Chapter 8 and 9

Lesson 1- ChromosomesLesson 2- Cell Cycle

Lesson 3-MitosisLesson 4-Meiosis

Chromosomes

Chromosomes

Structures made of DNA and associated proteins on which genes are located.

Sets of ChromosomesDiploid-a cell that contains two sets

of chromosomes. (2n)

Haploid- a cell that contains one set of chromosomes. (n)

The number of chromosomes in cells is constant within a species.

Each human cell normally has two pairs oftwo pairs of 2323 different chromosomes for a total of 46total of 46 chromosomes.

The 23 pairs of chromosomes differ in size, shape, and genetic content.

Each pair consists of two homologous chromosomes or homologues (one from each parent).

Homologous Examplexx XX

1 2

•Within each homologous pair, the chromosomes are similar in size, shape, and genetic content. However, each pair is different from the next.

Autosomes

Are chromosomes that are not directly involved in determining the sex (gender) of an individual.

Of the 23 pairs of chromosomes, 22 pairs are called autosomes.

Sex (Gender) ChromosomesAre chromosomes that are directly

involved in determining the sex (gender) of an individual.

Of the 23 pairs of chromosomes, 1 pair is called sex chromosomes.

Males – XY

Females - XX

The sex of the offspring is determined by the male, who can

donate either an X or Y chromosome.

The presence of all 46 chromosomes is essential for

normal development and function.

Chromosome Variations

A genetic disorder is caused by an abnormality in an individual's DNA.

Abnormalities can range from a small mutation in a single gene to the addition or subtraction of an entire chromosome or set of chromosomes.

RESULTS:1. Down’s Syndrome

2. Turner’s Syndrome

3. Huntington’s Disease

4. Sickle Cell Anemia

5. Cystic Fibrosis

And other genetic disorders . .

The Cell Cycle

The Eukaryotic Cell Cycle

The eukaryotic cell cycle consists of phases of growth, DNA replication,

preparation for cell division, and division of the nucleus and cytoplasm.

Stages of the Cell Cycle

1.1. First Growth (GFirst Growth (G11) Phase) Phase

2.2. Synthesis (S) PhaseSynthesis (S) Phase

3.3. Second Growth (GSecond Growth (G22) Phase) Phase

4.4. Mitosis (M)Mitosis (M)

5.5. Cytokinesis (C)Cytokinesis (C)

The Cell Cycle: InterphaseThe Cell Cycle: Interphase

1.1. First Growth (GFirst Growth (G11) Phase) Phase: cell grows rapidly : cell grows rapidly and carries out its routine functions.and carries out its routine functions.

– Cells that are not dividing remain in the GCells that are not dividing remain in the G11 phase. phase.

2.2. Synthesis (S) PhaseSynthesis (S) Phase: cell: cell’’s DNA is copied.s DNA is copied.

3.3. Second Growth (GSecond Growth (G22 )Phase )Phase: preparations : preparations are made for the nucleus to divide.are made for the nucleus to divide.

A cell spends (90%) of its time in InterphaseA cell spends (90%) of its time in Interphase

Final Stages

MitosisMitosis: : process during cell process during cell

division in which division in which the nucleus of a the nucleus of a

cell is divided cell is divided into two nuclei.into two nuclei.

CytokinesisCytokinesis: : process during cell process during cell

division in which division in which the cytoplasm the cytoplasm

divides.divides.

Importance of Mitosis and Cytokinesis

Mitosis and Cytokinesis produce new cells that Mitosis and Cytokinesis produce new cells that are identical to the original cells and allow are identical to the original cells and allow organisms to grow, replace damaged tissues, organisms to grow, replace damaged tissues, and, in some organisms, reproduce and, in some organisms, reproduce asexually.asexually.

How do cells know when to divide?

How is the cell cycle controlled?

Check Points

Cells have check points that control the phases of the cell cycle.

At each checkpoint, feedback signals from the cell can trigger the next phase of the cell cycle.

Cell Cycle Review

1. Define cell cycle.

2. List the 5 phases of the cell cycle.

3. List the 3 phases of the cell cycle.

4. What phases make up Interphase?

5. How much time does a cell spend in Interphase?

6. What regulates the cell cycle?

7. Do all cells go through all stages of the cell cycle?

MitosisMitosis

MitosisMitosis

•Process in which the Process in which the nucleus of the cell divides nucleus of the cell divides and maintains the parental and maintains the parental chromosome number for chromosome number for daughter cells.daughter cells.

Stages of MitosisStages of Mitosis

•PROPHASE

•METAPHASE

•ANAPHASE

•TELEPHASE

PPMMAATT

ProphaseProphaseChromosomes coil up and Chromosomes coil up and become visible.become visible.

