1 meiosis insures that a. each gamete receives the same genes b. chromosome number is doubled in the...

1

Meiosis insures that

A. Each gamete receives the same genes

B. Chromosome number is doubled in the gametes

C. Zygotes produced by fertilization have the normal number of chromosomes

D. All paternal chromosomes end up in the same gamete

How much do you remember about cell division?

2

Which of the following is not true about interphase?

A. The cell grows larger during interphase.

B. Chromosomes are duplicated during interphase.

C. Interphase is divided into three phases.

D. Chromosomes segregate to daughter cells during interphase.

© 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 3

Which of the following is true about

homologous chromosomes?

A. Both were received from the same parent.

B. One of each segregates to each daughter cell

during mitosis.

C. Both stay together in meiosis I.

D. All 23 pairs are always homologous.


Cell Division Renewal and repair of tissues with stem

cells

Reproduction Prokaryotes divide through binary fission Eukaryote cell division is more complicated

6

Prokaryotes divide through binary fission


Eukaryote cell division is more complicated: Cell cycle Cell cycle

Series of events in life cycle of a cellTwo main stages

Interphase Most cells spend 90% of lifespan in this stage

Cell division by two different mechanisms Mitosis: occurs in nonreproductive cells, called somatic

cells Meiosis: occurs in sexual reproduction cells,called germ

cells


The Cell Cycle


DNA Packaged as Chromosome DNA molecules are enormously long

Double helix nearly 2 meters in length DNA is tightly packaged with proteins Chromatin

DNA and proteins Chromosome

Tightly packed


KaryotypeChromosomes are

visible during mitosis

Their number and shape can be studied

Humans have 46 chromosomes


Homologous Chromosomes 46 chromosomes are arranged in 23

pairs One came from each parent

22 pairs are autosomes Both chromosomes are homologues

1 pair are sex chromosomes Can be homologous; XX for females Can be different; XY for males


Interphase: The Longest Stage

The period between divisions: The cell prepares to divide

Divided into 3 stages: G1: growth after mitosis

S: synthesis of DNA

G2: growth before mitosis


Mitosis

Consists of ProphaseMetaphase Anaphase Telophase

Cytokinesis: division of the cytoplasm


Prophase

Cell enters mitosis Chromosomes condense Centrosomes move apart

Go to the poles of the cell

Mitotic spindle begins to form


Metaphase

Chromosomes line up Metaphase plate Align sister chromatids

Equal and balanced segregation


Anaphase

Chromatids separateBreak free and dragged

to opposite sides

Microtubules shorten Result:

Equal segregation of chromosomes in two daughter cells


Telophase and Cytokinesis Telophase:

Chromosomes reach the poles Mitotic spindle falls apart Chromosomes unfold Nuclear membrane reforms

CytokinesisCytoplasm is dividedTwo cells are formed

CytokinesisCytoplasm is divided

Two cells are formed

Cancer Tumor: inappropriate proliferation of cells

Benign tumor: confined to one siteMalignant tumor: cells migrate and invade


Cancer and Lifestyle: Lung Cancer

Lung cancer cells (300X) Portrait of a cancer

Environmental factors: Smoking‑related cancers Lung, oral, kidney, stomach, bladder

Tobacco smoke 40 known carcinogens


Retinoblastoma: mutation of a gene

An inherited form of cancer Occurs in the retina Causes blindness Due to missing Rb gene

A tumor suppressor gene

Cancer: A Multi-step Process Example: Colon cancer

Early polyp: Loss of tumor suppressor gene

Polyp: Mutation of proto-oncogene

Late Polyp: Loss of two additional tumor

suppressor genes

Malignant tumor: Inactivation of p53 tumor

suppressor



Meiosis

Used to make gametes Eggs and sperm

Chromosome number is halved (haploid)

Zygote is diploid after fertilization

Meiosis

Fertilization

Mitosis

involves two divisions, meiosis I

DNA is replicated only before meiosis I meiosis I separates the homologues in a homologous pair

meiosis II meiosis II separates the replicate sister chromatids

when meiosis is complete, the result is that one diploid cell has become four haploid cells

