Pregnancy is an event in our life that often feels magical and like destiny just takes us along for the ride when in fact, it’s the result of a complex and fascinating process that begins with the union of an egg and sperm and results with the formation of a completely unique new being.
Of course, you want to know what he’s going to look like, if his personality is going to be like yours and what he will turn out to be one day. If you’re like me, you probably had some fun combining your picture and your partner’s using a site like Morph Thing to see the different possibilities. But what makes it that our children inherit physical and personality traits from their parents and even other family members?
Heredity
When you conceived your baby, he inherited 23 chromosomes from you and 23 from his father in every one of his cells. It’s in those cells that resides his genetic information and DNA, which code over 25 000 characteristics named genes. These genes are responsible for defining his physical characteristics and the functioning of his body. This genetic heritage will make your child unique and he will in turn transmit it to his children one day.
Dominant, recessive and co-dominant genes
As your child receives two copies of the genes from his parents, these genes can become dominant, recessive or co-dominant. A dominant gene, even when present in a single copy, will always impose its instructions and prevent another gene to be expressed, while a recessive gene is only expressed when two copies of the gene are present. In some cases, both copies of the gene can be expressed equally and are then called co-dominant. This is what happens for example when a child’s « small » gene is co-dominant with the « tall » gene: he will be of average size.
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Frequency of eye color based on parent’s eye color |
Father |
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Blue eyes |
Brown eyes |
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Alleles: blue & blue |
Alleles: blue & brown |
Alleles: brown & brown |
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Mother |
Blue eyes |
Alleles: blue & blue |
100% blue |
50% blue |
100% brown |
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50% brown |
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Brown eyes |
Alleles: blue & brown |
50% blue |
25% blue |
100% brown |
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50% brown |
75% brown |
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Alleles: brown & brown |
100% brown |
100% brown |
100% brown |
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Genetic mutation
Sometimes a child is born with a certain characteristic that neither his parents possesses, as in the case of children born with two different colour eyes for example. This happens when a genetic mutation occurs which is only in rare cases. The child will then have a 50% chance to pass this characteristic on to his child, as it will have become part of his genetic makeup.
Sources : Corporation de recherche et d’action sur les maladies héréditaires, ODHQ – Espace parents, vol. 3 No. 1, 2009, Mount Sinai Hospital – Introduction and general information on the principles of genetics, L’internaute: Science.
