Chromosomes and Meiosis Unit Cell Types 1) Somatic Cells (aka: body cells) - are diploid (2n) - DNA not passed on Cell Types 2) Gametes (aka: sex cells) - ex: ova (egg) and spermatozoa (sperm) - are haploid (1n) - DNA passed on Egg and Sperm Comparative Size Diploid vs. Haploid Diploid cells have two copies of each chromosome: one copy from the mother and one from the father. Haploid cells have only one copy of each chromosome Look at the following chromosome numbers of these living things. Do you notice anything about the numbers? Chromosome Numbers of Various Living Things Algae 148 Kangaroo 12 Shrimp 254 Hedgehog 90 Cow 60 Mosquito 6 Deer 70 Giraffe 62 Dog Earthworm 78 36 Pigeon Tiger 80 38 Turkey Horse 82 64 Cabbage Carp 18 104 Chromosomes Each species has a characteristic number of chromosomes That fact prevents this from happening That fact allows this to happen That fact allows this to happen That fact allows this to happen Mule = male donkey and a female horse That fact allows this to happen Liger Tigon Chromosomes (cont) Types 1) Autosomes 2) Sex Chromosomes - female = XX male = XY The sex of some species is determined by the temperature of the environment during incubation (mostly occurs in reptiles) Chromosomes (cont) Humans have 46 chromosomes (23 pairs) - 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair) - a diploid # (2n) of 46 and a haploid # (1n) of 23 Karyotype = picture of an individual’s chromosomes Homologous Chromosomes vs. Sister Chromatids Homologous Chromosomes = two separate chromosomes, one from mom and one from dad - very similar in size and carry the same genes, but they are not copies of one another Homologous Chromosomes vs. Sister Chromatids (cont) In contrast, each half of a duplicated chromosome is called a chromatid - together, the two chromatids are called sister chromatids - thus, sister chromatids refers to the duplicated chromosome that remain attached (by the centromere) Homologous Chromosomes Homologous chromosomes (shown duplicated) are two separate chromosomes – one inherited from the mother and one from the father Sister Chromatids Sister Chromatids Homologous Chromosomes vs. Sister Chromatids (cont) Homologous chromosomes split in Meiosis I Sister chromatids split in Meiosis II Meiosis = a form of nuclear division that divides a diploid cell into a haploid cell - makes egg and sperm - 2 rounds of division (Meiosis I and Meiosis II) Meiosis (cont) Meiosis I – divides homologous chromosomes Meiosis II – divides sister chromatids The overall process produces haploid cells. Meiosis I Meiosis II Gametogenesis 1) spermatogenesis = sperm production (4 haploid cells) - even distribution Spermatogenesis Gametogenesis (cont) 2) oogenesis = egg production (1 haploid cell) - uneven distribution (polar bodies created) Oogenesis Comparing Mitosis and Meiosis Mitosis - Produces genetically identical cells - Results in diploid cells - Takes place throughout an organism’s life - Involved in asexual reproduction Meiosis - Produces genetically unique cells - Results in haploid cells - Takes place only at certain time in life cycle - Involved in sexual reproduction