Chapter 8 - Mitosis and Meiosis

Question 1

Why do cells need to multiply?

Answer 1

Asexual reproduction.
Development (increasing complexity).
Growth (replacing cells).
Repair of damaged tissues (tub your toe and yell MY TOE SIS!).
Increase surface area to volume.

Question 2

What is asexual reproduction? Is mitosis or meiosis involved?

Answer 2

Creation of genetically identical offspring by a single parent, without use of sperm or eggs. Only mitosis is involved NOT meiosis.

Question 3

What are two types of asexual reproduction?

Answer 3

Binary fission (dividing in half, to form two identical daughter cells)
Budding (mitosis followed by cytokinesis?, the new individual develops from an outgrowth of a parent and splits off (e.g., Hydra))

Question 4

What type of asexual reproduction do prokaryotes and eukaryotes use? Example?

Answer 4

Prokaryotes use binary fission (bacteria).
Eukaryotes use mitosis followed by cytokinesis (aka budding?) (yeast or Hydra).

Question 5

What is mitosis?
What is cytokensis?

Answer 5

M: Division of a single nucleus (genetic material) into two genetically identical nuclei. (nuclear division)
C: Division of the cytoplasm to form two separate daughter cells usually right after mitosis. (cellular division)

Question 6

______ results in the formation of 2 identical daughter cells. It is important for tissue repair, growth and development.

Answer 6

Mitosis!

Question 7

______ results in the formation of 4 haploid and genetically different daughter cells. It occurs only in the _______ cells and is important for _______ reproduction.

Answer 7

Meiosis.
Reproductive/gamete cells.
Sexual reproduction.

Question 8

What are genes? Where are they located?

Answer 8

Separate units of hereditary information made of specific DNA (or RNA) sequences.
Located on chromosomes inside the nucleus of eukaryotic cells (and in mitochondria and chloroplasts).

Question 9

What is chromatin?
What are chromosomes?
What are chromatids?

Answer 9

Chromatin: loose, extended thin fibres of DNA + protein in the nucleus.
During mitosis and meiosis, chromatin condenses to form chromosomes made of two identical strands called chromatids.

Question 10

Name the 4 phases of the cell cycle and identify what happens in each one.

Answer 10

Gap 1 (G1), cell growth.
Synthesis (S), DNA replication.
Gap 2 (G2), prep for mitosis.
⬆️ All part of interphase.
Mitotic (M Phase), mitosis and cytokinesis.

Question 11

What is the cell cycle?
How much time is spent in interphase vs. mitosis?

Answer 11

The duration of time between one division and the next made of phases.
Approx. 90% in interphase and 10% in mitosis.

Question 12

If we could see chromosomes in a condensed form would they be single or double stranded during G1 and G2?

Answer 12

Single stranded in G1, but double stranded in G2 because DNA is replicated during the S phase.

Question 13

Name the 4 phases of mitosis. What happens in each stage?

Answer 13

P = Prophase (chromosomes pair up)
M = Metaphase (chromosomes align at the metaphase plate)
A = Anaphase (sister chromatids pull apart)
T = Telophase (cells split down the middle)
For more details see written notes.

Question 14

What are centrioles and how are they related to centrosomes?
Are centrosomes and centromeres the same?

Answer 14

Centrosomes are structures made from two centrioles. Centrioles are microtubule rings. Centrosomes organize microtubules, provide structure for the cell, and pull chromatids apart during cell division.
NOT the same. -some = microtubules. -mere = part of a chromosome.

Question 15

If you can see condensed double stranded chromosomes within a body cell, is it in a mitotic phase or interphase?

Answer 15

A mitotic phase.
The chromatin does not condense into chromosomes until prophase and loosens again during telophase.

Question 16

What is a centromere? A kinetochore?

Answer 16

A narrow “waist” where two identical sister chromatids join together in a chromosome.
A protein structure at the centromere region in each sister chromatid. Where the mitotic spindles attach.

Question 17

What are mitotic spindles? When do they first appear and disappear?

Answer 17

Microtubules growing out from the centrosomes that are used in the separation of chromosomes.
Appear during prophase. Disappear in telophase.

Question 18

What are sister chromatids?
Are they identical or not?

Answer 18

Sister chromatids are simply double stranded chromosomes.
Yes, they are identical.

Question 19

What are sister chromatids called when they separate?

Answer 19

Daughter chromosomes.

Question 20

A cell with double or single-stranded chromosomes contains the same functional amount of DNA – true or false?

Answer 20

True?

Question 21

What phase is telophase quickly followed by? What happens in this phase?

Answer 21

Cytokinesis in which the cytoplasm divides and the daughter cells fully separate.

Question 22

How is cytokinesis different in animal and plant cells?

Answer 22

Cytokinesis in animals occurs via a cleavage furrow (like tightening a string around the cell).
In plants, a cell plate forms from the inside out making a new cell wall.

Question 23

How many chromosomes do humans have during prophase and metaphase? How many chromosomes do we have during anaphase?

