Talk:Noa Keawe/@comment-34049573-20180213122039/@comment-36277500-20191222014449

Twins aren't always monozygotic and identical. Actually, much more often (about 75%) they are dizygotic, so this way they really don't have to be identical, nor more similar to each other than other siblings - they just have different DNA, like their non-twin siblings. And twins with different genders are always dizygotic.

Siblings in general (not only twins) can differ, because of different complete of chromosomes from their parents. Humans are diploidal (two DNA strands), but gametes are haploid due to division called meiosis.

Every gene in that diploid cell (start it from height to eyes colour) has two versions called alleles. They can be two dominant, two recessive or one dominant and one recessive. And there are also genes with more than two versions! But diploid organisms always have two genes.

And each haploid cell can get very random combination of chromosomes and genes and their versions - not always the whole complet of recessive or dominant genes, but billions of combinations!

Two people have together four DNA strands (two strands for each of them). Let's just say that both of them are heterozygous (have two different alleles), let's mark the genes A (dominant) and a (recessive), so both parents are Aa. Possible combinations in children: AA, 2xAa and aa. And think about genes Bb, Cc and others. Each new gene counts, you have to multiply the number of combinations...

And sometimes you inherit some features from your grandparents instead of parents!

Example:

My first brother is similar to my mother (tan skin, brown eyes, black hair), while my second brother and I have fair skin (from my father's family) and hazel eyes (my mother has brown eyes and my father has blue eyes). However, my second brother has straight blond hair, my first brother has black and curly, and mine are brown and curly (my mother has black straight hair, and my father has dark curly hair, while our both grandmothers had dark blond hair).

That's why it's not so simple. Its rather never simple...