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Meiosis Part 1 . Reduction Division Production of Gametes Part 1 . Mitosis: Review . What is the purpose of mitosis? To allow cell copy itself completely To grow, repair, and for non sexual organisms to reproduce What are the four phases of mitosis? Prophase Metaphase Anaphase

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meiosis part 1

Meiosis Part 1

Reduction Division

Production of Gametes

Part 1

mitosis review
Mitosis: Review
  • What is the purpose of mitosis?
    • To allow cell copy itself completely
    • To grow, repair, and for non sexual organisms to reproduce
  • What are the four phases of mitosis?
    • Prophase
    • Metaphase
    • Anaphase
    • Telophase
slide3

Mitosis: Review

  • Name the parts of mitosis below
mitosis review1
Mitosis: Review
  • 2n= normal cell
  • Mitosis forms what type of cells?
meiosis vocabulary
Meiosis vocabulary
  • Diploid – (2n) the normal number of chromosomes (one from mom and one from dad)
  • Haploid – (n) half the normal number of chromosomes
  • Somatic cells – normal bodycells

– these are diploid (2n)

What are some examples of somatic cells?

What cells are not somatic?

  • Gametes – Reproductive cells (egg and sperm)
    • These are haploid (n)
meiosis
Meiosis

Meiosis: a form of cell divisionthat creates gametes

The process halves the number of chromosomes turning diploid cells (2n) into haploid cells (n)

chromosome
Chromosome
  • Chromosome- ____________________
  • Chromatid - is one of two identical strands of DNA making up a chromosome
  • Centromere– holds two chromatids together to make a chromosome
chromosome draw this
Chromosome- Draw this

Chromosome

Chromatid

Chromatid

Centromere

homologous chromosomes
Homologous Chromosomes
  • Each organism has chromosomes almost identical sets of chromosomes from each parent. (Hence the 2n)
  • Each set of these are considered Homologous Chromosomes
  • Homologous Chromosomes are Chromosomes in cell that pair (synapse) during meiosis

Chromosome from mom

Chromosome from dad

meiosis2
Meiosis
  • Meiosis has two parts
    • Meiosis I
    • Meiosis II
meiosis i
Meiosis I
  • At the beginning of meiosis I, homologous chromosomes are attached together to form a tetrad
  • Homologous chromosomes then cross over with each other exchanging genetic information
  • Tetrads separate during meiosis I and each new cell has only one of the original homologous chromosomes

Tetrad

slide13

Meiosis 1 has 4 phases:

Prophase I, Metaphase I, Anaphase I, Telophase I

MEIOSIS I: Homologous chromosomes separate

INTERPHASE

PROPHASE I

METAPHASE I

ANAPHASE I

Centrosomes(withcentriolepairs)

Microtubules attached tokinetochore

Metaphaseplate

Sister chromatidsremain attached

Sites of crossing over

Spindle

Nuclearenvelope

Sisterchromatids

Tetrad

Centromere(with kinetochore)

Homologouschromosomes separate

Chromatin

Figure 8.14, part 1

crossing over
Crossing Over
  • Crossing over- the exchange of corresponding segments between two homologous chromosomes
  • Happens during meiosis I
  • Crossing over mixes the genes from the parents increasing variation
crossing over1
Crossing Over

Chromosome from mom

Chromosome from dad

slide16

MEIOSIS I

Crossed over chromosomes

PROPHASE I

METAPHASE I

ANAPHASE I

END OF

INTERPHASE

meiosis ii
Meiosis II
  • Meiosis II is essentially the same as mitosis
  • sister chromatids of each chromosome separate
  • result is four haploid daughter cells

Do not change this slide until you watch the animation

slide18

MEIOSIS

METAPHASE II

TELOPHASE I

PROPHASE II

ANAPHASE II

TELOPHASE II

slide19

Meiosis II has four phases also

MEIOSIS II: Sister chromatids separate

TELOPHASE IAND CYTOKINESIS

TELOPHASE IIAND CYTOKINESIS

PROPHASE II

METAPHASE II

ANAPHASE II

Cleavagefurrow

Sister chromatidsseparate

Haploiddaughter cellsforming

Figure 8.14, part 2

slide20

MITOSIS

MEIOSIS

PARENT CELL(before chromosome replication)

Site ofcrossing over

MEIOSIS I

PROPHASE I

Tetrad formedby synapsis of

homologous chromosomes

PROPHASE

Chromosomereplication

Chromosomereplication

Duplicatedchromosome(two sister chromatids)

2n = 4

Chromosomes align at the metaphase plate

Tetradsalign at themetaphase plate

METAPHASE I

METAPHASE

ANAPHASE I

TELOPHASE I

ANAPHASETELOPHASE

Sister chromatidsseparate duringanaphase

Homologouschromosomesseparateduringanaphase I;sisterchromatids remain together

Haploidn = 2

Daughtercells of meiosis I

2n

2n

No further chromosomal replication; sister chromatids separate during anaphase II

MEIOSIS II

Daughter cellsof mitosis

n

n

n

n

Daughter cells of meiosis II

Figure 8.15

meiosis part 2

Meiosis Part 2

Karyotypes

Differences between sperm and eggs

Problems that can occur in Meiosis

karyotype
Karyotype
  • A diagram which arranges all of a cell’s chromosomes in order from largest to smallest
spermatogenesis vs oogenesis
Spermatogenesis vs Oogenesis
  • Spermatogenesis- Process that makes sperm.
    • Produces 4 sperm
  • Oogenesis – Process that makes eggs
    • ONLY produces 1 egg cell
slide25

SPERMATOGENESIS

b

OOGENESIS

a

spermatogonium

oogonium

primary

spermatocyte

primary

oocyte

meiosis l

secondary

spermatocyte

secondary

oocyte

polar

body

meiosis ll

spermatids

polar bodies

(will be degraded)

egg

nondisjunction
Nondisjunction

Nondisjunctionin meiosis I

  • Nondisjunction- when a mistake occurs during meiosis leading to an abnormal about of chromosomes in a gamete

Normalmeiosis II

Gametes

slide27
Fertilization after nondisjunction in the mother results in a zygote with an extra chromosome

Eggcell

n + 1

Zygote2n + 1

Spermcell

n (normal)

Figure 8.21C

connection an extra copy of chromosome 21 causes down syndrome
Connection: An extra copy of chromosome 21 causes Down syndrome
  • An extra copy of chromosome 21 shown in the karyotype below causes Down syndrome
  • Also called trisomy 21

Figure 8.20A, B