• No results found

C. 8 outline

N/A
N/A
Protected

Academic year: 2020

Share "C. 8 outline"

Copied!
9
0
0

Loading.... (view fulltext now)

Full text

(1)

CHAPTER

8

The Cellular Basis of Reproduction and Inheritance

Lecture Outline

I. Introduction

A.Cancer cells

1. start out as normal body cells,

2. undergo genetic mutations,

3. lose the ability to control the tempo of their own division, and

4. cause disease.

B.Cancer therapy seeks to disrupt one or more steps in cell division.

C.In a healthy body, cell division allows for

1. growth,

2. the replacement of damaged cells, and

3. the development from an embryo into an adult.

D.In sexually reproducing organisms, eggs and sperm result from

1. mitosis and

2. meiosis.

II. Cell Division and Reproduction

A.8.1 Cell division plays many important roles in the lives of organisms

1. The ability of organisms to reproduce their own kind is a key characteristic of life.

2. Cell division

a. is reproduction at the cellular level,

b.produces two “daughter” cells that are genetically identical to each other and the original “parent” cell,

c. requires the duplication of chromosomes, the structures that contain most of the cell’s DNA, and

d.sorts new sets of chromosomes into the resulting pair of daughter cells.

3. Cell division is used

a. for reproduction of single-celled organisms,

b.growth of multicellular organisms from a fertilized egg into an adult,

c. repair and replacement of cells, and

d.sperm and egg production.

4. Living organisms reproduce by two methods.

a. Asexual reproduction

i. produces offspring that are identical to the original cell or organism and

ii. involves inheritance of all genes from one parent.

b. Sexual reproduction

i. produces offspring that are similar to the parents but show variations in traits and

ii. involves inheritance of unique sets of genes from two parents.

5. Cell division is used for

a. reproduction of single-celled organisms,

b. growth of multicellular organisms from a fertilized egg into an adult,

(2)

B. 8.2 Prokaryotes reproduce by binary fission

1. Prokaryotes(single-celled bacteria and archaea) reproduce by binary fission

(“dividing in half”).

2. The chromosome of a prokaryote is typically

a. a singular circular DNA molecule associated with proteins and

b.much smaller than those of eukaryotes.

3. Binary fission of a prokaryote occurs in three stages:

a. duplication of the chromosome and separation of the copies,

b.continued elongation of the cell and movement of the copies, and

c. division into two daughter cells.

III. The Eukaryotic Cell Cycle and Mitosis

A.8.3 The large, complex chromosomes of eukaryotes duplicate with each cell division

1. Eukaryotic cells

a. are more complex and larger than prokaryotic cells,

b.have more genes, and

c. store most of their genes on multiple chromosomes within the nucleus.

2. Each eukaryotic species has a characteristic number of chromosomes in each cell nucleus.

3. Eukaryotic chromosomes are composed of chromatin consisting of

a. one long DNA molecule and

b.proteins that help maintain the chromosome structure and control the activity of its genes.

4. To prepare for division, the chromatin becomes

a. highly compact and

b.visible with a microscope.

5. Before a eukaryotic cell begins to divide, it duplicates all of its chromosomes, resulting in two copies called sister chromatids.

6. The sister chromatids are joined together along their lengths and are cinched especially tightly at a narrowed “waist” called the centromere.

7. When a cell divides, the sister chromatids

a. separate from each other and are then called chromosomes, and

b.sort into separate daughter cells.

B. 8.4 The cell cycle includes growing and division phases

1. The cell cycle is an ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division.

2. The cell cycle consists of two stages, characterized as follows:

a. Interphase: duplication of cell contents

i. G1—growth, increase in cytoplasm ii. S—duplication of chromosomes

iii. G2—growth, preparation for division b. Mitotic phase: division

i. Mitosis—division of the nucleus

(3)

C.8.5 Cell division is a continuum of dynamic changes

1. Mitosis progresses through a series of stages:

a. prophase,

b. prometaphase,

c. metaphase,

d. anaphase, and

e. telophase.

2. Cytokinesis often overlaps telophase.

3. A mitoticspindle

a. isrequired to divide the chromosomes,

b.guides the separation of the two sets of daughter chromosomes, and

c. is composed of microtubules and associated proteins.

d.Spindle microtubules emerge from two centrosomes, microtubule-organizing regions in the cytoplasm of eukaryotic cells.

