Download Biology 3201 Unit 1 Chapter 12

Biology 3211
Unit I: Cell Reproduction & the Continuity of Life
Chapter 12: Cell Reproduction and the Continuity of Life
“The number of cells in our bodies
is defined by an equilibrium of
opposing forces: mitosis adds cells,
while programmed cell death
removes them. Just as too much
cell division can lead to a
pathological increase in cell number,
so can too little cell death.”
~H. Robert Horvitz
Somatic Cell Reproduction
Text Reference: NL Biology, Pages 454 - 461
Organization of Genetic Material
In this section you will learn how genetic material is organized
within the nucleus of eukaryotic cells.
recall- eukaryotic: “true nucleus”; a cell that contains a
membrane-bound, structurally distinct nuclei and other
membrane-bound organelles
2
● the structure and function of a cell are determined by its
genetic material
● the genetic material of a cell is DNA (deoxyribonucleic
acid):
○ a molecule of nucleic acid that governs processes of
heredity
○ is located within the nucleus
3
● a segment of DNA is known as a gene: governs expression
of a trait
● many genes have more than one allele: one of the
different forms of the same gene
● DNA is wrapped around histones: proteins in the nucleus
4
○ histones act as spools which DNA winds around,
allowing it to be packaged into more condensed
structures
5
● for most of a cell’s life cycle, DNA exists as chromatin:
○ non-condensed form of genetic material
○ long strands of DNA and histones that will later form
chromosomes
6
● however, during cell division, DNA is compacted into
structures called chromosomes:
○ a length of DNA and associated protein;
condensed form of genetic material
○ is condensed chromatin
7
Figure 12.2 The
levels of
organization of
genetic
material in a
eukaryotic cell
8
○ X-shaped structure of a duplicated chromosome is
made up of two sister chromatids which are held
together by a structure called a centromere
9
●
sister chromatid: one of two chromosomes that are
genetically identical and held together at the centromere
○each sister chromatid contains an identical copy of
the genetic information (DNA)
10
● the difference between chromatin
and chromosomes:
○ chromatin consists of the unravelled
structure of DNA for the purpose
of packaging into the nucleus
○ a chromosome consists of the
condensed structure of DNA for the
division of genetic material
11
● there are two types of chromosomes present in cells:
1. sex chromosome: X or Y chromosome; determines
genetic sex
2. autosome: chromosome other than sex chromosome
12
➢ in humans, each cell normally contains 23 pairs of
chromosomes, for a total of 46 chromosomes
➢ 22 of these pairs are autosomes:
○ look the same in both males and females
○ are referred to as homologous chromosomes:
chromosomes with the same gene sequence
➢ the 23rd pair (sex chromosomes) differ between
males and females
○ XY = male; XX = female
13
14
➢ each gamete (male or female reproductive cell;
sperm or egg) contain 23 chromosomes and two
gametes join together to form a zygote with 46
chromosomes
15
● the number of chromosomes differ depending upon cell
type:
○ somatic cells
■ somatic cells: body cells; not a germ/sex cell
■ are diploid: cell with pairs of homologous
chromosomes
■ expressed as 2n (where n = # of chromosomes)
16
■ one copy of the gene/allele
that resides at a specific locus
(location on a chromosome)is
inherited from each parent
■ This inheritance pattern means
that each somatic cell contains
two copies of every
chromosome
17
○ gametes
■ are haploid: cell with half the number of
chromosomes as diploid: unpaired chromosomes
■ expressed as n (where n = # of chromosomes)
■ contain only one copy of every chromosome
18
❏ the total number of chromosomes in
somatic cells is referred to as the diploid
number
❏ the total number of chromosomes in
gametes is referred to as the haploid
number; this number is always half of the
diploid number
19
○
example:
20
Complete Launch Lab: Page 463
21
The Cell Cycle
In this section you will learn about the stages of the cell cycle
within somatic cells.
● the life cycle of the cell is
called the cell cycle:
a continuous sequence
of cell growth and
division
22
● the reproduction rate
of somatic cells vary,
based on their type
and their environment
○ example:
■ stomach (2-9
days), red blood
cells (4 months)
23
● different cells have different
timing for their cell cycles;
some take longer than others
and may also spend different
amounts of time in each stage
24
The Cell Cycle
(and cancer)
[Updated]
(4:40- 6:40 min)
25
Stages of the cell cycle
● to divide, a cell must complete several important tasks: it
must grow, copy its genetic material (DNA), and physically
split into two daughter cells
● consists of two main stages:
1. growth stage (aka interphase)
2. division stage
26
Stages of
the cell
cycle
27
1. Interphase
interphase: growth stage of cell cycle
● is the longest stage of the cell cycle
● is a stage in which the cell grows and makes a copy of its
DNA
● the cell carries out its regular metabolic processes and
prepares for cell division
28
1. Interphase (continued)
● divided into three phases:
➢
I.
G1 phase
❏ growth or Gap 1 phase
❏ the cell grows rapidly and makes the molecular
building blocks (except DNA) it will need in later
steps
❏ it is during the G1 phase that a cell does whatever
a cell does, other than dividing
29
➢
II.
S phase
❏ synthesis phase
❏ DNA in the chromatin replicates to create an
identical copy
❏ S phase begins with replication and ends when
replication is complete
❏ at the end of S phase, the cell contains two
complete sets of DNA
30
S phase of
Interphase
31
➢
III. G2 phase
❏ second growth or Gap 2 phase
❏ the period between the DNA
replication and the various steps of the division stage
❏ allows the cell to rebuild its energy reserves for cell
division
❏ the cell grows more, makes proteins and organelles
required for division, and begins to reorganize its
contents in preparation for mitosis
32
2. Division
● also known as the mitotic (M) phase
● is the shorter stage of the cell cycle
● the cell divides its copied DNA and cytoplasm to make
two new cells
33
mitotic (M) phase
34
1. Division (continued)
● begins with a parent cell: original cell
that divides to produce two new
daughter cells during cell division
● results in the formation of two new
identical cells known as daughter cells:
either of two cells produced from the
division of a parent cell
35
Mitosis (0 - 1:31
min)
36
1. Division (continued)
● occurs in two stages:
I.
