(soft lullaby music) (baby cooing) - Aw.
Recognize this cutie?
(giggling) Well he'll grow up and teach himself to be a lawyer, become the 16th American President, and wind up on a five dollar bill.
But first, let's slow down.
He'll have to grow that iconic Abe beard, right?
Well, it's less about the how, and more about the why.
The Y chromosome, see what I did there?
Abe's DNA's bundled into 46 chromosomes, that's 23 from his Ma, and 23 from his Pa. (throat clearing) Excuse me.
44 of these chromosomes pair off with it's match, which has different versions of the same genes.
These chromosomes are like packages of genes.
Oh, they look delicious, don't they?
Genes that make proteins.
Those proteins make everything, from beards to toenails.
(buzzing) But the last two comes in two flavors, X and Y.
Now the X chromosome contains 800 protein making genes, and the Y chromosome contains only 70 protein making genes.
It's Pa that determines whether this pioneer baby is an Abe, or an Abe-alina.
(baby giggling) If Pa gives up an X chromosome to combine with Ma's X, then it's Abe-alina.
But if Pa squirts out a Y, graphic, then wa-boosh, it's an Abe.
(baby giggling) If we look a little closer at this Y chromosome we'll find the SRY gene.
Like an excited kid in class, I'm sure you know who you are, settle down, the SRY gene makes a protein that switches on another gene, and so on and so forth.
Pretty soon it's influenced the whole body so much that female parts can't even develop.
(throat clearing) Just to be clear I am talking about private kind of parts.
(gasping) Settle down.
From there, the male parts begin to pop out a hormone called testosterone.
Females make testosterone too, but not enough to make all the genes, proteins, hormones, and anatomy that makes a male.
That interplay between hormones and the Y chromosome will continue throughout old Lincy's childhood, puberty and adulthood, keeping his body decidedly male and healthy.
And triggering the hair follicles on his face to grow that trademarked Abe Lincoln beard.
(American folk music) (calm jazz music)