chromosomes and meiosis. recall, dna on each chromatid is sectioned into many segments called genes:...
TRANSCRIPT
![Page 1: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/1.jpg)
Chromosomes and Meiosis
![Page 2: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/2.jpg)
Recall,
• DNA on each chromatid is
Sectioned into many segments called
• Genes: govern the expression of a particular trait
![Page 3: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/3.jpg)
Diversity of chromosomes among organisms
• The number and length of chromosomes differ among organisms
• There is no relationship between size of an organism and number of chromosomes
![Page 4: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/4.jpg)
Numbers of Pairs of Chromosomes in Some Plant and Animal Species
Common name Species # chrom. Pairs
Mosquito Culex pipiens 3
Housefly Musca domestica 6
Toad Bufo americanus 11
Rice Oryza sativa 12
Frog Rana pipiens 13
Alligator Alligator mississippienis 16
Rhesus monkey Macaca mulatta 21
Wheat Triticum aestivum 21
Human Homo sapiens 23
Potato Solanum tuberosum 24
Donkey Equus asinus 31
Horse Equus caballus 32
Dog Canis famliaris 39
Carp Cyprinus carpio 52
![Page 5: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/5.jpg)
Most animal species contain two types of cells:
• 1. Somatic/Body Cells– Contain two sets of chromosomes written as
2n (called diploid cells)
• 2. Gamete/Sex Cells– Contain one set of chromosomes written as n
(called haploid cells)
![Page 6: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/6.jpg)
• (I.e. Humans)
– Somatic Cells = 2n (46 chromosomes)– Sperm/egg Cells = n (23 Chromosomes)
![Page 7: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/7.jpg)
Humans have 46 chromosomes or 23 pairs of chromosomes [ 2(23) ]
• 22 pairs = autosome chromosomes– not involved in sex
determination
• 1 pair = sex chromosomes– responsible for sex
determination
![Page 8: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/8.jpg)
Why do we need meiosis?
• If all cells including sex cells/gametes were diploid (2n) then….
2n (male) 2n (female)
4n (offspring) ?
![Page 9: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/9.jpg)
Meiosis:
• Occurs in reproductive organs
• Produces gametes (haploid cells) to maintain the diploid number in offspring
• Involves 2 sequences of phases– each similar to mitosis– Called meiosis I and meiosis II
![Page 10: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/10.jpg)
Meiosis I:
• DNA replication
– (Same as mitosis)
![Page 11: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/11.jpg)
• Homologous chromosomes – Identical in size and
appearance– Corresponding genes may
differ in form
• One chromosome comes from the female gamete and one from the male gamete
![Page 12: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/12.jpg)
• Homologous chromosomes pair to form homologous pairs– All 4 chromatids are
called a Tetrad
![Page 13: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/13.jpg)
• One spindle from one pole attaches to one chromosome
• One spindle from the other pole attaches to the other
• Tetrads are pulled to the equator of the cell– Not in single file
![Page 14: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/14.jpg)
• Homologous chromosomes separate and move to opposite poles of the cell– Centromere does not
split – holds sister chromatids together
![Page 15: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/15.jpg)
• The chromosomes gather into nuclei, and the original cell divides
![Page 16: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/16.jpg)
• Brief interphase:– No DNA replication
![Page 17: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/17.jpg)
Results of Meiosis I:
• Reduction division– Chromosome number is reduced by half
• 2n n
• Each daugher cell going into Meiosis II is haploid (n)
![Page 18: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/18.jpg)
Meiosis II
• (same as mitosis)
(see notes from last class)
![Page 19: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/19.jpg)
• Same as mitosis
![Page 20: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/20.jpg)
• Same as mitosis
![Page 21: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/21.jpg)
• Same as mitosis
![Page 22: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/22.jpg)
RESULT FROM MEIOSIS II:
• 4 Haploid daughter cells
• Containing single unreplicated chromosomes
• Gamete cells (n)
![Page 23: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/23.jpg)
P.162
![Page 24: Chromosomes and Meiosis. Recall, DNA on each chromatid is Sectioned into many segments called Genes: govern the expression of a particular trait](https://reader035.vdocuments.net/reader035/viewer/2022062801/56649e745503460f94b74fe4/html5/thumbnails/24.jpg)
Recap:
2n 2(23) = 46 chromosomes
Meiosis I n (23) = 23
chromosomes (each with 2 sister
chromatids)
Meiosis II n (23) = 23 single
chromosomes