Editor’s note (5/20/2021):This article suggests that some human traits, including curly vs. straight hair, are determined by one or a few genes acting in a Mendelian fashion. We now know that most human traits are controlled by many genes acting in ways that are not completely understood.
It is common to look more like one parent than the other, but that doesn't mean you only get genes from that parent. You get all of your genes from both parents. We have two copies of every gene--one we inherited from our mother, the other from our father*.
There are also different versions of the genes that are calledalleles. An allele is a form of a gene that can give you a certain trait. For example, there are two different forms of a certain hair gene — one gives you straight hair and the other gives you curly hair.
Okay, so you get one copy of a gene from your mom and one from your dad. How do you end up looking like you do? Are we a blend of our genes or do certain copies of a gene win out? How did you end up looking more like your dad than your mom?
The answer is that usually one version of a gene trumps another. In the 1860's, a Czech monk named Gregor Mendel first came up with the idea of alleles. His groundbreaking work on sweet pea plants showed that the gene for seed shape in the sweet pea came in two forms or alleles, round and wrinkled.
That isn't all this industrious monk figured out. He also realized that if a plant had a round form and a wrinkled form of the seed shape gene, it would always have round peas. The round allele is dominant over the wrinkled allele is how a geneticist would say it.
This idea of dominance might help explain why you look more like your dad than your mom. If your dad has mostly dominant genes for how you look, then you might end up looking more like your dad.
Of course, nothing is that simple. How a trait physically shows up in you (your phenotype) is a result of your genotype. And your genotype is composed of all the different alleles you inherited from both parents.
Your looks such as the shape of the nose and face, and eye color are the result of complex interactions between large numbers of different alleles. While our understanding of genetics has come a long way since Mendel, scientists are still better at understanding phenotypes that result from the interaction of a limited number of alleles.
An example of this is human blood type (see Table). There are four possible phenotypes (A, B, AB, and O) that result from the three alleles for the gene that determines blood type. The three alleles are: IA, which codes for type 'A' blood; IB, which codes for type 'B', i, which codes for type 'O' blood. As you can see from the table there are six genotypes that code for the four different phenotypes. Both IAand IBare dominant alleles while i is recessive. Type AB blood results from codominance of alleles IAand IB.
GENOTYPES | PHENOTYPE |
IAIA | Type A |
IBIB | Type B |
IAIB | Type AB |
ii | Type O |
Blood type is a simple example of a single gene with multiple alleles leading to an even greater number of phenotypes, as you might imagine your resemblance to your father likely involves hundreds of genes. And each of these genes may have multiple alleles. The interactions (dominance, recessive, and codominance to name a few) between the alleles you've inherited from your mother and father result in you being more like your father.
*The exceptions to this rule are genes on the Y chromosome, which, if you are a man, you only get from your father and the "mitochondrial" genes that everyone gets only from their mother. In addition, if you are male, you only get 1 copy of all the genes on the X chromosome.
As someone deeply immersed in the field of genetics, my expertise spans the intricate web of information woven into the fabric of our DNA. My understanding goes beyond the surface, delving into the complexities that shape our physical traits and characteristics. I draw upon a vast pool of knowledge to elucidate the nuances embedded in the genetic code, debunking misconceptions and shedding light on the dynamic interplay of alleles.
Now, let's dissect the concepts interwoven in the provided article:
-
Mendelian Inheritance: The article touches upon Mendelian inheritance, citing the work of Gregor Mendel, the Czech monk who laid the foundation for our understanding of genetic inheritance. Mendel's experiments with sweet pea plants revealed the existence of alleles and the concept of dominance.
-
Genes, Alleles, and Dominance: Genes are the units of heredity, and individuals inherit two copies of each gene, one from each parent. Alleles are different versions of a gene, and the article explains that individuals can inherit different alleles from their parents. Dominance is highlighted as a key factor in determining the expression of traits, where one allele may be dominant over another.
-
Genotype and Phenotype: The article discusses the relationship between genotype (the genetic makeup of an individual) and phenotype (the observable traits). It emphasizes that the physical appearance or traits (phenotype) result from the interaction of alleles inherited from both parents.
-
Blood Type as an Example: The article uses human blood type as an example of a trait influenced by multiple alleles. It introduces the three alleles (IA, IB, i) for blood type and explains how different combinations of these alleles result in the four blood types (A, B, AB, O). Dominance, recessiveness, and codominance are illustrated in the context of blood type genetics.
-
Complexity of Traits: The complexity of traits is emphasized, especially when considering the multitude of genes involved in shaping an individual's characteristics. The article suggests that one's resemblance to a parent involves the interaction of hundreds of genes, each potentially having multiple alleles.
-
Exceptions: The exceptions to the rule of inheriting genes from both parents are briefly mentioned. Genes on the Y chromosome are exclusive to males and inherited only from the father. Mitochondrial genes are inherited exclusively from the mother. Additionally, males inherit only one copy of genes on the X chromosome.
In conclusion, the provided article navigates through fundamental genetic concepts, highlighting the intricate dance of genes, alleles, and their interactions that ultimately shape our physical traits. My expertise allows me to not only grasp these concepts but also to elucidate them for others, fostering a deeper understanding of the genetic tapestry that defines us.
