meiosis 3/27

Question 1

what is the primary difference between sperm cell meiosis and ovarian cell meiosis?

Answer 1

sperm cells can complete meiosis to yield 4 gametes while ovarian cells cannot complete meiosis on their own and will only yield 1 gamete

Question 2

what is oogenesis?

Answer 2

a diploid oogonia will produce a primary oocyte that will undergo meiosis to produce one haploid cell and 2-3 polar bodies

Question 3

how many eggs are produced from the meiosis of oocytes?

Answer 3

one haploid egg, the other cells become polar bodies

Question 4

why is only one cell produced in meiosis of oocytes?

Answer 4

the amount of cytoplasm the egg receives will be maximized

Question 5

when a diploid oogonia produces a diploid oocyte, what happens?

Answer 5

the primary oocyte will undergo meiosis I but will be arrested at prophase one until sexual maturity

Question 6

what what stage are primary oocytes arrested? how long?

Answer 6

primary oocytes are arrested at prophase I when homologous chromosomes synapse and recombine, they will remain dormant until sexual maturity

Question 7

at sexual maturity, are all oocytes activated at once?

Answer 7

no, they will periodically be released

ex) humans will release one oocyte per month

Question 8

when meiosis I begins on a primary oocyte, how does it divide?

Answer 8

it divides asymmetrically, where one large secondary oocyte and one small polar body will be produced

Question 9

when a secondary oocyte begins meiosis II, can it complete it all the way?

Answer 9

no, the oocyte will be arrested at metaphase II and will be released into the oviduct in ovulation

Question 10

when can meiosis complete for a secondary oocyte

Answer 10

when the oocyte is fertilized by a sperm cell, it can continue meiosis II to completion

Question 11

what is the end result of Meiosis II for a oocyte?

Answer 11

if fertilized, it will produce a large haploid cell and another polar body

Question 12

when can meiosis complete in female germ cells?

Answer 12

only when the secondary oocyte is fertilized by a sperm cell

Question 13

true or false: males can undergo complete meiosis but females cannot

Answer 13

true, females need to be fertilized

Question 14

when do homologs synapse?

Answer 14

prophase I

Question 15

when do homologs follow the law of independent assortment?

Answer 15

metaphase

Question 16

when do homologous chromosomes follow the law of segregation

Answer 16

anaphase I when the two homologous chromosomes separate

Question 17

what is it called when chromosomes fail to segregate

Answer 17

nondisjunction

Question 18

what is the law of independent assortment

Answer 18

it is where homologous chromosomes will arrange themselves independently of how the other pairs arrange themselves

the way the one pair arranges does not affect how the other will arrange

Question 19

what is the law of segregation

Answer 19

it is when homologous chromosomes segregregate in anaphase

Question 20

what is X inactivation

Answer 20

it is when one of the X chromosomes in females may be silenced to compensate for the fact that they have two X chromosomes while males only have one

Question 21

why can Y not be inactivated?

Answer 21

Y is a fundamental sex determining chromosome

X is important for genes

Question 22

why is the silencing of an X chromosome in XX different from turner’s? XO

Answer 22

XX is leaky, meaning it still has some level of gene expression from the other X chromosome. In XO, the chromosome is completely gone

Question 23

how does XXY (Kleinfelter) get affected by X inactivation?

Answer 23

the extra chromosome will be silenced but still be squeaky and have some level of affect

Question 24

in X inactivation, which chromosome gets inactavted?

Answer 24

it is random

Question 25

what is a Bar body?

Answer 25

it is a highly condensed "inactivated" X chromosome

Question 26

why do calico cats exist in females?

Answer 26

female cats have an XX chromosome, the silencing of one X chromosome with black stripes will occur alongside the silencing of another X chromosome with orange stripes

Question 27

when does random X chromosome inactivation occur

Answer 27

during an early stage of embryonic development

Question 28

what is the X inactivation center?

Answer 28

it controls the initiation of X inactivation by coding for a gene that codes for Xist

Question 29

what is Xist

Answer 29

it is a RNA that is only transcribed on the X chromosome to be silenced, it will coat the inactive X chromosome and promote condensation

Question 30

where is the Xist chromosome expressed

Answer 30

on the X chromosome to be inactivated

Question 31

What is Tsix? what does it do?

Answer 31

it is a gene that overlaps with Xist but in the opposite direction it prevents Xist expression on the active chromosome so it cannot be condensed

Question 32

how do pluripotent stem cell factors affect X inactivation

Answer 32

the stem cell factors will choose an X chromosome to remain active and will activate the expression of Tsix on one of the chromosomes the chromosome that is not chosen will express Xist and become inactive

Question 33

what happens to the chromosome that is not selected by stem cell factors?

Answer 33

it will express Xist and be inactivated

Question 34

what are genome mutations

Answer 34

changes in the number of sets of chromosomes or changes in individual chromosomes in a set

Question 35

what is polyploid

Answer 35

change in number of sets

Question 36

what is aneuploid

Answer 36

change in numbers of individual chromosomes in a set

Question 37

what does aneuploid cause

Answer 37

it causes an imbalance in te amount of gene products

Question 38

out of the types of cells, when is anueploid more rare?

