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anatomy FB1 > L2: gametogenesis > Flashcards

L2: gametogenesis Flashcards

1
Q

gamete are what type of cells?

A

haploid sex cells (oocytes & sperms)

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2
Q

gametogenesis is characterized in 4 stages

A
  1. The extraembryonic origin of the germ cells and their migration into the gonads.
  2. An increase in the number of germ cells by mitosis.
  3. A reduction in chromosomal number by meiosis.
  4. Structural and functional maturation of the eggs and spermatozoa
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3
Q

when are they ready for fertilization?

A

till puberty

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4
Q

What is the difference between mitosis and meiosis role in Gametogenesis?

A
  • Mitosis > increase in the number of germ cells.

* Meiosis > reduction in chromosomal number.

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5
Q

When is the differences between male and female Gametogenesis start to exist?

A

The first phase of gametogenesis is identical in males and females,
whereas distinct differences exist between the male and female patterns in the last three phases.

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6
Q

Phase 1: Origin and Migration of Germ Cells: what happens?

A
  • during development (proliferation) Primordial Germ > layers forming small disc > each layer of the disk develops to different systems of the body
  • This procedure is very intricate anything can go wrong causing a defect
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7
Q

What could go wrong in phase 1?

A

Teratomas > when primordial germ cells stray and move to other places rather than the gonads

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8
Q

What is the chromosomal theory of inheritance?

A

It identifies chromosomes as the carriers of genetic material

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9
Q

who developed the chromosomal theory?

A

Sutton and Boveri in 1902.

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10
Q

How many genes do humans have?

A

35,000 genes on 46 chromosomes

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11
Q

what are autosome?

A

22 pairs of matching chromosomes

- 1 pair is of sex chromosome

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12
Q

each gamete contains how many chromosome?

A

Each gamete contains haploid number of 23 chromosomes

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13
Q

Why do we mean by linked genes?

A

Genes that are on the same chromosome

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14
Q

What is karyotyping

A

It’s a map of chromosomes

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15
Q

What can we define using karyotyping?

A
  • if there is any defect

* the sex of the fetus

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16
Q

When does each chromosome replicate it’s DNA?

A

Before entering mitosis

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17
Q

How many chromosomes does each daughter cell receives?

A

the complete complement of 46 chromosomes- diploid progeny

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18
Q

how does The pattern of mitotic divisions differs from male and female germ cells

A

Female > high surge of mitosis five days after conception

Male > the surge happens after puberty

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19
Q

what happens in interphase

A
  • uncoiled chromatin

- its the longest phase of mitotic division

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20
Q

what happens in prophase?

A
  • condensation & duplication
  • centrosome appears
  • nucleus breaks down
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21
Q

what happens in metaphase?

A
  • microtubules help align & pull chromosomes

- they align in the metaplate (in the middle) for equal segregation

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22
Q

what happens in anaphase?

A
  • sister chromatids move away
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23
Q

what is the result in mitosis

A

results in 2 exact copies of the parent cell.

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24
Q

What is meiosis?

A

Cell division that takes place in germ cells to generate male and female gametes.

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25
Q

How many cell divisions are required to reduce the number of chromosomes to haploid (number
of 23)?

A

Requires two cell divisions.

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26
Q

Define homologous chromosomes

A

a pair of 2 chromosomes each pair with two chromatids

(Homologous chromosomes in meiosis one are haploid but the sister chromatids are
still together so we need another division to separate them)

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27
Q

When does each of the sister chromatids separate and why

A

each then separates into two daughter cells in meiosis two > resulting in a total of four
haploid daughter cells (each gamete then contains 23 chromosomes)

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28
Q

Why are the homologous chromosomes different than the parent cell?

A

Due to Crossover

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29
Q

What do you mean by crossover ?

A
  • critical events in meiosis I
  • interchange of chromatid segments between paired
    homologous chromosomes.
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30
Q

What is the role of crossover in meiosis?

A

It enhances genetic variability

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31
Q

How is the genetic variability enhanced in meiosis?

A
  • crossover

* random distribution of homologous chromosomes to the daughter cells

32
Q

What are the results of ooginia ( one primary oocytes)?

A
  • It gives rise to four daughters cells > each 22 plus 1 X chromosomes
  • But only one develops into a mature gamete

o One mature gamete
o three polar bodies

33
Q

How is spermatocyte similar to ooginia ?

A

In which it gives four daughters cells; however, all are mature gametes!

o two 22 plus 1 X
o two 22 plus 1 Y

34
Q

What are the difference between ooginia and spermatogonia?

A
  • Numerous oogonia undergo programmed degeneration called atresia until menopause
  • Spermatogonia maintain the ability to divide throughout postnatal life
35
Q

when does the number of germ cells peaks?

A

from 2nd to 5th month of pregnancy (due to mitosis)

36
Q

For how long does ooginia undergo mitotic divisions?

A

Till the end of the third month

37
Q

What happens in the end of the third month of pregnancy?

A

The ooginia stop undergoing mitotic division and arrange in clusters surrounded by a
layer of flat epithelium.

38
Q

What is a primordial follicle?

