Question

. Consider Down syndrome. The MZ concordance for monozygotic twins is 89% and 7% for dizygotic twins. The numbers are significantly different. What is your conclusion? 5 points

What is the difference between broad and narrow sense heritability? 5 points

Answer 1

   Monozygotic twins originte from a single ovum and sperm and it's further division in the uterus cause genetically and phenotypically same individual. So both of them have same genes. That means there is more chance of getting the same defect which is imprinted in their genome. In contrast, the dizygotic twins are products of different sperm and ovum. So they have lesser gene similarity as the different sperm and ovum may carries different genes. That means there is lesse chance of getting the same defect which is imprinted in their genome. Therefore, there will be significant difference in percentage of concordance between monozygotic and dizygotic twins in Down syndrome.

Broad sense heritability is defined as the fraction or ratio of total gentic variations to total phenotypic variations, whereas the narrow sense heritability is termed as the fraction or ratio of additive variations to total phenotypic variations.