MEIOSISMEIOSISAND PRODUCTION AND PRODUCTION
OF GAMETESOF GAMETES
Mr. TaylorMr. Taylor
BiologyBiology
Rainier High SchoolRainier High School
Meiosis and Gamete Meiosis and Gamete ProductionProduction
Meiosis is the process of creating new Meiosis is the process of creating new cells (called cells (called gametesgametes) by performing ) by performing two separate cell divisions.two separate cell divisions.
Process closely resembles mitosis, Process closely resembles mitosis, shares similar names with mitosis.shares similar names with mitosis.
Begins with chromosomes replicating Begins with chromosomes replicating in late Interphase.in late Interphase.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
PROPHASE IPROPHASE I– Chromosomes have replicated, now coil Chromosomes have replicated, now coil
into tight rodsinto tight rods– Nuclear membrane breaks downNuclear membrane breaks down– Spindle begins to formSpindle begins to formHomologous chromosomes pair up.Homologous chromosomes pair up.
This forms a structure called a TETRAD.This forms a structure called a TETRAD.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
METAPHASE IMETAPHASE I– Homologous pairs (tetrads) align along Homologous pairs (tetrads) align along
the equator (middle) of the cell.the equator (middle) of the cell.
ANAPHASE IANAPHASE I– Centromeres DO NOT divide, chromatids Centromeres DO NOT divide, chromatids
DO NOT separate.DO NOT separate.– Homologous chromosome pairs go to Homologous chromosome pairs go to
oppositeopposite poles. poles.– This is called the REDUCTION DIVISION. This is called the REDUCTION DIVISION.
The resulting cells will be The resulting cells will be haploidhaploid as they as they only have one set of chromosomes. only have one set of chromosomes.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
METAPHASE IMETAPHASE I– Homologous pairs (tetrads) align along Homologous pairs (tetrads) align along
the equator (middle) of the cell.the equator (middle) of the cell.
ANAPHASE IANAPHASE I– Centromeres DO NOT divide, chromatids Centromeres DO NOT divide, chromatids
DO NOT separate.DO NOT separate.– Homologous chromosome pairs go to Homologous chromosome pairs go to
oppositeopposite poles. poles.– This is called theThis is called the REDUCTION DIVISION. REDUCTION DIVISION.
The resulting cells will beThe resulting cells will be haploidhaploid as they as they only haveonly have one set of chromosomes. one set of chromosomes.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
TELOPHASE ITELOPHASE I– Nucleus reforms, chromosomes begin to Nucleus reforms, chromosomes begin to
uncoiluncoil– Cytokinesis occurs, cell membrane Cytokinesis occurs, cell membrane
connects to form 2 new cells.connects to form 2 new cells.– These new cells are HAPLOID. They These new cells are HAPLOID. They
contain pairs of chromosomes, but only contain pairs of chromosomes, but only ONE set. No chromosome has its ONE set. No chromosome has its homologous partner present.homologous partner present.
NOW OCCURS ONE NOW OCCURS ONE BIGBIG DIFFERENCE DIFFERENCE BETWEEN MITOSIS AND MEIOSIS…BETWEEN MITOSIS AND MEIOSIS…
Meiosis and Gamete Meiosis and Gamete ProductionProduction
THERE IS THERE IS NO INTERPHASENO INTERPHASE BETWEEN BETWEEN MEIOSIS I AND MEIOSIS II.MEIOSIS I AND MEIOSIS II.– This means that the chromosomes DO This means that the chromosomes DO
NOT REPLICATE again. The cells go NOT REPLICATE again. The cells go directly from Telophase I into …directly from Telophase I into …
PROPHASE IIPROPHASE II– Nuclear membranes dissolve again.Nuclear membranes dissolve again.– New spindles form, centromeres attachNew spindles form, centromeres attach– Chromosomes coil tightly again.Chromosomes coil tightly again.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
METAPHASE IIMETAPHASE II– Chromatids align along the equator Chromatids align along the equator
(middle) of the cell(middle) of the cell
ANAPHASE IIANAPHASE II– Centromeres divide.Centromeres divide.– Chromosomes are pulled to opposite Chromosomes are pulled to opposite
poles of the cells by the spindle fibers.poles of the cells by the spindle fibers.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
TELOPHASE IITELOPHASE II– Nuclear membranes reform.Nuclear membranes reform.– Chromosomes uncoil.Chromosomes uncoil.– Spindles break down.Spindles break down.– Cytokinesis occurs… Cell membranes Cytokinesis occurs… Cell membranes
divide cells (now have 4 cells).divide cells (now have 4 cells).
Meiosis and Gamete Meiosis and Gamete ProductionProduction
Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis and Gamete Meiosis and Gamete ProductionProduction
Meiosis II
Prophase II Metaphase II
Anaphase IITelophase II
Meiosis and Gamete Meiosis and Gamete ProductionProduction
CROSSING OVER
During Prophase I while the homologous sister chromatids are sitting tightly against each other as a tetrad, small portions of “identical” chromatids can swap places.
The end result is that a chromatid from “mom” has a section of a chromatid from “dad” (and vice versa). This greatly increases the genetic variation possible…and the whole reason for sexual reproduction is to create individuals that are different from each other.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
LAW OF INDEPENDENT ASSORTMENT
Each chromosome of each homologous pair will be pulled toward the poles of the new cells independently. This results different mixtures of chromosomes in the gametes.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
LAW OF INDEPENDENT ASSORTMENT
Each chromosome of each homologous pair will be pulled toward the poles of the new cells independently. This results different mixtures of chromosomes in the gametes.
Meiosis and Gamete Meiosis and Gamete ProductionProduction
By this method of independent assortment:•2 chromosomes make 1 pair and will yield
2 combinationsAAA pairs to A and A
•4 chromosomes make 2 pair and will yield4 combinations
AABB pairs AB, AB, AB, AB
•6 chromosomes make 3 pair and will yield8 combinations
AABBCC pairs ABC, ABC, ABC, ABC,ABC, ABC, ABC, ABC
Meiosis and Gamete Meiosis and Gamete ProductionProduction
By this method of independent assortment:8 chromosomes make 4 pair and will yield
16 combinations
AaBbCcDd pair ABCD, ABCd, ABcD, ABcd,AbCD, AbCd, AbcD, Abcd, aBCD, aBCd, aBcD, aBcd,abCD, abCd, abcD, abcd
46 chromosomes make 23 pair and will yield223 or 8,388,608
combinations and this is not including crossing over!!
Meiosis and Gamete Meiosis and Gamete ProductionProduction
Spermatogenesis
•The process of forming male gametes / spermatozoa
•One spermatogonia leaving Interphase I will produce 4 sperm
DIPLOID
HAPLOID
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Meiosis and Gamete Meiosis and Gamete ProductionProduction
Oogenesis
•The process of forming female gametes / ova
•One oogonia will produce only one ovum. The three polar bodies will not mature and will be reabsorbed by the female’s body.
DIPLOID
HAPLOID
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Thank you for Thank you for
your attention.your attention. You may now You may now
complain to complain to your teacher your teacher about writer’s about writer’s cramp. It cramp. It probably won’t probably won’t do any good, do any good, but you can but you can complain.complain.