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Cell CycleMitosis & Meiosis

Nancy DowJill Hansen

Tammy Stundon

December 1, 2012

Gulf Coast State College Panhandle Area Educational Consortium

5230 West Highway 98 753 West Boulevard

Panama City, Florida 32401 Chipley, Florida 32428

850-769-1551 877-873-7232

www.gulfcoast.edu

Biology Partnership

(A Teacher Quality Grant)

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Pre-testQ and A board

What is Mitosis?What is Meiosis? When do they happen?

What is alike and what is different about them?

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Florida Next Generation Sunshine State Standards

BENCHMARK • SC.912.L.16.16 Describe the process of meiosis, including

independent assortment and crossing over. Explain how reduction division results in the formation of haploid gametes or spores. (MODERATE)

• SC.912.L.16.17* Compare and contrast mitosis and meiosis and relate to the processes of sexual and asexual reproduction and their consequences for genetic variation. (HIGH)

Clarifications • Students will differentiate the processes of mitosis and meiosis.

• Students will describe the process of meiosis, including independent assortment and crossing over.

• Students will explain how meiosis results in the formation of haploid gametes or spores.

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Content Limits• Items addressing mitosis or meiosis are limited to

identification of phases, structures, and major events of each phase.

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The cell cycle has four main stages.• The cell cycle is a regular pattern of growth,

DNA replication, and cell division.

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Parent cell

centrioles

spindle fibers

centrosome

nucleus withDNA

• Interphase prepares the cell to divide.

• During interphase, the DNA is duplicated.

Mitosis and cytokinesis produce two genetically identical daughter cells.

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Mitosis divides the cell’s nucleus in four phases.– During prophase, chromosomes condense and

nuclear membrane breaks down. – centrioles ‘move’ to the poles and spindle fibers form

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– During metaphase, chromosomes line up in the middle of the cell.

Mitosis divides the cell’s nucleus in four phases.

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– During anaphase, sister chromatids separate to opposite sides of the cell.

Mitosis divides the cell’s nucleus in four phases.

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– During telophase, the new nuclei form, spindle fibers break down and chromosomes begin to uncoil.

Mitosis divides the cell’s nucleus in four phases.

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Cytokinesis differs in animal and plant cells.

– In animal cells, the membrane pinches closed.

– In plant cells, a cell plate forms.

It's Mitosis---My-Sharona

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For sexual

reproduction

Number of chromosomes

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KEY CONCEPT Gametes have half the number of chromosomes that body cells have.

Two types of cell divisions• Mitosis – one cells divides to form

TWO identical cells.– Occurs for growth and repair

• Meiosis – a cell in the testes or ovaries divides into four cells which contain half the number of chromosomes.– Occurs for reproduction (make gametes)

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You have body cells and gametes. • Body cells are also called somatic cells.

• Germ cells develop into gametes.– Germ cells are located in the ovaries and testes.– Gametes are sex cells: egg and sperm.– Gametes have DNA that can be passed to offspring.

body cells sex cells (sperm) sex cells (egg)

Diploid (2n)Haploid (n)

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INHERITANCE OF GENES

Maternal chromosome pair

Paternal chromosome pair

Gene

Paternal gamete: spermMaternal gamete: egg

Gametes unite during fertilization.

Child inherits one set of chromosomes from each parent and, thus, two copies of each gene.

Humans have 23 pairs of chromosomes (46 individual chromosomes) and, thus, two copies of each gene.

Each human gamete has just one copy of each chromosome and, thus, one copy of each gene.

ALLELES

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• Your body cells have 23 pairs of chromosomes.– Homologous pairs of

chromosomes have the same structure.

– For each homologous pair, one chromosome comes from each parent.

• Chromosome pairs 1-22 are autosomes.

• Sex chromosomes, X and Y, determine gender in mammals.

Your cells have autosomes and sex chromosomes.

Karyotype

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Body cells are diploid; gametes are haploid. • Fertilization between egg and sperm occurs in

sexual reproduction.

• Diploid (2n) cells have two copies of every chromosome.– Body cells are diploid.– Half the chromosomes come from each parent.

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Haploid (n) cells have one copy of every chromosome.

– Gametes are haploid.– Gametes have 22 autosomes and 1 sex chromosome.

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Chromosome number must be maintained in animals.

• Many plants have more than two copies of each chromosome.

• Mitosis and meiosis are types of nuclear division that make different types of cells.

• Mitosis makesmore diploid cells

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Meiosis makes haploid cells from diploid cells.

– Meiosis occurs in sex cells. – Meiosis produces gametes.

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Compare and Contrast

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KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

Meiosis Square Dance

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Cells go through two rounds of division in meiosis.

• Meiosis reduces chromosome number and creates genetic diversity.

