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Biology MCAT > Chapter 2 > Flashcards

Chapter 2 Flashcards

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1
Q

Where does mitosis/meiosis occur in? What is the result for both ?

A

Mitosis occurs in somatic tissue; Result: 2 identical daughter cells

Meiosis occurs in germ cells; Result: Up to 4 non identical sex cells

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2
Q

What are the similarities of mitosis and meiosis?

A

In both processes:
1) Genetic material must be duplicated (Prophase)
2) Chromatin is condensed to form chromosomes (Prophase)
3) Microtubules emanating from centrioles are involved in dividing genetic material

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3
Q

What are the differences of mitosis and meiosis?

A

Mitosis:
(A) consists of one round each of replication and division
(B) 2n -> 2n
(C) Occurs in all dividing cells
(D) Homologous pairs do not pair up
(E) no crossing over

Meiosis:
(A) consists of one round of replication followed by two rounds of division (Meiosis I and Meiosis II)
(B) 2n -> n
(C) Occurs in sex cells only
(D) Homologous chromosomes align on opposite sides of the metaphase plate (2nd major difference seen in Metaphase I)
(E) Crossing over occurs (1st major difference seen in Prophase I)

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4
Q

What is the chronological order of meiosis?

A

Interphase < Meiosis < prophase I < metaphase I < anaphase I < telophase I < metaphase II < anaphase II < telophase II

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5
Q

Meiosis I vs Meiosis II. What is the name of their respective division? Is any of them similar to mitosis?

A

Meiosis I : Results in homologous chromosomes being separated, which results in haploid daughter cells (REDUCTIONAL DIVISION)

Meiosis II (Similar to Mitosis): Results in the separation of sister chromatids without a change in ploidy (EQUATIONAL DIVISION)

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6
Q

Meiosis I vs Meiosis II. What is the name of their respective division? Is any of them similar to mitosis?

A

Meiosis I : Results in homologous chromosomes being separated, which results in haploid daughter cells (REDUCTIONAL DIVISION)

Meiosis II (Similar to Mitosis): Results in the separation of sister chromatids without a change in ploidy (EQUATIONAL DIVISION)

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7
Q

Define ploidy

A

The # of sets of Chromosomes in a cell

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8
Q

Explain 23 homologous pairs, 46 chromosomes, and 92 chromatid. How does a chromosome look like?

A

A chromosome looks like an X

Human genome is composed of 23 homologous pairs of chromosomes (each of which contains one chromosome inherited from each parent), therefore there are 46 chromosomes, each chromosome has two chromatids, therefore there are 92 chromatids

1 chromosome = 2 chromatids
1 pair = 2 chromosomes (maternal chromosome and paternal chromosome) = 4 chromatids

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9
Q

Briefly explain prophase I

A

1) Chromatin condenses into homologous chromosomes
2) the spindle apparatus forms
3) the nucleoli and nuclear membrane disappear
4) Homologous Chromosomes can exchange genetic material via crossing over

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10
Q

What is the first major difference between meiosis and mitosis? Where does it occur in meiosis?

A

Prophase I of meiosis: homologous chromsomes come together and intertwine in a process called synapsis allowing for the beginning of genetic material exchange via crossing over

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11
Q

Explain synapsis of prophase I. What occurs?
Use the following terms: synapsis, synaptonemal complex, tetrad, crossing over, chiasma, genetic recombination

A

1) Synapsis: Homologous chromosomes come together and intertwine; they are connected by a group of proteins called synaptonemal complex
2) Forms the tetrad complex (this refers of the two homologous chromosomes that are intertwined and contain a total of 4 chromatids)
3) Crossing over: chromosomes can break off at the point of contact (at the Chiasma) and exchange material
4) Genetic recombination occurs

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12
Q

What are the 2 types of crossing over events?

A

Single crossovers and double crossovers

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13
Q

The crossing over event occurs between _____________ and not between ___________ of the same chromosome.

