Almost every expectant parent will imagine being a parent. In doing so, you created a mental portrait of your baby. You might have thought, “She’ll have her father’s eyes” or “He’ll have his mother’s sense of humor.” You might have hoped to look at your child and think, “There is my mini me!” You created these expectations before your child is even born; expecting your child to look at least a little bit like you is human nature. If you find yourself asking this question, disappointed or perplexed, you are not alone.
While people have long recognized that physical traits like hair color tend to be passed down through family generations, many families are also surprised at how their children turn out: the only son with blue eyes in the immediate family, or the only daughter with red hair. Such surprises reflect the immense complexity and variability of human biological inheritance. You may have heard a lot about inheritance. “It’s all in the genes” – “It runs in the family” – “You don’t look anything like your siblings!” But how exactly does this all happen?
Genes are the biological units of heredity. They are the body’s chemical blueprint, coding for the proteins that together not only determine your possibilities and limitations at conception, but also keep your body functioning throughout your lifetime. Most genes are made of strands of genetic material called deoxyribonucleic acid (DNA). Long strands of genes, made of DNA, are further packaged within your body into larger structures called chromosomes. Almost every cell of your body contains 46 chromosomes, and together, the human body is estimated to contain over 30,000 genes. To get a sense of how complex this is, imagine that each gene is like a string of beads on a necklace. Then imagine how many different ways you can arrange each bead in the necklace, and then mix-and-match the necklaces. That is a lot of different possibilities that could make up a person, and not all of them will lead to your baby looking like you!
The relationship between genes, DNA, and chromosome can be easier to understand when visualized. Here is a video describing how chromosomes, DNA, and genes make up who you are. // source: Youtube, Science Explained
Let’s talk about a specific example now: for example, why might a daughter have blue eyes, even though both her parents have brown eyes? A physical trait such as eye color is dictated by alleles, variant forms of a gene. For example, one allele might be said to produce hazel eyes; a different allele might be said to produce blue eyes. Genes come in pairs; in our example, the daughter will always inherit one allele for eye color from their mother, and one from their father. When the two alleles code for the same feature (e.g., two alleles for blue eyes) then that trait will certainly be expressed. However, if the two alleles code for different features (e.g., one for blue eyes and one for brown eyes), then one allele, the dominant allele, will prevail over the other allele, the recessive allele. If brown eyes is the dominant allele, then a person will have brown eyes even if they are also a carrier of the blue eye allele!
Here is a visual explanation of what dominant and recessive alleles are, and how you can use them to understand some aspects of genetic inheritance. // source: Youtube, 2 minute classroom
Now let us return to our example: a daughter with blue eyes, even though both her parents have brown eyes. Given what you have just learned, can you imagine how this might be possible? The answer lies within our previous discussion of dominant and recessive alleles. Both parents might have brown eyes but be carriers for the recessive blue eye allele. If, by a small chance, both parents pass down this blue eye allele to their child, then their child will carry two blue eye alleles, and thus be born with blue eyes!
This is just one example that shows that passing down traits to your child might not be as straightforward as you thought. The whole genetic story is far more complex. Ultimately, remember that your child has half of his or her genes from the father, and half from the mother. So while your child might be half you, your child is also someone new!
Supplementary Material
Remember that genes are not the only thing you pass down to your child. Inheritance reaches far beyond biology. At this time, you are one of the most important individuals in your child’s life. Your child will come to look up to you and learn much from you, including:
- Your culture. Here is a commentary on how to keep your child in touch with your culture.
- Your health habits. From diet and exercise to smoking and drinking, see this article from familydoctor.org on how to pass healthy habits on to your children.
- Your family traditions. Do you eat a certain food on certain holidays, or take an annual vacation? See this commentary on the power of family traditions, and how they can strengthen the bonds within your family.
- Your values. What is important to you — family, career, money, happiness, friendship? What is the right thing to do? These are all parts of an individual’s identity that are built starting at a young age, and you learn much of this from your parents. Here is an opinion article by Forbes on the importance of passing values down to your children.
References
Finegold, D. Genes and Chromosomes. (n.d.). Merck Manual, Consumer Version. Retrieved from http://www.merckmanuals.com/home/fundamentals/genetics/genes-and-chromosomes.
Mayes, L. C. & Cohen, D. J. (2002). The Yale Child Study Center Guide to Understanding Your Child: Healthy Development from Birth to Adolescence. Boston: Little, Brown, and Company.
Miko, I. (2008). Genetic dominance: genotype-phenotype relationships. Nature Education, 1(1), 140.