MITOSIS (Part I of Division stage of the Cell Cycle)
❏ mitosis: division of genetic material and the contents
of the cell’s nucleus
❏ four stages of mitosis:
❖ prophase, metaphase, anaphase, and
telophase (PMAT)
37
(i) prophase:
❖ chromatin coils up into tightly packed chromosomes
➢ imagine the difference between a slinky fully stretched out, and a
slinky that has been pressed back together; chromosomes during
prophase coil up into tight packages
➢ recall that the DNA has already been replicated during the S phase
of interphase so that the chromosomes will be duplicated and have
an X-shaped appearance
38
39
(i) prophase (continued):
❖ the nuclear membrane breaks down and nucleolus
disappears
❖ centrioles produced during interphase migrate to
opposite poles of the cell
➢ centriole: a pair of cylindrical-shaped organelles that
moves to opposite poles of the cell during prophase
and to which the spindle fibres are attached
40
(i) prophase (continued):
➢ spindle fibres start to form from each of the two
centrioles
➢ spindle fibres: a network of fibres made from
microtubules which will attach to chromosomes
41
(ii)
metaphase:
❖ spindle fibres attach to the centromere of each
chromosome and pull the chromosomes to the center, or
equator, of the cell
42
❖ spindle fibres from opposite poles also attach to the
centromere of each duplicated chromosome to ensure
that each new daughter cell will contain one of the sister
chromatids (and therefore the same genetic information)
43
(iii) anaphase:
❖ the centromere splits apart and
each sister chromatids is separated
from its copy
❖ each sister chromatid (now referred
to as a chromosome) is pulled to
opposite poles of the cell by
shortening spindle fibres
44
❖ at the end of anaphase, one complete diploid (2n)
set of chromosomes has been gathered at each pole
of the cell
45
(iv) telophase:
❖ begins when the separated chromatids (chromosomes)
reach the opposite poles of the cell
❖ chromosomes uncoil and form chromatin again
❖ spindle fibres break down and disappear
❖ a nuclear membrane forms around the chromatin
❖ a nucleolus forms within each nucleus
46
telophase
47
48
49
➢
II. CYTOKINESIS (Part II of Division stage of the Cell Cycle)
❏ cytokinesis: separation of the cytoplasm and
organelles to form two separate daughter cells
❏ takes place differently in animal and plant cells
50
Animal Cells
Plant Cells
●
animal cells can be pinched in ●
two because they’re relatively
soft and squishy
plant cells are much stiffer than
animal cells because they are
surrounded by a rigid cell wall
●
division of the cytoplasm
(cleavage) occurs at the
cleavage furrow: indentation
produced as a ring contracts
inward
●
division of the cytoplasm occurs at
the cell plate: membrane which
extends across the diameter of the
cell
●
the cell plate is reinforced by
cellulose and proteins to create a
new cell wall
●
the cell membrane pinches
inward along the cell's equator
51
Animal Cells
●
process involves both centrioles ●
and spindle fibres
Plant Cells
do not have centrioles; have
spindle fibres only
52
53
54
Cell Cycle Summary
Interphase
Division
55
Functions of MItosis & Cytokinesis
● the linked processes of mitosis and cytokinesis have three
important functions:
○ growth: enable organisms to grow from a single-celled
zygote into a mature organism that may contain
hundreds of trillions of cells
○ maintenance: produce new cells to replace worn out
or dead cells (like red blood cells)
○ repair: they can regenerate damaged tissues (such as
cuts, sunburn that blisters)
56
●
in addition, these processes ensure that the chromosome
number in each cell is maintained
○ the purpose of mitosis is to make more diploid (2n)
cells because there is a copy of each chromosome
(i.e. two sister chromatids), it is possible for each of the
daughter cells to receive a full set of the parent cell’s
genes
○ when the cell undergoes mitosis and cytokinesis, each
new daughter cell gets its own copy of each
chromosome
57
58
Mitosis: The Amazing
Cell Process that Uses
Division to Multiply!
(Updated) (5:30-8:08
min)
59
Complete
Questions: Page 461 #s 1, 2 (a-c), 7, 9
Cell Cycle Worksheet
STSE Article: Why is Henrietta Lacks Important?
Investigation 12.C: Page 471 - Observing Mitosis
60
Complete Questions: Page 461 #s 1, 2 (a-c), 7, 9
1. The following diagram represents the cell cycle.
a) What are the names of the processes represented by the letters A, B, and C?
b) The cell cycle consists of a growth stage and a cell division stage. What parts
of this diagram represent these stages? Summarize events that occur during
each of these stages.
61
Complete Questions: Page 461 #s 2 (a-c), 7, 9
2. Contrast the two terms in each pair of terms.
a) haploid and diploid
b) chromatin and chromosome
c) XX and XY
7. The somatic cells of a horse have 64 chromosomes.
a) What is the diploid number for a horse?
b) What is the haploid number for a horse?
c) How many chromosomes are in a normal horse gamete?
9. The scientists in a lab have isolated a substance that prevents cells
from synthesizing microtubules. What impact would this substance have
on cell division? Explain.
62
1. The following diagram represents the cell cycle.
a) What are the names of the processes represented by the
letters A, B, and C?
