Transcript Chapter 6 Notes

Unit 4: Reproduction
Chapter 6
Meiosis is the basis of sexual
reproduction.
Mitosis Recap
https://www.youtube.com/watch?v=
JayldCyv5eQ
Sexual Reproduction
Section 6.1: Meiosis
• Sexual Reproduction: a method of
reproduction involving two parents, producing
offspring that are genetically different from
each other, either parent, and from other
members of their species.
The Process of Sexual Reproduction
• Sexual reproduction involves uniting specialized cells called
Gametes. In animals, male gametes are called sperm and
female gametes are called eggs.
• Fertilization occurs when the gametes unite,
with the sperm penetrating an egg cell.
• The process of fertilization results in a cell called a Zygote.
The Zygote undergoes cell division and mitosis and develops
into an Embryo. The embryo grows continuously to form a
new organism.
Chromosome Numbers
• Diploid number (2n): body cells (all cells excluding sperm and egg) have
two sets of chromosomes. The diploid number for humans is 46 (2 x 23).
Humans inherit one set of 23 from their male parent and one set of 23
from their female parent.
• Haploid number (n): gametes (sperm and egg cells) have only one set of
chromosomes and are termed haploid. Human gametes have one set of
23 chromosomes. So, the haploid number for humans is 23.
• During fertilization, a haploid (n) sperm cell unites with a haploid (n) egg
cell to form a diploid (2n) zygote.
https://www.youtube.com/watch?v=BAOFVwQj1yg
Meiosis
• Meiosis: process of producing gametes (sperm
and egg cells) with the haploid (n) number of
chromosomes. Meiosis occurs in the male and
female sex organs (respectively the testes and
ovaries).
Meiosis
Meiosis involves two rounds of cellular
division:
1. Meiosis I
2. Meiosis II
Homologous Chromosomes
• Homologous Chromosomes: are pairs of
chromosomes that are the same size, shape and
have genes that are in the same locations.
Meiosis I: Stages
Meiosis I involves:
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I
Prophase I
• Homologous chromosomes pair up.
Metaphase I
• Homologous chromosomes pair up at the
equator.
Anaphase I
• Homologous chromosomes separate and are
pulled towards opposite poles (ends) of the
cell.
Telophase I
• Homologous pairs have moved to opposite
ends of the cell and the cell begins to divide.
Interkenesis
• Interkenesis: is the stage between cell
divisions. The cells grow and make various
proteins.
End Products of Meiosis I
• The end products of Meiosis I are two diploid
(2n) daughter cells.
• These cells now go on to enter Meiosis II.
Meiosis II
Meiosis II involves:
1. Prophase II
2. Metaphase II
3. Anaphase II
4. Telophase II
Prophase II
• There is one chromosome of the homologous
pair in each cell.
Metaphase II
• Chromosomes line up at the equator (middle
of the cell).
Anaphase II
• Half of each X-shaped chromosome is pulled apart
towards opposite poles (ends) of the cell.
Telophase II
• A nucleus forms around each set of
chromosomes and the cell begins to divide to
produce 4 gametes.
Comparing/Contrasting
Mitosis verses Meiosis
Mitosis
Meiosis
Types of Cells
Body Cells
Sex Cells (sperm
and eggs)
Number of
Daughter Cells
produced
2
4
Amount of Genetic
Material in each
daughter cell
Same number of
chromosomes (2n)
in each cell. Each
daughter cell is
diploid.
Half the number of
chromosomes (n) in
each cell. Each
gamete (sex cell) is
haploid.
Meiosis Video
• https://www.youtube.com/watch?v=AdfrH3J5
Cwc
Section 6.2: Sexual Reproduction
• Sexual reproduction involves two parents.
• Sexual Reproduction does not necessarily
require sexual intercourse.
Method of Fertilization
Fertilization may be:
1. Internal Fertilization – sperm cells are deposited
inside the female’s body where they meet an egg
cell. Requires sexual intercourse.
2. External Fertilization- sperm and egg cell unite
outside the bodies of parents. This is common in
animals that live in water.
Organisms that reproduce sexually
• Mosses
• External fertilization occurs in mosses.
• Water is needed to transport gametes, allowing sperm cells
and egg cells to unite.
• Male and female sex organs develop on the end of stems or
branches.
• Asexual reproduction may also occur by spore production.
Organisms that reproduce sexually
• Flowering Plants
• Internal fertilization occurs in flowering plants.
• The process of Pollination occurs. Male gametes are formed
in special cases called Pollen. Pollination is the transfer of
pollen to the female part of the flower.
• The male reproductive organ in a flower is called the Stamen.
The female reproductive organ in a flower is called the Pistil.
• Pollination and fertilization occurs at the female reproductive
organ, at the pistil. The pollen lands on the pistil and sperm
are delivered to the egg cells. The fertilized egg becomes a
seed. The seed protects the developing embryo.
Organisms that reproduce sexually
• Insects
• The life cycle of insects involves metamorphosis.
Metamorphosis is the change in an individual's form
as it develops.
Incomplete Metamorphosis
• Incomplete Metamorphosis: involves subtle (minor) changes
through 3 life cycle stages:
1. Egg
2. Nymph (smaller immature version of adult)
3. Adult
Grasshoppers go through Incomplete
Metamorphosis.
https://www.youtube.com/watch?v=lXV6B7qnnmg
Complete Metamorphosis
• Complete Metamorphosis: a change in the form of an insect
as it matures, where the adult is completely different than the
larval stage.
•
The four common stages of complete metamorphosis,
as seen in the butterfly are:
1.
Egg
2.
Larva (caterpillar)
3.
Pupa
4.
Adult
https://www.youtube.com/watch?v=Am0aq8SYeio
Asexual verses Sexual Reproduction
Asexual
Sexual
1
2
Gametes (eggs or sperm)
None (cell divides)
2 (egg cell and a sperm cell
unite to form a zygote)
Variation (difference) in
offspring
Lesser (all offspring
identical)
Greater (genetic diversity)
Amount of Energy required
Lesser
Greater
Parental care
Lesser
Greater
Mitosis or Meiosis?
Mitosis
Meiosis
# of parent cells
Section 6.4: Studying Genetic Changes
Genetic conditions that cannot be solved
using current scientific & technological
knowledge include:
1. Down Syndrome
– Result of an extra 21st chromosome
– Individuals have characteristic facial features and
a shorter stature. They may be prone to heart
defects and other diseases such as Alzheimer’s
and leukemia.
Genetic Conditions
2. Allderdice Syndrome
– Unique to Sandy Point, NL.
– An increase in genetic birth defects was noticed
due to geographic isolation.
– Result of a mutation on a single maternal
chromosome.
– 31% chance of developing the syndrome.
Genetic Conditions
3. Cystic Fibrosis
– Chronic disease that causes all bodily mucous to
become thick, sticky and difficult to expel.
– Caused by a gene mutation on a single
chromosome. An individual only needs one gene
to prevent it but most people have two (one on
each homologous chromosome). So the individual
must inherit an absence of both genes to develop
disease.
Shifts in the Field of Genetics
• Our understanding of genetics has changed
over time as new technologies have become
available. New technologies have made it
possible to get a better look at genes and their
influence on traits.
Mendel’s Experiments
• In the mid 1800’s, Gregor Mendel experimented with inherited traits in
pea plants, including color and shape.
• Mendel’s studies of pea plants demonstrated that traits were inherited
from one generation to the next.
• Mendel’s studies suggested the involvement of “dominant” and
“recessive” factors in the transmission of traits from parents to offspring.
Dominant traits are always expressed, however recessive traits are not
always expressed.
Watson and Crick: The double helix
model of DNA
•
•
A more clear understanding of genes came about when Francis Crick and James
Watson, described the structure of DNA in 1953.
Crick and Watson showed that DNA is an organization of genes in a double helix
shape, like a twisted ladder. Specific base pairing on this ladder helped to explain
how DNA could replicate (copy itself). This development also helped to explain
how and why mutations occur.
Human Genome Project
• In the Human Genome Project, scientists around the
world collaborated for about 20 years to identify
every gene in human DNA, mapping the human
genome.
• The Human Genome Project made a sort of map that
can be used to search for and identify particular
genes.
• The Human Genome Project has provided
information into how and why various genetic
diseases come about.
Genetic Engineering
• Genetic Engineering: is biotechnology that
deals with the manipulation of the genome.
• Scientists have figured out how to cut a gene
out of one DNA strand and place it into
another. The ability to recombine DNA
(recombinant DNA) has made significant
contributions to food and medicine.
Genetic Engineering & Food
Production
• Plants and animals have improved through recombinant DNA
technology. Such organisms are labeled as Genetically
Modified Organisms (GMOs). This plays an important role in
the agricultural industry, specifically crop production.
• Genes have been altered to produce plants that are resistant
to colder temperatures, chemicals and disease.
• Genetic engineering has been used to produce organisms
with desired traits.
Genetic Engineering & Medicine
• Scientists use recombinant DNA technology to
produce drugs and provide human gene therapy.
• Recombinant DNA technology is being used to help
Diabetes patients, in which the correct human gene
for insulin production, is placed within the genome of
a bacterium. The bacterium then produces insulin
which can be used as medicine.
• Humans who lack a specific gene or who have a
defective gene can have a healthy, functioning gene
inserted into their DNA. This is human gene therapy.
• https://www.youtube.com/watch?v=_IgSDVD4QEc