Y-chromosome traits occur only in males. Female offspring do not develop any Y-chromosome-related diseases, nor can they pass them to their offspring. Y-chromosome disorders include hypertrichosis (hairiness of the ears) and XYY syndrome, manifesting as increased height, severe cystic acne in adolescence, behavioral problems, and learning disabilities. Fortunately, Y-related disorders are rare because there are so few genes on the Y chromosome and they do not pass to females, even as carriers.

Incomplete and codominant genes are similar but not the same. An incomplete pairing of genes dilutes the dominant gene, allowing the recessive gene to play a part, too. Height is one example of incomplete allele pairing. When one parent is tall and the other is short, resulting children are usually anywhere in the range between the two parents’ heights. Other incomplete-gene traits include eye color, hand size, skin color, and voice pitch.

When codominance occurs, two alleles are expressed together, rather than there being a gene-driven decision of one or the other. One obvious example of codominance is blood type. The blood type AB is the result when one parent has type A and the other has type B. Hair texture is another example of codominant genes. Even though curly hair is considered dominant, when a curly haired gene matches with a straight one, the result is a pleasant wavy coexistence of both.

The explosion of information about genetics has given rise to a needed specialty: genetic counseling. One might wish to see a genetic counselor for many reasons. Couples considering having children may consult a genetic counselor to learn what awaits when one set of chromosomes meets the other. A genetic counselor can also use a patient’s medical and family history to suggest tests, help make diagnoses, or answer questions about their own risk of developing an inherited disorder.

Being informed can allow a person to take steps to lessen the effects of a disease or at least better plan for the eventuality of developing it. Thanks to giant steps in the field of genetics, a genetic counselor can answer questions, educate, and assess an individual’s risk, as well as provide guidance and support regarding the conditions individuals have in their DNA. For example, many women with a family history of genetic breast cancer consult a genetic counselor if considering a preventative mastectomy and/or hysterectomy.

“Most people do not know what exactly goes on at a genetics clinic until they are in need of services,” says Lori Bassett, MS, CGC, director of communication at the Greenwood Genetic Center and a board-certified genetic counselor. “At the Greenwood Genetic Center’s office in Columbia, patients might be referred because of a family history of a genetic disorder or if they have a child who has health or developmental challenges that could be genetic, such as developmental delay, autism, or a birth defect. Clinical geneticists (MDs) and genetic counselors work with patients and their families to identify the cause of a disorder, order genetic testing to confirm the diagnosis, and educate them about the disorder and the chances for it to happen again. They also manage treatment for genetic conditions and support families though all sorts of decision making about genetic testing, treatments, and planning for future children.”

It is astounding to think how far the field of genetics has come since the days when Gregor was quietly nursing his pea plants. He studied only seven traits. Today, we know that genes number between 20,000 to 25,000, with more being discovered all the time. Science teaches so much about the many characteristics that make humans unique — that determine whether we will write with our left hand or our right, if we are short or tall, athletically gifted or not so much, or whether we are brunette or blonde or red-headed or somewhere in between … or whether we have hair at all. It is our genes that determine the shapes we can roll with our tongues, whether we can lift one eyebrow, and they decide if we like cilantro. Genetics, without question, make an enormous impact on our lives.