A: mitosis; B: cytokinesis; C: interphase
b) The cell cycle consists of a growth stage and a cell division
stage. What parts of this diagram represent these stages?
Summarize events that occur during each of these stages.
The growth stage is interphase and the cell division stage is
mitosis and cytokinesis.
63
2. Contrast the two terms in each pair of terms.
a) haploid and diploid
● Haploid cells have one set of chromosomes (n)
● Diploid cells have pairs of homologous chromosomes (2n)
b) chromatin and chromosome
● Chromatin is non-condensed form of DNA
● Chromosome is the condensed form of DNA; condensed
chromatin
c) XX and XY
XX is female; XY is male
64
7. The somatic cells of a horse have 64 chromosomes.
a) What is the diploid number for a horse? 64
b) What is the haploid number for a horse? 32
c) How many chromosomes are in a normal horse gamete?
32
65
9. The scientists in a lab have isolated a substance that
prevents cells from synthesizing microtubules. What impact
would this substance have on cell division? Explain.
Without spindle fibres, the chromosomes would not move to
the equator of the cell during metaphase or to the poles of
the cell during anaphase.
As a result, the duplicated chromosomes would not
separate and daughter cells would not receive an equal
number of chromosomes.
66
Assess Your Learning
Using the micrograph image to the
right, identify the phase of mitosis
shown and explain your reasoning.
67
Using the micrograph image to the
right, identify the phase of mitosis
shown and explain your reasoning.
The phase of mitosis shown is
metaphase; spindle fibres are
attached to the centromere of each
chromosome and the chromosomes
are pulled to the center, or equator,
of the cell.
68
Cancer and the Cell Cycle
Text Reference: NL Biology, Page 462
Read STSE Case Study, Page 462 - Cancer and the Cell Cycle
69
Cancer and the Cell Cycle
In this section you will examine the connection between the
cell cycle and cancer.
● the cell cycle is regulated by a checkpoint system used to
maintain healthy cell reproduction during an organism’s
lifetime
70
71
● the checkpoints consist of various regulatory
proteins at different stages of the cycle
● however, sometimes the genes that code for a
regulatory protein become altered through
mutation
○ mutation: permanent change to a cell’s DNA
72
● the protein does not function properly and may result in
the formation of cancer: uncontrolled cell division caused
by a mutation
● uncontrolled cell growth in cancer can result in the
formation of a tumour which may alter the function of
normal body tissues, and is able to invade other parts of
the body
73
74
● cancer research and treatment illustrates the difference
between scientific questions and technological problems:
○ determining how regulation of the cell cycle relates to
the development of cancer is a scientific question
○ developing therapies (i.e., technological products and
processes) to target cancer cells and cell cycle
regulation is a technological problem
75
Complete
STSE Video/Article: Why Do So Many People Get
Cancer?
Cancer Therapies Assignment
76
Formation of Reproductive Cells
Text Reference: NL Biology, Pages 463 - 472
Meiosis
In this section you will examine how meiosis results in the
production of gametes and describe the ways in which it
contributes to genetic variation.
meiosis: cell division that produces haploid gametes
77
recall: gamete: male or female reproductive cell; sperm or
egg
haploid: cell with half the number of chromosomes as diploid;
one copy of each chromosome (n)
78
● a sexual reproduction process that begins with a diploid parent
cell (two sets of chromosomes; 2n) and ends with haploid
daughter cells (single set of chromosomes; n)
● occurs in germ cells: gamete-producing cells which are
found in the testes and ovaries
● produces four daughter cells, each with half the number of
chromosomes as the parent cell
79
80
● during fertilization, a haploid gamete from a male (sperm)
and a haploid gamete from a female (egg) fuse to create
a diploid zygote, reestablishing the chromosome number
● the zygote has genetic information from both parents and
the same number of chromosomes as its parents
81
Stages of Meiosis
● germ cells proceed through interphase before dividing by
meiosis
● therefore, prior to beginning meiosis, a germ cell
contains duplicated chromosomes just as a somatic
cell does
82
● two phases of meiosis:
○ meiosis I; and meiosis II
■ two successive nuclear divisions; both resemble mitosis
(PMAT x 2)
83
MEIOSIS I: Four Stages (PMAT)
(i)
prophase I:
● chromatin condenses to form chromosomes
● nuclear membrane and nucleolus disappear
● centrioles produced during interphase migrate towards
opposite poles of the cell
● spindle fibres begin to form between the two centrioles
84
● unique events:
1. synapsis: aligning of replicated
homologous chromosomes in
prophase I
❏ grouping together of homologous chromosomes:
chromosomes with the same gene sequence
❏ they are similar but not identical since they contain
the same genes but carry different alleles of those
genes
85
❏ humans receive one of two homologous
chromosomes from each parent
86
❏ because each duplicated chromosome consists of
two sister chromatids, a pair of homologous
chromosomes is made up of four chromatids and is
called a tetrad: homologous chromosome pair; a
pair of sister chromatids synapsed with another pair
of sister chromatids
87
a chromosome tetrad is made up of a pair of sister
chromatids synapsed with another pair of sister chromatids
88
2. crossing over: exchange of genetic material between
non-sister chromatids
❏ non-sister chromatids: chromatids in a tetrad that do
not belong to the same
chromosome
❏ in the middle of a tetrad, two homologous but not
identical (i.e. non-sister chromatids) lie side by side
89
❏ non-sister chromatids cross over each other and exchange
segments of chromosomes (trade parts)
❏ as a result, individual chromosomes contain some
genes of maternal origin and some genes of paternal
origin
❏ in addition, crossing over can occur at several points
along non-sister chromatids
90
91
Meiosis and
Crossing Over
(1:46)
92
(ii) metaphase I:
● a spindle fibre from one pole attaches to the centromere
of one pair of sister chromatids in the tetrad, and a spindle
fibre from the opposite pole attaches to the centromere
of the other pair of sister chromatids
● the tetrads line up across the equator of the cell
● one pair of sister chromatids lie on each side of the
equator
93
Metaphase 1
94
● unique event:
❏ independent assortment: separation, or assortment, of
homologous chromosomes is random therefore the
alleles of different genes get sorted into gametes
independently of one another
■ in each pair of homologous chromosomes, the
maternal chromosome is oriented toward one pole
while the paternal chromosome is oriented toward
the other pole
95
■ because some maternal chromosomes and some
paternal chromosomes face each pole of the cell,
not all maternal chromosomes will be separated
into one cell versus all paternal chromosomes
being separated into another
■ therefore, the orientation of each pair of
homologous chromosomes is independent of the
orientation of the other pairs; the relative positions of
the pairs that align are random
96
■ the resulting gametes (after meiosis II)have different
combinations of parental chromosomes, making each
one unique!
