mitosis & meiosis lesson 3
DESCRIPTION
TRANSCRIPT
![Page 1: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/1.jpg)
![Page 2: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/2.jpg)
Cells in living things do not last forever, for they…
• Wear out after some time• Get damaged (through cuts, by ultraviolet
radiation or by hazardous environmental pollutants)
• Grow old naturally and die
![Page 3: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/3.jpg)
Importance of new cells produced are genetically identical to their parent cells:
• Continue with the specific cell functions of their parent cells within a particular tissue
• Avoid disrupting the stable internal environment of life or its processes
• Produce offspring that have the complete functions of an adult organism (in asexual reproduction) to ensure the survival of that species
![Page 4: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/4.jpg)
Significance of mitosis
• Nucleus contains chromosomes.• Each chromosome consists of a long DNA
molecule which carries genes in a linear sequence
• Gene determines the individual characteristics of an organism
![Page 5: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/5.jpg)
Significance of mitosis
• The characteristic number of chromosomes is referred to as the chromosomal number of the species
• Exp: Onion cell – 16 chromosomes• Exp: Fruit fly - 8 chromosomes
![Page 6: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/6.jpg)
Human genetics = 46 chromosome (2n)23 pairs of chromosome
![Page 7: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/7.jpg)
Significance of mitosis
• Somatic cells have two sets of chromosomes, one set inherited from each parent.
• Each cell contains a diploid number of chromosomes (2n)
• In humans, each set consist of 23 chromosomes.
• Typical human somatic cell, 46 chromosomes arranged in 23 pairs or 2n = 46
![Page 8: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/8.jpg)
Significance of mitosis• The two
chromosomes in each pair have the same structural features and are referred to as homologous chromosomes
![Page 9: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/9.jpg)
Significance of mitosis
• Gametes contain only one set of unpaired chromosomes, or haploid number of chromosomes (n)
![Page 10: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/10.jpg)
Cell Cycle
![Page 11: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/11.jpg)
Uncontrolled Mitosis in Living Things
• Cancer• Cancerous cell - tumour
![Page 12: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/12.jpg)
Application of mitosis
• Cloning
![Page 13: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/13.jpg)
Application of mitosis
Tissue culture
![Page 14: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/14.jpg)
![Page 15: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/15.jpg)
MEIOSIS
![Page 16: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/16.jpg)
Human genetics = 46 chromosome (2n)23 pairs of chromosome
![Page 17: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/17.jpg)
![Page 18: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/18.jpg)
Stages of Meiosis
• Meiosis I– Prophase I– Metaphase I– Anaphase I– Telophase I
• Meiosis II– Prophase II– Metaphase II– Anaphase II– Telophase II
![Page 19: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/19.jpg)
Prophase I
• The homologous chromosomes come together to form bivalents through synapsis process
![Page 20: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/20.jpg)
Prophase I
• Each bivalent is visible under the microscope as a four-part structure called a tetrad
![Page 21: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/21.jpg)
Prophase I
• A tetrad consists of two homologous chromosomes, each made up of two sister chromatids
![Page 22: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/22.jpg)
Prophase I
• Non-sister chromatids exchange segments of DNA in a process known as crossing over. This results a new combination of genes on a chromosome
![Page 23: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/23.jpg)
Prophase I
• The points a at which segments of chromatids cross over are called chiasmata.
![Page 24: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/24.jpg)
![Page 25: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/25.jpg)
Metaphase I
• Chromosomes are lined up side by side as tetrads on the metaphase plate. The chromosomes are still in homologous pairs
![Page 26: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/26.jpg)
Metaphase I
• One chromosome of each pair is attached to the spindle fibre from one pole while its homologue is attached to the fibre from the opposite pole
![Page 27: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/27.jpg)
Metaphase I
• The centromere does not divide
![Page 28: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/28.jpg)
![Page 29: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/29.jpg)
Anaphase I
• The spindle fibres pull the homologous chromosomes away from one another and move them to the opposite poles of the cell. Each chromosome still consist of two sister chromatids which move as a single unit.
![Page 30: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/30.jpg)
Anaphase I
• Although the cell started with four chromosomes, only two chromosomes (each with two sister chromatids) move towards each pole.
![Page 31: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/31.jpg)
![Page 32: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/32.jpg)
Telophase I
• The chromosomes arrive at the poles. Each pole now has a haploid nucleus because it contains only one set of chromosomes
![Page 33: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/33.jpg)
Telophase I
• The spindle fibres disappear. The nuclear membrane reappears to surround each set of chromosomes. The nucleolus then reappears in each nucleus
![Page 34: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/34.jpg)
![Page 35: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/35.jpg)
Prophase II
• The nuclear membranes of the daughter cells disintegrate again. The spindle fibres re-form in each daughter cell
![Page 36: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/36.jpg)
![Page 37: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/37.jpg)
Metaphase II
• The chromosomes, each still made up of sister chromatids, are positioned randomly on the metaphase plate with the sister chromatids of each chromosome pointing towards the opposite poles.
![Page 38: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/38.jpg)
Metaphase II
• Each sister chromatid is attached to the spindle fibres at the centromere
![Page 39: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/39.jpg)
![Page 40: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/40.jpg)
Anaphase II
• The centromeres of the sister chromatids finally separate, and the sister chromatids of each chromosome are now individual chromosomes.
• The chromosomes move towards the opposite poles of the cell.
![Page 41: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/41.jpg)
![Page 42: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/42.jpg)
Telophase II
• Finally, the nucleoli and nuclear membranes re-form. The spindle fibres break down.
• Cytokinesis follows and four haploid daughter cells are formed, each containing half the number of chromosomes and is genetically different from the parent diploid cell.
![Page 43: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/43.jpg)
Telophase II
• These haploid cells will develop into gametes.
![Page 44: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/44.jpg)
Significance of Meiosis
(1) Crossing over in bivalent- Produces new combinations of genes in both
chromosomes
![Page 45: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/45.jpg)
Significance of Meiosis
(2) Reduction and fusion of gametes- Meiosis produces haploid gametes- In sexual reproduction, a male gamete
fertilizes a haploid female gamete to produce a normal diploid zygote
![Page 46: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/46.jpg)
Significance in Mitosis
(3) Independent (random assortment)- During metaphase I, homologous pairs of
chromosomes align at the equator- It is by chance which “way round” each pair
lies, before these homologous pairs of chromosomes separate into two different daughter cells.
![Page 47: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/47.jpg)
APPRECIATING THE MOVEMENT OF CHROMOSOMES DURING MITOSIS AND MEIOSIS
![Page 48: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/48.jpg)
Mutation
• Mutation is a change in structure, arrangement or quantity of the DNA in the chromosome
• May be caused by:– Mistakes in the replication of DNA– Damage to the DNA by radioactive and
carcinogenic substance– Disruption to the orderly movement of
chromosomes during cell division
![Page 49: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/49.jpg)
In Mitosis
• If the functions of these genes are disrupted due to mutation, cancers may form.
• Somatic mutations are not transmitted to the offspring, but may cause body cells to malfunction
• Cancers are caused by somatic mutation
![Page 50: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/50.jpg)
In Meiosis
• Meiosis involves an orderly movement and reduction (in meiosis I) of a diploid cell to two haploid cells that subsequently divide (in meiosis II) to form four haploid gametes
• Since these are gametes, so any mistakes – caused by disorderly movement of chromosomes during meiosis --- are inherited by the offspring.
![Page 51: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/51.jpg)
Example: non-disjunction or improper segregation (separation) of chromosome
• During anaphase I, certain homologous chromosomes fail to segregate, resulting in the production of gametes with either an extra chromosome (n+1) or a missing chromosome (n-1)
• If this abnormal gametes unites with a normal gamete, an abnormal zygote will be produced.
![Page 52: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/52.jpg)
![Page 53: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/53.jpg)
Down’s syndrome or mongolism
• 3 copies of chromosomes number 21, instead of the normal 2 chromosomes
• This means a down syndrome patient has (2n+1 = 47) 47 chromosomes instead of the normal (2n=46) chromosomes
![Page 54: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/54.jpg)
![Page 55: Mitosis & meiosis lesson 3](https://reader033.vdocument.in/reader033/viewer/2022061221/54bef8624a795924778b45e9/html5/thumbnails/55.jpg)