Meiosis I divided into four stages

1. Prophase I Homologues pair up and exchange

segments: crossing over

2. Metaphase I The paired homologous chromosomes align

on a central plane in any combination: independent assortment

3. Anaphase I Homologues separate from the pairing and

move to opposite poles

4. Telophase I Individual chromosomes gather at each of

the two poles

Meiosis II basically a mitotic division of the products of meiosis I,

except that the sister non-identical chromatids

four stages 1. Prophase II

new spindle forms to attach to chromosome clusters 2. Metaphase II

spindle fibers bind to both sides of the centromere and individual chromosomes align along a central plane

3. Anaphase II sister chromatids move to opposite poles

4. Telophase II the nuclear envelope is reformed around each of the four

sets of daughter chromosomes

Practice questions1. Prokaryotes reproduce new cells byA) copying DNA then undergoing binary fission.B) splitting in halfC) undergoing mitosisD) copying DNA then undergoing the M phase.

2. The eukaryotic cell cycle is different from prokaryotic cell division in all the following ways except:A) the amount of DNA present in the cellsB) how the DNA is packagedC) in the production of daughter cellsD) the involvement of microtubules.

3. In eukaryotes, the genetic material is found in chromosomes and:A) the more complex the organism, the more pairs of chromosomes it hasB) a few organisms have only one chromosomeC) most eukaryotes have between 10 and 50 pairs of chromosomesD) most eukaryotes have between 2 and 10 pairs of chromosomes.

4. Homologous chromosomes:A) are also referred to as sister chromatidsB) are genetically identicalC) carry information about the same traits located in the same places on the chromosomesD) are connected to each other at their centromeres.

5. In mitosis, when the duplicated chromosomes line up in the center of the cell, that stage is called:

A) Prophase B) metaphase C) anaphase D) telophase.

6. The division of the cytoplasm in the eukaryotic cell cycle is called:A) interphase.B) karyokinesis.C) cytokinesis.D) binary fission.

7. The cell cycle is controlled by:A) a series of checkpointsB) an internal clockC) the completion of one phase triggering the next phaseD) cell size-when it grows large enough the cell cycle is triggered.

8. When cell division becomes unregulated, and a cluster of cells begins to grow without regard for the normal controls, that is called:

A) a mutation.B) cancer.C) metastases.D) oncogenes.

9. During which stage of meiosis does crossing over occur?A) prophase IB) anaphase IC) metaphase IID) interphase

10. The purpose of mitosis is to ____, while the purpose of meiosis is to _____.A) make diploid cells/make haploid cellsB) make haploid cells/make diploid cellsC) make cells which are either haploid or diploid/make cells which are haploidD) make cells which are haploid/make cells which vary in chromosome number

11. An egg and a sperm unite to form a new organism. In order to prevent the new organism from having twice as many chromosomes as its parents:

A) half of the chromosomes in the new organism quickly die off, leaving the correct number

B) half of the chromosomes from the egg, and half from the sperm, are ejected from the new cell

C) the large egg contains all the chromosomes, the tiny sperm only contributes some DNA

D) germ cells went through meiosis; the egg and sperm only have half the parental chromosomes.

12. The diploid number of chromosomes in humans is 46. The haploid number is:A) 138 B) 92 C) 46 D) 23.

13. In organisms that have sexual life cycles there is a time when there are:A) 1n gametes (haploid), followed by 2n zygotes (diploid)B) 2n gametes (haploid), followed by 1n zygotes (diploid)C) 2n gametes (diploid), followed by 1n zygotes (haploid)D) 1n gametes (diploid), followed by 2n zygotes (haploid).

14. The purpose of meiosis I is to:A) duplicate all chromosomesB) randomly separate the homologous pairs, called independent assortmentC) separate the duplicated sister chromatidsD) divide the original material into four complete haploid cells.

15. The purpose of meiosis II is to:A) duplicate all chromosomesB) randomly separate the homologous pairs, called independent assortmentC) separate the duplicated sister chromatidsD) divide the original material into four complete haploid cells.

1 meiosis insures that a. each gamete receives the same genes b. chromosome number is doubled in the...

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