97
98
anaphase I:
● homologous chromosome pairs (tetrads) separate
● each pair of sister chromatids is pulled to opposite poles
of the cell by the spindle fibres
99
(iv) telophase I:
● homologous chromosomes uncoil to form chromatin
● spindle fibres disappear
● cytoplasm divides
● nucleolus and nuclear membrane forms around each
group of chromosomes and two cells are formed
100
(iv) telophase I (continued):
● only one set of replicated chromosomes (sister chromatids)
is in each cell; each of these new cells are haploid
2 genetically different daughter cells, each haploid (n)
101
Phases of Meiosis I
102
MEIOSIS II: Four Stages (PMAT)
● each cell that enters meiosis II is haploid and contains
replicated chromosomes; at the end of meiosis II, the
daughter cells contain unreplicated chromosomes
● in animals, the daughter cells develop into gametes and
in plants they turn into spores or gametes
103
● MEIOSIS II contains four stages identical to mitosis:
(i)
●
●
●
prophase II:
spindle fibres reform
centrioles at opposite ends
chromosomes coil up
(ii) metaphase II:
● spindle fibres attach to
centromere and guide
chromosomes to equator where they line up
104
(iii) anaphase II:
● centromeres split apart and
sister chromatids (now chromosomes)move to opposite
poles of the cell
(iv)
●
●
●
telophase II:
chromosomes uncoil
spindle fibres disappear
nuclear membrane and nucleolus reappear
and cytokinesis
105
106
MEIOSIS - MADE SUPER
EASY - ANIMATION
(5:32 MIN)
107
3 key aspects of meiosis which contribute to genetic variation:
1. reduction division: it is a form of cell division that produces
cells with fewer chromosomes than the parent cell; occurs via
meiosis I when a diploid cell divides to produce haploid cells
108
○ genetic recombination: the products of meiosis have
different combinations of genes; gives rise to offspring that
are genetically distinct from one another and from their
parents
■ due to two processes:
2. crossing over (prophase I)
3. independent assortment (metaphase I)
109
Comparing Mitosis & Meiosis
Feature
cell type
Mitosis
somatic
Meiosis
germ
# of daughter cells two
four
# of chromosomes diploid (2n)
haploid (n)
daughter cells
genetic variation identical to parent
cell and to each
other
daughter cells
genetically distinct
(differ from parent
and each other)
110
111
Complete Questions: Page 472 #s 1, 5, 7, 9, 10
Meiosis Worksheet
Modelling Meiosis Assignment
112
1. What two main functions does meiosis accomplish?
5. Explain what you think is happening in the following image.
Why is this significant?
7. A human germ cell in interphase has 23 pairs of chromosomes. If this cell undergoes cell
division, how many chromosomes are found in each of the following phases? Indicate
whether the chromosomes are found as linked sister chromatids (duplicated), single
chromatids (single chromosomes), or homologous pairs (tetrads).
a) metaphase (mitosis)
b) metaphase I (meiosis) c) metaphase II (meiosis)
9. In what stage of meiosis do chromosome tetrads align at the cell equator? What feature
of this alignment contributes to genetic diversity?
10. Explain how meiosis contributes to the diversity of living things on Earth.
113
1. What two main functions does meiosis accomplish?
● produces haploid gametes from diploid parent cells as is
necessary for sexual reproduction (ie. reduction division)
● contributes to genetic variation by producing many
genetically different gametes through:
○ crossing over; and
○ independent assortment
114
5. Explain what you think is happening in
the following image. Why is this significant?
● Crossing over in Prophase I
● Crossing over is significant because it
results in the production of genetically different gametes
115
7. A human germ cell in interphase has 23 pairs of chromosomes. If
this cell undergoes cell division, how many chromosomes are found
in each of the following phases? Indicate whether the
chromosomes are found as linked sister chromatids (duplicated
chromosome), single chromatids (chromosomes), or homologous
pairs (tetrads).
a) metaphase (mitosis)
b) metaphase I (meiosis)
c) metaphase II (meiosis)
(a) 23 pairs of duplicated chromosomes
(b) 23 pairs of homologous chromosomes arranged as
tetrads
(c) 23 pairs of duplicated chromosomes split between 2 cells
116
9. In what stage of meiosis do chromosome tetrads align at
the cell equator? What feature of this alignment contributes
to genetic diversity?
● metaphase I of meiosis
● Independent assortment
117
10. Explain how meiosis contributes to the diversity of living
things on Earth.
Meiosis contributes to the diversity of life through the
production of gametes, which are genetically distinct from
the parents and each other. Gametes then combine to form
a genetically unique individual.
