2 Chromosome Number of Different Species Homo sapiens (human)46Mus musculus (house mouse)40Zea mays(corn or maize)20Drosophila melanogaster (fruit fly)8Xenopus laevis (South African clawed frog)36Caenorhabditis elegans (microscopic roundworm)12Saccharomyces cerevisiae (budding yeast)32Canis familiaris (domestic dog)78Arabidopsis thaliana (plant in the mustard family)10Muntiacus reevesi (the Chinese muntjac, a deer)Muntiacus muntjac (its Indian cousin)6Myrmecia pilosula (an ant)2Parascaris equorum var. univalens (parasitic roundworm)Cambarus clarkii (a crayfish)200Equisetum arvense (field horsetail, a plant)216
3 Chromosome Vocabulary DNADoubles during interphase (S phase)ChromosomeForms during prophaseBecome sister chromatids
4 Homologous Chromosomes: Members of a pair of chromosomesOne – MomOne – DadSame sizeSame shape (centromere location)Same number and type of genes
5 Homologous Chromosomes: Specific gene information may differ(brown eyes from mom, blue eyes from dad)
6 Homologous Chromosomes: Same banding pattern when stained and viewed under a microscope.Bands DO NOT indicate genes.
7 Types of Chromosomes:Humans have 23 pairs of chromosomes.
8 Types of Chromosomes: 2 Types: Autosomes: Members of chromosome pairs #1-22.
9 Types of Chromosomes: 2 Types: Sex Chromosomes: Members of chromosome pair #23Females = XXMales = XY
10 Sex ChromosomesALL pairs are homologous in females because they have two X chromosomesThe sex chromosomes of males are NOT homologous, they have one X and one Y
11 Diploid vs. Haploid Diploid: two sets of chromosomes Each chromosome has a homologous pair– there is one from each parent!They have the same type of genes but are not identicalHuman body cells:23 PAIRS 46 total
12 Diploid vs. Haploid Haploid: one set of chromosomes Why would you want just one set of chromosomes in a cell?SEXUAL REPRODUCTION!Human gametes: 23 total
13 Why do we need meiosis?Meiosis is necessary to halve the number of chromosomes going into the sex cellsGametes are haploid (1n)+1 N sperm1 N egg2N zygote
14 Why do we need meiosis? + Fertilization Male and female sex cells will provide ½ of the chromosomes eachOffspring has genes from both parents1n + 1n = 2n+1 N sperm1 N egg2N zygote
16 Meiosis Summary Two divisions - Meiosis 1: - like mitosis, but not quite- creates 2 cells (haploid)- Meiosis 2:- divides again- creates 4 gametes (haploid)
17 Meiosis Summary Parent cell – chromosome pair Chromosomes copied 1st division - pairs split2nd division – produces 4 gamete cells with ½ the original # of chromosomes
18 Meiosis I – Prophase INuclear envelope dissolves
19 Meiosis I – Prophase I Tetrads form Crossing Over Homologous pair links togetherCrossing Over
20 Crossing Over in Prophase I Homologues break at identical locations,Rejoin opposite partnersOccurs randomly several times on every chromosomeResults in mixing of the genes you inherited from your parentsCrossing over is NOT a mutation
21 Meiosis I – Metaphase I Tetrads line up in middle Spindle fibers attachIndependent Assortment
22 Independent Assortment Metaphase I Principle of Independent Assortment—Genes for different traits (on differentchromosomes) can separate independently of each other.--Happens because homologous pairs line up in random order on random sidesduring Metaphase I
23 Meiosis I – Anaphase I Fibers pull homologous chromosomes apart Sister chromatids are still connected!(2 X’s are separating from each other)
24 Meiosis I – Telophase I Cell separated into two cells Nuclear membrane forms
25 Meiosis II – Prophase II Nuclear membranes dissolveNew spindle fibers form
26 Meiosis II – Metaphase II Sister chromatids connect to spindle fibersLine up in the middle
27 Meiosis II – Anaphase II Sister chromatids separate
28 Meiosis II – Telophase II Cells divideNow there are 4 haploid cells!