4. Interphase

a. The cytoplasmic contents double.

b.Two centrosomes form.

c. Chromosomes duplicate in the nucleus during the S phase.

5. Prophase

a. In the nucleus, chromosomes become more tightly coiled and folded.

b. In the cytoplasm, the mitotic spindle begins to form as microtubules rapidly grow out from the centrosomes.

6. Prometaphase

a. The nuclear envelope breaks into fragments and disappears.

b.Microtubules extend from the centrosomes into the nuclear region.

c. Some spindle microtubules attach to the kinetochores.

7. Metaphase

a. The mitotic spindle is fully formed.

b.Chromosomes align at the cell equator.

c. Kinetochores of sister chromatids are facing the opposite poles of the spindle.

8. Anaphase

a. Sister chromatids separate at the centromeres.

b.Daughter chromosomes are moved to opposite poles of the cell as motor proteins move the chromosomes along the spindle microtubules and kinetochore

microtubules shorten.

c. Spindle microtubules not attached to chromosomes lengthen, moving the poles farther apart.

d.At the end of the anaphase, the two ends of the cell have equal collections of chromosomes.

9. Telophase

a. The cell continues to elongate.

b.The nuclear envelope forms around chromosomes at each pole, establishing daughter nuclei.

c. Chromatin uncoils.

d.The mitotic spindle disappears.

10. During cytokinesis, the cytoplasm is divided into separate cells.

11. Cytokinesis usually occurs simultaneously with telophase.

(4)

1. In animal cells, cytokinesis occurs as

a. a cleavage furrow forms from a contracting ring of microfilaments, interacting with myosin, and

b.the cleavage furrow deepens to separate the contents into two cells.

2. In plant cells, cytokinesis occurs as

a. a cell plate forms in the middle, from vesicles containing cell wall material,

b.the cell plate grows outward to reach the edges, dividing the contents into two cells, and

c. each cell now possesses a plasma membrane and cell wall.

E. 8.7 Anchorage, cell density, and chemical growth factors affect cell division

1. The cells within an organism’s body divide and develop at different rates.

2. Cell division is controlled by

a. anchorage dependence, the need for cells to be in contact with a solid surface to divide,

b. density-dependent inhibition, in which crowded cells stop dividing,

c. the presence of essential nutrients, and

d. growth factors, proteins that stimulate division,

F. 8.8 Growth factors signal the cell cycle control system

1. The cell cycle control system is a cycling set of molecules in the cell that triggers and coordinates key events in the cell cycle.

2. Checkpoints in the cell cycle can

a. stop an event or

b.signal an event to proceed.

3. There are three major checkpoints in the cell cycle.

a. G1 checkpoint: allows entry into the S phase or causes the cell to leave the cycle,

entering a nondividing G0 phase b.G2 checkpoint

c. M checkpoint

4. Research on the control of the cell cycle is one of the hottest areas in biology today.

G.8.9 CONNECTION: Growing out of control, cancer cells produce malignant tumors

1. Cancer currently claims the lives of 20% of the people in the United States and other industrialized nations.

2. Cancer cells escape controls on the cell cycle.

3. Cancer cells divide excessively and invade other tissues of the body.

4. A tumor is mass of abnormally growing cells within otherwise normal tissue.

a. Benign tumors remain at the original site but may disrupt certain organs if they grow in size.

b. Malignant tumors can spread to other locations in a process called metastasis.

c. An individual with a malignant tumor is said to have cancer.

5. Cancers are named according to the organ or tissue in which they originate.

a. Carcinomas originate in external or internal body coverings.

b.Leukemia originates from immature white blood cells within the blood or bone marrow.

c. Localized tumors can be

i. removed surgically and/or

ii. treated with concentrated beams of high-energy radiation.

(5)

H.8.10 SCIENTIFIC THINKING: Tailoring treatment to each patient may improve cancer therapy

1. It is increasingly possible to personalize cancer treatment by:

a. sequencing the genome of tumor cells and

b.tailoring treatment based on the tumor’s specific genetic profile.

IV. Meiosis and Crossing Over

A.8.11 Chromosomes are matched in homologous pairs

1. In humans, somatic cells have 46 chromosomes, forming 23 pairs of homologous chromosomes.

2. Homologous chromosomes are matched in

a. length,

b.centromere position, and

c. staining pattern.

