Mitosis and Meoisis

Question 1

P. A. Levene

Answer 1

(1919) Discovered that:
- DNA is made up of nucleotides (phosphate group, deoxyribose, and nitrogenous base) that are linked in a string
- Nitrogenous bases are purines: double ringed (Adenine and Guanine) and pyrimidines: single ringed (Thymine and Cytosine)
- The bases are held together by hydrogen bonds

Question 2

Erwin Chargaff

Answer 2

(1940s) Discovered that in any species, the amount of A and T were the same and the amount of C and G were the same

Question 3

(**)Hershey and Chase

Answer 3

(1952)
- Marked protein coat with bacteriophage (viruses that attack bacteria) with radioactive sulfur (S-35) and the DNA with radioactive phosphorus (P-32)
- Found that protein coat remained outside the bacterial cell and the DNA moved into the cell, directing it to make new bacteriophages
(Before this scientists thought proteins carried the genetic information but know they know it is in the DNA)

Question 4

Franklin and Wilkins

Answer 4

(1952)
- Used X-rays to photograph molecules
- Research indicated that DNA was like a coil with a constant diameter of 2nm (1 mm = 1 000 000 nm)

Question 5

Watson and Crick

Answer 5

(1953)
- Made scale models of DNA
- Proposed that DNA is like a spiral staircase with two twisted strands, the sides (“handrails”) were alternating deoxyribose and phosphate molecules and the “rungs” are joined by hydrogen bonds
- Called this the DOUBLE HELIX
- Determined that A is always with T and C is always with G (confirming Chargaff)

Question 6

What are histones?

Answer 6

Histones are special proteins that DNA is coiled with to form chromosomes
DNA + histones = chromosomes

Question 7

What are genes and what do they do?

Answer 7

Genes are specific sequences of DNA on a chromosome
They determine the production of proteins that will determine the traits of an individual

Question 8

Do nucleotides differ in organisms?

Answer 8

No, the DNA of all organisms is made up of the same type of nucleotides

Question 9

What determines different organisms since nucleotides are the same?

Answer 9

• The sequence of A’s and T’s, C’s and G’s
• The number of chromosomes
• Different proteins

Question 10

What is a genome?

Answer 10

A complete set of DNA sequence

Question 11

What determines our genetic information?

Answer 11

The order of A, T, C, and G

Question 12

How many chromosomes do humans have?

Answer 12

46

Question 13

What are autosomes?

Answer 13

Chromosomes that are not sex chromosomes

Question 14

Which pair are the sex chromosomes?

Answer 14

23rd pair

Question 15

Are sex chromosomes homologous?

Answer 15

The female sex chromosomes are XX so they ARE homologous
The male sex chromosomes are XY so they are NOT homologous

Question 16

What does homologous chromosomes mean?

Answer 16

Homologous chromosomes appear similar, but are not identical, have the same banding pattern, centromere position, and length.
They contain genes for the same trait but may carry different forms of the trait

Question 17

What are alleles?

Answer 17

Different forms of a gene

Question 18

What is the difference between a gene and an allele?

Answer 18

A gene is a section of a gene that encodes a certain gene while alleles are the different forms of the gene.
Ex. Gene= eye colour

Question 18

What is the difference between a gene and an allele?

Answer 18

A gene is a section of a gene that encodes a certain gene while alleles are the different forms of the gene.
Ex. Gene = eye colour
Allele = green eyes

Question 19

Haploid

Answer 19

One copy of each type of chromosome (half the chromosomes)

Question 20

Diploid

Answer 20

Two copies of each type of chromosome (normal amount of chromosomes)

Question 21

Gametes

Answer 21

Egg or Sperm
(Sex Cells)

Question 22

Crossing Over

Answer 22

Homologous non-sister chromatids exchange genes
This genetically varies the chromosomes
A chromosome now has genes from both the biological mother and father

Question 23

When does crossing over occur

Answer 23

Prophase I of meiosis

Question 24

Random (Independent) Assortment

Answer 24

The random aligning of homologous chromosomes on the equator of the cell in metaphase I Therefore when the cell divides, some chromosomes are from each parent

Question 25

What is the difference between interphase in mitosis and meiosis?

Answer 25

NOTHING!!

Question 26

Prophase I

Answer 26

Chromatin shortens and thickens Nuclear membrane and nucleolus break down Centrioles move to opposite poles Spindle fibres form Homologous chromosomes pair up Crossing over occurs

Question 27

Metaphase I

Answer 27

Spindle fibres attach to the centromere of each chromosome Homologous chromosomes line up at the equator of the cell Random assortment occurs

Question 28

Anaphase I

Answer 28

Homologous chromosomes separate and move to opposite poles They are pulled apart by shortening of the spindle fibres **Chromosomes are still double stranded**

Question 29

Telophase I

Answer 29

Chromosomes uncoil into chromatin Spindle fibres disappear Cytoplasm divides Nuclear membrane forms around chromosomes Some cells remain like this indefinitely

Question 30

Do all cells undergo Telophase I in meiosis?

Answer 30

No, because they will divide again in meiosis II but they all undergo cytokinesis

Question 31

Prophase II

Answer 31

Centrioles move to opposite poles Spindle fibres form Nuclear membrane breaks down **Meiosis II occurs in both new cells**

Question 32

Metaphase II

Answer 32

Single chromosomes line up at the centre

Question 33

Anaphase II

Answer 33

Double stranded chromosome splits at the centromere One chromatid from each chromosome gets pulled to each pole

Question 34

Telophase II

Answer 34

Nuclei reassemble Cytokinesis occurs

Question 35

What is the end result of meiosis?

Answer 35

Four cells that have half the number of chromosomes as the original cell These cells have new combinations of genetic material compared to each other and their original parent cell