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3.3 Flashcards

1
Q

What is meiosis

A

a form of nuclear division that produces four haploid nuclei from one diploid nucleus

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2
Q

What happens prior to meiosis

A

the DNA of the cell is replicated during the S phase of interphase

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3
Q

What happens n sexual reproduction

A

two diploid individuals each contribute half of their DNA to produce offspring with a new and unique combination of alleles

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4
Q

What are reproductive cells called

A

gametes

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5
Q

What are they two cycles of division in meiosis

A

meiosis I and II

each have four phases
prophase, metaphase, anaphase and telophase

at the end cytokinesis occurs

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6
Q

What does cytokinesis do

A

divides the cytoplasm of the parent cell to create two daughter cells

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7
Q

What type of nuclei does meiosis produce

A

haploid nuclei

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8
Q

What is reduction division

A

cells begin with two copies of each chromosome and end with only one

DIploid (2n) - haploid (n)

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9
Q

What happens in Prophase I

A

Chromosomes become visible due to supercoiling

replicated chromosomes from closely linked homologous pairs (tetrads of bivalents) which have two chromosomes and four total chromatids

non sister chromatids may cross over at chiasmata and exchange equivalent segments of DNA

centrioles If present migrate to opposite poles and spindle fibres start to form, the nucleolus and nuclear membrane disintegrate

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10
Q

Where does crossing over take place

A

in prophase I

between the non-sister chromatids

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11
Q

What happens in metaphase I

A

Homologous pairs move together along the metaphase plate, maternal and homologs show random orientation towards the pole

spindle fibres attach to the centromeres of each chromosome and gently pull to align them along the equatorial metaphase plate

spindle fibres connect each chromosome to one pole only

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12
Q

When does random orientation take place

A

Metaphase I

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13
Q

What happens in Anaphase 1

A

Spindle microtubules shorten, pulling homologous chromosomes apart towards opposite poled, unlike mitosis, sister chromatids remain connected at the centromere and move to the same pole

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14
Q

What happens during telophase I

A

the first meiotic division effectively ends when the chromosomes arrive at the poles, each chromosomes consists of a pair of chromatids,

the chromatids partially uncoil and a nuclear membrane then reforms around each nucleus formed.

cytokineses results in two daughter cells with haploid nuclei from meiosis

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15
Q

When does cytokinesis generally take place

A

during telophase 1

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16
Q

When does reduction division take place

A

Meiosis 1

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17
Q

What does meiosis 1 do to the cell

A

DIploid to haploid
2n to n

cells with two copies to only one

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18
Q

What happens to the cell in meiosis II

A

separation of chromatids in haploid cells (n- n)

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19
Q

What happens in prophase !!

A

chromosomes condense again

centrioles migrate to opposite poles and spindle fibres start to form

nuclear membrane and nucleolus disintegrate

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20
Q

What happens in Metaphase II

A

Spindle fibres attach to the centromere and connect each centromere to both poles, they exert a gentle pull to align them

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21
Q

What takes place during Anaphase II

A

centromeres divid and chromatids are moved to opposite poles by spindle fibres

once sister chromatids are separated they are celled chromosomes

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22
Q

What happens during telophase II

A

Chromosomes reach opposite poles and uncoil, cytokinesssis then takes place

four haploid daughter cells are now produced and they are all genetically distinct

