Download CHAPTER 1 Genetics: An Introduction

The Continuity of Life
How Cells Reproduce
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Cell division is at the heart of the
reproduction of cells and organisms
Organisms can reproduce sexually or
asexually.
Some organisms make exact copies of
themselves, asexual reproduction.
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Other organisms make similar copies of
themselves in a more complex process,
sexual reproduction
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Cells arise only from preexisting cells
Cellular reproduction is called cell division
Cell division allows an embryo to develop into
an adult
„ It also ensures the continuity of life from one
generation to the next
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What Occurs During the Prokaryotic Cell
Cycle?
Prokaryotic cells divide asexually
„ These
cells possess a single
chromosome, containing genes
„ The chromosome is replicated
„ The cell then divides into two cells, a
process called binary fission
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What Occurs During the Eukaryotic Cell
Cycle?
The cell cycle consists of two major phases:
„Interphase,
where chromosomes duplicate and
cell parts are made.
„The mitotic phase, when cell division occurs
„Interphase consists of three main stages:
G1 or Gap 1
S or Synthesis
G2 or Gap 2
Cell division
cell
division
cell growth and
DNA replication
The chromosomes of eukaryotes
duplicate with each cell division
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A eukaryotic cell has many more genes than
a prokaryotic cell
The genes are grouped into
multiple chromosomes,
found in the nucleus
„ The chromosomes of this
plant cell are stained
dark purple
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Chromosomes contain a very long DNA
molecule with thousands of genes
Sister chromatids
Individual chromosomes are
only visible during cell
division
„ They are packaged as
chromatin.
„ Before a cell starts dividing,
during S, the chromosomes
are duplicated. This process
produces sister chromatids
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Centromere
There Are Two Types of division in Eukaryotic
Cells: Mitotic Cell Division and Meiotic Cell
Division
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Mitotic cell division
is the type of cell division when a mother cell
produces two genetically identical daughter
cells. For example: If the mother cell has 46
chromosomes the daughter cells will also have
46 chromosomes.
Cell division has two steps: Mitosis or division of
the nucleus and cytokinesis or division of the
cytoplasm.
Mitosis has four phases: Prophase, Metaphase,
Anaphase and Telophase.
Cytokinesis begins at the end of anaphase.
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The process of mitotic cell division is
used for growth, healing, repair and
regeneration.
Meiosis
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Meiosis is the process of cell division that we
use for the formation of sex or reproductive
cells.
In humans, Meiosis takes place in the
reproductive organs: the testis in males and the
ovaries in females.
In plants, Meiosis takes places in the anthers
(male structures) and in the ovary (female
structure) of the flower.
When a mother cell divides, it produces four
genetically different daughter cells with half the
number of chromosomes than the mother cell.
Chromosomes are matched in
homologous pairs
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Somatic cells of each
species contain a
specific number of
chromosomes
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Chromosomes
Centromere
Human cells have 46,
making up 23 pairs of
homologous
chromosomes
Sister chromatids
Gametes have a single set of
chromosomes
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Cells with two sets of chromosomes are said to be
diploid
Gametes are haploid, with only one set of
chromosomes
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The human
life cycle
Haploid gametes (n = 23)
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
Diploid
zygote
(2n = 46)
Multicellular
diploid adults
(2n = 46)
Mitosis and
development
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At fertilization, a sperm fuses with an egg,
forming a diploid zygote
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Repeated mitotic divisions lead to the
development of a mature adult
The adult makes haploid gametes by meiosis
All of these processes make up the sexual life
cycle of organisms
mitotic cell division,
differentiation, and growth
adults
baby
mitotic cell division,
differentiation,
and growth
meiotic cell
division in
ovaries
embryo
egg
mitotic
cell division,
differentiation,
and growth
fertilized
egg
sperm
fertilization
meiotic cell
division in
testes
Homologous chromosomes carry
different versions of genes
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The differences between homologous
chromosomes are based on the fact that
they can carry different versions of a gene at
corresponding loci
Coat-color genes
Eye-color genes
Brown
Black
C
E
c
e
White
Pink
Tetrad in parent cell
(homologous pair of
duplicated chromosomes)
C
E
C
E
c
e
c
e
Chromosomes of
the four gametes
Some DNA information
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Cellular DNA is organized into
chromosomes.
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The genome is all the genetic information
(all the genes) of one organism.
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A gene is a fragment of DNA that has the
information for one specific trait.
Examples: color of the eyes.
All the variations of one gene are called
alleles: for example, blue, green, almond,
brown, red, etc.