S EXUAL R EPRODUCTION & M EIOSIS. S EXUAL R EPRODUCTION During Sexual Reproduction, two sex cells...
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Transcript of S EXUAL R EPRODUCTION & M EIOSIS. S EXUAL R EPRODUCTION During Sexual Reproduction, two sex cells...
SEXUAL REPRODUCTION & MEIOSIS
SEXUAL REPRODUCTIONDuring Sexual Reproduction, two sex
cells (sperm & egg) come togetherSperm are formed in male reproductive
organsEggs are formed in female reproductive
organsThe joining of egg and sperm is
called FertilizationThe new cell that is formed is called
a Zygote
DIPLOID CELLSYour body forms two types of cells
Body Cells & Sex CellsA human body cell has 46
chromosomesEach chromosome has a “mate” that
is similar in size and has similar DNAThe “mates” are paired into 23 pairsWhen cells have pairs of similar
chromosomes they are called diploid.
HAPLOID CELLSSex cells do NOT have pairs of chromosomes
Human sex cells have 23 chromosomes
They are called haploid
MEIOSIS AND SEX CELLSA process called meiosis produces haploid sex cells
During meiosis, two divisions of the nucleus occurMeiosis IMeiosis II
MEIOSIS
MEIOSIS IBefore the start
of meiosis I, the chromosomes are duplicated just like mitosisEach set of
duplicated chromosomes is called a chromatid
MEIOSIS I In Prophase I the chromatids are tightly coiled together, each duplicated chromosome comes near its mate.
What are chromatids?
MEIOSIS I In Metaphase I, the pairs of duplicated chromosomes, or chromatids, line up at the equator. Each chromatid pair attaches to a _spindle at the centromere.What is a centromere?
Homologous Chromosomes
MEIOSIS I
In Anaphase I the chromosome pairs are pulled to _opposite_sides of the cell. Each duplicated chromosome still has two _chromatids_.
MEIOSIS I
In Telophase I the _cytoplasm divides and two new cells form. Each cell has one duplicated chromosome from each pair.
MEIOSIS II
NO chromosome duplication occurs before meiosis II
The two cells formed during meiosis I will begin meiosis II
MEIOSIS II
In Prophase II the __chromosomes__ and __spindle reappear in each of the cells
In Metaphase II the chromatid pairs move to the equator. Where is the equator?However, each centromere
attaches to the spindleindividually.
MEIOSIS II
In Anaphase II the __centromere divides and the _chromatids___ separate and move to opposite sides of the cell. Each _chromatid is now an individual chromosome.
MEIOSIS II
In Telophase II the spindle disappears and the nuclear membrane forms. The cytoplasm divides and produces __4_ cells.
SUMMARY OF MEIOSISDuring meiosis I, two cells formedDuring meiosis II, both of these
cells formed two cellsFour sex cells were formedEach sex cell has ½ the number
of chromosomes that was in the original nucleus
= 4 sex cells with 23 unpaired chromosomes
ZDONK
Donkey (62 chromosomes) + Zebra(46 chromosomes) = Zonkey How many chromosomes does the Zdonk have?
What happens when meiosis occurs in the Zdonk?
MISTAKES IN MEIOSIS
Mistakes in meiosis can produce sex cells with too many or too few chromosomes
If the zygote survives, every cells in that organism will have the wrong number of chromosomes
Down Syndrome (Trisomy 21)