80 CHAPTER 11 



QUESTIONS FOR DISCUSSION 



11.1. In determining whether or not twins are dizygotic, why must traits be studied for which 

 one or both parents are heterozygotes? 



11.2. Are mistakes ever made in classifying twins as being dizygotic in origin? Why? 



11.3. When nonidentical twins are discordant for AB blood type, why must one or both 

 parents have been heterozygous for /"^ or /^? 



11.4. Invent a particular situation which would result in greater discordance for identical 

 than for nonidentical twins. 



11.5. What would be the probability of twins being dizygotic in origin if both had the 

 genotype aa Bb CC Dd Ee Ff, each pair of alleles segregating independently, if the 

 parents were genotypically Aa Bb CC DD Ee Ff and Aa BB CC dd ee FFl 



11.6. How would you proceed to test whether, in women, there is a genetic basis for the 

 maturation of more than one egg at a time? 



11.7. In what way can you imagine that the paternal genotype could influence the frequency 

 of twinning? 



11.8. Is tuberculosis inherited? Explain, 



11.9. What can twin studies by themselves tell you about genes? about genetic recombi- 

 nation? 



11.10. Is it valid to apply the conclusions from twin studies to nontwin members of the 

 population? Explain. 