Genetic Diversity is due to:
1. Reduction division
2. Crossing over
3. Independent Assortment
118
Assess Your Learning
1. Compare anaphase in mitosis, meiosis I, and meiosis II.
2. Sea star cells have 36 chromosomes. If anaphase I does
not occur, how many chromosomes will be present in
daughter cells produced by meiosis?
119
Assess Your Learning
1. Compare anaphase in mitosis, meiosis I, and meiosis II.
Mitosis: separation of duplicated chromosomes
Meiosis I: separation of tetrads
Meiosis II: separation of duplicated chromosomes
120
2. Sea star cells have 36 chromosomes. If anaphase I does
not occur, how many chromosomes will be present in
daughter cells produced by meiosis?
After Meiosis I: daughter cell 1 will contain 36 chromosomes
and daughter cell 2 will contain 0
After Meiosis II: daughter cells 1 & 2 will contain 18
chromosomes; daughter cells 3 & 4 will contain 0
Overall: 18,18, 0,0
121
Gamete Formation
In this section you will learn about the processes of
gametogenesis: spermatogenesis and oogenesis.
Spermatogenesis
spermatogenesis: process of male gamete production
● production of sperm cells: male gamete
● in most male animals, sperm production takes place in the
testes
● 300 to 500 million sperm are produced each day in a
male’s lifetime
122
● steps of spermatogenesis:
○ begins with a spermatogonium (plural =
spermatogonia): diploid germ cell from which sperm
are produced
○ Each spermatogonium eventually undergoes meiosis to
form four haploid sperm
123
Spermatogenesis
124
Oogenesis
oogenesis: process of female gamete
production
● produces an ovum (plural = ova):
female gamete; an egg cell
● egg production takes place in the
ovaries
125
● at birth, a female’s ovaries contain all the eggs she
will ever produce (~ 2 million primary oocytes);
however, the eggs do not fully mature until puberty
126
● steps of oogenesis:
○ begins with a oogonium (plural = oogonia): diploid
germ cell from which ova are produced
○ each oogonium undergoes mitosis to form two primary
(1o) oocytes: each of two cells formed when an
oogonium undergoes mitosis
127
○ the primary oocytes will begin meiosis I but will stop in
prophase I before birth and remain that way until
puberty when a hormone signal triggers a single
primary oocyte to resume meiosis
128
○ every month after puberty, one primary oocyte
undergoes meiosis I:
■ this involves an unequal division of cytoplasm
which produces:
● a secondary oocyte: cell which has the larger
portion of the cytoplasm and eventually
becomes the ovum; and
● a polar body: cell that receives the smaller
portion of cytoplasm; is not functional and
129
soon degenerates (or may further divide)
oogenesis
130
○ Each of these cells undergoes meiosis II
which again involves unequal division
of the cytoplasm producing an ovum
(egg) and polar bodies
○ the end result of oogenesis is one ovum and
3 polar bodies
131
132
133
Comparing Sperm & Egg
Feature
Sperm
physical
structure
head with acrosome
which contains
enzymes used to
enter the egg cell; tail
for motility
covered by a thick
outer coating; after
one sperm penetrates
the egg no more can
enter
small
large
size
Egg
134
Comparing Sperm & Egg
Feature
energy
reserves
Sperm
Egg
before ejaculation,
can only live for about
uses fat for energy;
one day with its food
after ejaculation: uses supply if unfertilized
sugar (fructose) for
energy
mitochondria 50 -100 mitochondria 140,000 mitochondria
per cell
per cell
135
Comparing Sperm & Egg
Feature
number
produced
motility
Sperm
Egg
millions produced
continuously (300
million-500 million)
one egg matures per
month from puberty to
menopause
motile
non-motile
136
Reproductive Strategies
Text Reference: NL Biology, Pages 473 - 480
Sexual vs. Asexual Reproduction
In this section you will learn how
the two forms of cell division,
mitosis and meiosis, operate
within the life cycle of different
organisms.
137
Sexual reproduction: reproduction involving fertilization of
gametes
● production of gametes by
meiosis, followed by
fertilization between
genetically distinct parental
gametes to produce
genetically distinct offspring
138
● example: Life Cycle of Humans
3 stages of sexual reproduction life cycle:
I. meiosis: forms haploid (n) gametes (sperm and egg)
II. fertilization: fusion of haploid gametes to form diploid
(2n) zygote which is genetically distinct from parents
III. mitosis: zygote develops; maintenance, growth and
repair of somatic cells
139
Life Cycle of
Humans
140
Asexual reproduction: reproduction that requires only one
parent
● offspring are clones or identical to the parent
● Six types of asexual reproduction:
1. budding: a new organism develops from an outgrowth of
the parent
❏
a complete but miniature version of the parent grows out
from the parent’s body
141
❏
the new organism then separates to become an
independent organism
❏
representative organism: hydra
142
BUDDING
Ex. hydra
143
2. binary fission: asexual form of reproduction in prokaryotes
that produces two identical cells
❏ recall prokaryote: cells that do NOT contain a nucleus
❏ DNA replication begins and the new chromosomes
move to opposite poles of the cell
144
❏ the membrane pinches inward and a septum (wall)
forms down the middle of the cell
❏ representative organism: bacteria
145
binary fission
146
3. vegetative reproduction: growth of new plant from a
modified stem
❏ new plants develop at the end of each stem
❏ once new plants take root, stem disintegrates and
new individual becomes detached from the parent
plant
❏ several methods exist including natural (runners, bulbs,
tubers) and artificial (cuttings, grafting)
❏ representative organism: strawberry plants
147
vegetative reproduction
Ex. Strawberry plants
148
4. fragmentation: a new organism forms from a part
of a parent
❏ a type of vegetative reproduction
when it occurs in plants
❏ representative organisms:
❏ potatoes grown from fragment or
tuber of parent plant
❏ sea stars regenerating from one
arm
149
150
5. parthenogenesis: development of an adult organism
from an unfertilized egg
❏ growth and development of embryos occur without
