Download CELLS – ASEXUAL AND SEXUAL RERODUCTION

CELLS – ASEXUAL AND SEXUAL RERODUCTION
Lesson Objective:
By the end of the lesson (s), I can:
1. Distinguish asexual and sexual reproduction.
2. Compare haploid and diploid cells.
3. Describe the purpose and the phases of meiosis AND distinguish between the
process of mitosis and meiosis.
4. Compare the process of spermatogenesis and oogenesis.
5. Describe the processes of fertilization and development.
Vocabulary:
Chromosome
Histone
Chromatid
Centromere
Chromatin
Sex chromosome
Autosome
Homologous
chromosome
Karyotype
Diploid
Haploid
Lesson Questions:
1.
2.
3.
4.
5.
6.
Binary fission
Mitosis
Asexual reproduction
Meiosis
Gamete
Interphase
Cytokinesis
Prophase
Spindle fiber
Metaphase
Anaphase
Telophase
Cell plate
Synapsis
Tetrad
Crossing over
Genetic recombination
Independent assortment
Spermatogenesis
Oogenesis
Polar body
Sexual reproduction
What are the differences between asexual and sexual reproduction
What are haploid and diploid cells?
What is the function of each stage of meiosis?
What are the differences between mitosis and meisosis?
What are spermatogenesis and oogenesis?
What are fertilization and development?
Focus Question:
1. How are the characteristics of one generation related to the previous generation?
2. Why do individuals of the same species vary in how they look, function, and
behave?
Overarching questions:
1.
2.
How are the characteristics of one generation passed on to the next?
How can individuals of the same species and even siblings have different
characteristics?
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CELLS – ASEXUAL AND SEXUAL RERODUCTION
CELL REPRODUCTION:
1. Chromosomes
a. Chromosome structure
 During cell division DNA in eukaryotes is in the nucleus coiled into very
compact structures called chromosomes.
 Chromosomes are rod shaped structures made up of DNA and proteins.
 Chromosomes of stained cells undergoing cell division are visible as
darkened structures inside the nucleus.
 Each chromosome is a single DNA molecule associated with proteins.
 The DNA is wrapped around proteins called histones.
 Histones help to maintain the shape of the chromosome and aid in the tight
packing of the DNA
 Generally involved in controlling the activity of specific regions of the
DNA.

 The following illustrates a chromosome. Notice that the chromosome
consist of 2 parts that are identical.
 Each half is called a chromatid.
 The two chromatids are attached by the centromere. The centromere holds
the two chromatids together until they separate during cell division.
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CELLS – ASEXUAL AND SEXUAL RERODUCTION

 During cell division DNA is not so tightly coiled. Regions of the DNA
uncoil so that the DNA can be read and the information can be used to
direct cell activities.
 The less tightly coiled DNA protein complex is called a chromatin.
b. Chromosome numbers
 Each species has a characteristic number of chromosomes in each cell.

 Sex chromosomes and Autosomes
 Human chromosomes are classified as either sex chromosomes or
autosomes.
 Sex chromosomes are chromosomes that determine the sex of an
organism and carry genes for other characteristics.
 In humans sex chromosomes are either X or Y.
 Females normally have 2 X chromosomes and males have
one X and one Y chromosome.
 All other chromosomes in an organism are called
autosomes.
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CELLS – ASEXUAL AND SEXUAL RERODUCTION




i. In humans 2 of the 46 chromosomes are sex
chromosomes and the remaining 44 are autosomes.
Every organism produced by sexual reproduction has 2
copies of each autosome. The organism receives one copy
of each autosome from each parent.
The 2 copies of each autosome are homologous
chromosomes or homologues.
Homologous chromosomes are the same size and shape and
carry genes for the same traits.
i. For example, one chromosome in a pair of
homologues contains a gene for eye color, so woll
the other chromosome in the homologous pair.
The figure below show a karyotype, a photomicrograph of
the chromosomes in a normally dividing cell found in
humans.

