FHMP 006 mitosis, meiosis, Mendel, and Hardy-Weinberg

Question 1

What is mitosis?

Answer 1

Cell division that generates identical new cells for growth and repair.
The division of one cell into two genetically identical diploid daughter cells

Question 2

What are the phases of mitosis?

Answer 2

prophase, metaphase, anaphase, telophase

Question 3

What happens in prophase?

Answer 3

Chromosomes condense
Nuclear membrane disintegrates
Centrioles move to opposite poles
Spindle apparatus formed by microtubules

Question 4

What happens in metaphase?

Answer 4

Chromosomes line up along equator of spindle via their kinetochores
most condensed and visible now

Question 5

What happens in anaphase?

Answer 5

Centromeres split,
microtubules/centrioles contract,
sister chromatids pulled apart to opposite poles.

Question 6

what happens in telophase?

Answer 6

Nuclear membrane reforms
Chromosomes decondense
2 indentical daughter cells are produced and go into interphase (also identical to the parental cells)
- cytokinesis = division of cytoplasm

Question 7

what is meiosis?

Answer 7

Meiosis is a type of cell division that produces genetically different gametes with half the normal amount of chromosomes (haploid)

Question 8

what are the phases of meiosis?

Answer 8

Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II

Question 9

what happens in prophase 1?

Answer 9

• leptotene = chromosomes become visible
• zygotene = homologous pairs of chromosomes become closely associated along their lenghts by synapsis and form bivalents
• pachytene = synapsis is complete and the bivalents are held toegther throughout their length by a structure known as the synaptonemal complex, homologous chromosomes cross over and swap sections of their DNA (recombination/allele shuffling)
• Diplotene = the homologous chromosomes appear to repel each other and remain held together only at chiasmata (where crossing happened) and at the centromere
  LZPD = lemon zest pancake day
  ( always at least 1 chiasmata per chromosome arm)

Question 10

what happens in metaphase 1?

Answer 10

• Bivalents chromosomes line up across the equator of the spindle attached to spindle fibers. The chiasmata are still present.
• Random assortment of the bivalents takes place with each member of a homologous pair facing opposite poles.

Question 11

what happens in anaphase 1?

Answer 11

spindle fibers split the homologous chromosome pair toward opposite poles/ends of the cell

Question 12

what happens in telophase 1?

Answer 12

• nuclear membrane forms around each set of chromosomes, and the cytoplasm divides forming two daughter cells
• each daughter cell has half the number of chromosomes, but each chromosome is a pair of chromatids ( 23 chromosomes, 46 sister chromatids)

Question 13

what happens in prophase 2?

Answer 13

the nuclear envelope breaks down, chromatids condense, centrioles form and the spindle apparatus forms

Question 14

what happens in metaphase 2?

Answer 14

• sister chromatids line up along the center of the cell along the spindle fibres attached by kinetochores
• the equatorial metaphase phase is rotated 90 degrees ( increase randomness)

Question 15

what happens in anaphase 2?

Answer 15

sister chromatids separate and move to opposite poles through contracting spindles

Question 16

what happens in telophase 2?

Answer 16

• New nuclear envelopes appear and cytokinesis begins to form 2 haploid cells per daughter cell (4 haploid cells in total)
• all the 4 daughter cells are genetically different and all have 23 chromosomes

Question 17

what are the differences between mitosis and meiosis?

Answer 17

mitosis =

• produces 2 daughter cells
• produces genetically identical cells to each other and parent cell
• 1 round of division
• diploid daughter cells (46 chromosomes)
• homologous chromosomes don’t pair up
• no crossing over/allele shuffling

meiosis =

• produces 4 daughter cells
• produces all genetically varied cells
• 2 rounds of division
• haploid daughter cells (23 chromosomes)
• homologous chromosomes pair up
• crossing over/allele shuffling

Question 18

what is Mendel’s zero law?

Answer 18

Inheritance is by particles, not fluids

Question 19

what is Mendel’s first law?

Answer 19

• Mendel’s First Law: The Law of Segregation.
• At meiosis, alleles separate (or segregate) from each other such that each gamete (egg or sperm) receives one copy from each allele pair.
• gametes are haploid, only have 1 allele of each gene

Question 20

What is Mendel’s second law?

Answer 20

• The Law of Independent Assortment.
• Mendel’s second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes.
• exception is when the genes are linked on the same chromosome

Question 21

what is Mendel’s third law?

Answer 21

Law of Dominance = the recessive alleles will always be masked by dominant alleles
- demonstrated by a mono hybrid cross experiment ( e.g green and yellow peas)

Question 22

What is sex-linked inheritance?

Answer 22

An inheritance that may result from a mutant gene located on either the X- or Y-chromosome.

Question 23

What are X-linked genes?

Answer 23

• gene located on the X chromosome; such genes show a distinctive pattern of inheritance.
• as males only have 1 X chromosome they have no back up X chromosome, so if they inherit an X-linked disorder men are much likely to develop the disease, whereas women have 2 X chromosomes so are more likely to be carriers

Question 24

give 4 examples of X-linked recessive disorders

Answer 24

1. Red-green colour blindness = 7-10% of men, 0.5-1% of women
2. Haemophilia A = blood clotting disorder from Factor VIII mutation
3. Haemophilia B = blood clotting disorder from Factor IX mutation
4. Duchenne muscular dystrophy = mutations in the dystrophin gene, leads to muscle degeneration, loss of skeletal muscle control, respiratory failure and death

Question 25

What is the Hardy-Weinberg principle?

Answer 25

allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change

Question 26

What is the Hardy-Weinberg equation?

Answer 26

p^2 + 2pq + q^2 = 1

where AA = p^2 Aa = 2pq aa = q^2

Question 27

what are the conditions for the Hardy-Weinberg?

Answer 27

• Random Mating
• No migration
• No natural selection
• Large population
• No mutations