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• Meiosis I and meiosis II each have four phases, similar to those in mitosis.

homologous chromosomes

sisterchromatids

sisterchromatids

– Pairs of homologous chromosomes separate in meiosis I– Homologous chromosomes are similar but not identical.– Sister chromatids divide in meiosis II.– Sister chromatids are copies of the same chromosome.

HOMOLOGUES AND SISTER CHROMATIDS

Homologues are the maternal and paternal copies of a chromosome. A sister chromatid is a chromosome and its identical duplicated version held together at a centromere.

Homologues Homologues

Maternal chromosome

Paternal chromosome

Sister chromatids

Replication (S Phase)

Centromere

Sister chromatids

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• Meiosis I occurs after DNA has been replicated.

• Meiosis I divides homologous chromosomes in four phases.

INTERPHASE

CentromereReplicated

chromosome

Nuclearmembrane

INTERPHASE• Chromosomes replicate in preparation for meiosis.

Meiosis I

INTERPHASE

Centromere

Replicatedchromosome

Nuclearmembrane

INTERPHASE• Chromosomes replicate in preparation for meiosis.

MEIOSIS DIVISION 1: HOMOLOGUES SEPARATE

Homologues

Homologuescross over

Spindle

PROPHASE I• Replicated chromosomes condense.• Spindle apparatus is formed.• Homologous pairs of sister chromatids come together and cross over.• Nuclear membrane disintegrates.

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Meiosis I

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Prophase I • Biology Media Gallery Clip – Meiosis (2 min)

MEIOSIS DIVISION 1: HOMOLOGUES SEPARATE

Homologues

Homologuescross over

Spindle

PROPHASE I• Replicated chromosomes condense.• Spindle apparatus is formed.• Homologous pairs of sister chromatids come together and cross over.• Nuclear membrane disintegrates.

1 METAPHASE I• Homologues move towardthe center of the cell andline up.

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Meiosis I

MEIOSIS DIVISION 1: HOMOLOGUES SEPARATE

METAPHASE I• Homologues move towardthe center of the cell andline up.

2 ANAPHASE I• Homologues separate and are pulled to opposite poles. Sister chromatids going to each side are a mix of maternal and paternal genetic material.

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Spindle fiber Meiosis I

ANAPHASE I• Homologues separate and are pulled to opposite poles. Sister chromatids going to each side are a mix of maternal and paternal genetic material.

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Spindle fiber

TELOPHASE I AND CYTOKINESIS• Sister chromatids arrive at thecell poles and the nuclear membrane reassembles around them.• The cell pinches into twodaughter cells.• Chromosomes may unwind slightly.

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Daughter cell 1

Daughter cell 2

Meiosis I

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• Meiosis II divides sister chromatids in four phases.

• DNA is not replicated between meiosis I and meiosis II.

TELOPHASE I AND CYTOKINESIS• Sister chromatids arrive at thecell poles and the nuclear membrane reassembles around them.• The cell pinches into twodaughter cells.• Chromosomes may unwind slightly.

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Daughter cell 1

Daughter cell 2

PROPHASE II• Chromosomesin daughter cellscondense.

METAPHASE II• Sister chromatidsline up at thecenter of the cell.

ANAPHASE II• Sister chromatid pairs are pulled apart by the spindle fibers toward opposite cell poles.

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Sister chromatid

s

There is a brief interphase prior to prophase II. Chromosomes are not replicated again at this stage.

MEIOSIS DIVISION 2: SISTER CHROMATIDS SEPARATE

ANAPHASE II• Sister chromatid pairs are pulled apart by the spindle fibers toward opposite cell poles.

7 TELOPHASE II AND CYTOKINESIS• The two daughter cells pinch into four haploid daughter cells. • The nuclear membrane reassembles around the chromosomes.

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MEIOSIS DIVISION 2: SISTER CHROMATIDS SEPARATE

Daughter cell 3

Daughter cell 4

Daughter cell 1

Daughter cell 2

Why is meiosis so important?

• The chromosome number of the species remains the same generation after generation.

• The sperm and egg produced are NOT identical to the cells of the parents and this increases genetic diversity.– Crossing over and independent assortment assure

genetic diversity.

SOURCES OF GENETIC VARIATION

There are multiple reasons why offspring are genetically different from their parents and one another.

CROSSING OVER Crossing over during meiosis produces a mixture of maternal and paternal genetic material on each chromatid.

REASSORTMENT OF HOMOLOGUES The homologues and sister chromatids distributed to each daughter cell during meiosis are a random mix of maternal and paternal genetic material.

ALLELES COME FROM TWO PARENTS Each parent donates his or her own set of genetic material.

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Meiosis differs from mitosis in significant ways.

– Meiosis has two cell divisions while mitosis has one.– In mitosis, homologous chromosomes never pair up.– Meiosis results in haploid cells; mitosis results in diploid cells

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Haploid cells develop into mature gametes. • Gametogenesis is the

production of gametes.• Gametogenesis differs between

females and males.– Sperm become streamlined and

motile.– Sperm primarily contribute DNA

to an embryo.

