Transcript Chapter 5 The Working Cell

CHAPTER 8
CELLULAR REPRODUCTION:
CELLS FROM CELLS
General Biology
CM Lamberty
BIOLOGY AND SOCIETY
Rain Forest Rescue
 Pollination of near extinction
 Endangered species of plants that normally
reproduce sexually can by propagated by asexual
reproduction.
 Cell division is at the heart of organismal
reproduction, whether by sexual or asexual
means

Figure 8.00a
WHAT CELLULAR REPRODUCTION
ACCOMPLISHES

Reproduction:

When a cell undergoes reproduction, or cell division,

Before a parent cell splits into two

During cell division, each daughter cell receives one set
of chromosomes.
Human kidney cell
LM
Colorized TEM
FUNCTIONS OF CELL DIVISION
Cell Replacement
Growth via Cell Division
Early human embryo
Figure 8.1a
Amoeba
LM
FUNCTIONS OF CELL DIVISION
Asexual Reproduction
Sea stars
African Violet
Figure 8.1b
WHAT CELLULAR REPRODUCTION
ACCOMPLISHES



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In asexual reproduction:
Some multicellular organisms, such as sea stars, can grow new
individuals from fragmented pieces.
Growing a new plant from a clipping is another example of asexual
reproduction.
In asexual reproduction,


Mitosis is the type of cell division responsible for:
Sexual reproduction requires fertilization of an egg by a sperm using a
special type of cell division called meisois
CELL CYCLE AND MITOSIS

In a eukaryotic cell:
Most genes are located on chromosomes in the cell
nucleus
 A few genes are found in DNA in mitochondria and
chloroplasts

EUKARYOTIC CHROMOSOMES
Each eukaryotic chromosome contains one very
long DNA molecule, typically bearing 1000s of
genes
 The number of chromosomes in a eukaryotic cell
depends on the species

Species
Indian muntjac deer
Koala
Opossum
Giraffe
Mouse
Human
Duck-billed platypus
Buffalo
Dog
Red viscacha rat
Number of chromosomes
in body cells
6
16
22
30
40
46
54
60
78
102
Figure 8.2
EUKARYOTIC CHROMOSOMES

Chromosomes
Are made of chromatin, a combination of DNA and
protein molecules
 Are not visible in a cell until cell divisions occurs

Chromosomes
EUKARYOTIC CHROMOSOMES

THE DNA in a cell is packed into an elaborate,
multilevel system of coiling and folding
DNA double helix
Histones
TEM
“Beads on
a string”
Nucleosome
Tight helical fiber
Duplicated chromosomes
(sister chromatids)
TEM
Looped domains
Centromere
Figure 8.4
EUKARYOTIC CHROMOSOMES

Before a cell divides, it duplicates all of its
chromosomes, resulting

Sister chromatids are joined together

When the cell divides,

Once separated, each chromatid is
Chromosome
duplication
Sister
chromatids
Chromosome
distribution to
daughter cells
Figure 8.5
THE CELL CYCLE

A cell cycle is the orderly sequence of events

The cell cycle consists of two district phases:
Most of the cell cycle is spent in interphase
 During interphase, a cell:

THE CELL CYCLE

The mitotic (M) phase includes two overlapping
processes:
Mitosis, in which the nucleus and its contents divide
evenly into two daughter nuclei
 Cytokinesis, in which the cytoplasm is divided in two

MITOSIS AND CYTOKINESIS

During mitosis the mitotic spindle,

Spindle microtubules grow from

Mitosis consists of four distinct phases:
INTERPHASE
Centrosomes
(with centriole pairs)
Chromatin
PROPHASE
Fragments of
Early mitotic
Centrosome nuclear envelope
spindle
Centromere
Spindle
microtubules
LM
Chromosome, consisting
Nuclear Plasma
envelope membrane of two sister chromatids
Figure 8.7.a
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Nuclear
envelope
forming
Spindle
Cleavage
furrow
Daughter
chromosomes
Figure 8.7b
MITOSIS AND CYTOKINESIS

Cytokinesis typically:
CANCER CELLS: GROWING OUT OF CONTROL
Normal plant and animal cells have a cell cycle
control system that consists of specialized
proteins, which send “stop” and “go-ahead”
signals at certain key points during the cell cycle.
 What is cancer?

Cancer cells can form tumors
 The spread of cancer cells beyond their original
site of origin is
 Malignant tumors can


A person with a malignant tumor is said to have cancer
CANCER CELLS: GROWING OUT OF CONTROL
CANCER TREATMENT

Cancer treatment can involve:
CANCER PREVENTION AND SURVIVAL

Certain behaviors can decrease the risk of cancer:
MEIOSIS, THE BASIS OF SEXUAL REPRODUCTION

Sexual Reproduction:
Uses meiosis
 Uses fertilization
 Produces offspring that contain a unique combination
of genes from the parents.
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HOMOLOGOUS CHROMOSOMES

Different individuals of a single

A human somatic cell

A karyotype is an image
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Homologous chromosomes are

Humans have:
GAMETES AND THE LIFE CYCLE OF
SEXUAL ORGANISMS
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The life cycle of a multicellular organism is the
sequence of stages
Humans are diploid organisms in which
In humans a haploid sperm fuses with a haploid
egg during

Sexual life cycles involve an alternation

Meiosis produces
THE PROCESS OF MEIOSIS

In meiosis
REVIEW: COMPARING MITOSIS AND
MEIOSIS
In mitosis and meiosis, the chromosomes duplicate
only once, during the preceding interphase.
 The number of cell divisions varies:


All the events unique to meiosis occur during
meiosis I
THE ORIGIN OF GENETIC VARIATION


Offspring of sexual reproduction
Independent Assortment of chromosomes
 When aligned during metaphase I of meiosis,


Every chromosome pair orients
For any species the to total number of
chromosome combinations that can appear in the
gametes due to independent assortment is

2n where n is the haploid number
RANDOM FERTILIZATION

A human egg cell is fertilized randomly by one
sperm,
CROSSING OVER
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In crossing over:

Genetic recombination,
WHEN MEIOSIS GOES AWRY
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What happens when errors occur in meiosis?
How Accidents during Meiosis can alter
chromosomes

In nondisjunction,
Nondisjunction can occur
 If nondisjunction occurs, and a normal sperm
fertilizes an egg with an extra chromosome,


If the organism survives,
WHEN MEIOSIS GOES AWRY
DOWN SYNDROME: AN EXTRA CHROMOSOME 21

Down Syndrome
Is also called trisomy 21
 Is a condition in which an individual has an extra
chromosome 21
 Affects about one out of every 700 children

DOWN SYNDROME: AN EXTRA CHROMOSOME 21

The incidence of Down Syndrome increases with
the age of the mother.
ABNORMAL NUMBERS OF SEX
CHROMOSOMES

Nondisjunction can also affect the sex
chromosomes.
EVOLUTION CONNECTION: THE
ADVANTAGE OF SEX


Asexual reproduction conveys
an evolutionary advantage
when plants are
Sexual reproduction may
convey an evolutionary
advantage by: