Exam 3- Meiosis

Question 1

What is meiosis?

Answer 1

• a special type of cell division
• sexual reproduction
• halves the chromosome number

Question 2

Where is meiosis present?

Answer 2

• in germ cells
  
  • gametes

Question 3

What are germ cells?

Answer 3

cells capable of meiosis

Question 4

How do the haploid cells become diploid in fertilization?

Answer 4

• gametes fuse in fertilization to form the diploid zygote
• n ( egg) + n ( sperm) = 2n zygote
• become the next diploid generation

Question 5

what are alleles?

Answer 5

alternate forms of a gene

• homozygous AA or aa
• heterozygous Aa
• Human 2n= 46

Question 6

What is the main event of Meiosis I?

Answer 6

reduction division
- homologous pairs will first synapse and then separate

Question 7

What is the main event of Meiosis II?

Answer 7

equatorial division- sister chromatids separate

Question 8

what happens in prophase I?

Answer 8

• most important
• create genetic versatility
• cross over
• S phase already complete

Question 9

what does synapsis mean?

Answer 9

homologous chromosomes pair up end to end
- end view shows four chromatids ( 2 chromosomes) = tetrad ( bivalent form)

Question 10

How does cross-over work?

Answer 10

chromosomes are aligned and connected by the nucleoprotein lattice

• enzymes come in at the chiasmata and graft the maternal genes on the paternal chromosome and vice versa
• the amount of cross-over in prophase is random

Question 11

What is chiasma?

Answer 11

• chiasma ( sg.)
• chiasmata ( pl.)

points where the chromosomes touch and swap genetic material.

Question 12

what forms the nucleoprotein lattice?

Answer 12

cohesions: sticky proteins allow homologous chromosomes to adhere to each other

Question 13

What happens in Prometaphase I and Metaphase I?

Answer 13

• independent assortment
  -homologous pairs attached to kinetochore fibers; arranged onto the middle of the metaphase plate
• The same stuff from mitosis also occurs simultaneously

Question 14

What happens in Anaphase I?

Answer 14

Homologous pairs separate
- synapsis breaks up
- centrosome stays

Question 15

What happens in Telophase I?

Answer 15

Daughter cells each have one internally duplicated chromosome from each homologous pair
- ( n haploid)

Question 16

What happens in Cytokinesis I?

Answer 16

• two daughter cells
• both with internally duplicate chromosomes of each type = haploid ( n)

Question 17

What happens in prophase II?

Answer 17

chromosomes condense

Question 18

what happens in prometaphase?

Answer 18

chromosomes attach to kinetochore fibers

Question 19

What happens in Metaphase II?

Answer 19

Align on the metaphase plate ( 23 chromosomes)

Question 20

What happens in anaphase II?

Answer 20

centrosomes dissolve
chromosomes pulled apart

Question 21

what happens in telophase II and cytokinesis?

Answer 21

• four haploid cells
• all genetically unique

Question 22

What are the three things that provide genetic variation?

Answer 22

• crossing over between homologous chromosomes
• independent assortment
• Fertilization

Question 23

How does fertilization contribute to genetic variation?

Answer 23

• when gametes fuse at fertilization
• chromosomes donated by parents are combined

Question 24

What is the importance of genetic variation?

Answer 24

reproduction may be advantages
- improves the chance of adaptability to the environment

Question 25

what is a zygote?

Answer 25

the fertilized fusion of sperm and egg - the one-celled stage of an individual of the next generation - results in the multicellular embryo that gradually takes on the features determined when zygote was formed

Question 26

What is gametogenesis?

Answer 26

Production of gametes

Question 27

What is spermatogenesis?

Answer 27

production of sperm

Question 28

What is spermiogenesis?

Answer 28

maturation process of the spermatids

Question 29

What are the secondary spermatocytes?

Answer 29

- meiosis II - haploid

Question 30

What are the primary spermatocytes?

Answer 30

- first stage of spermatogenesis - meiosis 1 at puberty - diploid

Question 31

What are the spermatids?

Answer 31

-to go from spermatocytes to spermatids spermiogenesis must occur

Question 32

What is the structure of sperm?

Answer 32

- the head is full of DNA - acrosome= coating ( important to fertilizing egg) - midpiece = full of mitochondria - flagellum= propeller motion

Question 33

What is oogenesis?

Answer 33

Production on eggs - only one of four nuclei gets cytoplasm

Question 34

What is the primary oocyte?

Answer 34

Diploid meiosis I - seen at birth and is stalled in prophase I until puberty

Question 35

What is a secondary Oocyte?

Answer 35

has one polar body - haploid - stuck at meiosis II until it's fertilized - this is where periods start to occur

Question 36

when is meiosis II completed?

Answer 36

Only completed after entry of sperm - adds a second polar body