A trait passed only by the mother isn't from a nuclear gene
- The idea
- Predict
- See it
- Why
- Check
The idea
“The mother carries the allele, so all her offspring get it from her nucleus.”
Most genetics problems are about alleles on chromosomes, so you look in the mother's nucleus. The egg carries more than a nucleus.
The short version
The mistake: The mother carries the allele, so all her offspring get it from her nucleus.
What's actually true: A trait that every offspring gets from the mother, and none get from the father, comes from organelle DNA in the egg.
- You carry two copies of each autosomal gene, one from each parent. The copies segregate in meiosis, so the offspring of one mother can differ.
- Mitochondria and chloroplasts have their own DNA. In most animals and flowering plants, offspring inherit these organelles only from the egg.
- So an organelle gene goes from a mother to all her offspring, sons and daughters alike. The father's copy isn't passed on.
On the exam: Every offspring matches the mother and none match the father? Look to organelle DNA in the egg.