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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.htmlSlide30Slide31Slide32
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”