Lecture 13 - Meiosis I And Meiosis II

Question 1

How many chromosomes do you have?

Answer 1

23 pairs. Total of 46

Question 2

Diploid

Answer 2

2 complete sets of chromosomes , one from each parent

Question 3

Haploid

Answer 3

GAMETES… single set of unpaired chromosomes

Question 4

What are the two functions of meiosis?

Answer 4

1. Reduce # of chromosomes in half (46 to 23)
2. Introduce genetic diversity (all daughter cells are genetically different from mother cell)

Question 5

what happens during prophase I?

Answer 5

Synapsis- homologous replicated chromosomes pair up forming tetrads (4 sister chromatids together)
Crossover- exchange of genetic material between homologous chromatids. Place of crossover rims called the chiasmata

Question 6

What happens during metaphase I?

Answer 6

Tetrads line up randomly at metaphase plate

Question 7

What happens during anaphase I?

Answer 7

Each tetrad is pulled apart into two replicated chromosomes, each chromosome is still made of two sister chromatids

Question 8

What happens during telophase I?

Answer 8

Nuclear envelope may or may not reform, depending on the cell.
NO DNA REPLICATION OCCURS AT THIS TIME

Question 9

Interkinesis

Answer 9

Brief rest period between meiosis I and meiosis II

Question 10

What is the result of meiosis I?

Answer 10

Each cell contains two copies (sister chromatids) of one member of each homologous pair (either the maternal or paternal chromosome) and none of the other chromosome.

Each cell will contain the haploid chromosomal number (n rather than 2n) because still-united sister chromatids are considered to be one chromosome as long as they are connected by a centromere (twice amount DNA in each chromosome).

Question 11

Meiosis II

Answer 11

Meiosis II is just like mitosis except that the cells are haploid.

Question 12

what happens during prophase II?

Answer 12

Chromosomes condense, and a new set of spindle fibres form

Question 13

What happens during metaphase II?

Answer 13

Chromosomes line themselves along the the metaphase plate

Question 14

What happens during anaphase II?

Answer 14

Sister chromatids separate and are pulled towards opposite poles of the cell

Question 15

What happens during telophase II?

Answer 15

Nuclear membranes form around each set of chromosomes, and the chromosomes decondense

Question 16

Summary of meiosis

Answer 16

During meiosis I, crossing over between maternal and paternal chromosomes result in an exchange of genetic material between members of a tetrad (pairs of homologous chromosomes); each tetrad randomly lines up at the equator, resulting in the independent assortment of single maternal and paternal homologues into two daughter cells.
Meiosis II resembles mitosis except the cells begin as haploid

Question 17

Mitosis vs meiosis

Answer 17

Mitosis has one round of division; meiosis has two.
Synapsis and crossing over occurs in meiosis but not in mitosis.
Mitosis produces two diploid (2n) daughter cells identical to the mother cell. Meiosis produces four haploid (n) daughter cells that are all different from each other and from the mother cell.
Mitosis produces somatic (body) cells. Meiosis produces gametes (eggs and sperm).

Question 18

Apoptosis

Answer 18

AKA programmed cell death
Causes certain cells to neatly self destruct

The process begins when mitochondrial membranes leak chemicals that activate enzymes called classes. These enzymes degrade the cell’s DNA and cytoskeleton, which leads to cell death.
The dead cell shrinks and is phagocytized by macrophages (a type of immune cell).

Question 19

Theories of cell aging

Answer 19

Wear and tear theory: a lifetime of chemical damage and free radicals have cumulative effects.
Mitochondrial theory of aging: free radicals in mitochondria diminish energy production in each cell.
Immune system disorders: autoimmune responses, as well as the progressive weakening of the immune response, lead to a loss of homeostasis.
Genetic theory: the cessation of mitosis and cell aging are programmed into genes.
telomeres are strings of nucleotides that protect ends of chromosomes (like caps on shoelaces).
Every time a cell divides, the telomere shortens, so telomeres may act like an hour-glass on how many times a cell can divide.
Telomerase is an enzyme that lengthens telomeres. It is found in germ cells of embryos but absent in adult cells, except for cancer cells.