In the process of Inheritance, genetic information passes on from parents to a child. This the reason that members of one family are tending to have quite similar characteristics.
We, humans, have two genomes each. Each of these two genomes contains all the information that’s needed to build up that organism and to allow it to develop and grow.
Each of our genomes is about 3 billion base pairs in length that are packaged in 23 chromosomes pairs. From each one of our parents, we receive 1 copy of our genome. Inheritance is describing how our genetic material is being passed on from a parent to a child.
How do we inherit genetic material? Most of the human cells contain 2 sets of 23 chromosomes (chromosomes are diploid). Chromosomes are threadlike structures in our cells, consisting of long DNA molecules, wrapped around protein scaffolds. We, humans, have 23 chromosomes pairs. Other organisms have chromosomes as well.
Exceptions to this rule are our sex cells (eggs, sperm), also named gametes. These cells have each only 1 set of chromosomes (they are haploid).
Gametes are female or male reproductive cells that contain only half the genetic information for organisms. In humans, our gametes are sperm and egg cells.
In sexual reproduction, however, sperm cells combine with the egg cells and form the first cells of new organisms in a process we call fertilization.
These cells (the fertilized eggs) have 2 sets of 23 chromosomes (now they are diploid) and so a complete set of genetic instructions needed for making more human cells and, eventually, a whole human being.
All cells in this new person contain genetic material coming from both parents.
This genetic material passing down becomes evident when you examine the characteristics and traits of the same family members, from the average height to eye and hair color to ear and nose shape. These are usually similar.
When there are mutations in the human genetic material, these can be passed on from parents to their children as well.
Mutations are changes occurring in DNA sequences. Mutations in our DNA are relatively common but usually don’t have a detectable effect.
This the reason that a disease can run in the family.
How about sex determination?
Our sex chromosomes determine the sex of individuals. These are called the X chromosome and the Y chromosome.
Females have 2 X chromosomes (XX).
Males have 1 X chromosome and 1 Y chromosome (XY).
A female gamete (egg) therefore, always carries an X chromosome.
A male gamete (sperm) carries either an X or a Y chromosome.
When a female egg is joined with a male sperm that contains an X chromosome, the result will be a girl. When a female egg is joined with a male sperm that contains a Y chromosome, the result will be a boy.
Next lesson: Patterns of Inheritance
Last Updated on April 7, 2021.