Answer 23

46 chromosomes during prophase and metaphase. They’re duplicated into 92 chromatids which are briefly split into 92 chromosomes during anaphase and before telophase ends.

Question 24

How many times does DNA replicate in mitosis? How many times does the cell divide in mitosis? How many daughter cells are made?
What about in meiosis?

Answer 24

In mitosis the DNA replicates once and divides once. Makes 2 daughter cells.
In meiosis the DNA only replicates once, but the cell divides twice. This halves the amount of DNA per cell and makes 4 daughter cells.

Question 25

What are haploid and diploid cells?

Answer 25

Diploid (2n) cells contain chromosomes in pairs (one from mom, one from dad).
Haploid (1n) cells only have one copy of each chromosome.

Question 26

The only haploid cells produced by mammals are the ______ .

Answer 26

Gametes (reproductive cells, ova and sperm).

Question 27

What is a locus or loci (plural)?

Answer 27

The location of a gene on a chromosome.

Question 28

What is an autosome?
Are pairs of autosomes identical?

Answer 28

Any chromosome not considered a sex chromosome.
They are identical.

Question 29

Humans have ____ pairs of autosomes and _____ pair(s) of sex chromosomes for a total of _____ individual chromosomes.

Answer 29

22 pairs of autosomes and 1 pair of sex chromosomes for a total of 46 chromosomes (22 + 1 = 23 x 2 = 46).

Question 30

What are homologous chromosomes? What makes them homologous?

Answer 30

A set/pair of one maternal and one paternal chromosome (can be single or double stranded) that code for similar traits.
They are identical in length, centromere position, and staining pattern.

Question 31

Which sex chromosomes do females and males have?
Which chromosome has more information?

Answer 31

A female has 2 X chromosomes
A male has 1X and 1Y chromosome.
The X chromosome has a lot more genetic information.

Question 32

Explain how most eukaryotic organisms have a haploid (1n) phase and a diploid phase (2n) in their life cycle.

Answer 32

We all start as gametes (eggs and sperm, 1n) which fuse into a zygote (2n) that grows into embryo, fetus, baby, etc. until we can produce our own gametes (1n).

Question 33

Why is meiosis important? What are the benefits?

Answer 33

Meiosis results in maintaining the chromosome number of organisms and increasing biodiversity.

Question 34

What are all the phases of meiosis called?

Answer 34

Meiosis 1
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1 and Cytokinesis
Interkinesis
Meiosis 2
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2 and Cytokinesis

Question 35

How is prophase 1 of meiosis different from prophase of mitosis?

Answer 35

In prophase 1 homologous chromosomes pair up and genetic material is exchanged (crossing over).
This creates recombinant (non-identical) sister chromatids.

Question 36

How are the kinetochores different in meiosis vs. mitosis?

Answer 36

In meiosis the microtubules attach to the kinetochore of each double stranded chromosome instead of each sister chromatid.

Question 37

What are recombinant sister chromatids? When are these created?
What are parental sister chromatids?

Answer 37

Sister chromatids that are no longer
identical to each other because crossing over has occurred.
Created in prophase 1 of meiosis.
Sister chromatids that remain unchanged after meiosis.

Question 38

What is a tetrad?
What is a chiasma or chiasmata (plural)?

Answer 38

A pair of homologous chromosomes in synapsis (pairing to cross over).
A place where two homologous chromosomes are attached to each other (an X-shaped region) when crossing over.

Question 39

After telophase 1 of meiosis are the cells effectively haploid or diploid?

Answer 39

Haploid.
Because the homologous chromosomes have been separated the cell now has one copy of each chromosome.

Question 40

How does the second interphase of meiosis differ from the interphase that precedes meiosis? What is it called?

Answer 40

Interkinesis.
It’s like interphase but the DNA does NOT replicate.

Question 41

During meiosis chromosomes separate into the gametes _________ of one another. What is this called?

Answer 41

Independently.
Independent assortment, which means we never know which genes will end up in a gamete.

Question 42

What are the two primary ways that meiosis increases genetic variability?

Answer 42

The independent assortment of the chromosomes into the gametes and the crossing over that occurred during Prophase I.

Question 43

In humans with 23 pairs of homologous chromosomes there are ________ possible gametes per parent.

Answer 43

2 to the power of 23 = 8,388,608
Just know it’s over 8 million!

Question 44

How can gametes end up with too many or too few chromosomes during meiosis? What is this called?

Answer 44

This happens if homologous chromosomes do not separate properly during meiosis 1. One gamete ends up with two copies and one gamete is missing the chromosome completely.
It’s called nondisjunction

Question 45

What evidence do we have to suggest that as we age, the chances of something going wrong with meiosis increases?

Answer 45

With Down’s syndrome, the risk of nondisjunction of chromosome #21 in women increases with age.

Question 46

What is a polyploid organism? How are they different from diploid organisms?

Answer 46

An organism that has more than 2 complete sets of chromosomes, creating a new species. Most common in plants. This increases their genetic diversity. They tend to be larger and more adaptable than their diploid counterparts.