Introduction in Genetics
The scientific study of heredity is called genetics. Modern genetics is based on the knowledge that traits are transmitted by means of chromosomes, rod-shaped structures within the nucleus of a cell. Offspring resemble parents because the chromosomes in sperm cells and egg cells contain units of hereditary information. These units are called genes. As an individual formed by a sperm cell and an egg, a cell grows into an adult, the genes influence its development. The genes cause it to resemble the parents who supplied the chromosomes.
The similarities are common biological characteristics or traits of the human species. Each species has its own traits. Heredity is passing of traits from parents to their young - the offspring. Genetics is the study of how traits are passed on and expressed in an organism.
To understand genetics, you must think about cells. Human skin cells, brain cells, and all the body cells have one thing in common. They all have 23 pairs of chromosomes (Fig. 2.3).
Chromosomes [soma, body]: one of the bodies in the cell nucleus containing genes in a linear order; visualized as threads or rods of chromatin, which appear in a contracted form during mitosis and meiosis. They are found within the nuclei of your cells and are made of DNA and many proteins. Chromosomes are visible when a cell is reproducing. All species have a certain number of chromosomes in their body cells. Cattle, for example, have 30 pairs of chromosomes in their body cells. Garden peas have 7 pairs (Table 2.1).
Included in the chromosomes are genes, which are sections of DNA. Genes carry coded instructions. Genes carry information for assembling the molecules that make up an organism’s body.
Long before people understood the basis of heredity, they bred animals and plants for certain desirable traits. Many breeds of dogs were developed during the middle Ages. In the 1800s biologists began to study heredity through scientific experiments. Discoveries made by one of these biologists, Gregor Mendel, became the basis of modern genetics.
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