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AIM: What is the difference between the chromosome number in our body cells and gametes? DN: What are gametes? How many chromosomes are in the gametes of humans? What is Sexual Reproduction? It involves the joining of two cells to begin the development of a new individual. These special cells are called: Sex Cells (Gametes) What are the names of these sex cells? Egg cell (Female) Sperm Cell (Male) The joining of a sperm cell with an egg cell is called fertilization. How many chromosomes do we have in our cells? • 46 chromosomes OR • 23 pairs of chromosomes Karyotype Why do we have 2 of each chromosome? One from mom and one from dad Each pair of chromosomes are called: Homologous Chromosomes Homologous Chromosomes: Mom Eye Color B Dad G Hair Color B R Gene Part of a chromosome that codes for a trait Have genes that code for the same trait, but may have different versions of that trait Chromatids •are exact copies of each other •Used during cell division Homologous chromosomes •A pair of chromosomes that contain genes for the same trait • can have different versions of that trait •One copy from each parent How many chromosomes do the offspring have after mitosis? 46X Mitosis 46X 46X Same amount as the parent cell Humans = 46 Do our sex cells have 46 chromosomes? NO!!! What would happen if our sex cells did have 46 chromosomes? 46 + 46 Egg 92 Offspring Sperm The offspring would have 92 chromosomes 1. Egg- 23 chromosomes A: Sexual Reproduction B: Egg Cell/23 chromosomes 2. Sperm- 23 chromosomes C: Zygote/46 chromosomes 3. Fertilization- Zygote formed with 46 chromosomes Sexual Reproduction: 23 + 23 Egg Sperm 46 Offspring Characteris A fertilized egg cell is called a Zygote The zygote has 46 chromosomes 1) Is the creation of a new individual from 2 parents. 2) Offspring are not genetically identical to the parents. Sex Cells (Gametes) • Sex Cells: SPERM and EGG • Sex cells should have 1/2 the normal number of chromosomes Chromosome Number • Diploid cells: (2n) normal number of chromosomes (Body Cells) • Haploid cells: (n) ½ the normal number of chromosomes (Sex Cells) Meiosis •The process by which sex cells are produced with half the number of chromosomes. Meiosis is 2 Cell Divisions 1st Cell Division 2nd Cell Division 1 Diploid cell 4 Haploid Cells What is the end result of meiosis? 46X Meiosis 23X 23X 4 cells with ½ the number of chromosomes 23X 23X Where does meiosis occur? Gonads – Ovaries and Testis Why is meiosis important? • Maintains the number of chromosomes from generation to generation • Provides genetic variation • . Gametogenesis Gameto = gametes Genesis = creation Production of gametes (sperm & egg) By meiotic cell division Oogenesis Creation of an ovum or egg cell by meiotic cell division in the ovary. How many eggs are produced? •There is an unequal sharing of cytoplasm •1 egg & 3 non functional polar bodies Egg vs. Polar Bodies The egg is very large, has most of the cytoplasm, which will provide nutrients for the offspring. Spermatogenesis Creation of sperm cells by meiotic cell division in the testes. How many sperm are produced by spermatogenesis? 4 equal sized sperms with flagella for swimming. Spermatogenesis vs. Oogenesis Practice Problems: