Download BDOL Interactive Chalkboard - Biology with​Mrs. Ellsworth

Asexual Reproduction
•When cells divide by mitosis, the new
cells have exactly the same number and
kind of chromosomes as the original
cells.
•This is one form of asexual (or without
sex) reproduction that occurs in mostly
single celled organisms.
•(Take notes on underlined words)
Sex requires a mixing of DNA between
two similar organisms.
 Every offspring will have some DNA from
both parents.
 In higher organisms, DNA will be present
in homologous chromosomes, one from
mom and one from dad.

Homologous chromosomes have the same type of
genes but one copy is from each parent.
• On homologous
chromosomes, the
genes are arranged in the
same order, but because
Axial
there are different
possible alleles for the
same gene, the two
Constricted chromosomes in a
homologous pair are not
Short
always identical to
each other.
Homologous Chromosome 4
a
A
D
d
T
t
Terminal
Inflated
Tall
•A cell with two of each kind of chromosome
is called a diploid cell.
•Why would it be called a diploid?
• What would happen if a diploid cell from a
male combined with a diploid cell from a
female?
Mom 46 + Dad 46 = Baby 92
chromosomes
 This is a problem!

If two diploid cells combined, then each
generation would have a double number of
chromosomes.
• Each pea plant parent, which has 14
chromosomes, would produce gametes that
contained a complete set of 14 chromosomes.
• The F1 pea plants would have cell nuclei
with 28 chromosomes, and the F2 plants
would have cell nuclei with 56 chromosomes.
How can it work?
Haploid cells
In the sex organs, organisms produce gametes
that contain one of each kind of chromosome.
•A gamete contains one of each kind of
chromosome or half the number of
chromosomes is called a haploid cell.
•Now, what would happen if two haploid cells
got together? 
Another type of cell division is needed for
sexual reproduction that would produce
gametes containing half the number of
chromosomes as a parent’s body cell.
It is called meiosis.
Diploid and haploid cells
Chromosome Numbers of Common Organisms
Organism
Body Cell (2n) Gamete (n)
4
Fruit fly
8
Garden pea
14
7
10
Corn
20
12
Tomato
24
Leopard Frog
26
13
Apple
34
17
Human
46
23
Chimpanzee
24
48
Dog
78
39
Adder’s tongue fern
1260
630
• This fact
supports
Mendel’s
conclusion that
parent organisms
give one allele
for each trait to
each of their
offspring.
What is meiosis?
• Meiosis consists of two separate divisions,
known as meiosis I and meiosis II.
*Meiosis I begins with one diploid (2n) cell.
*By the end of meiosis II, there are four
haploid (n) cells.
*Or from one cell, four gametes are made.
Why meiosis?
*These haploid cells are called sex cells—
gametes.
*Male gametes are called sperm.
*Female gametes are called eggs.
*When the egg is fertilized, the
resulting zygote once again has the
diploid number of chromosomes.
Why meiosis?
Meiosis
Haploid gametes
(n=23)
Sperm Cell
Meiosis
Egg Cell
Fertilization
Diploid zygote
(2n=46)
Mitosis and
Development
Multicellular
diploid adults
(2n=46)
• This pattern of
reproduction,
involving the
production and
subsequent
fusion of haploid
sex cells, is called
sexual reproduction.
The Phases of Meiosis
Click image to view movie.
Interphase
*At the end of
interphase, each
chromosome replicates
to form two identical
sister chromatids, held
together by a
centromere.
Interphase
Prophase I
• The chromosomes coil
up and a spindle forms.
*As the chromosomes coil,
homologous chromosomes
line up with each other
gene by gene along their
length, to form a four
part structure called a
tetrad.
Prophase I
Prophase I
•*Homologous
chromosomes can break and
exchange genetic material in a
process known as crossing over
•Crossing over can
occur at any location on a
chromosome, and it can occur
at several locations at the same
time.
Prophase I
Crossing Over
Sister chromatids
Tetrad
Nonsister chromatids
Crossing over in tetrad
Homologous chromosomes
•Why?
Gametes
• It is estimated
that during
prophase I of
meiosis in
humans, there is
an average of two
to three
crossovers for
each pair of
homologous
chromosomes.
Prophase I
Sister chromatids
Tetrad
Nonsister chromatids
Crossing over in tetrad
Homologous chromosomes
Gametes
*Crossing over
results in new
combinations
of alleles on a
chromosome for
more genetic
variety.
Metaphase I
*During metaphase I, the
centromere of each
chromosome becomes
attached to a spindle fiber.
• The spindle fibers pull
the tetrads into the
middle, or equator, of the
spindle.
Metaphase I
*This is where independent assortment occurs
as different chromosomes are pulled apart.
This and crossing over is why you look different from your siblings.
Anaphase I
*Anaphase I begins as
homologous chromosomes,
each with its two
chromatids, separate and
move to opposite ends of the
cell.
• This critical step ensures that
each new cell will receive
only one chromosome from
each homologous pair.
Anaphase I
Telophase I
• Events occur in the reverse
order from the events of
prophase I.
*In telophase, the spindle is
broken down, the
chromosomes uncoil,
and the cytoplasm divides to
yield two new cells.
Telophase I
Telophase I
• Each cell has half the
genetic information of
the original cell because
it has only one
chromosome from each
homologous pair.
Telophase I
The phases of meiosis II
* During prophase II,
a spindle forms in
each of the two new
cells and the
spindle fibers
attach to the
chromosomes.
Prophase II
The phases of meiosis II
* During metaphase II,
the chromosomes,
still made up of sister
chromatids, are
pulled to the center of
the cell and line up
randomly at the
equator.
Metaphase II
The phases of meiosis II
*Anaphase II begins as
the centromere of
each chromosome
splits, allowing the
sister chromatids to
separate and move to
opposite poles.
Anaphase II
The phases of meiosis II
* In Telophase II, nuclei
reform, the spindles
break down, and the
cytoplasm divides.
Telophase II
Meiosis Provides for Genetic Variation
• Cells that are formed by mitosis are identical
to each other and to the parent cell.
In meiosis, reassortment of chromosomes
and the genetic information they carry, either
by crossing over or by independent
segregation of homologous chromosomes, is
called genetic recombination.
• Thus, variability is increased.
Meiosis video more life like
 Flower reproduction roles

Asexual reproduction

Some plants can make
new plants from
cuttings or buds from
the original plant

The new plants from
asexual reproduction
have the same genetic
makeup as the original
plant. (Clone)
Sex for plants (sounds familiar)

The female gamete is an egg and the male is
a sperm.

When a sperm fertilizes an egg, a diploid
zygote (later embryo) forms. This is sexual
reproduction.

The embryo develops to maturity as a seed.
Many seeds are surrounded by fruit (the
ovary) to provided nourishment to develop the
seed into a plant .
The structure of a flower is for plant sex

Petals are colorful structures at the top of a
flower stem. Petals are to attract birds and
insects that transfer pollen between plants.

The flower stem is called peduncle and
supports the flower.

Sepals are usually leaf-like and encircle the
peduncle below the petals. Sepals protect the
flowers before blooming
The structure of a flower – male parts

Inside the petals are the stamens. A stamen
is the male reproductive organ of a flower. It is
made up of the filament that holds up the
anther.

At the tip of the stamen is the anther. The
anther produces pollen that contain sperm. A
flower makes millions of pollen grains.
The structure of a flower
Stigma
Petals
Style
Ovary
Anther
Stamen
Filament
Sepal
Peduncle
Pistil
The structure of a flower
The pistil is the female organ of the flower.
The pistil is made of the stigma which is sticky
to catch the pollen and the style that hold up
the stigma.
 At the bottom portion of the style is the ovary,
a structure with one or more ovules, each
usually contains one egg.


A plant makes fewer eggs than sperm (‘cause
most sperm get lost and never reach the
eggs).
Development of the female ovules
In flowers, the female
ovule forms within the
ovary.
 In the ovule, a cell
undergoes meiosis and
produces haploid cell
(half the genetic info).


In most flowering plants, these haploid cells
undergoes mitosis three times, producing eight
haploid nuclei. Only three of the eggs cells will
be fertilized.
Development of the male parts (pollen)

Haploid cells (sperm) are produced by meiosis
within the pollen sac.

The nucleus of each haploid cell undergoes
mitosis.

A thick, protective wall surrounds these cells.
This structure is the immature male cells or
pollen grain.
Pollination

In flowering plants,
pollination (sex) is the
transfer of the pollen grain
from the anther (male part)
to the stigma (top of female
part).
 Depending on the type of
flower, the pollen can be
carried to the stigma by
wind, water, or animals
(birds and bees) that are
attracted by nectar (sugar
water).
Two plants having artificial sex

This is what Mendel did to control the
cross pollination of his plants.
Fertilization

Inside each pollen grain are two haploid nuclei, the tube
nucleus (grows tube) and the generative nucleus (to
fertilize egg). Sperm is delivered by the pollen tube to the
ovules (female).
Stigma
Style
Pollen grain
Two sperm
nuclei
Pollen tube
Tube nucleus
Ovary
Central cell
Ovule
Egg cell
Fertilization

One of the sperm unites with the
egg forming a diploid zygote
which begins the new baby plant
as the beginning of a seed.

Double Fertilization
The wall of the ovule becomes
the seed coat, which can aid
in seed dispersal and help
protect the embryo until it
begins growing.
Seeds are alive just
dormant!
One sperm
fertilizes the
egg cell (2n)
One sperm
fertilizes the
central cell
(3n)
Seed formation
Click this to view movie.

As the seeds develop, the surrounding ovary
enlarges and becomes the fruit.
Fruit
Ovary
Ovules
Sepals
Stamen
Fused
petals
Seeds and Fruits
Fruit formation
Click this to view movie.
Germination – the dormant seed wakes up


Water is important because it activates the
embryo’s metabolic system.
The first part of the plant embryo to appear is
the embryonic root that will grow toward the
pull of gravity.

A second shoot
grows away from
gravity to make
leaves. It
straightens, bringing
with it the cotyledons
and the plant’s first
leaves.