Advantages of twin studies Twin studies allow disentanglement of the shared genetic and environmental factors for the trait of interest. Researchers can estimate the proportion of variance in a trait attributable to genetic variation versus the proportion that is due to shared environment or unshared environment.

Critics of twin studies argue that they are based on false or questionable assumptions, including that monozygotic twins share 100% of their genes and the equal environments assumption.

Twin studies. Twin studies support the contention that a heritable trait may increase risk for criminal behavior. To the extent that the similarity observed in MZ twins is greater than that in DZ twins, genetic influences may be implicated.

Researchers use this method, and variations on it, to estimate the heritability of traits: The percentage of variance in a population due to genes. Modern twin studies also try to quantify the effect of a person’s shared environment (family) and unique environment (the individual events that shape a life) on a trait.

Homburg and colleagues found that older women have higher levels of a hormone called FSH, prompting greater likelihood of having fraternal twins. The study appears online in Human Reproduction.

Most women will ovulate 7 to 10 days after taking Clomid pills, which means you’re most likely to conceive on days 11 through 21 of your cycle. Statistics indicate that when taken as directed, the success rate of clomid shows 80 percent of women will respond to the treatment and successfully ovulate on Clomid.

Conceiving Twins While Taking Clomid. For every 20 pregnancies conceived with Clomid, only one will result in twins. Clomid (clomiphene), a pill taken by mouth to induce ovulation, causes twin pregnancies between 5% and 12% of the time. 1 That’s fewer than one in 10 pregnancies.