Genes are the units of chromosomes that code for heritable traits and occur in pairs in normal body cells or singly in sex cells, such as the sperm and egg.
By crossing purple and white pea plants, Mendel conceived the idea of heredity units, which he called “factors”. Mendel said that factors or genes normally occur in pairs in ordinary body cells, yet segregate during the formation of sex cells. Genes are the section of chromosomes that determine specific characteristics by coding specific proteins.
Genes can be passed on from a parent to offspring via sex cells of sperm and egg. These are haploid cells and only carry 23 chromosomes whereas normal cells are diploid and contain 46 chromosomes. The pairing of parent chromosomes during fertilization means that a nucleus contains two genes for each feature known as alleles. One from the mother one from the father.
Practice Questions
Khan Academy
Key Points
• Genes or “factors” are heredity units that occur in pairs in normal body cells yet segregate during the formation of sex cells.
• Genes, the functional units of chromosomes, determine specific characteristics by coding specific proteins.
Key Terms
gene: a unit of heredity which is transferred from a parent to offspring and is held to determine some characteristic of the offspring
chromosome: a threadlike structure of nucleic acids and protein carrying genetic information in the form of genes
diploid: a nucleus containing two complete sets of chromosomes, one from each parent
haploid: a nucleus containing one set of chromosomes, 23.
allele: one of several alternative forms of the same gene occupying a given position on a chromosome
fertilization: the joining of sperm and egg to form an embryo with 46 chromosomes.
