Heredity
HEREDITY
Heredity is the passing of traits/ characteristics from parent to offspring.
THE CELL
The cell contains a nucleus. The nucleus contains chromosomes.
CHROMOSOMES
Chromosomes are long and thin. They come in pairs called homologous pairs. They twist around each other. The chromosomes contain genes. The genes are made up of Deoxyribonucleic Acid (DNA). Each chromosome has a centromere which separates the chromosome into two parts called ‘arms’. The ‘p’ arm is the shorter arm and the ‘q’ arm is the longer arm.
Males have 22 pairs of XX chromosomes and 1 pair of XY chromosomes (a total of 46 chromosomes in each cell). Females have 23 pairs of XX chromosomes (a total of 46 chromosomes in each cell). The male chromosomes determine the sex of the child.
GENES
Genes contain the information that is passed on from parent to offspring. Genes are made up of DNA. Each parent passes on one form of each gene to the offspring.
GENES ARE ON THE CHROMOSOMES. CHROMOSOMES ARE IN THE NUCLEUS. THE NUCLEUS IS IN THE CELL.
CELL DIVISION
Cells divide in two ways: (1) MITOSIS and (2) MEIOSIS.
MITOSIS
This is a form of cell division that makes identical cells. This type of cell division is for GROWTH. Mitosis takes place in all the body cells (except the sperm and egg). Human cells each have 46 chromosomes. They are called diploid cells.
STEPS IN MITOSIS
First each chromosome makes a copy of itself. Then the nucleus divides into two. The whole cell then divides into two cells. Each cell is exactly like the parent cell. Each cell has the same number of chromosomes as the parent cell. Each cell has the same genes as the parent cell.
MEIOSIS
This is a form of cell division that halves the number of chromosomes in the cell. Meiosis takes place only in the SPERM AND EGG which each only have 23 chromosomes. This is half of what the other body cells have. The sperm and egg are called haploid cells.
STEPS IN MEIOSIS
First each chromosome makes a copy of itself. Then the nucleus divides into two. The whole cell then divides into two cells. Each new cell then divides again into two cells. Each resulting cell has half the number of chromosomes as the parent cell.