fertilization by sperm
❏ representative organisms:
❏ honey bee: fertilized eggs develop into female
worker bees, while unfertilized eggs develop into
male drones (only purpose is mating)
151
152
6. spores: reproductive cells able to develop into a new
organism
❏ does not require offspring to develop in close
proximity to parent; allows offspring to be dispersed
long distances
❏ dispersed by wind and water
❏ surrounded by a protective sheath or wall that
protects the contents until conditions are favourable
for the organism to develop
153
❏ spores may be haploid or diploid (and not all spores
are the product of asexual reproduction; some
organisms produce spores by meiosis, resulting in an
alternation of generations (more later…)
❏ representative organisms:
❏ plants, such as ferns
❏ Fungi (mushrooms)
❏ Bread mould
154
❏ fungi (mushrooms)
❏ bread mould
155
Summary: Advantages of Sexual & Asexual Reproduction
Sexual Reproduction
Asexual Reproduction
pairing of homologous
chromosomes and crossing
over offer opportunities to
replace or repair damaged
chromosomes
proceeds more quickly than
sexual reproduction and
does not require the
presence of a second
parent organism
competition among siblings usually requires less energy
may be reduced if they are than sexual reproduction
genetically diverse
156
Sexual Reproduction
Asexual Reproduction
offers a population a way to
adapt to a changing
environment; at least some
offspring may have a greater
ability to resist environmental
pressures or an ability to take
advantage of new food
sources
many forms (ex: vegetative
reproduction and budding)
help to maximize the
chances that individual
offspring will survive since the
daughter organism does not
fully separate from the parent
until it is capable of
independent survival
157
Complete
Questions: Page 480 #s 3, 4, 5, 6, 7, 8
Asexual & Sexual Reproduction Worksheet
158
Assess Your Learning
An adult organism produces gametes that quickly go through
fertilization and form diploid zygotes. The zygotes mature into
adults, which live for many years. Eventually the
adults produce gametes and the cycle repeats. What type of
life cycle does this organism exhibit?
159
Questions: Page 480 #s 3, 4, 5, 6, 7, 8
3. In what way is fragmentation similar to budding? In
what way are the two forms of reproduction different?
4. In one species of fish, the females lay eggs that are not fertilized. The
eggs hatch and develop into adult fish.
a) What is the name of this form of reproduction?
b) What proportion of the offspring are likely to be male?
Explain.
5. Draw a diagram that illustrates the life cycle of a mammal. Use the
following terms to label your diagram: haploid phase, diploid phase,
meiosis, mitosis, fertilization, zygote. (You may need to use some of these
terms more than once.)
160
Questions: Page 480 #s 3, 4, 5, 6, 7, 8
6. The photograph below shows the release of spores from a puffball
mushroom. What reproductive advantage does a spore offer over
vegetative reproduction?
7. Briefly explain two advantages and two disadvantages of a life cycle
that requires sexual reproduction.
8. Sea anemones can reproduce asexually by budding and sexually by
means of fertilized eggs, which hatch into larvae. Adult sea anemones
exist only as polyps, which remain fixed in one location. Their larvae,
however, are free-swimming. Explain how sexual reproduction could
help a population of sea anemones overcome a
toxic-waste spill.
161
3. In what way is fragmentation similar to budding? In what
way are the two forms of reproduction different?
Similarities
Differences
offspring
produced are genetically
identical to the parent
budding: bud forms from the
parent and remains attached to
parent until maturity
both develop from a portion of
the parent
fragmentation: a piece of
mature tissue from the parent
separates initially and begins to
grow into a new, complete
organism on its own
162
4. In one species of fish, the females lay eggs that are not
fertilized. The eggs hatch and develop into adult fish.
a) What is the name of this form of reproduction?
b) What proportion of the offspring are likely to be male?
Explain.
(a) parthenogenesis
(b) None; the female parent fish would not have any copies of
the Y chromosome and male fish have not fertilized the
eggs
163
5. Draw a diagram that illustrates the life cycle of a mammal.
Use the following terms to label your diagram: haploid phase,
diploid phase, meiosis, mitosis, fertilization, zygote. (You may
need to use some of these terms more than once.)
164
6. The photograph below shows the release of spores from a
puffball mushroom. What reproductive advantage does a
spore offer over vegetative reproduction?
Spores
Vegetative Reproduction
small and easily dispersed by wind
and water; greater chance of finding
favourable environmental conditions
where it will not compete with the
parent organism
does not allow for motility; offspring
usually grow close to the parent
plant and may have to compete for
space and nutrients
formed by sexual or asexual
reproduction; sexual reproduction
allows for the genetic variation and
increases the offspring’s ability to
adapt to a changing environment
asexual and does not allow for
variation and possible adaptation in
offspring
165
7. Briefly explain two advantages and two disadvantages of a life cycle
that requires sexual reproduction.
Advantages of sexual reproduction:
●
●
●
genetic variability offers a population a way to adapt to a changing
environment
competition among siblings may be reduced if they are genetically
diverse
pairing of homologous chromosomes and crossing over offer opportunities
to replace or repair damaged chromosomes.
DISAdvantages of sexual reproduction:
●
●
●
●
the process is slower than asexual reproduction, which may not allow the
offspring to take advantage of favourable environmental conditions
a male and female organism are required to produce gametes
requires more energy than asexual reproduction
offspring are completely separate from their parents at birth and cannot
166
always rely on them for survival.
