Eli5: What are recessive genes? Why do we always get passed down genes that don’t show?
In: 5
Recessive genes are genes we carry that do not have a phenotype, meaning whatever they code for is not actively displayed in the creature, unless you carry both alleles of it (alleles are one half of a gene pair).
For instance, if you carry two alleles for the recessive gene for blue eyes, your eyes will be blue.
But if you carry one Brown allele and one Blue allele, you eyes will be brown. This is because blue is recessive, weak, while brown is dominant, strong. The dominant gene will always be expressed.
The only way to have blue eyes therefore is to inherit a recessive blue allele from each parent.
It looks something like this:
*Father_____B________b*______________________________________________________________________
**Mother**____________________________________________________________________________________
**B**__________BB________Bb___________________________________________________________________
**b**__________Bb________ bb___________________________________________________________________
In this table, you can see both the mother and father have both B and b alleles, so they themselves both have brown eyes.
In terms of their children, there are 3 possibilities:
1. 25% chance of BB child – BROWN EYES
2. 50% chance of Bb child – BROWN EYES
3. 25% chance of bb child – BLUE EYES
Two blue eyed parents can NEVER have a brown eyed child, because they carry only the recessive gene, otherwise their eyes would be brown!
Hope this helps!
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