Meiosis Cycle Flashcards
is a special type of cell division
that creates gametes (sperm & egg) with
half the chromosome number.
Meiosis
What is the purpose of Meiosis?
It ensures genetic diversity in offspring.
Chromosome numbers:
● Somatic (body) cells: 46 chromosomes (23 pairs, diploid, 2n).
● Gametes (sperm & egg): 23 chromosomes (haploid, n).
Why is meiosis important?
● Halves the chromosome number so fertilization restores the correct number (46).
● Mixes genetic material through crossing over & independent assortment.
● Prevents genetic overload (polyploidy), which is fatal in humans.
Which phase of meiosis involves the condensation of chromosomes, pairing of homologous chromosomes, and crossing over, where homologous chromosomes exchange genetic material to create new gene combinations?
Meiosis 1: Prophase 1
In which phase of meiosis do homologous pairs align randomly in the center of the cell, leading to independent assortment and increased genetic diversity?
Metaphase I
In which phases of meiosis do homologous chromosomes separate into two haploid cells, with each cell having 23 chromosomes, but the sister chromatids still remain attached?
Anaphase I & Telophase I
TRUE OR FALSE: Meiosis occurs in both sexes but follows different pathways after division.
TRUE
TRUE OR FALSE: Sperm & oocytes are both haploid (23 chromosomes) but differ in size, structure,
and function.
TRUE
What is the difference between gamete maturation In male and female?
Males: Start producing sperm at puberty and continue for life.
○ Females: Begin meiosis before birth but only complete it if fertilization occurs.
Process of sperm cell development in the testes (seminiferous tubules).
Spermatogenesis
Spermatogenesis begins with _____
A diploid spermatogonium (stem cell) that divides mitotically.
TRUE OR FALSE: Some cells become sperm, others remain as stem cells for
ongoing sperm production.
TRUE
In the steps of spermatogenesis, what step is the diploid stem cell that divides mitotically to maintain sperm production?
- Spermatogonium (2n):
In the steps of spermatogenesis, what step undergoes Meiosis I → divides into two haploid secondary spermatocytes
(n).
- Primary Spermatocyte (2n):
A step in spermatogenesis that undergo Meiosis II → produce four equal-sized spermatids (n).
- Secondary Spermatocytes (n):
During spermatogenesis, what happens to spermatids as they mature into spermatozoa?
- Spermatids mature into Spermatozoa (Sperm):
Gain a flagellum (tail) for movement.
Mitochondria in the midpiece provide energy (ATP) for swimming.
Acrosome (head region) contains enzymes to penetrate the oocyte.
Structure of a Mature Sperm Cell
Head, Midpiece, Tail (Flagellum)
What structures in sperm contain genetic material and assist in penetrating the oocyte?
Sperm Head
Enzyme-filled cap that helps sperm penetrate the oocyte.
Acrosome
Packed with mitochondria to produce energy for swimming.
Midpiece
Enables movement toward the oocyte.
Tail (Flagellum)
TRUE OR FALSE: Males produce billions of sperm over their lifetime.
FALSE
trillions
TRUE OR FALSE: Damaged spermatogonia (due to toxins) will mature into sperm.
FALSE
will not mature
TRUE OR FALSE: Toxic exposure to mature sperm may impair their swimming ability, preventing
fertilization.
TRUE
Meiosis II (Equational Division, 23 → 23 chromosomes):
- Prophase II: Chromosomes condense again.
- Metaphase II: Chromosomes align in the center.
- Anaphase II: Sister chromatids separate and move to opposite poles.
- Telophase II: Four genetically unique haploid gametes (sperm or eggs) form.
New combinations of genes from both parents.
Crossing over (Prophase I):
What process in meiosis results in the random alignment of chromosomes, leading to trillions of possible gene combinations?
Independent assortment.
TRUE OR FALSE: Without mitosis, fertilization would double chromosome numbers, leading to genetic
disorders.
FALSE:
MEIOSIS
TRUE OR FALSE: Crossing over & independent assortment make each person unique.
TRUE
is the process of egg (oocyte) formation in females.
Oogenesis
A stage of oogenesis: What is the process that begins with a diploid oogonium (2n), which grows, undergoes DNA replication, and becomes a primary oocyte (2n), starting meiosis but halting at Prophase I before birth?
Before Birth
At puberty, how many oocytes remain, and what happens each month in response to hormones
Around 400,000 oocytes remain, and each month, one or more oocytes resume meiosis in response to hormones.
During the completion of Meiosis I, what happens to the oocyte and the first polar body?
Meiosis I completes, dividing into two uneven haploid cells:
The secondary oocyte (large, n) continues development.
The first polar body (small, n) usually degenerates.
What happens during ovulation in the mid-menstrual cycle, and what is the status of meiosis at this time?
The secondary oocyte is released into the uterine (fallopian) tube, and meiosis halts again at Metaphase II until fertilization occurs.
What happens if fertilization occurs, and what are the outcomes of Meiosis II?
If fertilization occurs, Meiosis II completes, producing:
The ovum (mature egg, n) with all the cytoplasm.
The second polar body (n), which degenerates.
Then, the nucleus of the sperm merges with the ovum, fertilization occurs, and a zygote (2n) is formed.