8. Sea anemones can reproduce asexually by budding and sexually by
means of fertilized eggs, which hatch into larvae. Adult sea anemones
exist only as polyps, which remain fixed in one location. Their larvae,
however, are free-swimming. Explain how sexual reproduction could
help a population of sea anemones overcome a toxic-waste spill.
● Free-swimming larvae could move and avoid the toxins
in the water
● Genetic variation among the larvae could also enable
some organisms to be better able to withstand the toxic
effects of the spill
167
Viral Reproduction
In this section you will learn how viruses reproduce despite
being non-living.
Virus: microscopic, infectious
particle that can
reproduce only by
infecting a host cell
168
● two pathways of viral reproduction:
1. lytic cycle: involves using a host cell to manufacture
more viruses; the viruses then burst out of the
cell
❏ destroys host cell genome (genetic material) and host
cell
❏ results in many copies of the virus being created very
quickly
169
❏ five stages of the lytic cycle:
(i) attachment: virus recognizes and binds to a host cell
(ii) entry:
❖virus injects its DNA/RNA into the host cell
❖destroys host cell genome
(iii) replication: the host cell’s machinery reproduces the
viral DNA/RNA and viral proteins
170
(iv) assembly: new viruses are assembled by the host
cell’s machinery
(v) lysis and release:
❖ the host cell undergoes lysis: the disintegration of a
cell by rupture of the cell wall or membrane
❖ host cell dies
❖ new viruses are released to infect other cells
171
172
OR
2. lysogenic cycle: involves the incorporation of the viral
genome into the host cell genome,
infecting it from within
❏viral DNA/RNA enters cell and becomes part of host
cell’s genome; referred to as a provirus
❏the provirus’ DNA/RNA is passed on to daughter cells
through normal cell reproduction
173
❏ viral DNA/RNA can exist in this form for years without
harm to host cell; referred to as latent
❏ host cell is not destroyed during latent phase
❏ environmental factors may induce the provirus to enter
the lytic cycle at any time
174
❏seven stages of the lysogenic cycle:
(i) attachment: virus recognizes and binds to a host cell
(ii) entry:
❖genetic material is injected into the host cell
❖viral DNA/RNA integrates into the host cell's genome
(iii) replication (lysogenic):
❖viral DNA/RNA is copied along with host cell genetic
material during the usual cell reproduction process
❖each new daughter cell is infected with the virus
175
(iv) induction:
❖infected cells are exposed to certain environmental
conditions
❖virus becomes active and enters the lytic cycle
(v) replication (lytic): the host cell’s machinery
reproduces the viral DNA/RNA and
viral proteins
(vi) assembly: new viruses are assembled by the host cell’s
machinery
176
(vii) lysis and release:
❖final host cell lyses and dies
❖new viruses are released
177
178
Lytic vs. lysogenic LIFE
CYCLE of Bacteriophages
(4:22 MIN)
179
Complete
Viral Reproduction Worksheet
180
Alternation of Generations
In this section you will learn about the phases of life cycles in
plants and cnidarians.
● the life cycle of several organisms
consists of two generations
● this is called alternation of
generations: life cycle that
alternates between a diploid
generation and a haploid
generation
181
alternation of generations in PLANTS:
❏ diploid (2n) generation
❖ begins at fertilization which creates a zygote
(diploid; 2n)
❖ zygote develops through mitosis to create a
sporophyte: spore-making body; diploid structure
(2n)
❖ the sporophyte carries out meiosis
182
❏ haploid (n) generation
❖ through the process of meiosis, the sporophyte
produces spores: reproductive cells; haploid (n)
❖ each haploid spore grows through the process of
mitosis
❖ develops into a male or female plant body called the
gametophyte: gamete - making body; haploid
structure (n)
➢ produce male or female gametes (sperm or egg)
183
❏ the gametes fuse at fertilization to create a zygote
(diploid; 2n) and the cycle repeats
❏ Note: some species have a dominant gametophyte
generation and some have a dominant sporophyte
generation meaning that they spend more of their life
cycle in that form
184
Alternation of
generations in
Moss
185
Representative Example: Life Cycle of a Moss
186
MOSS LIFE CYCLE
(0:35 - 7:47 MIN)
187
➢ male gametophyte is called the antheridium;
produces sperm
➢ female gametophyte is called the archegonium;
produces eggs
○ plant surface must be moist enough for the sperm to
swim to the egg in the archegonium; is dependant on
water
➢ gametophyte generation is dominant (ie. moss plant cells
are haploid for most of their life cycle)
188
alternation of generations in CNIDARIANS:
❏ diploid (2n) generation
❖ begins at fertilization which creates a zygote (diploid;
2n)
❖ zygote develops through mitosis to eventually become
a polyp: sessile (immobile), cylinder-shaped asexual
form of cnidarian; diploid structure (2n)
189
❖ the polyp reproduces asexually by budding and release
larvae
❖ an immature larva develops through mitosis to form a
medusa: free-swimming, umbrella-shaped sexual form
of cnidarian; diploid structure (2n)
❖ the medusa carries out meiosis
190
❏ haploid (n) generation
❖ through the process of meiosis, the medusa
produces male or female gametes [sperm or
egg; haploid (n)]
❏ the gametes fuse at fertilization to create a zygote
(diploid; 2n) and the cycle repeats
191
alternation of generations in CNIDARIANS
192
Representative Example: Life Cycle of a JELLYFISH (Aurelia aurita)
193
➢ diploid generation is dominant (ie. jellyfish are
diploid for most of their life cycle)
194
Moon Jelly LIfe Cycle
(0:20 - 5:50 MIN)
195
Complete
Alternation of Generations Worksheet
Reproductive Strategies Assignment
196
Assess your Learning
Pictured to the right is the
life cycle of an unknown
organism. Identify the
haploid and diploid
stages. Which stage is
dominant?
