2.4: Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores




The process of meiosis reduces the amount of genetic material to half.
Meiosis must be highly SPECIFIC. When successfully completed, meiosis ensures GENETIC
CONTINUITY from generation to generation.
Meiosis also helps to ensure GENETIC VARIATION. How?
It results in gemmates with unique combinations of maternal and paternal chromosomes.
Also, crossing over allows for genetic exchange between homologous chromosomes.
Meiosis is the major form of GENETIC RECOMBINATION within species.
2.5: The Development of Gametes Varies during Spermatogenesis and Oogenesis
There are certain DIFFERENCES between the production of male and female gametes.
SPERMATOGENESIS



Spermatogenesis takes place in the TESTES/TESTICLES.
All sperm produced during spermatogenesis contain the HAPLOID number of chromosomes
and equal amounts of CYTOPLASM.
Spermatogenesis may be continuous or may occur PERIODICALLY in mature male animals.
o Animals that can breed year-round will produce sperm CONTINUOUSLY.
o Animals that breed during a season produce sperm only during that time.
OOGENESIS





Oogenesis takes place in the OVARIES.
The daughter cells produce receive EQUAL amounts of genetic material but do NOT receive
equal amounts of CYTOPLASM.
The concentration of cytoplasm is needed to allow the mature ovum to NOURISH the
developing embryo after FERTILIZATION.
The smaller cells produced during meiosis of an ovum are known as POLAR bodies.
Unlike spermatogenesis, oogenesis is typically not continuous.
o In some animal species, the two divisions may DIRECTLY FOLLOW EACH OTHER.
o In humans, the first division of oocytes begins in the EMBRYONIC OVARY and arrests in
PROPHASE I. Meiosis then resumes in each oocytes prior to OVULATION (release of a
mature egg from an ovary). The second phase of meiosis is completed AFTER
FERTILIZATION.
*Rewrite the ESSENTIAL POINT on page 31 below in your own words.
2.6: Meiosis is Critical to the Sexual Reproduction Cycle of All Diploid Organisms



Meiosis is the mechanism which REDUCES the amount of genetic information from the DIPLOID
amount to the HAPLOID amount.
In plants, meiosis results in haploid SPORES which lead to the formation of haploid GAMETES.
Describe, from page 33, HOW genetic variation occurs in gametes.
(hint: paragraph starts with “Each diploid organism…”)
Haploid gametes contain SOME combination of maternal and paternal information from
homologous pairs of chromosomes. In some cases, crossing over may have occurred which is
similar to shuffling a deck of cards. This results in genetic variation.

In fungi and plants:
o The predominant life cycle in fungi consists of a HAPLOID vegetative cells. They arise
through meiosis and then proliferate by MITOTIC CELL DIVISION
o In multicellular plants, the life cycle alternates between the:
 Diploid SPOROPHYTE stage and the
 Haploid GAMETOPHYTE stage.
o This alternation is called ALTERNATION of GENERATIONS.
o WHEN does fertilization occur in multicellular plants?
Fertilization bridges between the sporophyte and gametophyte stages. It is essential
in the life cycle of the plants.


PLEASE READ THE REST OF CHAPTER 2 (one section)
ATTEMPT to answer the questions in “Insights and Solutions” on page 35. Questions and
answers are on the same page, so don’t cheat and read ahead. Try them out and see how you
do.
DON’T FORGET…… QUEST ON MONDAY!

HAVE A FANTASTIC HOMECOMING WEEK!
GOOD LUCK IF YOU ARE PARTICIPATING IN LIP SYNC,
POWDER PUFF, or HOMECOMING COURT!
SEE YOU AT THE DANCE ON SATURDAY!