Chapter 11 - Meiosis And Sexual Reproduction

Question 1

Haploid cells are produced by a type of cell division called what?

Answer 1

Meiosis

Question 2

Gametes unit to form what? Which has two sets of chromosomes (one from each gamete)

Answer 2

A zygote

Question 3

Cells with two sets of chromosomes are called what? While one set is called what?

Answer 3

2 sets - diploid (2n)

1 set - haploid (n)

Question 4

Sexual reproduction requires diploid cells to do what with their chromosome count?

Answer 4

Reduce their chromosome number by half and produce haploid cells, otherwise it would double the chromosomes every generation

Question 5

Meiosis always starts with what type of cells and the daughter cells being what type?

Answer 5

Starts with diploid ends with haploid

Question 6

How does meiosis achieve the reduction in chromosome number?

Answer 6

By undergoing one round of nuclear replication immediately followed by 2 rounds of nuclear reduction

Question 7

What is the difference in named stages from mitosis to meiosis?

Answer 7

Meiosis has the same name but 2 stages of each. Pro/meta/ana/telophase 1 and 2 instead of just 1.

Question 8

Are G1, S, and G2 similar to mitosis in meiosis?

Answer 8

Yes, virtually identical

Question 9

What happens in prophase 1? (Be very specific) include as much details as possible.

Answer 9

-Homologous (in form of sister chromatids) are brought together forming a synaptonemal complex of four chromatids

-a dense lattice of proteins tightly pairs the homologous called synapsis, during synapsis the genes of the sister chromatids align precisely with each other

-the precise alignment of homologous non-sister chromatids allows for crossing over (exchange of the ends of the homologous non sister chromatids, visible as chiasmata)

-a short area of homology attaches the X and Y chromatids in males

Question 10

What is crossing over and what does it do?

Answer 10

Crossing over is a form of genetic recombination between nonsister chromatids (mothers and fathers homologues)

-it mixes mother and father genes producing recombinant chromosomes (red and blue)

Question 11

What does recombination nodules do? And what are they?

Answer 11

They are large proteins complexes that mark the location of chiasmata in the process of crossing over

-an enzyme cuts the double strand of DNA and makes new connections between nonsister chromatids

Question 12

When the synaptonemal complex breaks down, the homologous chromosomes are attached only at what point?

Answer 12

The chiasmata and centromers

Question 13

The groups of four chromatids when visible are called…

Answer 13

Tetrads

Question 14

In terms of DNA exchange what does crossing over do in simple terms?

Answer 14

It leads to one chromosome having both maternal and paternal DNA

Question 15

What happens in prometaphase 1?

Answer 15

-Spindle fiber microtubules attach to kinetochore proteins at the centromeres

-each member of the homologous pair attaches to the opposite pole assuring that the homologous pairs are pulled apart at metaphase 1

-homologous chromosomes are still held together at the chiasmata

-nuclear membrane breaks down completely

Question 16

What happens at metaphase 1? (Be specific) list as much detail as possible.

Answer 16

-homologous chromosomes align on metaphase plate

-homologous pair align themselves randomly regarding which side they are on (maternal vs paternal) -(random alignment and crossing over accounts for genetic variation)

-orientation of each tetrad is independent of the orientation of the other 22 tetrads

Question 17

Diploid cells is denoted as 2^n representing the number of chromosomes per haploid set for n, what could this number be in humans?

Answer 17

2^23 being over 8million possible genetically distinct gametes just from one independent assormtnet alone

Question 18

What happens in anaphase 1?

Answer 18

-microtubules pull the homologous chromosomes apart

-the sister chromatids remain tightly bound at their centromeres

-the chiasmata are broken

Question 19

What happens in telophase 1? And cytokinesis

Answer 19

Seperated chromosomes arrive at opposite poles, a cleavage seperates the two daughter cells in cytokinesis

Question 20

Meiosis 2 will produce how many haploid cells when the sister chromatids seperate?

Answer 20

4

Question 21

What happens between meiosis 1 and 2? What is this phase called?

Answer 21

Not much, the time discrepancy is brief, no interphase occurs and is called interkinesis

Question 22

What is more similar to mitosis, meiosis 1 or 2?

Answer 22

Meiosis 2, only major difference is that there are half the number of chromosomes present

Question 23

Since meiosis 2 is pretty similar to mitosis, in brief terms go through each step (in order)

Answer 23

Prophase 2) MTOCs reform new spindles at opposite ends of each cell

Prometaphase 2) each sister chromatid forms an individual kinetochore that attaches to microtubules from opposite poles

Metaphase 2) sister chromatids align at the equilateral plate

Anaphase 2) sister chromatids are pulled apart by the kinetochore microtubule and moved towards opposite poles, nonkinetochore microtubules elongate the cell

Telophase 2, and cytokinesis) chromosomes arrive at opposite poles and begin to decondense, nuclear envelop develops around the chromosomes, cytokinesis separates the two cells into four unique haploid cells

(These 4 cells are genetically unique to random assortment in metaphase 2 and recombination during crossing over)

Question 24

Why is sexual reproduction so vital? Hense why asexual organisms are rare

Answer 24

Because variation is important for survival and reproducing populations, EVOLUTION.

Question 25

Plants have a strategy of multinuclear diploid and haploid stages called what?

Answer 25

Alternation of generations

Question 26

Specialized diploid cells are produced in the gonads in embryonic development called what?

Answer 26

Germ cells

Question 27

Germ cells first undergo what time of division? Then what after?

Answer 27

They undergo mitosis and eventually meiosis

Question 28

A zygote is formed when haploid cells produce two mating types (+/-) but does not undergo mitosis but immediately meiosis producing what?

Answer 28

4 haploid cells called spores

Question 29

What happens to the spores?

Answer 29

They can remain dormant and eventually will divide by mitosis to produce multinuclear haploid bodies

Question 30

Diploid dominant life cycles, haploid dominant life cycles, and both diploid and haploid dominant life cycles are seen in what species/organisms respectively?

Answer 30

Diploid dominant life cycles - animals

Haploid dominant life cycles - fungi and some algae

haploid and diploid dominant life cycles - some algae and all plants

Question 31

What is the haploid dominant stage and diploid dominant stage called in life cycles that do both? What does it produce?

Answer 31

Haploid dominant stage is called the gametophyte (produces hanged by mitosis since its cells are already haploid)

Diploid dominant stage is called sporophyte (produce spores that grow into haploid plants called gametophytes)