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Aim: How do organisms create offspring through sexual reproduction? Aim 2: How are the Chromosomes Described in Meiosis? 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? Karyotype We have 46 chromosomes in each of our body cells. We can also say that we have 23 pairs of chromosomes Why do we have 2 of each chromosome? We get one chromosome from each parent Each pair of chromosomes are called: Homologous Chromosomes Homologous Chromosomes: Mom Eye Color Dad B G Hair Color B R Allele 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 How are chromatids different than homologous chromosomes? chromatid Chromatids are exact duplicates of each other chromatid Homologous chromosomes have genes that code for the same trait, but they may code for different versions of that trait Chromatid vs. Chromosome When 2 DNA molecules are joined together, each is called a chromatid. Together they are a called a duplicated chromosome. When DNA is not attached to another one then that single molecule of DNA is called an unduplicated chromosome (not a chromatid). How many chromosomes do the offspring have after mitosis? 46X Mitosis 46X 46X Daughter cells have the same number of chromosomes as the original parent cell. 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 Sexual Reproduction: 23 23 + Egg 46 Offspring A fertilized egg cell is called a Sperm Zygote Characteristics of Sexual Reproduction: • Creation of a new individual from 2 parents. • Offspring are not genetically identical to the parents. Sex Cells (Gametes) • Sex Cells are: 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) Diploid vs Haploid Movie Clips Each 1 min. Meiosis The process by which haploid (sex) cells are produced with half the number of chromosomes. What is the end result of meiosis? 46X Meiosis 23X 23X 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 • Only during fertilization (union of sperm and egg) is the full (diploid) set of chromosomes restored. Practice Problems: