MEIOSIS AND SEXUAL REPRODUCTION
I. SEXUAL REPRODUCTION-involves the production of gametes-what are these?
A. In this process, an individual receives genetic information from two parents.
B. In sexual reproduction, haploid gametes fuse to form a diploid zygote which develops into a
new individual.
C. Meiosis is a type of cell division that produces haploid gametes for living organisms.
1. Both plants and animals can produce haploid gametes.
2. Without meiosis, living organisms would not be able to produce haploid gametes.
II. MEIOSIS-process through which haploid gametes arise from diploid cells.
A. Characteristics/Features of Meiosis
1. It occurs in germ cellsa. Where are germ cells stored in humans?
2. Since diploid germ cells undergo meiosis to produce haploid gametes, then meiosis is
referred to as a reduction division. What does this mean?
3. Meiosis requires 2 separate divisions to occur. Due to this, meiosis produces 4
genetically different haploid gametes.
B. The Events/Phases of Meiosis
1. Meiosis I-Events/Phases
a. Prophase I-Events/Steps
1) Chromatin condenses to form homologous chromosomes.
2) Next, the homologous chromosomes fuse together through a process
known as synapsis.
a) This is a key process in meiosis. It does not occur in mitosis.
b) In synapsis, pairs of homologous chromosomes attach or fuse
together.
3) While these pairs of chromosomes are attached to each other, a
process known as crossing over occurs.
a) What is crossing over?
b) Why is crossing over important?
c) Why is genetic recombination useful to living organisms?
4) Centrioles appear and form the Spindle Apparatus.
5) The now unattached pairs of homologous chromosomes attach to the
spindle fibers.
b. Metaphase I-Steps/Events
1) What major event occurs in this phase of Meiosis?
c. Anaphase I-Steps/Events
1) Homologous chromosomes separate and move towards the poles of
the dividing cell.
d. Telophase I-Steps/Events
1) The chromosomes reach opposite ends of the cell.
2) Cytokinesis occurs. What is this?
3) The cell partially divides to form 2 new cells.
4) The 2 cells formed at this point are haploid; therefore, reduction
occurs in Meiosis I.
2. Interkinesis-brief period of time that resembles interphase in mitotic cells. DNA
replication does not occur during this period.
3. Meiosis II-is identical to mitosis in every way.
C. Spermatogenesis-meiosis that produces four sperm.
D. Oogenesis-meiosis that produces eggs
III. COMPARISON OF MITOSIS AND MEIOSIS
A. What types of cells does each process occur in?
B. How many division occur in mitosis?
In meiosis?
C. What are the end results of each process?
D. Define the following: synapsis, crossing over. Where do these two processes occur?
E. Why is genetic recombination important to sexually reproducing organisms?