3. A locus (plural, loci) is the position of a gene.

4. Different versions of a gene may be found at the same locus on the two chromosomes of a homologous pair.

5. The human sex chromosomes X and Y differ in size and genetic composition.

6. The other 22 pairs of chromosomes are autosomes with the same size and genetic composition.

B. 8.12 Gametes have a single set of chromosomes

1. An organism’s life cycle is the sequence of stages leading from the adults of one generation to the adults of the next.

2. Humans and many animals and plants are diploid, because all somatic cells contain pairs of homologous chromosomes.

3. Gametes

a. are eggs and sperm and

b.are said to be haploid because each cell has a single set of chromosomes.

4. The human life cycle begins when a haploid sperm fuses with a haploid egg in

fertilization.

5. The zygote, formed by fertilization, is now diploid.

6. Mitosis of the zygote and its descendants generates all the somatic cells into the adult form.

7. Gametes are made by meiosis in the ovaries and testes.

(6)

C.8.13 Meiosis reduces the chromosome number from diploid to haploid

1. Meiosis is a type of cell division that produces haploid gametes in diploid organisms.

2. Two haploid gametes may then combine in fertilization to restore the diploid state in the zygote.

3. Meiosis and mitosis are preceded by the duplication of chromosomes. However,

a. meiosis is followed by two consecutive cell divisions and

b.mitosis is followed by only one cell division.

4. Because in meiosis, one duplication of chromosomes is followed by two divisions, each of the four daughter cells produced has a haploid set of chromosomes.

5. Interphase: Like mitosis, meiosis is preceded by an interphase, during which the chro-mosomes duplicate.

6. Meiosis I – Prophase I – events

a. The nuclear membrane dissolves.

b.Chromatin tightly coils up.

c. Homologous chromosomes, each composed of two sister chromatids, come together as pairs in a process called synapsis.

d.During synapsis, chromatids of homologous chromosomes exchange segments in a process called crossing over.

e. The chromosome tetrads move toward the center of the cell.

7. Meiosis I – Metaphase I – Tetrads align at the cell equator.

8. Meiosis I – Anaphase I

a. Homologous pairs separate and move toward opposite poles of the cell.

b.Unlike mitosis, the sister chromatids making up each doubled chromosome remain attached.

9. Meiosis I – Telophase I

a. Duplicated chromosomes have reached the poles.

b.Usually, cytokinesis occurs along with telophase.

10. Meiosis II follows meiosis I without chromosome duplication.

11. Each of the two haploid products enters meiosis II.

12. Meiosis II – Prophase II

a. A spindle forms and moves chromosomes toward the middle of the cell.

13. Meiosis II – Metaphase II – Duplicated chromosomes align at the cell equator like they are in mitosis.

14. Meiosis II – Anaphase II a. Sister chromatids separate.

b.Individual chromosomes move toward opposite poles.

15. Meiosis II – Telophase II

a. Chromosomes have reached the poles of the cell.

b.A nuclear envelope forms around each set of chromosomes.

c. With cytokinesis, four haploid cells are produced.

D.8.14 VISUALIZING THE CONCEPT: Mitosis and meiosis have important similarities and differences

1. Mitosis and meiosis both begin with diploid parent cells that have chromosomes duplicated during the previous interphase.

2. However, the end products differ.

a. Mitosis produces two genetically identical diploid somatic daughter cells.

(7)

E. 8.15 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring

1. Genetic variation in gametes results from

a. independent orientation at metaphase I and

b.random fertilization.

2. Independent orientation at metaphase I

a. Each pair of chromosomes independently aligns at the cell equator.

b.There is an equal probability of the maternal or paternal chromosome facing a given pole.

c. The number of combinations for chromosomes packaged into gametes is 2n, where

n = haploid number of chromosomes.

3. Random fertilization means that the combination of each unique sperm with each unique egg increases genetic variability.

F. 8.16 Homologous chromosomes may carry different versions of genes

1. Separation of homologous chromosomes during meiosis can lead to genetic differences between gametes.

a. Homologous chromosomes may have different versions of a gene at the same locus.

b.One version was inherited from the maternal parent and the other came from the paternal parent.

c. Because homologous chromosomes move to opposite poles during anaphase I, ga-metes will receive either the maternal or paternal version of the gene.