 Diploid and Haploid Cells
 Cells containing 2 sets of chromosomes are diploid.
 Diploid cells have 2 autosomes for each homologous pair.
 Diploid cells also have 2 sex chromosomes, including humans.
 All human cells, except reproductive cells (sperm and egg) are
diploid.
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CELLS – ASEXUAL AND SEXUAL RERODUCTION


Commonly abbreviated as 2n. In humans, the diploid, or 2n,
number of chromosomes is 46 – 22 pairs of homologous
autosomes and 2 sex chromosomes.
Sperm cells and eggs are haploid cell, which contain only one set
of chromosomes.
 Therefore they have half the
he number of chromosomes that
are present in a diploid cell.
 Thus haploid cells have only one autosome of each
homologous pair and only one sex chromosome (total = 23)
 Haploid is abbreviated as 1n. When the sperm (1n) and egg
(1n) combine to create the first cell of a new organism, the
new cell will be a diploid (2n).
 If the reproductive cells were each diploid,, the new cell
would have too many chromosomes and would not be
functional.

2. Cell Division
a. Cell Division in Prokaryotes
 Prokaryotes have cell walls but lack nuclei and membrane bound
organelles.
 The DNA is not coiled around proteins to form chromosomes.
 Instead it DNA is a circular chromosome attached to the inner surface
sur
of
the plasma membrane like a rope attached to the inner wall of a tent.
 For most prokaryotes cell division takes place in the form of a process
known as binary fission.
 Binary Fission is the division of a prokaryotic cell into 2 offspring
cells

b. Cell Division In E
Eukaryotes
 In eukaryotic cell division both the cytoplasm and the nucleus divide.
 Mitosis results in new cells with genetic material that is identical to the
genetic material of the original cell.
 Mitosis occurs in organisms undergoing growth, development, repair, or
asexual reproduction.
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CELLS – ASEXUAL AND SEXUAL RERODUCTION

Asexual reproduction is the production of offspri
offspring from one
parent.
 Cell Cycle
 The repeating set of events in the life of a cell.
 Cell division is one phase of the cycle.
 The time between cell divisions is called INTERPHASE
 Divis
Division is divided into 2 parts.


Mitosis has 2 phases that are what termed as place holders:
Interphase and cytokinesis.
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CELLS – ASEXUAL AND SEXUAL RERODUCTION

c. Control of Cell Division
 Control occurs at three checkpoints:
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CELLS – ASEXUAL AND SEXUAL RERODUCTION

 When Control is lost: CANCER
 The proteins that regulate cell growth and division are coded for by
genes. If a mutation occurs at these genes, the proteins may not
function properly.
 Cell growth and division can be disrupted leading to CANCER.
 CANCER is the uncontrolled growth of cells.
3. Meiosis
a. Formation of haploid cells
 In animals meiosis produces gametes or sex cells.
 These gametes are haploid reproductive cells.
 Therefore they contain 23 chromosomes or half the 4 total.
 Cell preparing to divide by meiosis undergo the G1, S, and G2 phases of
interphase. During interphase the cell grows to a mature size and copies
its DNA.
 Therefore cells begin meiosis with a duplicate set of chromosomes.
 Cells undergoing meiosis divide twice, diploid (2n) cells that divide
meiotically result in 4 haploid (1n) cell rather than 2 diploid (2n) cells.
 The stages of the first cell division are called meiosis I and the stages of
the second cell division are celled meiosis II.
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CELLS – ASEXUAL AND SEXUAL RERODUCTION
Called a synapsis.
Each pair is called a
tetrad.
Portions of the
chromosome break off
and attach to adjacent
chromatids on the
homologous
chromosome througha
process called crossingover. Thus creating
gentic recombination.
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CELLS – ASEXUAL AND SEXUAL RERODUCTION
b. Development of gametes.
 In males,
s, meiosis produces sperm cells or spermatozoa in a process known
as spermatogenesis.
 In females, meiosis produces a mature egg cell or ovum (ova Plural) and 3
polar bodies that will eventually degenerate.

 Sexual reproduction is the production of offspring through the process of
meiosis and the union of a sperm and an egg. Offspring are genetically
different from the parents because the genes are ccombined
mbined in new ways
through meiosis.
 Evolutionary
volutionary advantage to sexual reproduction is that it enables species to
adapt rapidly to new conditions
conditions.
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