General Genetic Information

Q: How do we inherit characteristics from our parents?

A: Through genes.

A: Genes are located on chromosomes, and are made of sections of DNA. Here is a picture showing a gene as a piece of DNA on a chromosome. Genes code for different things. Some are very observable in everyday life, such as eye color, hair color, and personality traits. Some things are not as observable, but affect our lives everyday nevertheless. These involve mechanisms going on in our bodies all the time. Humans have about 25,000 to 30,000 genes.

A: Our chromosomes are found in all nuclei in the center of all cells in our bodies. Here is a drawing of a cell with chromosomes inside. Humans have 46 chromosomes, and they typically come in pairs, so humans have 23 pairs of chromosomes. In order to look at all the chromosomes in an organism, a karyotype can be made. This just means that the all the pairs of chromosomes are lined up and numbered according to size. Here is what a normal human karyotype might look like for a male. What is the difference between a male’s karyotype and one for a female? Well, as you can see, each pair of chromosomes are identical except for X and Y at the bottom right corner. These are male sex chromosomes.

A: Two of the 46 chromosomes are sex chromosomes. While some genes come from your father and some from your mother, everyone typically inherits one sex chromosome from each parent. Men have one smaller Y chromosome and one larger X chromosome. (These are in the picture above.) Women have two equal-sized X chromosomes. (A karyotype for a woman would have two X chromosomes in the bottom right corner instead of an X and a Y.) Genetically speaking, for humans, having a Y chromosome means the child will be male.

A: Genetic disorders ensue. These are conditions or disorders that are the result of an absent or otherwise defective gene or chromosomal alteration. There are many, many genetic disorders. Lesch-Nyhan Syndrome (LNS) is a sex-linked genetic disorder; specifically an X-linked recessive disorder.

A:  These result from a defective gene on an X chromosome. LNS is a recessive disorder, which means it is a syndrome inherited due to a defective gene on only one of the X chromosomes.

A: 
Females: Since women have two X chromosomes, inheriting one defective X chromosome will mean the female is a “carrier.” Inheriting two X chromosomes (one from each parent) will result in the inheritance of the disorder only when the disorder is dominant (instead of recessive).

Males: Since men only have one X chromosome, inheriting one defective X chromosome will mean the man has inherited the disorder.