Human genetic variation / diversity causes
Human genome is 23 pairs of chromosomes, numbered 1-23.
In each pair one chromosome from Mother, the other Paternal.
(Each column below represents a chromosome pair):
M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 M15 M16 M17 M18 M19 M20 M21 M22 M23
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23
Gametes (sex cells, i.e. sperm or egg) each have only one chromosome from
each pair.
A random selection of each chromosome happens.
Here are five example possible gametes:
Gamete 1:
M1 M2 P3 P4 M5 M6 M7 M8 P9 P10 P11 P12 M13 P14 M15 M16 M17 P18 P19 P20 P21 P22 M23
Gamete 2:
P1 M2 M3 P4 M5 M6 M7 P8 P9 P10 P11 M12 P13 M14 M15 P16 P17 P18 M19 P20 M21 P22 M23
Gamete 3:
M1 M2 P3 M4 M5 P6 M7 P8 M9 M10 P11 P12 P13 P14 P15 M16 M17 M18 P19 P20 M21 M22 P23
Gamete 4:
P1 P2 M3 M4 M5 M6 P7 M8 M9 M10 M11 M12 M13 M14 P15 M16 P17 P18 P19 M20 M21 M22 P23
Gamete 5:
M1 P2 P3 P4 P5 P6 P7 P8 M9 P10 P11 P12 P13 P14 P15 P16 M17 P18 M19 P20 M21 P22 M23
As there are two choices for each chromosome and there are 23 chromosome pairs,
there is a total of 223 = 8M possible different gametes.
But wait, there's more.
Recombination crossing-over between each chromosome pair happens at meiosis when the
gametes are made, further greatly adding to the variety.
For example, the M chromosome the Child got from its Mother is not
one of the Mother's M or P chromosomes but is a recombination of them, as
the colors indicate. Similarly, the M chromosome in the Mother is a
recombination of her mother's (i.e. the child's maternal Grandmother) M and P
chromosomes. And similarly in all branches all the way back.
The grandparents' solid colors here are just for illustration purposes, in actuality they are a
large patchwork of many ancestors' bits.
On average, each ancestor n generations back is supplying you with
1/2n of your genome.
Refresher on meiosis:
