Meiosis, Germ Cells and Fertilization (Lec 6)

Question 1

Define diploid

Answer 1

contains two sets of chromosomes, one from each parent

Question 2

Define haploid

Answer 2

contains one set of chromosomes

Question 3

Define gamete

Answer 3

specialized reproductive cell; sperm or eggs generated through meiosis

Question 4

Define fertilization

Answer 4

haploid gametes fuse to form a diploid cell (zygote)

Question 5

Define zygote

Answer 5

divides by mitosis to become a multicellular organism

Question 6

Define germline cells

Answer 6

gametes and their precursors

Question 7

Define somatic cells

Answer 7

form the rest of the body and leave no progeny

Question 8

Define autosomes

Answer 8

chromosomes common to both sexes: one form each parent in each diploid nucleus

Question 9

Define sex chromosomes

Answer 9

X and Y

Question 10

What are the two ways meiosis creates genetic diversity?

Answer 10

random segregation of homologs during meiosis, crossing over

Question 11

In meiosis, are gametes haploid or diploid?

Answer 11

haploid

Question 12

In regards to meiosis I, what phase of the cell cycle do chromosomes replicate?

Answer 12

S phase

Question 13

Besides chromosome replication, what else occurs in meiosis I?

Answer 13

homologs pair, recombine and separate

Question 14

What occurs in Meiosis II?

Answer 14

sister chromatids are divided to produce 4 haploid daughter cells

Question 15

What occurs in prophase I in meiosis?

Answer 15

homologs begin to pair, 4 chromatid structure is called bivalent, stable pairing requires crossing over, homologs are joined by protein structure called synaptonemal complex, small region of homology between X and Y called pseudoautosomal region allows them to pair

Question 16

Describe the 5 phrases of prophase

Answer 16

Leptotene: homologs begin to condense/pair
Zygotene: homologs pair and synaptonemal complexes form
Pachytene: Synapsis is complete; crossing over occurs
Diplotene: synaptonemal complex begins to break down
Diakinesis: reach maximum condensation; separation of homologs and transition stage into metaphase

Question 17

What is the synaptonemal complex made up of?

Answer 17

transverse filaments between homologs, cohesion complexes that assemble on DNA during S phase and bind sister chromatids

Question 18

What are the distinguishing features of meiosis?

Answer 18

kinetochores, homologs separate at anaphase I, arms of sister chromatids separate at anaphase I, sister chromatids separate in anaphase II

Question 19

In females, when is meiosis I is completed?

Answer 19

only at ovulation

Question 20

In females, when is meiosis II completed?

Answer 20

after fertilization

Question 21

What is nondisjunction?

Answer 21

homologs fail to separate properly

Question 22

What is aneuploidy?

Answer 22

cells with abnormal chromosome number

Question 23

What is euploidy?

Answer 23

cells with normal number of chromosomes

Question 24

When and where does meiosis begin for male mammals?

Answer 24

in testes at puberty

Question 25

Compare the error rates in meiosis between males and females

Answer 25

20%% in eggs vs. 3% of sperm

Question 26

In regards to gonadal development, what determines if gonad is ovary or testes?

Answer 26

sex chromosomes in genital ridge

Question 27

What determines the sex of an embryo?

Answer 27

sperm; presence or absence of Y

Question 28

What is the SRY gene necessary for?

Answer 28

testis development

Question 29

Expression of SRY causes cells to differentiate into ____ cells

Answer 29

sertoli

Question 30

What do sertoli cells serete?

Answer 30

anti-Mullerian hormone - suppresses female development

Question 31

True or False?

Eggs are not specialized

Answer 31

false, highly specialized

Question 32

What are the stages of oogenesis?

Answer 32

primordial germ cell enters gonad, diploid oogonia undergo mitotic cell divisions before entering meiosis, primary oocytes are formed and arrest in prophase I of meiosis I, after ovulation process resumes and cytoplasm divides forming small polar body and large secondary oocyte which arrests in metaphase II, meiosis is finished after fertilization

Question 33

What are the stages of spermatogenesis?

Answer 33

meiosis does not begin until puberty; in prophase I of meiosis, paired homologs cross over; primary spermatocytes complete Meiosis I to produce two secondary spermatocytes with 22 duplicated autosomes and X or Y; each secondary spermatocyte enters meiosis II to produce 4 haploid spermatids; differentiate into sperm which escape into lumen of seminiferous tubule; pass into epididymis

Question 34

Where does spermatogenesis occur?

Answer 34

in seminiferous tubules where close contact with sertoli cells is maintained

Question 35

What are the requirements of fertilization?

Answer 35

albumin, Ca2+ and HCO3-

Question 36

What are the stages of fertilization?

Answer 36

egg released, sperm penetrates granulosa cells, sperm binds to zone pellucida, zone pellucida induces sperm to undergo acrosome reaction, sperm binds egg plasma membrane, egg activation = meiosis resumes

Question 37

What is the cortical reaction?

Answer 37

fusion of sperm causes change in egg plasma membrane so other sperm can’t fuse

Question 38

What happens after fertilization?

Answer 38

2 haploid nuclei fuse in the zygote, sperm contribute centrosomes and centrioles, centrosome duplicates - assembles mitotic spindle