A

It is Primary oocytes together with its surrounding flat epithelial cells.

39
Q

when do primary oocytes starts prophase?

A

At birth, all primary oocytes have started prophase of meiosis I.

40
Q

At birth, Do the primary oocytes completes meiosis one?

A

No they do not enter metaphase they enter diplotene stage until puberty.

41
Q

how many oocytes are present by puberty

A

Most oocytes become atretic (die)during childhood- only 40,000 are present by puberty

and less than 500 will be ovulated

42
Q

Why do the oocytes that reach maturity (ovulated late) late in life has a
higher probability to cause defects to the fetus?

A

Because the oocytes could have been dormant for 40 years or more before ovulation

• the longer the oocytes are arrested in meiosis the more
mutations

43
Q

When does the primary oocyte complete

the first meiotic division?

A

At the time of ovulation

44
Q

What results from the first meiotic

division?

A

The first polar body (non-functional cell) and a secondary oocyte (n).

45
Q

The secondary oocyte arrest at?

A

In metaphase,2nd meiotic division

46
Q

All Primordial follicle start meiosis 1?

A

Yes, all start meiosis one, however, not all of them complete it

47
Q

All of oocyte will continue meiosis 1?

A

No, only for oocyte that need to be ovulated.

48
Q

All secondary oocyte will complete meiosis

2?

A

No, only one which is fertilized by a sperm.

49
Q

What results from the second meiotic

division (only when sperm is present)?

A

An ovum or a zygote + a second polar body

50
Q

Which results from the fuse of the ovum

and sperm?

A

A zygote

51
Q

What causes the completion of second

meiotic division?

A

Sperm penetration (fertilization).

52
Q

What happens to the primordial follicles at puberty?

A

pool of growing follicles is established from primordial
follicles.

  • Each month 15 to 20 follicles selected from this pool begin to mature
53
Q

The selected follicles pass through three stages? what are the stages?

A
  1. Primary (preantral)
  2. Secondary (antral)
  3. Preovulatory (Graafian follicle)
54
Q

What happen to the follicular cells surrounding the primary oocyte as 1*
oocyte begin to grow? and why ?

A

They change from flat to cuboidal > produce stratified epithelium of granulosa cells

  1. primordial follicle >
  2. growing follicle (secondary)à zona pellucida >
  3. vascular follicle (tertiary, Graafian follicle)àzona pellucida & Theca follicle
55
Q

When does meiosis in males begin?

A

Begins after puberty.

in contrast to primary oocytes, not all
spermatogonia enter meiosis at the same time

56
Q

First spermatogonium enters the meiotic phase as

A

primary spermatocytes (they spend several weeks dividing)

57
Q

whats the result of primary spermatocytes?

A

This results in 2 secondary spermatocytes which enter the second meiotic division

Finally, four haploid spermatids are made

58
Q

how long does the whole cycle of meiosis in males take?

A

This cycle takes 64 days

59
Q

what happens in maturation of the sperm?

A
  1. formation of the acrosome
  2. Condensation of the nucleus.
  3. Formation of the neck, middle piece, and tail.
  4. Shedding of most of the cytoplasm as residual bodies
60
Q

What is the importance of acrosome?

A

It covers half of the nuclear surface and contains enzymes to assist in fertilization

61
Q

what’s the importance of maturation?

A

Important for mortality

62
Q

what is nondisjunction

A

when Chromosomes fail to separate during meiosis.

63
Q

what an example of nondisjunction?

A

One haploid gamete contains both members of chromosomal pair for a total of 24 chromosomes whereas the other haploid gamete has only 22

64
Q

Define aneuploidy

A

General term for abnormal number of chromosomes in an embryo.

65
Q

Why is Down syndrome known as trisomy 21?

A

Because there is an extra copy of chromosome 21

66
Q

What are the symptoms of down syndrome?

A
  • delayed growth
  • distinct facial characteristics
  • intellectual disability
67
Q

What is the cause of down syndrome?

A

• Results from having 3 copies of chromosome 21

68
Q

What increases the risk of having a child with down syndrome?

A

• The increase with the maternal age

69
Q

Patients with down syndrome suffer from?

A

• Premature aging, thyroid dysfunction, infections

70
Q

What are the symptoms of Trisomy 18?

A
  • mental retardation
  • conginetal heart defects
  • low-set ears
  • flexion of fingers and hands
71
Q

What is the incidence rate of trisomy 18 ?

A

incidence rate is 1:5000

72
Q

What is the estimated age for patients with trisomy 18?

A

• 2 months of age

73
Q

What are the symptoms of trisomy 13?

A
  • show cleft lip and palate
  • eye defects
  • Deafness
  • mental retardation
74
Q

What is the incidence rate of trisomy 13 ?

A

incidence rate is 1:20,000

75
Q

What is the estimated age for patients with trisomy 13?

A

More than 90% die in their first month after birth

76
Q

Ways to determine whether the patient has a

Chromosomal Abnormality

A
  • Karyotyping

* Fluorescence in situ Hybridization (FISH)

77
Q

Defects can occur also due:

A
  • Family history

* relative marriage

anatomy FB1 (9 decks)

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