G.8.17 Crossing over further increases genetic variability

1. Genetic recombination is the production of new combinations of genes due to crossing over.

2. Crossing over is an exchange of corresponding segments between separate nonsister chromatids on homologous chromosomes.

a. Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and crossing over.

b.Corresponding amounts of genetic material are exchanged between maternal and paternal (nonsister) chromatids.

V. Alterations of Chromosome Number and Structure

A.8.18 Accidents during meiosis can alter chromosome number

1. Nondisjunction is the failure of chromosomes or chromatids to separate normally during meiosis. This can happen during

a. meiosis I, if both members of a homologous pair go to one pole, or

b.meiosis II, if both sister chromatids go to one pole.

2. Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes.

B. 8.19 A karyotype is a photographic inventory of an individual’s chromosomes

1. A karyotype is an ordered display of magnified images of an individual’s chromosomes arranged in pairs.

2. Karyotypes

a. are often produced from dividing cells arrested at metaphase of mitosis and

b.allow for the observation of

i. homologous chromosome pairs,

ii. chromosome number, and

(8)

C.8.20 CONNECTION: An extra copy of chromosome 21 causes Down syndrome

1. Trisomy 21

a. involves the inheritance of three copies of chromosome 21 and

b.is the most common human chromosome abnormality.

2. A person with trisomy 21has a condition called Downsyndrome, which produces a characteristic set of symptoms, including

a. characteristic facial features,

b.short stature,

c. heart defects,

d.susceptibility to respiratory infections, leukemia, and Alzheimer’s disease, and

e. varying degrees of developmental disabilities.

3. The incidence increases with the age of the mother.

D.8.21 CONNECTION: Abnormal numbers of sex chromosomes do not usually affect survival

1. Sex chromosome abnormalities seem to upset the genetic balance less than an unusual number of autosomes. This may be because of

a. the small size of the Y chromosome or

b.X-chromosome inactivation.

2. The following table lists the most common human sex chromosome abnormalities. In general,

a. a single Y chromosome is enough to produce “maleness,” even in combination with several X chromosomes, and

b.the absence of a Y chromosome yields “femaleness.”

E. 8.22 EVOLUTION CONNECTION: New species can arise from errors in cell division

1. Errors in mitosis or meiosis may produce polyploid species, with more than two chro-mosome sets.

2. The formation of polyploid species is

a. widely observed in many plant species but

b.less frequently found in animals.

F. 8.23 CONNECTION: Alterations of chromosome structure can cause birth defects and cancer

1. Chromosome breakage can lead to rearrangements that can produce genetic disorders or, if changes occur in somatic cells, cancer.

2. These rearrangements can lead to four types of changes in chromosome structure.

a. A deletion is the loss of a chromosome segment.

b.A duplication is the repeat of a chromosome segment.

c. An inversion is the reversal of a chromosome segment.

d.A translocation is the attachment of a segment to a nonhomologous chromosome. A translocation may be reciprocal.

3. Inversions are less likely than deletions or duplications to produce harmful effects because in inversions all genes are still present in their normal number.

4. Many deletions cause serious physical or mental problems.

5. Translocation may or may not be harmful.

6. Chronic myelogenous leukemia (CML)

a. is one of the most common leukemias,

b.affects cells that give rise to white blood cells (leukocytes), and

(9)

7. Such an exchange causes cancer by activating a gene that leads to uncontrolled cell cycle progression.

References

Related documents

1) To develop an insight-based visual approach to assist the process of pure IL design, with multi properties consideration, to provide insight to user regarding

chromosomes separation of chromatids 4 daughter cells (haploid) Homologous. chromosomes

9 This neoplasm is the most frequent worldwide, with high prevalence and mortality rates, thus being the main cause of death in women living in the most

 Be able to recognize and sketch the arrangement of chromosomes when attached to the spindle just prior to the chromosome divisions in mitosis and meiosis and to relate

11.2 Mitosis Cell division where 2 daughter cells are produced that have the same number of chromosomes as the parent 11.2 Haploid Cells have half the number of chromosomes..

• Daughter cells produced by meiosis, which are haploid (1n), contain only half of the genetic material of the parent cell (one of each chromosome). • Daughter cells produced

meiosis has one DNA replication but two divisions (reductive division), resulting in up to four genetically distinct daughter cells; in the process, homologous chromosomes

Article III, “Insulting the Sacred in a Multicultural Society: The Conviction of Jussi Halla-aho Under the Finnish Religious Insult Section”, originally published in the