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CHAPTER 8 CELLULAR REPRODUCTION: CELLS FROM CELLSGeneral 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.
Cell Replacement Growth via Cell Division
FUNCTIONS OF CELL DIVISION
Human kidney cell Early human embryo
LMColo
rize
d T
EM
Figure 8.1a
Asexual ReproductionFUNCTIONS OF CELL DIVISION
Sea stars
LM
Amoeba African Violet
Figure 8.1b
WHAT CELLULAR REPRODUCTION ACCOMPLISHES 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
Number of chromosomesin body cells
Indian muntjac deer
Species
Opossum
Koala
Human
Mouse
Giraffe
Buffalo
Dog
Red viscacha rat
Duck-billed platypus
102
78
60
54
46
40
30
22
16
6
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
Duplicated chromosomes(sister chromatids) T
EM
Tight helical fiber
Looped domains
TEM
Centromere
Nucleosome
“Beads ona string”
Histones
DNA double helix
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
Chromosomeduplication
Sisterchromatids
Chromosomedistribution todaughter 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:
Nuclearenvelope
LM
Plasmamembrane
Chromosome, consistingof two sister chromatids
Spindle microtubules
Fragments of nuclear envelopeCentrosome
Centromere
Early mitotic spindle
Centrosomes (with centriole pairs)
Chromatin
PROPHASEINTERPHASE
Figure 8.7.a
ANAPHASEMETAPHASE TELOPHASE AND CYTOKINESIS
Spindle Daughterchromosomes
Cleavagefurrow
Nuclearenvelopeforming
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.
HOMOLOGOUS CHROMOSOMES
Different individuals of a single
A human somatic cell
A karyotype is an image
Homologous chromosomes are
Humans have:
GAMETES AND THE LIFE CYCLE OF SEXUAL ORGANISMS
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
In crossing over:
Genetic recombination,
WHEN MEIOSIS GOES AWRY
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: