Ch 11

Question 1

Humans somatic cells have how many pairs of chromosomes?

Answer 1

23 pairs

Each pair consists of homologous chromosomes.

Question 2

The two chromosomes in each pair are called what?

Answer 2

homologous chromosomes

They are the same length and shape and carry genes controlling the same inherited characters.

Question 3

The sex chromosomes that determine the sex of the individual are called what?

Answer 3

X and Y

Human females have a homologous pair of X chromosomes (XX), while males have one X and one Y chromosome (XY).

Question 4

Human females have a homologous pair of which chromosomes?

Answer 4

X chromosomes (XX)

This indicates the female sex in humans.

Question 5

Human males have which chromosomes?

Answer 5

one X and one Y chromosome (XY)

This indicates the male sex in humans.

Question 6

The remaining 22 pairs of chromosomes are called what?

Answer 6

autosomes

These chromosomes are not involved in determining sex.

Question 7

A diploid cell (2n) has how many sets of chromosomes?

Answer 7

two sets

In humans, this means 2n = 46 chromosomes.

Question 8

A karyotype is defined as what?

Answer 8

an ordered display of the pair of chromosomes from a cell

It is used to examine chromosomal abnormalities.

Question 9

Fertilization is the union of which gametes?

Answer 9

the sperm & the egg

The fertilized egg is called a zygote.

Question 10

The fertilized egg is called a what?

Answer 10

zygote

It has one set of chromosomes from each parent.

Question 11

Gametes are the only types of human cells produced by what process?

Answer 11

meiosis

This process results in one set of chromosomes in each gamete.

Question 12

Meiosis results in how many sets of chromosomes in each gamete?

Answer 12

one set

This is in contrast to mitosis, which produces diploid cells.

Question 13

What is the process that precedes meiosis?

Answer 13

Replication of chromosomes

Like mitosis, meiosis is preceded by the replication of chromosomes.

Question 14

Meiosis takes place in two sets of cell divisions called _______ and _______.

Answer 14

meiosis I and meiosis II

These divisions result in four daughter cells.

Question 15

How many daughter cells are produced in meiosis compared to mitosis?

Answer 15

Four daughter cells

Mitosis results in two daughter cells.

Question 16

Each daughter cell in meiosis has only _______ as many chromosomes as the parent cell.

Answer 16

half

This reduction is essential for sexual reproduction.

Question 17

During Prophase I, what begins to condense?

Answer 17

Chromosomes

Homologous chromosomes loosely pair up, aligned gene by gene (synapsis).

Question 18

What is the process called where nonsister chromatids exchange DNA segments?

Answer 18

Crossing over

The chiasmata is the point where crossing over has occurred.

Question 19

In Metaphase I, paired chromosomes (tetrads) randomly line up at the _______.

Answer 19

metaphase plate

One chromosome faces each pole during this alignment.

Question 20

During Anaphase I, what separates instead of sister chromatids?

Answer 20

Pair of homologous chromosomes

One chromosome moves toward each pole, while sister chromatids remain attached at the centromere.

Question 21

What forms during Telophase I and Cytokinesis?

Answer 21

• Cleavage furrow forms
• Two haploid daughter cells are formed

Cytokinesis usually occurs simultaneously with Telophase I.

Question 22

What occurs during Prophase II of meiosis?

Answer 22

• Spindle apparatus forms

This marks the beginning of the second meiotic division.

Question 23

What happens during Prometaphase II?

Answer 23

• Spindle fiber microtubules attach to kinetochore of chromosomes

This is crucial for the movement of chromosomes during meiosis.

Question 24

During Metaphase II, where are the sister chromatids arranged?

Answer 24

At the metaphase plate

This arrangement is essential for their separation in the next phase.

Question 25

What occurs in **Anaphase II**?

Answer 25

* Sister chromatids separate * Move toward opposite poles ## Footnote This separation is critical for the formation of haploid cells.

Question 26

What forms during **Telophase II**?

Answer 26

* Nuclei form * Cytokinesis occurs ## Footnote This results in the final separation of the daughter cells.

Question 27

At the end of meiosis, how many daughter cells are there and what is their chromosome set?

Answer 27

Four daughter cells, each with a haploid set of chromosomes ## Footnote This is the result of two rounds of division.

Question 28

Name the **three mechanisms** that contribute to genetic variation.

Answer 28

* Crossing over * Independent assortment of chromosomes * Random fertilization ## Footnote These mechanisms enhance genetic diversity in offspring.

Question 29

What happens during **crossing over** in prophase I?

Answer 29

Homologous portions of two nonsister chromatids trade places ## Footnote This process combines DNA inherited from each parent.

Question 30

During **metaphase I**, how do chromosomes line up?

Answer 30

Completely randomly ## Footnote This random arrangement contributes to genetic variation.

Question 31

What does **random fertilization** add to genetic variation?

Answer 31

Any sperm can fuse with any ovum ## Footnote This increases the genetic diversity of the resulting offspring.