Gametogenesis Flashcards
form from special cells, called germline cells, in a type of cell division called meiosis that halves the chromosome number
Gametes
Gametes contain___ different chromosomes—half the usual amount of genetic material, but still a complete genome.
23
somatic cells contain
23 pairs, or 46 chromosomes.
gametes are haploid
1n
somatic cells are diploid (___), with two copies of each chromosome type.
2n
genetically overloaded cell, called a______, usually does not develop normally, or at all.
About one in a million newborns has _____ cells, and has abnormalities in all organ systems and usually only lives a few days.
polyploid
, as the mechanism of sexual reproduction, provides genetic diversity, which enables a population to survive a challenging environmental change.
meiosis
A population of______ reproducing organisms is made up of individuals with different genotypes and phenotypes.
sexually
population of_____ reproducing organisms such as bacteria, or genetically identical crops, consists of individuals with the same genome sequence.
asexually
A male begins manufacturing sperm at_____ and continues throughout life, whereas a female begins meiosis when she is a_____.
puberty
fetus
Meiosis in the female completes only if a sperm fertilizes an_____.
oocyte
Spermatogenesis, the formation of sperm cells, begins in a diploid stem cell called a
spermatogonium
This cell divides mitotically, yielding two daughter cells. One continues to specialize into a mature sperm, and the other remains a stem cell, able to self-renew and continually produce more sperm.
Spermatogonium
Bridges of cytoplasm attach several spermatogonia, and their daughter cells enter meiosis together. As these spermatogonia mature, they accumulate cytoplasm and replicate their DNA, becoming
primary spermatocytes
During reduction division (meiosis I), each primary spermatocyte divides, forming two equal-sized haploid cells called
secondary spermatocytes
n meiosis II, each secondary spermatocyte divides to yield two equalsized____
spermatids
Each spermatid then develops the characteristic ____
sperm tail, or flagellum.
The base of the tail has many____, which will split ATP molecules to release energy that will propel the sperm inside the female reproductive tract.
mitochondria
After spermatid differentiation, some of the cytoplasm connecting the cells falls away, leaving mature, tadpole-shaped____
spermatozoa (singular, spermatozoon), or sperm
A sperm, which is a mere 0.006 centimeter (0.0023 inch) long, must travel about 18 centimeters (____) to reach an oocyte
7 inches
Each sperm cell consists of a
tail, body or midpiece, and a head region
_____, contains enzymes that help the cell penetrate the protective layers around the oocyte.
Within the large sperm head,___ is wrapped around proteins.
acrosome
DNA
Key Concepts
1._____ divide mitotically, yielding one stem cell and one cell that accumulates_____ and becomes a primary spermatocyte.
- In meiosis I, each primary spermatocyte halves its genetic material to form_____
- In meiosis II, each secondary spermatocyte divides, yielding two equal-sized____ attached by bridges of cytoplasm. Maturing spermatids separate and shed some____.
- A mature sperm has a tail, body, and head, with an enzyme-containing acrosome covering the head.
Spermatogonia; cytoplasm
two secondary spermatocytes
spermatids; cytoplasm
Meiosis in the female, called oogenesis (egg making), begins with a diploid cell, an____
oogonium
follicle cells surround each oogonium.
As each oogonium grows, cytoplasm accumulates, DNA replicates, and the cell becomes a_____
primary oocyte
In meiosis I, the primary oocyte divides into two cells: a small cell with very little cytoplasm, called a____, and a much larger cell called a____
first polar body (haploid)
secondary oocyte (haploid)
In meiosis II, the tiny______ may divide to yield two polar bodies of equal size, with unreplicated chromosomes; or the first polar body may decompose.
The______, however, divides unequally in meiosis II to produce another small polar body, with unreplicated chromosomes, and the mature egg cell, or ovum, which contains a large volume of cytoplasm.
first polar body
secondary oocyte
Most of the cytoplasm among the four meiotic products in the female ends up in only one cell, the____
ovum
The woman’s body absorbs the____, which normally play no further role in development.
polar bodies
Rarely, a sperm fertilizes a polar body. When this happens, the woman’s hormones respond as if she is pregnant, but a disorganized clump of cells that is not an embryo grows for a few weeks, and then leaves the woman’s body. This event is a type of miscarriage called a
“blighted ovum.”
Before birth, a female’s million or so oocytes arrest in_____. (This means that when your grandmother was pregnant with your mother, the oocyte that would be fertilized and eventually become you was already there.)
prophase I
Key Concepts
- An____ accumulates cytoplasm and replicates its DNA, becoming a____
- In meiosis I, the primary oocyte divides, forming (2)
- In meiosis II, the secondary oocyte divides, yielding another (2)
- Oocytes arrest at ____until puberty, after which one or several oocytes complete the first meiotic division each month. The second meiotic division completes at fertilization.
oogonium; primary oocyte
small polar body and a large, haploid secondary oocyte
small polar body and a mature haploid ovum
prophase I
A prenatal human is considered an——- for the first 8 weeks. During this time, rudiments of all body parts form.
The embryo in the first week is considered to be in a “_____” stage because it has not yet settled into the uterine lining.
Some biologists do not consider a prenatal human an embryo until it begins to develop tissue layers, at about 2 weeks.
embryo
preimplantation
Prenatal development after the eighth week is the______, when structures grow and specialize.
fetal period
From the start of the ninth week until birth, the prenatal human organism is a_____.
fetus
result when one fertilized ovum splits.
Monozygotic twins
result from two fertilized ova.
Dizygotic twins
Organs form throughout the embryonic period. The primitive streak, notochord and_____, arm and leg buds, heart, facial features, and skeleton develop.
neural tube
A substance that causes birth defects is a_____.
teratogen
