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)