AP BIOLOGY

Detailed explanation-1: -Fertility treatment Some fertility drugs work by stimulating a woman’s ovaries, which can sometimes cause them to release more than one egg. If sperm fertilizes both of these eggs, this can result in twins. In vitro fertilization (IVF) can also increase the chance of conceiving twins.

Detailed explanation-2: -To form identical or monozygotic twins, one fertilised egg (ovum) splits and develops into two babies with exactly the same genetic information. To form fraternal or dizygotic twins, two eggs (ova) are fertilised by two sperm and produce two genetically unique children.

Detailed explanation-3: -While the circumstances are very rare, there are numerous incidences of families with multiple multiples. Although some are related to reproductive assistance, many are completely spontaneous. For example, Kevin and Lorraine Horan of Ireland, have three sets of twins and never used any fertility treatment.

Detailed explanation-4: -If one egg is fertilised by two sperm, it results in three sets of chromosomes, rather than the standard two-one from the mother and two from the father. And, according to researchers, three sets of chromosomes are “typically incompatible with life and embryos do not usually survive".