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: