DNA Day experts answer your questions about heredity

14 May 2013

Above: Image © c12, iStockphoto.com

Can genes be related to other people other than your parents?

Absolutely. In fact, your genome is made up entirely of DNA from your grandparents. And, by extension, your DNA comes also from your great grandparents. And, by extension, from your great-great-grandparents. You see where this is going? You share stretches of DNA inherited from a common ancestor with people from all over the world because all humans share common ancestry.

- Answer provided by Dr. Sean Myles

Can mental disorders that are passed down hereditary advance and mutate into another? (Can a parent or grandparent whom has depression, could their offspring or grandchild develop bipolar disorder or something similar?)

These types of disorders have many factors that contribute into their expression, far beyond only genetics. It is possible that if both parents contribute genetics for some traits, it can be expressed more strongly in the offspring, however it isn't likely that one genetic mutation will become a more advanced type of a certain symptom in the offspring.

- Answer provided by Dr. Monique Haakensen

How does the DNA of parents get equally transferred to the child? How does the cell make the correct combination of DNA?

The egg and the sperm each have one copy of the chromosomes, whereas normal cells have 2 copies, so when the sperm fertilizes the egg no "transfer" occurs, both copies just coexist.

- Answer provided by Dr. Paul Gordon

Are genetic mutations, like nondisjunction, hereditary?

Yes, genetic mutations are generally inheritable, assuming that the offspring survives to adulthood and is fertile. In the specific case of non-disjunction though, the answer for humans is (usually) "no". Nondisjunction leads to extra or missing copies of chromosomes in a fetus, and most of these anomalies lead to spontaneous abortion, stillbirth or early childhood death usually. The primary exceptions are Down's Syndrome (extra chromosome 21) Klinefelter's Syndrome (extra X chromosome in a male) and Turner syndrome (missing an X chromosome in a female) where survival into adulthood in normal. In terms of heritability, only 5% of Down's Syndrome patients are explainable by what's called "familial risk" (i.e. something in the family's DNA makeup makes disjunction more likely). Disjunction is well tolerated by plants, and is a way that desirable traits are amplified in plants.

- Answer provided by Dr. Paul Gordon

Is there a chance for a person with Ehler Danlos syndrome to have a baby with the same syndrome?

Ehler Danlos syndrome can be X-linked, autosomal dominant or autosomal recessive. So, it is unlikely to be a female with X-linked, and a male with X-linked would have to have a partner who also has the mutation. For the Autosomal Recessive (2 copies damaged), the affected person would have both copies of their DNA with a mutation, their partner would have to have one copy with a mutation, and in this case there would be a chance. For Autosomal dominant (one copy damaged), yes, there is a 50% chance.

- Answer provided by Dr. Karen Bedard

If a person's original DNA make up is damaged by say drugs or an accident would that become hereditary and be passed down through their genomes?

Only if the damage was done to the sex chromosomes, or the mother's mitochondrial DNA. this is the only DNA that is inherited by offspring.

- Answer provided by Dr. Dennis McCormac

Can recessive genes get wiped out after a certain number generations?

Hi there! It depends on the effects of the recessive gene. If the presence of the recessive gene does not reduce the overall fitness of the species, then it most likely would not be wiped out. What I mean is that an individual with both recessive copies may be unfit but if a heterozygous does not show a decrease in overall fitness, then these individuals carrying the recessive gene would survive and pass on their gene. If the homozygous dominant individual has a much better chance of survival the frequency of the dominant gene may be higher than in the gene pool but that would not completely wipe out the recessive gene.

- Answer provided by Ethan Yang

Can the genes from a mother and father counteract one another? Do some genes dominate over others?

Absolutely. In medical genetics there is every genetic variant combination of bad+bad=good, bad+good=good, good+good=good, bad+bad=bad, etc., though obviously some are very rare indeed.

- Answer provided by Dr. Paul Gordon


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