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 Cow 60 Dog 78 Earthworm 36 Kangaroo 12 Mosquito 6 Pigeon 80 Tiger 38 Shrimp 254 Deer 70 Turkey 82 Horse 64 Hedgehog 90 Giraffe 62 Cabbage 18 Carp 104

Chromosomes Each species has a characteristic number of chromosomes

That fact allows this to happen + Pug Beagle

That fact allows this to happen = Puggle

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

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 - 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