L02 Meiosis

Question 1

Contrast Mitosis and Meiosis

Answer 1

• produces two daughter cells with the full diploid compliment that the parent cell had while meiosis produces haploid gametes
• Meiosis has two discrete steps in order to reduce the amount of genetic material by half while mitosis is a single cycle

Question 2

Why does meiosis produce gametes with a haploid set of chromosomes?

Answer 2

Ensures that during sexual reproduction, haploid gametes combine to reconstitute the diploid content found in parents

Question 3

What is the purpose of crossing over?

Answer 3

Ensures genetic variation

Question 4

State the events of prophase 1 of Meiosis 1

Answer 4

Homologous chromosomes pair up (synapses) to form a bivalent which condenses and shortens to form a tetrad.

Chromatin intertwine to form a chiasmas, crossing over occurs, centromeres attach to the spindle fiber

Question 5

State the events of Metaphase 1 in Meiosis 1

Answer 5

• Chromosomes at maximum shortness
• Chiasmas hold non-sister chromosomes together
• binding of spindle fibers to centromeres moves chromatids to metaphase plate

Question 6

State the occurrences of Anaphase 1

Answer 6

• Cohesin is degraded between sister chromatids
• Genetic material at crossovers can now separate.
• Homologous chromosomes separate to and move toward each pole

Question 7

State the events of Telophase 1

Answer 7

• Nuclear membranes form
• Cytokinesis
• Two haploid cells result for Prophase 2
• Each cell has one of the homologous chromosomes which still has duplicated DNA (the sister chromatid)

Question 8

Early Prophase 1 of meiosis where homologous chromosomes pair up is

Answer 8

Is called the synapse

A synapse pair is initially called a Bivalent

The Bivalent will condense, shorten and the Bivalent is then called a tetrad

Question 9

How does prophase 1 ensure Genetic Variation?

Answer 9

• homologous chromosomes pair up(synapsis)
• synapsis is initially called Bivalent
• Bivalent condenses to tetrad
• As prophase 1 continues, Chiasmas are formed in one or more areas - here, non sister chromatids exchange information
• At the end of prophase 1 the tetrad pair of chromosomes separate but are still intertwined by Chiasmas
• Nuclear envelope breaks down and centromeres attach to spindle.

Question 10

State the events of prophase 2

Answer 10

• The second Meiotic division begins at Prophase 2 with one each homologous chromosomes which were separated at Telophase 1
• Spindle fibers from the centrioles are attached to the centromeric region of each sister chromatid

Question 11

State the events of metaphase 2

Answer 11

• The centromeres are positioned at the equatorial plate
• The centromeres of each sister chromatid are attached to a spindle fiber which were protected by Shugoshin complex until here at metaphase 2 where Shugoshin is degraded

Question 12

What are the events of Anaphase 2?

Answer 12

• Shugoshin is completely degraded and sister chromatids are separated to opposite poles of the cell(Shugoshin is degraded by APC)
• Each haploid daughter cell from this meiosis 2 has one member of an original pair of homologous chromosomes

Question 13

State the events of Telophase 2

Answer 13

• One sister chromatid from an original homologouspair is present at each pole
• Each chromosome is now a monad
• Nuclear membrane forms

Question 14

Describe the cytokinesis of Telophase 2

Answer 14

• Each gamete achieves the haploid State
• Each gamete has a unique mixture of maternal and paternal genetic information originally from grandparents
• Meiosis significantly increases genetic variation in each generation

Question 15

In sex chromosomes in meiosis……… does not occur

Answer 15

Crossing over

Question 16

Which regions in sex chromosomes form the synapse in Prophase 1?

Answer 16

The short homologous psuedo-autosomal regions

These are only present at one end of each sex chromosome

Question 17

In mitosis, sister chromatids are separated during ___________, while in meiosis, sisters are separated in ____________________.

Answer 17

Anaphase

Anaphase 2

Question 18

How and where are male gametes produced?

Answer 18

By spermatogenesis in the Testes

Question 19

How and where are female gametes produced ?

Answer 19

Female gametes are produced by oogenesis in the ovary

Question 20

Describe spermatogenesis

Answer 20

Spermatogonia undergo growth and maturation to form primary spermatocytes

Primary spermatocyte undergoes meiosis 1
- this produces two secondary spermatocytes

Spermatocytes undergo meiosis 2
- Produces a total of four haploid spermatids

Question 21

Which male animals would spermatogenesis occur continuously/ periodically in?

Answer 21

• Animals that reproduce sperm year-round would produce sperm continuously
• Animals that have breeding periods only produce sperm during breeding time

Question 22

Describe oogenesis

Answer 22

• Formation of ova in the ovaries
• Oogonium undergoes growth and maturation to create a primary oocyte
• the primary oocyte undergoes meiosis 1 and in Telophase 1, the dyads at one pole get very little cytoplasm
• This yields one secondary oocyte and the first polar body
• Secondary oocyte undergoes Meiosis 2 and genetic material is equally distributed with very little cytoplasm in one of the daughter cell
• This yields one ootid which will mature to the ovum and a secondary polar body

Question 23

How do spermatogenesis and oogenesis differ in their continuous events?

Answer 23

Unlike spermatogenesis, the two meiotic events of oogenesis may not be continuous

Question 24

Explain the arrest/continuation of oogenesis

Answer 24

• In some animals such as humans, the first division of all oocyte’s begins in the embryonic ovary but arrests in prophase 1
• Years later, meiosis resumes in each oocyte just prior to ovulation
  
  • The second division is completed only after fertillization

Question 25

Crossing over…

Answer 25

Ensures genetic variation

Question 26

Which stage generates dyads?

Answer 26

Anaphase 1

Question 27

Which phase does synopsis occur?

Answer 27

Prophase 1

Question 28

Describe sex chromosomes during meiosis

Answer 28

• sex chromosomes X and Y have short homologous pseudo-autosomal regions
• these regions form synapsis in Prophase 1
• Only present at one end of each sex chromosome
• crossing over does not occur

Question 29

Describe development of gametes

Answer 29

The development of gametes occurs between spermatogenesis and oogenesis

Question 30

Discuss the genetic content “n” and chromosome number “c” of each type of gamete

Answer 30

Primary gametocytes- 2n, 2c becomes 2n, 4c(after DNA is replicated relight before meiosis 1)

Secondary gametocytes -n, 2c

Potential gametes- n, c