– Eggs contribute DNA, cytoplasm, and organelles to an embryo.

– During meiosis, the egg gets most of the contents; the other cells form polar bodies.

Mitosis vs. Meiosis• Mitosis

– Occurs in every cell of the body (Somatic cells = body cells)

– One cell divides to form 2 identical cells

• Meiosis– Occurs only in the testes and ovaries (sex cells)– One cell divides TWICE to form 4 cells with half the

number of chromosomes– There are some small differences in the individual

steps of both cycles… make note!

Chromosome number in humans

• 2n 46 chromosomes (23 pairs)

Diploid

mitosis produces diploid cells

• 1n 23 chromosomes

Haploid

meiosis forms haploid cells side by side comparison

Topic Mitosis Meiosis

Location Somatic cells Sex cells

Description 2N 2N 2N N

# of cells produced 2 4

Purpose Growth/repair Produce gametes

Number of divisions 1 2

Comparison of the cell cyclesGroup activity

Side by side comparison of Mitosis and Meiosis

Topic Mitosis Meiosis

• Foldable

Mitosis vs. Meiosis Manipulative

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Meiosis Simulation with pop-beads

15 minutes!!

HOW SEX IS DETERMINED IN HUMANS

Individuals have two copies of the sex chromosomes in every cell.

Females have two copies of the X chromosome ( XX)

Males have one X chromosome and one Y chromosome. (XY)

XXX Y

Males determine the sex of the child.

Mistakes during meiosis• Non-disjunction

– Uneven splitting of chromosomes during meiosis (problem with spindle fibers)

– occurs during meiosis I when homologous chromosomes do not separate or during meiosis II when duplicated chromosomes do not separate

– The end result is a sperm or egg with too many or too few chromosomes

1 2 3 4 5

6 7 8 11 129 10

13 14 15 17 1816

19 20 X Y21 22

Examples of Autosomal non-disjunction

DOWN SYNDROME (TRISOMY-21) --Usually due to a problem with the egg Characteristics:Short stature, stubby fingers, round head, fissured tongue, often mental retardation

Autosomes – for humans, chromosomes 1-22, non-sex chromosomes

Examples of autosomal non-disjunction• Down’s syndrome

– The frequency of non-disjunction in women increases with age.• 1 in 800 births for women under 40 and 1 in 80 births for women over 40

– In men, the frequency of non-disjunction is the same throughout life.

Cri Du Chat Syndrome

(Cats’s Cry Syndrome)

-Part of chromosome #5 is missing while other chromosomes are normal

Characteristics:

Malformed larynx so cry sounds like cat, moon face, small head, severe mental retardation

Examples of autosomal non-disjunction

Examples of sex-linked non-disjunction

Turner Syndrome-the female only has one X

chromosome (XO)-occurs 1 in 6000 birthsCharacteristics-short, broad chest, webbed

neck, no puberty, infertile, normal intelligence, small finger nails, deformed elbows, low hairline

Klinefelter Syndrome-the male has an extra X chromosome (XXY)-occurs one in 1500 birthsCharacteristics:No facial hair, male reproductive glands not fully developed, sterile, some female development,

Examples of sex-linked non-disjunction

Poly-X syndrome-has more than 2 X chromosomes (XXX)-occurs 1 in 1500 births-no abnormalities except sometimes

menstrual irregularities (ex. early menopause)

Jacob Syndrome-males have extra Y chromosome (XYY)-1 in 1000 births-taller, persistent acne; speech/reading

problems

Examples of sex-linked non-disjunction

Fragile X SyndromeThe X chromosome is broken with a piece hanging off Occurs in 1 in 1000 male births and 1 in 2500 females

Examples of sex-linked non-disjunction

Fragile X SyndromeCharacteristics:Short in stature with long face with prominent jaw and large ears, delayed speech development, often heart defects

Examples of sex-linked non-disjunction

Karyotype Lab

Cross-Dressing or Crossing-Over: Sex Testing of Women Athletes

Maureen Knabb, Department of Biology, West Chester University, and Joan Sharp, Biological Sciences, Simon Fraser University

Case studies

• http://sciencecases.lib.buffalo.edu/cs/ collection of case-studies problem based learning lessons

• Cross-Dressing or Crossing-Over? Sex Testing of Women AthletesIn this “clicker case,” students learn about sex determination, meiosis, and chromosomal “crossing over” through the story of Santhi Soundararajan, an athlete from Kathakkurichi, India, who was stripped of a medal at the 2006 Asian Games after failing to pass a sex test. 

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Computer Lab

• Web Quest Mitosis and Meiosis

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Additional Resources

• Meiosis Tutorial

• Mitosis and Meiosis Simulation with Beads

• Side by side animation of mitosis and meiosis

• http://learn.genetics.utah.edu/content/begin/tour/mitosis.swf mitosis to meiosis tutorial

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Follow up

• Q & A

• Post Test