Answer to Question #343339 in Genetics for Flower

Question

If height were entirely genetically controlled, what concordance would you expect between monozygotic twin pairs?

Answer 1

Height is indeed genetically controlled, and in terms of twins, there is concordance, that is, a certain probability that they will be the same height.

Concordance with respect to the height of monozygotic twins at different ages was calculated experimentally as the ratio of the number of pairs that have the same height to the total number of pairs. These results were entered into a following table (which was obtained from here: https://desklib.com/document/leaflet-27-leaflet-information-leaf/):

Based on the table, in monozygotic twins, the highest concordance is observed after the age of 5 years and equals 0.94. But from birth to the age of 5 years, concordance between monozygotic twins gradually increased from 0.62 to 0.94, being lowest at birth and highest at the age of 5 years.

This may indicate that before birth histones in monozygotic twins in the region of genes responsible for height were methylated during the same period of ontogenesis only in 62% of cases, which contributes to the fact that only with this probability the genes responsible for height in monozygotic twins will work the same and the twins will be the same height at the time of birth. But with birth, the level of histone methylation gradually decreases, which contributes to the synchronization of the work of similar genes.

But the decrease in the level of histone methylation occurs differently in each individual, if monozygotic twins at birth were of different heights. This contributes to the fact that the probability of establishing the same height in monozygotic twins will increase with age. Accordingly, the probability that by the age of 5 years monozygotic twins will be the same height reaches 94%.