Gametogenesis

Question 1

form from special cells, called germline cells, in a type of cell division called meiosis that halves the chromosome number

Answer 1

Gametes

Question 2

Gametes contain___ different chromosomes—half the usual amount of genetic material, but still a complete genome.

Answer 2

23

Question 3

somatic cells contain

Answer 3

23 pairs, or 46 chromosomes.

Question 4

gametes are haploid

Answer 4

1n

Question 5

somatic cells are diploid (___), with two copies of each chromosome type.

Answer 5

2n

Question 6

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.

Answer 6

polyploid

Question 7

, as the mechanism of sexual reproduction, provides genetic diversity, which enables a population to survive a challenging environmental change.

Answer 7

meiosis

Question 8

A population of______ reproducing organisms is made up of individuals with different genotypes and phenotypes.

Answer 8

sexually

Question 9

population of_____ reproducing organisms such as bacteria, or genetically identical crops, consists of individuals with the same genome sequence.

Answer 9

asexually

Question 10

A male begins manufacturing sperm at_____ and continues throughout life, whereas a female begins meiosis when she is a_____.

Answer 10

puberty

fetus

Question 11

Meiosis in the female completes only if a sperm fertilizes an_____.

Answer 11

oocyte

Question 12

Spermatogenesis, the formation of sperm cells, begins in a diploid stem cell called a

Answer 12

spermatogonium

Question 13

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.

Answer 13

Spermatogonium

Question 14

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

Answer 14

primary spermatocytes

Question 15

During reduction division (meiosis I), each primary spermatocyte divides, forming two equal-sized haploid cells called

Answer 15

secondary spermatocytes

Question 16

n meiosis II, each secondary spermatocyte divides to yield two equalsized____

Answer 16

spermatids

Question 17

Each spermatid then develops the characteristic ____

Answer 17

sperm tail, or flagellum.

Question 18

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.

Answer 18

mitochondria

Question 19

After spermatid differentiation, some of the cytoplasm connecting the cells falls away, leaving mature, tadpole-shaped____

Answer 19

spermatozoa (singular, spermatozoon), or sperm

Question 20

A sperm, which is a mere 0.006 centimeter (0.0023 inch) long, must travel about 18 centimeters (____) to reach an oocyte

Answer 20

7 inches

Question 21

Each sperm cell consists of a

Answer 21

tail, body or midpiece, and a head region

Question 22

_____, contains enzymes that help the cell penetrate the protective layers around the oocyte.

Within the large sperm head,___ is wrapped around proteins.

Answer 22

acrosome

DNA

Question 23

Key Concepts

1._____ divide mitotically, yielding one stem cell and one cell that accumulates_____ and becomes a primary spermatocyte.

2. In meiosis I, each primary spermatocyte halves its genetic material to form_____
3. In meiosis II, each secondary spermatocyte divides, yielding two equal-sized____ attached by bridges of cytoplasm. Maturing spermatids separate and shed some____.
4. A mature sperm has a tail, body, and head, with an enzyme-containing acrosome covering the head.

Answer 23

Spermatogonia; cytoplasm

two secondary spermatocytes

spermatids; cytoplasm

Question 24

Meiosis in the female, called oogenesis (egg making), begins with a diploid cell, an____

Answer 24

oogonium

Question 25

follicle cells surround each oogonium.

As each oogonium grows, cytoplasm accumulates, DNA replicates, and the cell becomes a_____

Answer 25

primary oocyte

Question 26

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____

Answer 26

first polar body (haploid)

secondary oocyte (haploid)

Question 27

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.

Answer 27

first polar body

secondary oocyte

Question 28

Most of the cytoplasm among the four meiotic products in the female ends up in only one cell, the____

Answer 28

ovum

Question 29

The woman’s body absorbs the____, which normally play no further role in development.

Answer 29

polar bodies

Question 30

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

Answer 30

“blighted ovum.”

Question 31

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.)

Answer 31

prophase I

Question 32

Key Concepts

1. An____ accumulates cytoplasm and replicates its DNA, becoming a____
2. In meiosis I, the primary oocyte divides, forming (2)
3. In meiosis II, the secondary oocyte divides, yielding another (2)
4. 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.

Answer 32

oogonium; primary oocyte

small polar body and a large, haploid secondary oocyte

small polar body and a mature haploid ovum

prophase I

Question 33

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.

Answer 33

embryo

preimplantation

Question 34

Prenatal development after the eighth week is the______, when structures grow and specialize.

Answer 34

fetal period

Question 35

From the start of the ninth week until birth, the prenatal human organism is a_____.

Answer 35

fetus

Question 36

result when one fertilized ovum splits.

Answer 36

Monozygotic twins

Question 37

result from two fertilized ova.

Answer 37

Dizygotic twins

Question 38

Organs form throughout the embryonic period. The primitive streak, notochord and_____, arm and leg buds, heart, facial features, and skeleton develop.

Answer 38

neural tube

Question 39

A substance that causes birth defects is a_____.

Answer 39

teratogen