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23
Q

Draw the stages of meiosis

A

kogntiy

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24
Q

Where does crossing over happen

A

prophase I

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25
What is a tetrad
also known as a bivalent, homologs chromosomes pair up
26
How many chromatids does a tetrad have
four chromatids two homologs chromosomes
27
What is a chromatid
a long single strand of double helical DNA organized by histones proteins.
28
What are non sister chromatids
they have the same gene but different alleles
29
What are sister chromatids
identical and joined at the centromere
30
Whaat does crossing over include
when equivalent portions of the non-sister chromatids are exchanges between homologs chromosomes
31
What is a chiasmata
a point where crossing over can occur multiple times in the same tetrad
32
What does crossing over do
crates new combinations of alleles that were not present in either original chromosomes.
33
What contributes to genetic variation
crossing over
34
What happens after crossing over has taken place
the tetrads complete the process of condensation and move towards the equatorial plate. the tetrad is then separated in anaphase I and then the sister crhoamtids are separate during anaphase II of meiosis II
35
What is the longest phase of meiosis
Prophase I involves,ves pairing of homologous chromosomes crossing over followed by condensation of DNA into highly organized chromosomes
36
What is it called when sister chromatids separate
becomes a chromosome
37
Between which structures does crossing over typically occur?
Between non-sister homologous chromatids
38
In what phase of meiosis does crossing over occur?
prophase I
39
What does a tetrad consist of
2 pairs of sister chromatids
40
Where does random orientation take place
metaphase I
41
What is the difference in mitosis and meiosis between the metaphase
in mitosis, homologues line up in the eqautor where is meiosis, chromosomes line up individually for genetic differences
42
What causes chromosomes to arrange themselves in pairs instead of individually
reduction division random orientation
43
What happens as a result of reduction division
daughter cells contain only half of the chromosomes that were present in the parent cell, the parent cell had four chromosomes the daughter has to
44
What happens as a result of random orientation
When pairs of homologous chromosomes line up at the equator of the cell, the paternal copy, has an equal chance of facing either pole, the orientation of one pair does not impact the orientation of any other pair, each gamete gets one copy of each chromosome but a random assortments of the maternal and paternal inherited versions
45
how many generations are actually involved in meiosis
three two from mother one from father
46
What is genetic variation responsible for
all unique and distinctive forms that life has taken on Earth. it also accounts for the diversity we see within each species
47
What is the original source of all genetic variations
mutations
48
How doe genetic variation play a role in natural selection
helpful variations become more common in a population as harmful variations diminish, enabling the species toe evolve.
49
How does meiosis allow for genetic variation
through crossing over random orientation
50
How does crossing over allow for genetic variation
in prophase I, homologous chromosomes come together and sections are exchanges between non-sister chromatids, allowing the mixing of alleles from the two parental chromosomes to form new combinations
51
How does random orientation increase genetic variation
tetrads during metaphase I, the orientation of the homologs chromosomes at the equatorial plate during metaphase I determines which pole each pair of sister chromatids will move toward during anaphase I the orientation is independent of other such pairs, thus, the allele is inherited differently which is known as independent assortment
52
What is independent assortment
the allele inherited for one gene will not affect the allele inherited for another cause by random orientation
53
How does sexual reproduction also increase genetic variation
by fusion of gametes from different parents
54
What is non-disjunction
when II sister chromatids fail to separate, leading with two copies of a particular chromosome and another game without any copies
55
What does non-disjunction lead to
trisomy, zygotę with three copies of a homologue
56
Where can non-disjunction occur
in Anaphase I and II
57
What is trisomy
having an extra copy of a single chromosome (2n + 1)
58
What is there correlation between non-disjunction
between father age and non-disjunction but it I difficult to establish a clear connection
59
Which is the most common cause of Down syndrome?
Non-disjunction during meiosis in the mother
60
What is a karyogram
An image of a cell's homologous chromosome pairs ordered by decreasing size
61
What can a karyotype check for
the number and type of chromosomes
62
When is the human an embryo
first 10 weeks
63
when does the baby become a fetus
after 10 weeks
64
What are two ways of obtaining fetal cells for karyotyping or other tests
Amnioticentesis and chronic villus sampling (CVS)
65
When does amniocentesis take place
14 - 20 weeks
66
when does CVs take place
10 - 13 weeks
67
What is the source of fetal cells in amniotic fluid
Amniotic fluid
68
What is the source of fetal cells in chorionic villus sampling
chorion (membrane)
69
What is the risk of miscarriage in amniocentesis
< less than 1%
70
What is the risk of miscarriage in chorionic villus sampling
less than 2%
71
What happens during amniocentesis
as the fetus develops in the uterus, it is cushioned by amniotic fluid. Amniocentesis is usually performed between 14 weeks and 20 of progeny. A doctor r uses ultrasound imagery to guide a syringe needle through the abdomen and uterine wall without piercing the fetus. The needle is then used to withdraw a small amount of amniotic fluid. Fetal cells floating in the fluid are cultured and karyotyped
72
What happens during chorionic villus sampling (CVS)
in early pregnancy through 10-13 weeks, CVS can be used with ultrasound imagnign to guide the medical proffesinal during the sampling and avoid harm to the developing embryo or fetus. Fetal cells are sampled by inserting a suctioning tool through the vagina or abdomen to reach the fetal cells in the chorion. The chorion is a membrane that surrounds the fetus and develops into part of the placenta.
73
If a diploid cell has 12 chromosomes in prophase I, how many chromatids will the cell have at the completion of anaphase I and anaphase II?
12 and then 6
74
During which phase of meiosis are chromatids pulled to opposite poles of the cell?
Anaphase II
75
When one diploid nucleus divides by meiosis, how many haploid nuclei are formed?
4
76
During which phase of meiosis do homologous pairs of chromosomes line up along the equator of the cell?
Metaphase I
77
Spindle fibres start to form during prophase I of meiosis. Where do spindle fibres attach during meiosis?
between the centromere of chromosomes and the centrioles
78
Which phase of cell division is photographed in order to make a karyogram?
metaphase of mitosis
79
Which genetic condition can be diagnosed by karyotyping?
Trisomy 21
80
What types of information are needed to construct a karyotype?
size of chromosomes
81
During which phases of meiosis does the nuclear envelope break down?
prophase I and II

Biology (51 decks)

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