Chapter 8 - Mitosis and Meiosis

Question 1

Asexual reproduction

Answer 1

The creation of genetically identical offspring by a single parent, without the participation of sperm or egg. Only mitosis is involved.

2 types:
- binary fission
- budding

Question 2

Binary fission

Answer 2

Only in prokaryotes (single celled organisms) :

The singular bacterial chromosome is duplicated. The cell continues to grow and elongate, while the copied chromosome moves to the opposite end. Then the 2 chromosomes are separated into two daughter cells. (Makes a new identical organism)

Happens approximately every half hour. (Rapid population growth)

Question 3

Budding

Answer 3

A new individual develops from an outgrowth of a parent. The new individual eventually splits off and lives independently.

Used by yeasts and hydra

Question 4

Chromatin

Answer 4

A long extended form of coiled, thin fibres of DNA + proteins that make up eucaryotic chromosomes.

Question 5

Mitosis

Answer 5

The division of a single nucleus, and two genetically identical nuclei.

(The splitting of a body cell)

Question 6

Cytokinesis

Answer 6

The division of the cytoplasm to form two separate daughter cells. It usually occurs in unison with telophase of mitosis.

• In animal cells it occurs from the outside to the inside.
• In plant cells it occurs from the inside to the outside. (Using a formation of a cell plate to grown and detach the two new cells)

Question 7

Gene

Answer 7

A unit of hereditary information, consisting of a specific sequence of DNA. Located on the chromosome inside of the cells nucleus

Chromosomes may contain hundreds to thousands of genes.

Question 8

The cell cycle

Answer 8

Interphase - (G1) cell growth, (S) DNA replication, (G2) preparation for mitosis.
(A cell spends 90% of its life in interphase)

Mitotic phase - consists of prophase, metaphase, anaphase, telophase

Cytokinesis - the splitting of the cytoplasm

Entire cell cycle may last about 24 hours

Question 9

Prophase

Answer 9

Early:
- coiled chromatin becomes visible as 2 chromatids joined at the centromere
- centrioles migrate to poles
- spindle fibres begin to form

Late:
- nuclear membrane starts disappearing
- astral rays radiate
- spindle fibres begin to attach to kinetochore of each centromere

Question 10

Metaphase

Answer 10

• chromatid pairs line up in the centre of cell at the metaphase plate
• spindle fibres from both poles fully attach to the respective kinetochore side of the centromere.

Question 11

Anaphase

Answer 11

• chromatids are pulled apart by the kinetochore fibres and are brought towards the respective poles of the cells.
• the nonkinetochore fibres lengthening and elongate the cell in preparation for the splitting of the cell.

Question 12

Telophase

Answer 12

• cleavage furrow forms as the cell is waiting for cytokinesis
• nuclear membrane and nucleolus reform on both sides of the cell surrounding each group of chromosomes.

Cytokinesis officially splits the original cell into 2 daughter cells.

Question 13

Homologous chromosomes

Answer 13

A pair of sister chromatids (or chromosomes) that join together at the centromere that code for the same traits.

Pairs must match in:
- length
- centromere position
- staining pattern

Question 14

Locus

Answer 14

The position of a gene on a chromosomes.

Different versions of a gene may be found at the same locus on the homologous pair. These are called alleles
(Ex. One may code for brown eyes, the other for blue eyes)

Question 15

How are human chromosomes arranged ?

Answer 15

Humans have 23 pairs of diploid chromosomes (46 individual chromosomes), 23 chromosomes from each parent.

22 pairs are somatic (diploid), and 1 pair is sex chromosomes (XX or XY) (haploid)

Question 16

Meiosis

Answer 16

The process, where a single cell divides twice to produce four (non identical) haploid cells containing half the original amount of genetic information.

It produces gametes which is either sperm or egg (when put together create a diploid cell)

Can only occur in either the ovaries or testes

Question 17

Prophase I

Answer 17

Same as mitosis prophase, except that chromosomes find their homologous pair (4 chromatids come together).

Crossing over also occurs when the chromosomes synapse (lie next to eachother). Crossing over means that the 2 central nonsister chromatids exchange genetic material.

Question 18

Chiasma

Answer 18

The part of a homologous pair where the 2 chromosomes overlap

Question 19

Metaphase I

Answer 19

Similar to mitosis metaphase, but they line up at the metaphase plate as homologous pairs and the kinetochore attach to each centromere on both sides of the homologous pair.

Independent assortment also occurs (random lining up)

Question 20

Anaphase I

Answer 20

Similar to mitosis anaphase but instead the sister chromatids remain attached while the homologous pair gets pulled apart.

Question 21

Telophase I

Answer 21

Similar to mitosis telophase, but now the cells are haploid.

Question 22

Telophase I

Answer 22

Similar to mitosis telophase, but the 2 cells are now haploid

Question 23

Meiosis II

Answer 23

The same as mitosis in that we are no separating the sister chromatids, except we are using haploid cells with sister chromatids that are not identical because of the crossing over.

Question 24

Nondisjunction

Answer 24

The the homologous pairs fail to separate properly during meiosis I. This leads to an extra chromosome which can cause several genetic disorders.

Question 25

Polyploid

Answer 25

An organism that contain more than 2 complete sets of chromosomes.
- creates a new species

Ex. Some frogs and leeches