3-1 Notes - Sexual Reproduction & Meiosis
Sexual Reproduction
Sexual Reproduction
Asexual Reproduction
 Reproduction in organisms produces new __________________.
needs two organisms of the
only needs one organism
 Organisms can reproduce their cells in two ways: by
same species
____________ reproduction and by ____________ reproduction. child is different from the
child is an exact copy of the
parents
parent
 Sexual reproduction occurs when the DNA from two
special cells
__________________ cells combine.
no special cells involved
called gametes are created
 Half the DNA is contained in an __________ cell.
 Half the DNA is contained in a __________ cell.
 In a process called fertilization, the sperm and egg cells fuse together forming something called a ______________.
Advantages of Sexual Reproduction
 __________________ variation – a variety of genetic traits in a species makes it more likely for the species to
survive changes in _________________________ conditions.
 __________________ breeding (the opposite) – when males and females with preferred traits are chosen to breed
so they produce offspring with the preferred traits – this _____________ genetic variation (offspring are very similar).
Disadvantages of Sexual Reproduction
 Getting egg and sperm together for fertilization can be __________________.
 It takes __________ for organisms to grow and develop before they are mature enough to reproduce.
Importance of Meiosis
 ________________ is a type of cell division that produces sperm or egg cells.
 Meiosis ensures that offspring inherit the ________________ number of chromosomes.
 Without meiosis, the chromosome number would _______________ with each generation.
Diploid vs. Haploid Cells
 ______________ cells have 2 sets of each homologous chromosome (they are similar,
not identical).
 ______________ cells have 1 set from each homologous chromosome pair.
 A diploid human cell has _____ pairs of (or ______ total) homologous chromosomes.
but
Meiosis
 Meiosis is split into two overall stages: _______________ and _______________.
Meiosis I
 Prophase I – Nuclear membrane breaks apart and pairs of ____________________ chromosomes condense.
(92 human chromosomes)
 Metaphase I – Sister chromatids line up along the ______________ of the cell. (92 human chromosomes)
 Anaphase I – Sister chromatids move to _______________ ends of the cell. (92 human chromosomes)
 Telophase I – Nuclear membrane forms around each set of sister chromatids and the ________________
divides, forming two ____________________ cells. (46 human chromosomes)
p. 121
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis II
 Prophase II – Chromosomes do ____ replicate before nuclear membrane breaks apart. (46 human chromosomes)
 Metaphase II – Chromosomes line up along the ________________ of the cell. (46 human chromosomes)
 Anaphase II – Sister chromatids separate, moving to ______________ ends of the cell. (46 human chromosomes)
 Telophase II – Nuclear membrane reforms and the ______________________ divides. (23 human chromosomes)
Prophase II



Metaphase II
Anaphase II
Telophase II
Meiosis results in ____ ________________ nuclei from 1 diploid nucleus.
Meiosis I produces 2 genetically ________________ cells.
Meiosis II produces 2 _________________ _____________ cells from
each cell produced in Meiosis I.
Review
____ 1. What is the new cell that forms from fertilization called?
A. sperm
B. egg
C. haploid
D. zygote
____ 2. How many chromosomes from each homologous pair does a haploid cell contain?
A. one
C. three
B. two
D. four
____ 3. How many daughter cells are produced in meiosis?
A. one
B. two
C. three
D. four
____ 4. What is one advantage of sexual reproduction?
A. produces many offspring
B. offspring are genetically identical
C. offspring have more genetic variation
D. can produce offspring quickly
____ 5. How many times does division of the nucleus and cytokinesis happen in meiosis?
A. one
C. three
B. two
D. four
3-1 Notes - Sexual Reproduction & Meiosis
Sexual Reproduction
Sexual Reproduction
Asexual Reproduction
 Reproduction in organisms produces new offspring.
needs two organisms of the
only needs one organism
 Organisms can reproduce their cells in two ways: by sexual
same species
reproduction and by asexual reproduction.
child is different from the
child is an exact copy of the
parents
parent
 Sexual reproduction occurs when the DNA from two different
special cells
cells combine.
no special cells involved
called gametes are created
 Half the DNA is contained in an egg cell.
 Half the DNA is contained in a sperm cell.
 In a process called fertilization, the sperm and egg cells fuse together forming something called a zygote.
Advantages of Sexual Reproduction
 Genetic variation – a variety of genetic traits in a species makes it more likely for the species to survive changes in
environmental conditions.
 Selective breeding (the opposite) – when males and females with preferred traits are chosen to breed so they
produce offspring with the preferred traits – this reduces genetic variation (offspring are very similar).
Disadvantages of Sexual Reproduction
 Getting egg and sperm together for fertilization can be difficult.
 It takes time for organisms to grow and develop before they are mature enough to reproduce.
Importance of Meiosis
 Meiosis is a type of cell division that produces sperm or egg cells.
 Meiosis ensures that offspring inherit the correct number of chromosomes.
 Without meiosis, the chromosome number would double with each generation.
Diploid vs. Haploid Cells
 Diploid cells have 2 sets of each homologous chromosome (they are similar, but not
identical).
 Haploid cells have 1 set from each homologous chromosome pair.
 A diploid human cell has 23 pairs of (or 46 total) homologous chromosomes.
Meiosis
 Meiosis is split into two overall stages: Meiosis I and Meiosis II.
Meiosis I
 Prophase I – Nuclear membrane breaks apart and pairs of replicated chromosomes condense. (92 human
chromosomes)
 Metaphase I – Sister chromatids line up along the center of the cell. (92 human chromosomes)
 Anaphase I – Sister chromatids move to opposite ends of the cell. (92 human chromosomes)
 Telophase I – Nuclear membrane forms around each set of sister chromatids and the cytoplasm divides,
forming two daughter cells. (46 human chromosomes)
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis II
 Prophase II – Chromosomes do not replicate before nuclear membrane breaks apart. (46 human chromosomes)
 Metaphase II – Chromosomes line up along the center of the cell. (46 human chromosomes)
 Anaphase II – Sister chromatids separate, moving to opposite ends of the cell. (46 human chromosomes)
 Telophase II – Nuclear membrane reforms and the cytoplasm divides. (23 human chromosomes)
Prophase II



Metaphase II
Anaphase II
Telophase II
Meiosis results in 4 haploid nuclei from 1 diploid nucleus.
Meiosis I produces 2 genetically different cells.
Meiosis II produces 2 identical haploid cells from each cell produced in Meiosis
I.
Review (Answers 1-D, 2-A, 3-D, 4-C, 5-B)
____ 1. What is the new cell that forms from fertilization called?
A. sperm
B. egg
C. haploid
D. zygote
____ 2. How many chromosomes from each homologous pair does a haploid cell contain?
A. one
C. three
B. two
D. four
____ 3. How many daughter cells are produced in meiosis?
A. one
B. two
C. three
D. four
____ 4. What is one advantage of sexual reproduction?
A. produces many offspring
B. offspring are genetically identical
C. offspring have more genetic variation
D. can produce offspring quickly
____ 5. How many times does division of the nucleus and cytokinesis happen in meiosis?
A. one
C. three
B. two
D. four