A

homologous chromosomes; sister chromatids

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14
Q

True or False: Homologous chromosomes of the same pair are identical

A

False; they come from different parents therefore they are not identical but they are similar
Ex: even if both are from the homologous pair of 15/23, each homologous chromosome comes from either the mother or father, therefore being not identical but similar because they are of the 15th pair

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15
Q

True or False: Sister chromatids are identical

A

True; sister chromatids come from the same homologous chromosome which comes from the same parent

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16
Q

What are the outcomes of genetic recombination from crossing over event?

A

1) Chromatids involved in crossing over have an altered but structurally complete set of genes
2) Can unlink linked genes thereby increasing the variety of genetic combinations that can be produced via gametogenesis (it is able to unlink linked genes because crossing over can move parts of the chromosome to the other chromosome) (in this case, the ‘parts’ are genes)

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17
Q

In the tetrad complex, how many chromatids are involved in crossing over? How many are left out?

A

2 chromatids are involved in crossing over, the other 2 chromatids are left out

Note: The point of contact of the homologous chromosomes occurs at only one chromatid for each chromosome. In other words, for chromosome pair 15th you have a maternal 15th homologous chromosome and a paternal 15th homologous chromosome. Each homologous chromosome has 2 chromatids. A total of 4 chromatids. However only 2 out of 4 chromatids participate in crossing event. 1 out 4 chromatid coming from the maternal 15th homologous chromosome and the other 1 out 4 chromatid coming from the paternal 15th homologous chromosome. Thus leaving 2 chromatids to not be involved in crossing event

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18
Q

What does linkage refer to?

A

Refers to the tendency for genes to be inherited together; genes that are located farther from each other are physically less likely to be inherited together but more likely to undergo crossing over

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19
Q

Crossing over explains the Mendez’s Second Law of Independent Assortment which states:

A

That the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes

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20
Q

What occurs in the Metaphase I (meiosis)?

A

1) Homologous pairs (tetrads) align at the metaphase plate
2) Each pair attaches to a separate spindle fiber by its kinetochore (search for an image on how this looks like)

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21
Q

What is the second major difference between meiosis and mitosis? Where does it occur in meiosis?

A

Metaphase I;

In mitosis, each chromosome is lined up on the metaphase plate by two spindle fibers (one from each pole); in meiosis, homologous chromosomes are lined up across from each other at the metaphase plate and are held by one spindle fiber

(You can visually see this in pages 65 and 71)

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22
Q

What occurs in the Anaphase I (meiosis)?

A

1) Disjunction occurs: Homologous pairs separate and are pulled to opposite poles of the cell

In other words, the tetrad (4 chromatids) is split. The paternal chromosome (2 chromatids) are separated from the maternal chromosome (the other 2 chromatids). Paternal chromosome goes to one side of the cell, while the maternal chromosome goes to the other side of the cell.

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23
Q

What accounts for Mendel’s First Law of Segregation?

A

Disjunction; the separation of the homologous pairs to opposite poles of the cell

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24
Q

What occurs in the Telophase I (meiosis) and cytokinesis?

A

1) A nuclear membrane forms around each new nucleus (in other words, a membrane forms around each chromosome)
2) Cytokinesis: the cell divides into two daughter cells
3) Each cell is now considered haploid

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25
Q

By the time we reach prophase II, the cells are considered diploid or haploid? How many cells are there? Describe the chromosome in the cell

A

There are 2 daughter cells. There is 1 chromosome for each cell, therefore each cell is considered haploid (one chromosome). Each chromosome has its own nuclear membrane. However, each chromosome has 2 sister chromatids.

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26
Q

Describe the difference between centromere, kinetochore, and centrosome?

A

The centromere is the middle of a chromosome (it is represented in pictures as a ball). The kinetochore binds to the left and right of the centromere. The centrosome is located in the poles of a cell, it contains the spindle fibers that binds to the kinetochore.

After the spindle fibers bind to the kinetochore, it pulls the chromosomes apart. It pulls them to the centrosome, which are located in the opposite sides of a cell. This is why there is a chromosome in the left of the cell, and the other one in the right of the cell (completely opposite directions).

