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Meiosis and
Meiosis and

Meiosis and - PowerPoint Presentation

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Meiosis and - Description

Sexual Reproduction SEXUAL REPRODUCTION Sex cells formed by meiosis Requires 2 parents Offspring not identical The process that results in the formation of gametes Sex cells egg or sperm which have ID: 541860 Download Presentation

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Presentation on theme: "Meiosis and"— Presentation transcript

Slide1

Meiosis and

Sexual ReproductionSlide2

SEXUAL REPRODUCTION

Sex cells formed by meiosis

Requires 2 parents

Offspring not identical

The process that results in the formation of

gametes

Sex cells, egg or sperm, which have

haploid chromosomes

Haploid means HALF, as in the number of chromosomes,written as n

Meiosis

Gametes

HaploidSlide3

Fertilization

The union of an egg and a sperm

The cell that is formed when the egg becomes

fertilized

by thesperm. This results in a full set of chromosomes.

Diploid means they have chromosome found in pairs,written as 2n

n

n

2n

Zygote

DiploidSlide4

Homologous Chromosomes

Similar chromosomes that are found in pairs. The paired

chromosomes come from the mother and father.

* Human body cells have

46 chromosomes each

* Human body cells have 23 homologous pairs

Meiosis and Fertilization

Important for survival of many species, because these processesresult in genetic variation of offspring.

Meiosis

A kind of cell division that results in gametes (sex cells) withhalf the number of chromosomes.Slide5

A. Gametes

do not

have homologous pairs, but instead they have only half the chromosomes from each pair. Gametes are referred to as haploid (n).

B. When fertilization occurs, the zygote will have a normal number of chromosomes (2n).

C. In meiosis, specialized cells divide 2 times producing 4 daughter cells.Slide6

Meiosis

Parent cell – chromosome pair

Chromosomes copied

1

st

division - pairs split

2

nd division – produces 4 gamete cells with ½ the original no. of chromosomesSlide7

Meiosis Notes 1Slide8

Meiosis Overview

Human body cells have 46 chromosomes. Each parent contributes 23 chromosomes. Takes place in sex cells (gametes): egg and spermDelete the next line. Slide9

Homologous Chromosomes

Chromosomes & chromosome numbersSame genesSame order (position)Carry DNA that control the genetic inherited traits. One is from the mother, one is from the father.Slide10

Haploid and Diploid Cells

An organism produces gametes to maintain the same number of chromosomes from generation to generation. Human gametes contain 23 chromosomes each. Delete the next 2 lines.Slide11

Interphase

Chromosomes duplicate (just like in Mitosis)Chromatid – Each strand of the Chromosome and held together with a Centromere. http://www.contexo.info/DNA_Basics/Meiosis.htmSlide12

Meiosis

Interphase

Meiosis is preceded by interphase. The chromosomes have not yet condensed. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide13

Meiosis

Interphase The chromosomes have replicated, and the chromatin begins to condense.

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide14

Prophase I

Pairing of all of the chromosomesEach chromosome consists of two chromatids The nuclear membrane breaks downSpindles formCrossing over produces an exchange of genetic informationCrossing over – chromosomal segments are exchanged between a pair of homologous chromosomesSlide15

Meiosis

Prophase IThe chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous chromosomes pair with one another

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide16

Metaphase I

Chromosomes attach to spindle fibers.Homologous chromosomes line up at the center.Slide17

Meiosis

Metaphase I The nuclear membrane dissolves and the homologous chromosomes attach to the spindle fibers. They are preparing to go to opposite poles.

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide18

Anaphase I

Homologous chromosomes separate and move to opposite poles of the cell. Slide19

Meiosis

Anaphase I The chromosomes move to opposite ends of the cell. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide20

Telephase

IThe nuclear envelope breaks downChromosomes migrate and form two new cellsSlide21

Meiosis

Telophase I The cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of maternal and paternal chromosomes.

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide22

Meiosis II – Prophase II

A second set of phases begins as the spindle apparatus forms and the chromosomes double Slide23

Meiosis

Prophase II The cell has divided into two daughter cells. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide24

Metaphase II

The chromosomes line up at the equator. Slide25

Meiosis

Metaphase II As in Meiosis I, the chromosomes line up on the spindle fibers. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide26

Anaphase II

The sister chromosomes are pulled apart at the centromeres by spindle fibers and move toward the opposite poles of the cell. Slide27

Meiosis

Anaphase II The two cells each begin to divide. As in Meiosis I, the chromosomes move to opposite ends of each cell. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide28

Telophase

IIDelete what is in this section – The cells divide, resulting in 4 haploid cells – gametes (sex cells – sperm and eggs). Note that these 4 daughter cells are not identical. Slide29

Telophase

II With the formation of four cells, meiosis is over. Each of these prospective cells carries half the number of chromosomes of somatic cells (23).

http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.htmlSlide30
Slide31
Slide32

Mitosis vs. MeiosisSlide33

The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis

Mitosis

The first (and distinguishing) division of meiosisSlide34

Boy or Girl? The Y Chromosome

Decides”

X chromosome

Y chromosomeSlide35

Boy or Girl? The Y Chromosome

Decides”