Answer 38

in autosomes/body cells

Question 39

why is aneuploid more permissable in sex chromosomes

Answer 39

if you have more than one X chromosome, it will be inactivated

Question 40

why is there a concern for older mothers and their offspring?

Answer 40

nondisjunction events are more common

Question 41

true or false: aneuploidy for autosomes is rare because the expression of genes needs to be in balance whereas sex chromosomes can often handle the gain or loss of a sex chromosome

Answer 41

true

Question 42

what is meiotic nondisjunction?

Answer 42

it is when chromosomes fail to segregate during anaphase I or anaphase II

Question 43

what is the result of meitoic nondisjunction

Answer 43

haploid cells with too many or too few chromosomes

Question 44

what happens to a gamete if it underwent meitoic nondisjunction

Answer 44

all of its cells will have abnormal chromosomal composition

Question 45

how often does meiotic nondisjunction occur in meiosis?

Answer 45

it can only occur once in either Meiosis I or Meiosis II

Question 46

what is the overall result when nonsegregation occurs in Meiosis I?

Answer 46

the homologous chromosomes will fail to segregate and all daughter cells will be affected, the resulting gamete will have two chromosomes from different homologs

Question 47

what is the overall result if nondisjunction occurs in Meiosis II

Answer 47

only half the gametes will be affected sister chromatids will fail to segregate and a gamete will have two chromosomes from the same homolog

Question 48

Arrange the following events in the proper order in which they occur during meiosis I. a = Separation of homologous chromosomes b = Synapsis c = Crossing-over d = Independent assortment

Answer 48

b, c, d,a

Question 49

when does separation of homologous chromosomes occur?

Answer 49

at meiosis I anaphase I

Question 50

when does synapsis occur?

Answer 50

prophase 1

Question 51

when does crossing over occur

Answer 51

prophase I

Question 52

when does independent assortment occur?

Answer 52

metaphase I

Question 53

Two normal parents have a son with hemophilia (an X-linked recessive disorder) that also has Klinefelter Syndrome. The nondisjunction event occurred in: Mother Father Either

Answer 53

Info: Klinefelter is XXY The son has the mutation, so both of the X's must carry the mutation (X-). The father is normal so he could not have given the allele Both alleles must have come from the Mother

Question 54

Two normal parents have a son with hemophilia (an X-linked recessive disorder) that also has Klinefelter Syndrome. The nondisjunction event occurred in which division? Meiosis I Meiosis II Either

Answer 54

Son is X-X-Y Both of the alleles must have come from the mother The mother is a carrier, so one of the homologs has the allele the disjunction occured in meiosis II where the sister chromatids fail to separate

Question 55

Two normal parents have a son that is a carrier for hemophilia (an X linked reccessive disorder) and has kleinfelter syndrome. Who did the non disjunction occur in?

Answer 55

Son: XX-Y Mom: X(-)X Dad; XY It could have come from either

Question 56

Two normal parents have a son that is a carrier for hemophilia (an X linked reccessive disorder) and has kleinfelter syndrome. When did the non disjunction occur in?

Answer 56

at Meiosis I

Question 57

two normal parents have a daughter wil hemophila that also has Turner syndrome: who did the nondisjunction occur in?

Answer 57

Mom: X(-)X Dad: XY it came from the dad, the mom had to have given her sex chromosome for the daughter to have the disease

Question 58

two normal parents have a daughter wil hemophila that also has Turner syndrome: what stage did the nondisjunction occur in?

Answer 58

occured in MII

Question 59

for males, is the Tisx gene expressed if they only have one X chromosome?

Answer 59

Yes, it is always expressed and is active in order to protect the X chromosome from being inactivated

Question 60

if nondisjunction occurs in meiosis 1, what is the resulting gamete chromosomes?

Answer 60

two cells will be n+1 with an extra chromosome from a different homolog and two cells will br n-1

Question 61

what is complete nondisjunction

Answer 61

this is when all chromosomes undergo nondisjunction and migrate to one daughter cell. it results in polyploidy

Question 62

what are the cellular results of complete nondisjunction

Answer 62

one diploid cell and one cell without chromosomes

Question 63

what is it called when nondisjunction occurs after fertilization?

Answer 63

mitotic nondisjunction

Question 64

what is mosaicism?

Answer 64

when mitotic nondisjunction occurs, a subset of cells will be genetically different from the rest. The severity of this depends on the time and location

Question 65

what is endopolyploid

Answer 65

specific tissues that are polyploid within a diploid individual

Question 66

what is a polytene chromosome

Answer 66

large interphase chromosomes that are formed by DNA replication without cell division

Question 67

polyploid organisms with an odd number of chromosomes are usually:

Answer 67

sterile

Question 68

what is an autopolyploid

Answer 68

an increase in the number of chromosome sets due to complete nondisjunction within a single species

Question 69

what is alloploidy?

Answer 69

changes in number of sets of chromosomes due to interspecies crosses

Question 70

what is allopolyploid

Answer 70

it is where an organism contains two or more sets of chromosomes from two species