meiosis and production of gametes mr. taylor biology rainier high school

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.


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.


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.


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.


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…


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.


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.


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 I

Prophase I

Metaphase I

Anaphase I

Telophase I


Meiosis II

Prophase II Metaphase II

Anaphase IITelophase II


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.


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.


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


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!!


Spermatogenesis

•The process of forming male gametes / spermatozoa

•One spermatogonia leaving Interphase I will produce 4 sperm

DIPLOID

HAPLOID

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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.

meiosis and production of gametes mr. taylor biology rainier high school

Documents

meiosis slide

gamete production meiosis

gamete production slide

gamete production telophase

gamete production prophase

gamete production metaphase

homologous chromosomes

gamete production crossing