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Genetics > Meiosis (Lec 2) > Flashcards

Meiosis (Lec 2) Flashcards

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Biology 101 flashcards
1
Q

What two key aspects of genetic variation occur in meiosis?

A

independent assortment, crossing over

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2
Q

Define meiosis

A

production of haploid gametes

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3
Q

Define fertilization

A

fusion of haploid gametes

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4
Q

What happens in Interphase of meiosis?

A

DNA synthesis and chromosome replication phase

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5
Q

What happens in meiosis I?

A

separation of homologous chromosome pairs, and reduction of the chromosome number by half

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6
Q

What happens in meiosis II?

A

separation of sister chromatids, also known as equational division

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7
Q

What are the major results of meiosis?

A

increase in cell numbers, daughter cells are not genetically identical, daughter cells are haploid, formation of gametes

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8
Q

What is the pairing of homologous chromosomes called?

A

synapsis

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9
Q

What is the first stage of prophase I and what happens in it?

A

Leptotene; chromosomes begin to condense

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10
Q

What is the second stage of prophase I and what happens in it?

A

Zygotene; Synaptonemal complex forms and homologous chromosomes pair (synapsis)

note: synapsis results in bivalents (tetrads)

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11
Q

What is the third stage of prophase I and what happens in it?

A

Pachytene; crossing over

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12
Q

What is the fourth stage of prophase I and what happens in it?

A

Diplotene; crossing over continues, chiasmata are well defined at this point

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13
Q

What is the fifth and final stage of prophase I and what happens in it?

A

Diakinesis; crossing over is incomplete, spindle apparatus is in place, and nuclear membrane is disrupted

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14
Q

Do centromeres divide?

A

no

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15
Q

What happens in metaphase I?

A

tetrads line up along equatorial plate

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16
Q

What happens in anaphase I?

A

homologous chromosomes move to opposite poles, each homologue consists of two chromatids because sister chromatids remain attached, daughter cells will be haploid

17
Q

What happens in telophase I?

A

cytokinesis occurs, nuclear membrane reform, chromosome number is halved, haploid daughter cells are genetically unique

18
Q

What happens in interkinesis?

A

spindle breaks down, chromosomes may uncoil

19
Q

What happens in prophase II?

A

chromosomes condense again, spindle apparatus reforms, each chromosome consists of two chromatids, each daughter cell has one complete set of chromosomes

20
Q

What happens in metaphase II?

A

chromosomes line up on equatorial plate, kinetochores face opposite poles

21
Q

What happens in anaphase II?

A

centromeres of sister chromatids separate, chromosomes move to opposite poles, each chromosome consists of a single chromatid

22
Q

What happens in telophase II?

A

chromosomes uncoil, cytokinesis completes, end result is four genetically unique haploid daughter cells

23
Q

What is cohesin?

A

enzyme that holds chromatids together during early part of mitosis, holds homologous chromosomes together at chiasmata through metaphase I in meiosis, meiosis-specific cohesin at centromere keeps sister chromatids together during anaphase;- protected by shugoshin

24
Q

What does separase do?

A

kept inactive during interphase and early mitosis, breaks down meiosis-specific cohesin at centromere during end of metaphase II

25
Q

What does securin do?

A

keeps separase inactive during interphase and early mitosis

26
Q

What does monopolins do?

A

keeps sister kinetochores oriented toward same pole during metaphase I

27
Q

In spermatogenesis, are primordial germ cells haploid or diploid?

A

diploid

28
Q

Primordial germ cells divide mitotically to produce diploid ___

A

spermatogonia

29
Q

Spermatogonia enter prophase I and give rise to ____ _____

A

primary spermatocytes

30
Q

Primary spermatocytes undergo meiosis I to produce haploid ___ _____

A

secondary spermatocytes

31
Q

Secondary spermatocytes undergo meiosis II to produce haploid _____

A

spermatids

32
Q

Spermatids differentiate into ___

A

sperm

33
Q

Primordial germ cells involved in Oogenesis divide mitotically to produce diploid ___

A

oogonia

34
Q

Oogonia initiate meiosis and enter into prophase I to give rise to ___ ____

A

primary oocytes

35
Q

Primary oocytes become frozen at what stage of prophase I

A

diplotene

36
Q

When does meiosis resume after being frozen in prophase I?

A

ovulation

37
Q

Meiosis stops again at what point?

A

metaphase II; resumes once egg is fertilized

38
Q

summarize oogeneis

A

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

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