Centuries ago, a monk named Gregor Mendel started mixing different pea plants together. He made fascinating discoveries about how traits are passed from parent to offspring. This science is called genetics, and it's all about studying genes—parts of our DNA that make us who we are!
Every gene has two versions, called alleles. An allele can be either dominant or recessive. Dominant alleles mask the recessive ones. For example, B (dominant) is the brown eye allele and b (recessive) is the blue eye allele. If one parent has blue eyes (bb) and the other has brown eyes (Bb), their offspring can end up with four different combinations. Here’s what each combo means:
We can use a diagram called a Punnett square to figure out the chances of each trait. In our example:
Why do some alleles dominate while others hide? Scientists think "working" alleles are dominant, and ""broken"" alleles are recessive. For instance, a gene called MC1R helps get rid of red pigment. If it’s broken, red pigment builds up, giving red hair, a recessive trait.
Genes are bundled up in structures called chromosomes. We have 23 pairs of chromosomes (46 in total) in every cell of our body.
Scientists use a technique called karyotyping to look at our chromosomes. They use special dyes to locate the chromosomes. Karyotyping helps check if all chromosomes are in pairs and if there are abnormalities like extra or missing pairs. For example, scientists can use karyotypes to detect Down Syndrome, a condition that happens when there’s an extra copy of chromosome 21.
Isn't genetics cool? It helps us understand why we look like our parents and why every person is unique!
A pedigree is a diagram that shows how traits are inherited across a family. In this pedigree, the family carries Fanconi Anemi. This defect results in slowed growth, heart defects, and bone marrow failure. This is a recessive trait so individuals affected by it must carry two recessive alleles. Use your knowledge of genetics to identify the genotype of Arlene and Ann.
Arlene: To express a recessive allele, an individual must have 2 copies of it. Genotype: ff. Anne: Anne inherits one recessive allele from Arlene (f). But she doesn’t express the recessive trait. She must carry one dominant allele that masks it. Genotype: Ff