Question: “How come your son Jimmie isn’t colorblind when his father is” Wrong answer: “It some times skips a generations, maybe his kids will inherent it” Right Answer: “it’s on the X chromosome, he got his fathers Y chromosome, so his kids will not inherent colorblindness from his side of the family!”
Question: “How come your daughter Susie isn’t colorblind when her farther is” Confused answer: “It some times skips a generations, maybe her kids will inherent it” Right Answer: “The confused answer is less wrong than with the son, it’s on the X chromosome, she got her fathers X chromosome, so half heir sons will be color blind”
Simple genetics, your Mother has XX your father has XY, let’s use little x to denote colorblindness, you get a random chromosome from each parent.
Colorblind father → sons have normal vision, daughters are carriers:
xY + XX - > 50% XY + 50% xX
Colorblind mother → sons are colorblind, daughters are carriers
XY + xx - > 50% xY + 50% xX
Carrier mother → half sons are colorblind, half of daughters are carriers
XY + xX - > 25% xY + 25% XY + 25% xX + 25% XX
Finally if colorblindness runs in both families:
xY + xX → 25% xY + 25% XY + 25% xx + 25% xX
both parents colorblind → all children colorblind
Question: “Have you ever wondered, how does the xX females know not to use the color blind gene?” Answer: “They do not, half the relevant cells in their eyes will have a bad photo receptor… but the brain is pretty smart, it quickly learns to boost the signal from the other half of the cells”
Warning: The above is strictly only true for X-linked dominant diseases such as colorblindness, a similar approach can be used to elucidate the inheritance pattern of Classical Mendelian traits, but does not work for complex trait such as height which is influenced by multiple genes.
Genetics: It sometimes skips a generation is a terrible explanation!
Question: “How come your son Jimmie isn’t colorblind when his father is”
Wrong answer: “It some times skips a generations, maybe his kids will inherent it”
Right Answer: “it’s on the X chromosome, he got his fathers Y chromosome, so his kids will not inherent colorblindness from his side of the family!”
Question: “How come your daughter Susie isn’t colorblind when her farther is”
Confused answer: “It some times skips a generations, maybe her kids will inherent it”
Right Answer: “The confused answer is less wrong than with the son, it’s on the X chromosome, she got her fathers X chromosome, so half heir sons will be color blind”
Simple genetics, your Mother has XX your father has XY, let’s use little x to denote colorblindness, you get a random chromosome from each parent.
Colorblind father → sons have normal vision, daughters are carriers:
xY + XX - > 50% XY + 50% xX
Colorblind mother → sons are colorblind, daughters are carriers
XY + xx - > 50% xY + 50% xX
Carrier mother → half sons are colorblind, half of daughters are carriers
XY + xX - > 25% xY + 25% XY + 25% xX + 25% XX
Finally if colorblindness runs in both families:
xY + xX → 25% xY + 25% XY + 25% xx + 25% xX
both parents colorblind → all children colorblind
Question: “Have you ever wondered, how does the xX females know not to use the color blind gene?”
Answer: “They do not, half the relevant cells in their eyes will have a bad photo receptor… but the brain is pretty smart, it quickly learns to boost the signal from the other half of the cells”
Warning: The above is strictly only true for X-linked dominant diseases such as colorblindness, a similar approach can be used to elucidate the inheritance pattern of Classical Mendelian traits, but does not work for complex trait such as height which is influenced by multiple genes.