Despite each parent having different genes for traits such as height and color, how does our genetic inheritance determine which specific genes we receive? Additionally, what mechanisms account for siblings from the same parents possessing different characteristics like height and color?
In: Biology
Most cells in your body undergo _mitosis_ which will create a (hopefully) genetically identical copy of the original cell, including all the same chromosomes that the original had, which are two full sets of all 23 chromosomes (46 in total), with half coming from your dad and the other half from your mom. Chromosomes are essentially groups of genes, which code for various traits like eye colour or height or whether you get diabetes. Cells with a full set of paired chromosomes are called _diploid_.
The sex cells in the body (eggs and sperm) on the other hand, are formed in their respective organs (ovaries and testicles) by _meiosis_, which creates new cells with only **half** the original cell’s chromosomes. The new cells will get a **single** set of 23 chromosomes, 1 of each, and which one they get will be decided completely randomly. Cells with only a half set of chromosomes are called _haploid_.
So, a randomly selected sperm cell will have some chromosomes from your mom, and some from your dad, but which ones come from which parent are completely by chance.
If the sperm cell gets a Y chromosome from the dad, then it has the potential to fertilize an egg with a boy, and if it gets an X chromosome (from either the mom _or_ the dad) then it has the chance to fertilize a girl.
Once the sperm cell meets the egg cell and fertilizes it, the half set of chromosomes from each join together and you get a full diploid cell again, that cell starts mitosis and a new organism is begun!
Siblings having different traits (including their sex) are down to that random chance of some chromosomes from the father and some from the mother merging. Traits are quite often determined by combinations of genes which might be present on different chromosomes, so you can have two siblings that look similar, but have different eye colours, or they can look nearly identical, or they can be wildly different. To take this to an extreme example, it’s theoretically possible (although _incredibly_ unlikely) for two siblings to have exactly the same sets of chromosomes, and be essentially identical twins (even if they weren’t formed in the same pregnancy).
Latest Answers