Journal Entry: 5/10 Write a sentence to describe each of the following terms: heredity, genotype, and phenotype. Is heredity necessarily a factor in both genotype and phenotype? Why or why not? Objectives: Explain the difference between mitosis and meiosis. Describe how chromosomes determine sex.

Asexual Reproduction Asexual reproduction Only one parent cell is needed. The structures inside the cell are copied, and then the parent cell divides, making two exact copies. This type of cell reproduction is called mitosis. Most of the cells in your body and most single-celled organisms reproduce this way.

Cell Cycle Interphase Mitosis G1 S G2 Prophase Metaphase Anaphase Telophase

Mitosis

Sexual Reproduction In sexual reproduction, two parent cells (sex cells) join together to form offspring that are different from both parents.

Chromosomes Chromosomes: Structure consisting of DNA that transmits genetic information from the previous generation of cells and organisms to the next generation. Chromosomes that carry the same sets of genes are called homologous chromosomes.

Sexual Reproduction, Continued Body Cells Human body cells have 46 chromosomes or 23 homologous chromosome pairs. Human body cells are referred to as somatic cells. Examples: Liver cells, heart cells Sex cells Sex cells have only one of the chromosomes from the homologous pair (total of 23 chromosomes per cell) Sex cells are made during meiosis. Sex cells are referred to as gametes. Examples: Sperm and Egg

Sexual Reproduction, Continued Genes and Chromosomes Walter Sutton studied meiosis in sperm cells in grasshoppers. Using his observations and his knowledge of Mendel’s work, Sutton proposed that: Genes are located on chromosomes.

Meiosis Meiosis is a copying process that produces sex cells (sperm and egg) with half the usual number of chromosomes. Why? When the sperm (23 chromosomes) combines with the egg (23 chromosomes) it produces a cell with 46 chromosomes.

DO NOW: 5/9 What do you think would happen if something went wrong during cell division and the sperm or egg cell ended up with either too few or too many chromosomes? Objectives: Explain why sex-linked disorders occur in one sex more often than in the other. Interpret a pedigree.

The Steps of Meiosis During meiosis, chromosomes are copied once, and then the nucleus divides twice. The resulting sex cells (sperm and eggs) have half the number of chromosomes of a normal body cell.

Mitosis vs. Meiosis

Meiosis and Mendel The steps of meiosis explain Mendel’s results. The following slide shows what happens to a pair of homologous chromosomes during meiosis and fertilization.

Meiosis and Mendel, Continued Sex chromosomes carry genes that determine sex. Human females have two X chromosomes. Human males have one X chromosome and one Y chromosome.

Meiosis and Mendel, Continued Sex-Linked Disorders The genes for certain genetic disorders, such as colorblindness, are carried on the X chromosome. Since the gene for these disorders is recessive, men are more likely to acquire the genetic disorder.

Meiosis and Mendel, Continued Genetic Counseling Genetic counselors use pedigrees to trace traits through generations of a family. These diagrams can often predict if a person is a carrier of a hereditary disease. Selective Breeding In selective breeding, organisms with desirable characteristics are mated.