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27
Q

Haploid vs diploid

A

Haploid = one copy of a Chromosome
Diploid = two copies of a chromosome

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28
Q

True or False: 1 chromatid can be considered a chromosome.

A

True; In mitosis, the product produced is two diploid cells with each cell having two chromatids. However, it is considered a diploid because each chromatid is its own chromosome. In meiosis, the product produced is four haploid cells with each cell having one chromatid. Each chromatid in each cell is its own chromosome, therefore allowing it to be called a haploid.

29
Q

Why is Meiosis I considered as “REDUCTIONAL Division”?

A

In the start of meiosis (interphase I), you have one diploid cell with two chromosomes. After meiosis I, you have two daughter haploid cells with one chromosome each

30
Q

What occurs in the Prophase II (meiosis)?

A

1) Nuclear envelope dissolves, nucleoli disappear, the centrioles migrate to opposite poles, and the spindle apparatus begins to form

31
Q

What occurs in the Metaphase II (meiosis)?

A

1) Chromosomes line up on the metaphase plate

32
Q

What occurs in the Metaphase II (meiosis)?

A

1) Chromosomes line up on the metaphase plate

33
Q

What occurs in the Anaphase II (meiosis)?

A

1) Centromeres divide, separating the chromosomes into sister chromatids
2) Chromatids are pulled to opposite poles by spindle fibers

34
Q

What occurs in the Telophase II (meiosis)?

A

1) A nuclear membrane forms around each new nucleus
2) Cytokinesis: forms 4 daughter cells from the two cells; 2 daughter cell from each cell

35
Q

True or False: Only mutations in the X chromosome can cause sex-linked disorders

A

True; Sex-linked is X-linked

36
Q

Males are termed hemizygous with respect to many of the genes on the X-chromosome. What does that mean?

A

Since males only have one copy of the X chromosome they are called hemizygous. If males get affected X chromosome that means they’ll express it. On the other hand, a woman needs to have two effected X chromosomes to be affected.

37
Q

Females can be termed homozygous or heterozygous with respect to many of the genes on the X-chromosome. What does that mean?

A

Females have two X chromosomes. They can have one affected X chromosome to be termed heterozygous, or have two affected X chromosomes to be termed homozygous.

38
Q

Define Carrier

A

Ex: Females carrying a diseased allele on an X chromosome but not exhibiting the disease

39
Q

X chromosome vs Y chromosome (in terms of genetic information)

A

X Chromosome = carries a sizable amount of genetic information
Y chromosome = contains very little genetic information

40
Q

Describe the pathway of sperm through the male reproductive system

A

SEVE(N) UP:

Seminiferous tubules
Epididymis
Vas deferens
Ejaculatory duct
(Nothing)
Urethra
Penis

41
Q

What are the 2 functional components of the testes?

A

1) the seminiferous tubules
2) the interstitial cells of Leydig

42
Q

Where is sperm produced?

A

Produced in the highly coiled seminiferous tubules

43
Q

What is the function of Sertoli cells?

A

They provide nourishment to Sperm

44
Q

What is the function of the cells of Leydig?

A

They secrete testosterone and other male sex hormones (androgens)

45
Q

It is important for the testes to be located in the scrotum, which lies outside the body because:

A

It is a position that allows it to maintain a temperature of 2 degrees Celsius to 4 degrees Celsius lower than the body

46
Q

What happens in sperm as they are passed to the epididymis?

A

Their flagella gain motility, and they are stored until ejaculation

47
Q

As sperm passes through the reproductive tract they are mixed with:

A

Seminal fluid; which is produced through a combined effort by the seminal vesicles, prostate gland, and bulbourethral gland

48
Q

What is the function of the seminal vesicles?

A

1) Contributes fructose to nourish sperm
2) Gives the seminal fluid mildly alkaline properties so that the sperm can survive in the relative acidity of the female reproductive tract

49
Q

What is the function of the prostate gland?

A

1) Gives the seminal fluid mildly alkaline properties so that the sperm can survive in the relative acidity of the female reproductive tract

50
Q

What is the function of the bulbourethral gland?