Nuclear envelope dissolves and Nuclear envelope dissolves and a spindle formsa spindle forms

MetaphaseMetaphase•Chromosomes move to the Chromosomes move to the center of the cell and line up center of the cell and line up along the equator (middle).along the equator (middle).

•Spindle fibers link the Spindle fibers link the chromosomes to opposite chromosomes to opposite poles.poles.

AnaphaseAnaphase

•Centromeres divide Centromeres divide (split)(split)

•Chromatids are pulled Chromatids are pulled away to opposite away to opposite poles of the cellpoles of the cell

TelophaseTelophase

Nuclear envelopes form around the chromosomes at each pole.

Two new cells are visible.

Cytokinesis

During cytokinesis, the cytoplasm of the cell membrane grows to enclose each cell, forming two separate cells as a result.

ASEXUAL AND

SEXUAL REPRODUCTION

REPRODUCTION

the process of producing offspring.

Types:Asexual ReproductionSexual Reproduction

SEXUAL REPRODUCTION• Definition: reproduction in which gametes

from opposite sexes or mating types unite to form a zygote (fertilized egg).

• Occurs in eukaryotic organisms.

• Two parents each form haploid reproductive cells.

-sperm cells contain 23 chromosomes (Father)

-egg cells contain 23 chromosomes (Mother)

SEXUAL REPRODUCTION CONTD.

• Both parents contribute genetic material

• The offspring has traits of both parents but are not exactly like either parent.

ADVANTAGES OF SEXUAL REPRODUCTION

Makes different combinations of genes among individuals.

Leads to greater genetic diversity.

ASEXUAL REPRODUCTION• Definition: reproduction that

involves only one parent and results in genetically identical offspring.

• Occurs in Prokaryotes and some eukaryotes.

• Parent passes copies of all of its genes to each of its offspring

ASEXUAL REPRODUCTION CONTD.

• There is no fusion of haploid cells

• = clone (an organism that is genetically identical to its parent)

TYPES OF ASEXUAL REPRODUCTION

1. Binary fission - reproduction in which the parent separates into one or more individuals of equal size.

1.1. Fragmentation Fragmentation -reproduction in which -reproduction in which the body breaks into several pieces.the body breaks into several pieces.

1. Budding - reproduction in which new individuals split off from existing ones.

AdvantagesSimpleAllows organisms to reproduce rapidlyOrganisms do not need a mate

DisadvantagesDNA is identical to that of the parentOrganism may not be able to adapt to a new environment

ASEXUAL REPRODUCTION

Let’s Review1. Define reproduction2. Some organisms have ______ parents,

while others have ________.3. Distinguish between asexual

reproduction and sexual reproduction.4. An individual produced by asexual

reproduction is a _____________.5. List the types of asexual reproduction.6. List the disadvantages/advantages of

asexual reproduction.

Meiosis

A form of nuclear division that creates four haploid cells from one diploid cell.

Meiosis reduces the chromosome number and creates genetic diversity.

Involves two rounds of cell division-meiosis I and meiosis II.

Points to Remember

Homologous Chromosomes

Are two separate chromosomes

One comes from the mother AND one comes from the father.

Very similar in size, shape, and genetic content

divided in meiosis I.

Sister ChromatidsHalf of a duplicated

chromosomeTwo chromatids

together joined at the

centromeredivided in meiosis II.

Meiosis

Meiosis – Prophase I

Nuclear membrane breaks downCentrosomes and centrioles move to opposite sides of the cell

Spindle fibers start to assembleChromosomes condense and homologous chromosomes pair up.

Meiosis – Metaphase I

Homologous chromosome pairs are randomly lined up along the middle of the cell

This arrangement mixes up the chromosomal combinations and helps create and maintain genetic diversity.

Meiosis – Anaphase I

Paired homologous chromosomes separate and move to opposite sides of the cell

sister chromatids are still connected.

Meiosis – Telophase I

Chromosomes are in two groups at opposite sides of the cell.

Cell divides into two haploid cells.

Meiosis – Prophase II

Nuclear membrane breaks downCentrosomes and centrioles move to opposite sides of the cell

Spindle fibers assemble

Meiosis – Metaphase II

Spindle fibers align the chromosomes along the cell’s equator.

Meiosis – Anaphase II

The sister chromatids are pulled apart from each other and move to opposite sides of the cell.

Meiosis – Telophase II

Nuclear membrane forms around each set of chromosomes at opposite ends of the cell

Spindle fibers break apart

Meiosis -- Cytokinesis

Cytoplasm and organelles finish replicating and the cell divides into two.

Cell membrane forms between the new cells.

Four haploid cells are formed.

Mitosis Overview

Meiosis Overview