This article is a non-technical introduction to the subject. For the main encyclopedia article, see Genetics. A long introduction to human genetics pdf that looks like a twisted ladder.
It is made of four types of simple units and the sequence of these units carries information, just as the sequence of letters carries information on a page. They form the rungs of the DNA ladder and are the repeating units in DNA. A package for carrying DNA in the cells. They contain a single long piece of DNA that is wound up and bunched together into a compact structure.
Different species of plants and animals have different numbers and sizes of chromosomes. Genes are like sentences made of the “letters” of the nucleotide alphabet, between them genes direct the physical development and behavior of an organism.
Genes are like a recipe or instruction book, providing information that an organism needs so it can build or do something – like making an eye or a leg, or repairing a wound. The different forms of a given gene that an organism may possess.
For example, in humans, one allele of the eye-color gene produces green eyes and another allele of the eye-color gene produces brown eyes. The complete set of genes in a particular organism. When people change an organism by adding new genes, or deleting genes from its genome. An event that changes the sequence of the DNA in a gene.
Genetics is the study of genes—what they are, what they do, and how they work. For example, offspring produced by sexual reproduction usually look similar to each of their parents because they have inherited some of each of their parents’ genes. Genetics identifies which features are inherited, and explains how these features pass from generation to generation.
Some phenotypic traits can be seen, such as eye color while others can only be detected, such as blood type or intelligence. Another example is a person’s height: it is determined by both genetics and nutrition.
Chromosomes are tiny packages which contain one DNA molecule and its associated proteins. This number varies between species—for example, many primates have 24 pairs. Meiosis creates special cells, sperm in males and eggs in females, which only have 23 chromosomes. These two cells merge into one during the fertilization stage of sexual reproduction, creating a zygote.
In a zygote, a nucleic acid double helix divides, with each single helix occupying one of the daughter cells, resulting in half the normal number of genes. By the time the zygote divides again, genetic recombination has created a new embryo with 23 pairs of chromosomes, half from each parent.