197
Assess your Learning
Pictured to the right is the
life cycle of an unknown
organism. Identify the
haploid and diploid
stages. Which stage is
dominant?
Haploid stage is the gametophyte that produce gametes,
eggs and sperm and the Diploid stage is the sporophyte
which produces spores (n) through meiosis. The stage
that is dominant is the gametophyte.
198
Reproduction in Flowering Plants
In this section you will learn about the structure and life cycle
of angiosperms (flowering plants).
● flowering plants undergo sexual reproduction
● have evolved to be away from water; not dependent on
water for reproduction
● have evolved specialized structures for reproduction
199
Did you know?
Some flowers smell like rotting
flesh in order to attract pollinators,
such as flies. The corpse plant,
which is native to Indonesia, is the
largest plant that produces
foul-smelling flowers. The corpse
plant reaches about 1.5 m in height
and weighs about 90 kg. The plant
produces a flower about once
every 10 years
200
201
Flower Terminology
Perfect Flower: a flower possessing BOTH male and female
reproductive structures; is capable of
undergoing self–pollination (fertilization)
Imperfect Flower: a flower possessing EITHER male OR female
reproductive structures only
202
Structure of angiosperms (flowering plants)
203
Stamen: the male reproductive organ in flowering plants
● made up of two parts:
1. anther: contains cells that
undergo meiosis to form
pollen grains
❖ is supported by the filament
❖ is the site of pollen formation
2. filament: stalk that supports the anther
204
Pistil: the female reproductive organ in flowering plants
● made up of three parts:
1.
stigma: sticky portion at the tip of the pistil
❖ traps pollen from the air for reproduction
❖ is the site of pollination
205
2. style: long, slender tube which connects the stigma
to the ovary
❖ is a passageway for pollen leading to the ovary
3. ovary: contains one or more ovules
❖ ovules: sacs that contain female
gametes produced through
meiosis [eggs; haploid (n)]
➢ is the site of fertilization
206
Life Cycle of
Flowering Plants
207
1. Development from Sporophyte to Gametophytes:
recall:
sporophyte: spore-making body; diploid structure (2n) that
produces haploid spores through meiosis; develops without
fertilization into a gametophyte
gametophyte: gamete-making body; haploid structure (n)
that produces male or female gametes (sperm or egg)
that fuse at fertilization to form a diploid sporophyte
208
209
FEMALE
● an ovule containing the embryo sac begins to grow
● inside the ovule, meiosis results in formation of four
megaspores: spores that develop into female
gametophytes
● three of the four megaspores disintegrate, leaving one
megaspore
210
● mitosis occurs in the remaining megaspore three times
● as a result, one megaspore contains cells with eight
haploid nuclei
○ one of cells become the egg
○ another of the cells contains two nuclei (known as
polar nuclei)
211
212
MALE
● in the anther, specialized cells undergo meiosis to
produce microspores:
spores that develop into male gametophytes
● each microspore undergoes mitosis to form a pollen
grain:
○ small round structure which contains the male
gametes [sperm; haploid (n)]
○ is an immature male gametophyte
213
● the pollen grain contains two nuclei:
1. tube nucleus: nucleus within a pollen grain that
forms the pollen tube
2. generative nucleus: nucleus that produces two
sperm nuclei
214
215
2. Pollination: the transfer of a male gametophyte (pollen
grain) to the female reproductive structure (pistil)
● when the pollen grain lands on a stigma of the correct
species, the tube nucleus forms a pollen tube
● as the pollen tube grows, the generative nucleus undergoes
mitosis, forming two sperm cells
● the pollen grain is now a mature male gametophyte
216
217
3. Fertilization:
● when the pollen tube reaches the ovule, it releases the
two sperm cells:
1.one sperm fuses with the egg, forming the zygote (will
develop into new sporophyte)
2.one sperm (n) fuses with the two polar nuclei (2n),
forming a triploid (3n) cell: cell that contains sets of
three homologous chromosomes
218
○ triploid cell divides to form a nutrient-rich tissue
called endosperm:
■ triploid (3n) structure which acts as a food
source to nourish the embryo as it grows
219
● referred to as double fertilization:
❖ first fertilization: sperm fertilizes the egg cell to form the
zygote
❖ second fertilization: sperm fuses with the two polar nuclei
that form the endosperm
220
4.
Development:
● the ovule develops into the seed: contains the zygote
(developing plant) and endosperm
● the ovary develops into the fruit: surrounds and helps to
protect the developing seed
221
222
Double Fertilization in
Angiosperms
(3:59 MIN)
223
Complete
Angiosperm Reproduction Worksheet
Investigation 12.1: Page 478 - Dissecting A Flower
224
Investigation 12.1 - Dissecting a Flower
Link to Pictures of Dissection & Cross-Section
225
Assess Your Learning
A herbicide prevents the formation of the tube nucleus.
How might this affect reproduction of the plant?
226
Assess Your Learning
1. A herbicide prevents the formation of the tube nucleus.
How might this affect reproduction of the plant?
The tube nucleus is responsible for formation of the pollen
tube. Without formation of the pollen tube, the sperm
formed from the generative nucleus have no means to
travel to the ovule and fertilization is prevented.
227
2. An adult organism produces gametes that quickly go
through fertilization and form diploid zygotes. The zygotes
mature into adults, which live for many years. Eventually the
adults produce gametes and the cycle repeats. What type
of life cycle does this organism exhibit?
This organism has a life cycle in which the diploid
generation is dominant.
228
229