A

Produces a clear viscous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal

51
Q

What is the function of the bulbourethral gland?

A

Produces a clear viscous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal

52
Q

Semen is the combination of:

A

Sperm + seminal fluid

53
Q

Provide the steps of spermatogenesis. What is it and where does it occur?

A

The formation of haploid sperm through meiosis; It occurs in the seminiferous tubules

1) Spermatogonia (1 diploid cell) undergoes mitosis and forms the
2) Primary spermatocyte (1 diploid cell) which undergoes meiosis I and forms the
3) Secondary spermatocyte (two haploid cells) which undergoes meiosis II and forms the
4) Spermatids (four haploid cells) which then fully mature and become
5) Spermatozoa cells (4 haploid sperm cells)

54
Q

What is the structure of a mature sperm? Describe each component

A

Head - midpiece - tail - end piece

Head: Contains genetic material and has the acrosome which allows it to penetrate the ovum
Midpiece: Filled with mitochondria which generates ATP from fructose in order to allow it to swim through the female reproductive tract
Tail: a flagellum used for motility

55
Q

Define ovaries. Where are they located?

A

The female reproductive gonads made of thousands of follicles which are multilayered sac that contain, nourish, and protect immature ova. These gonads produce estrogen and progesterone. They are located in the pelvic cavity

56
Q

Between puberty and menopause, what occurs? (In regards to an egg)

A

One egg per month is ovulated into the peritoneal sac, which lines the abdominal cavity, then it goes t the fallopian tube which is lined with cilia to propel the egg forward

57
Q

Describe the structure of the female reproductive system. (Use fallopian tube, uterus, cervix, and vagina)

A

The fallopian tubes are connected to the muscular uterus. The lower end of the uterus (the cervix) connects to the vaginal canal where sperm are deposited

58
Q

What is the site of fetal development called?

A

Uterus

59
Q

Prior to puberty, the hypothalamus restricts production of:

A

Gonadotropin-releasing hormone (GnRH)

60
Q

Prior to puberty, the hypothalamus restricts production of:

A

Gonadotropin-releasing hormone (GnRH)

61
Q

At the start of puberty, the hypothalamus releases ________, which triggers the ___________ to synthesize and release ________ and __________.

A

At the start of puberty, the hypothalamus releases GnRH which triggers the anterior pituitary gland to synthesize and release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

62
Q

In male sexual development, what are the roles of FSH and LH?

A

FSH = stimulates the Sertoli cells and triggers sperm maturation
LH = causes the interstitial cells to produce testosterone in order to develop the secondary sexual characteristics

63
Q

What are examples of secondary sexual characteristics?

A

Facial and auxiliary hair, deepening of the voice, and increased muscle and bone mass

64
Q

What is the function of androgens ?

A

Results in male sexual differentiation; they are produced in the presence of Y chromosome

65
Q

Define oogenesis

A

The production of female gametes

66
Q

What is the difference between male spermatogonia and female oogonia? (In terms of supply)

A

Males have a unending supply of stem cells; females have a limited supply of oogonia produced by birth

67
Q

Primary oocytes vs secondary oocytes

A

Primary oocytes = all of the oogonia have already undergone DNA replication and become primary oocytes; they are diploid cells that are arrested in prophase I

Secondary oocytes = After the first menstrual cycle (menarche), one primary oocyte per month will complete meiosis I, producing a secondary oocyte and a polar body ; the secondary oocyte will be arrested in metaphase II and does not complete the remainder of meiosis II unless fertilization occurs

68
Q

Secondary oocytes vs Polar body

A

Secondary oocyte can undergo Meiosis II; a polar body can no longer divide and will never produce functional gametes

69
Q

What triggers Meiosis II for secondary oocytes? What happens after it occurs?

A

A sperm cell, with the help of acrosomal enzymes, penetrates the layers of the oocyte which leads it to produce a mature ovum and another polar body; the haploid pronuclei of the sperm and the ovum join, creating a diploid zygote

Biology MCAT (2 decks)

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