pair.                                                                                homozygosity

6. Type of cell division that occurs in germ cells, producing gametes.  meiosis

7. "Building blocks" of DNA.                                                              nucleotides

8. Describes the situation when a gene has multiple effects on

phenotype.                                                                                        pleiotropy

9. 90% of the cell cycle is spent in the phase.                                    interphase

10. The phenotype of an individual with only one X and no Y chromosome

Turner syndrome

Terms

(the following may be used once, more than once, or not at all)

allele                amino acid               autosome                  centromere

chromosome       DNA                 dominant                      Down syndrome

gamete           genotype             heterozygosity                 homozygosity

interphase    Klinefelter syndrome   meiosis                          mitosis

non-disjunction                          nucleotides                        phenotype

pleiotropy           recessive               RNA                    crossing-over

monosomy          trisomy         Turner syndrome             X-linkage                zygote

Match the following events to the terms below:

11. When DNA is replicated .                                      interphase

12. When crossing-over occurs                                    meiosis I

13. When pairing of homologous chromosomes occurs meiosis I

14. When separation of sister chromatids occurs.          Mitosis and meiosis II

15. When genes are able to be expressed .                  interphase

17. Splicing out of introns                                            RNA processing

Terms

(each term can be used once, more than once, or not at all)

mitosis             meiosis I              meiosis II         interphase              transcription

translation       replication          RNA processing                      polymerization

SECTION B

Distinguish between the following terms

16. codominance and incomplete dominance

codominance - both alleles at one locus are expressed in the phenotype

incomplete dominance - phenotype of the heterozygote is intermediate between that produced by the corresponding homozygotes

17. phenotype and genotype

phenotype - outward, measurable, expression of genes and environment

genotype - genetic constitution of an individual at a locus (ie. which alleles are present)

18. Explain the term "non-disjunction".

Unequal separation of genetic material during cell division

Give an example of a disorder caused by non-disjunction and briefly explain how this disorder arises.

Example Down syndrome (trisomy 21)

How it arises non-disjunction of either homologous pairs or sister chromatids during meiosis resulting in a gamete with 2 chromosome 21s instead of 1. On fertilization, the trisomic condition is produced.

19. If the following sequence shows the triplet codons in part of an RNA molecule,

a. show how a nonsense mutation might result in no polypeptide being produced

on translation of this part of the sequence:

AAA  CAC   UUA   GAC   AAA  CUA   UAA

lys         his      phe      asp       lys      leu       stop

UAA............................................................

stop no translation

b. show a CAG 5 repeat

AAA CAG CAG CAG CAG CAG UUA GAC AAA CUA UAA

lys glu glu glu glu glu phe asp lys leu stop

20. penetrance = frequency (%) with which a genotype, when present, expresses itself in the phenotype

HD allele is fully penetrant (although age-dependent) fragile X allele is only 50% penetrant in females, 80% in males

21. a. 0.25 b. 0.125 c. 0.375

22. If one gene, cross between mouse blind because of one allele and mouse blind due to other allele would yield all blind offspring, since no dominant allele at locus

If 2 genes same cross would produce all non-blind offspring (assuming each blind parent mouse was true-breeding for normal allele at second locus), since offspring would be double heterozygotes.