Human Genetics > Topic 11 - Prenatal Development > Flashcards

Topic 11 - Prenatal Development Flashcards

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1
Q

What are the sites of gametogenesis?

A

Gonads

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2
Q

How many chromosomes does Gametes have? Where are they produced from?

A

23 produced by meiosis

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3
Q

What is the word for the formation of sperm?

A

Spermatogenesis

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4
Q

Primary spermatocytes undergo meiosis I, what do they produce?

A

Secondary spermatocytes (haploid, n)

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5
Q

Secondary spermatocytes undergo meiosis II, what do they produce?

A

Spermatids (haploid, n)

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6
Q

What is the result of spermatids being modified?

A

Four sperm cells (spermatoza), all haploid (n)

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7
Q

How many gametes does a female produce from meiosis?

A

One gamete

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8
Q

During what phase of meiosis are the primary oocytes stalled during fetal development?

A

Prophase I

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9
Q

When is the second polar body formed during meiosis?

A

After fertilization by a sperm cell

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10
Q

For females, what part of meiosis II is stalled?

A

Metaphase II

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11
Q

What happens after fertilization of egg by sperm cell?

A

The cell is now considered haploid and called an ovum but also contains the sperm’s chromosomes

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12
Q

What has more of the cytoplasm: the oocyte or polar bodies?

A

The oocyte

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13
Q

How do polar bodies degrade?

A

Apoptosis

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14
Q

What is the mature ovum?

A

The larger cell in meiosis II

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15
Q

What is a zygote?

A

Mature ovum fusing with mature sperm cell

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16
Q

What happens when the larger secondary primary oocyte undergoes meiosis II?

A

Produces 2 more cells from the non-polar body that are different sizes

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17
Q

Most of a women’s eggs are …

A

Primary oocytes

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18
Q

How are spermatocytes made?

A

Under the influence of testosterone, starting at puberty, and continuing through life

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19
Q

What things are formed from meiosis in males?

A

4 small equal-sized functional cells are formed

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20
Q

How much DNA does Sperm have?

A

Half of the DNA of a somatic cell

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21
Q

How big is the sperm’s head?

A

It’s about 5 micrometers

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22
Q

What are the 3 specialized functions for the sperm?

A
  1. Locating the egg
  2. Fusing with the surface of the egg
  3. Injecting the sperm nucleus (DNA) into the egg cell’s cytoplasm
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23
Q

When are all oocytes made?

A

They are made before birth

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24
Q

When is meiosis completed in females?

A

Once the egg is fertilized

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25
What is the result of one oocyte undergoing meiosis?
1 large egg & 3 other small cells (polar bodies)
26
How much DNA does an egg have?
Half the DNA of a normal body
27
What is an Egg's diameter?
140 micrometers or larger
28
How many mRNA does an egg have in its cytoplasmic storehouse of proteins
25,000-50,000
29
During the ovulation stage of the menstrual cycle where is the egg located?
The fallopian tube (oviduct)
30
What is the zygote intially surrounded by?
The Zona Pellucida
31
What is the function of the Zona pellucida?
A layer of glycoproteins that isolates the cytosol of the ovum
32
What are the 5 steps of Fertilization?
1. Modification of sperm (capicitation) 2. Recognition & binding of sperm by egg 3. Sperm-egg fusion 4. Fusion of sperm & egg pro-nuclei 5. Activation of the zygote
33
Explain Modification of sperm capacitation does
i) Increased membrane permeability ii) Influx of Ca2+ & loss of cell surface antigens iii) increased motility
34
Explain the recognition & binding of sperm by egg
Binds Zona pellucida to start an acrosomal reaction
35
Explain sperm-egg fusion
Sperm nucleus transferred into ovum
36
Explain Fusion of sperm & egg pro-nuclei
Chromatin decondenses & form new nuclear envelope -> diploid nucleus
37
Explain the activation of the zygote
Cortical reaction to prevent polyspermy
38
What does a cleavage result in?
Blastomeres that form a morula of 16 cells
39
What is a totipotent cell? | *is a blastomere
A cell that can form an entire, complete organism on its own.
40
What does blastulation result in?
Results in the formation of a fluid-filled blastocoel surrounded by blastomeres
41
When are blastocysts formed?
Day 5 following zygote formation
42
What does a blastocysts consist of?
Contains a fluid-filled cavity surrounded by a layer of cells called the trophoblast
43
What does the inner cell mass do?
Continues to develop into the embryo
44
When does the blastocyst reach the uterus and attach itself to the wall?
Day 8-9 following zygote formation
45
What is Chorion?
Two-layered structure formed from trophoblast
46
What are the two functions of Chorion?
i) Releases Human Chorionic Gonadotropin (hCG) hormone ii) Grows and forms villi that exchanges nutrients to form the placenta
47
What does hCG do?
It's a hormone that maintains uterine lining and stimulates endometrial cells to produce hormones
48
What is Gastrulation?
It begins after day 9 of zygote formation and involves formation of a recess: blastopore
49
What is a blastopore
The blastopore is the first opening that forms in an embryo. It becomes either the mouth or the anus.
50
What are the 3 layers formed from Gastrulation?
i) Outer layer = ectoderm ii) Mid layer = mesoderm iii) Inner layer = endoderm
51
What is Organogenesis?
When germ layers begin to develop into discrete organs during 4 to 8 weeks post fertilization
52
What is the first organ to fully develop?
The heart
53
What 4 things happens during the 1st month of the first trimester?
i) Implantation occurs ii) Basic body plan begins forming iii) Neural tube starts developing iv) Heart begins to form
54
What 4 things happens during the 2nd month of the first trimester?
i) Organogenesis ii) Limbs develop iii) Facial features start forming iv) Heart is beating
55
What 4 things happens during the 3rd month of the first trimester?
i) Is considered a fetus ii) Organs mostly formed and start functioning iii) External genitalia begin to differentiate iv) Movement begins but not felt
56
What 4 things during Second Trimester?
i) Increase in size and organ-system development ii) Bony parts of skeleton form iii) Heartbeat is heard with a stethoscope iv) Fetal movements begin
57
What 3 things happen during Third Trimester? | *final one
i) Rapid growth ii) Circulatory and respiratory systems mature iii) Birth which is a hormonally induced process happens at the end of trimester
58
What is Teratogen?
Any physical or chemical agent that brings about an aincrease in congenital malformations
59
What is Fetal alcohol syndrome? (FAS)
A Teratogen that is a constellation of birth defects caused by maternal alcohol consumption during pregnancy
60
What is bimodal sex?
Sex is mostly divided into male and female, but not perfectly—there is some variation in between.
61
When is chromosomal sex established?
At fertilization
62
What are the 4 levels of sex of an individual?
i) Chromosomal sex ii) Gonadal sex iii) Hormonal sex iv) Phenotypic sex
63
When do both male & female reproductive systems develop?
For the first 6-8 weeks
64
What is the SRY gene and what does it do?
The SRY gene (Sex-determining Region of the Y chromosome) is a gene on the Y chromosome (short arm) that triggers male development by initiating the formation of testes, which then produce hormones that lead to male physical characteristics.
65
What transcription factor does the SRY gene code for?
SRY protein or testis determining factor
66
What is Swyer syndrome?
Loss of SRY gene region
67
What are the 2 hormones of the testes?
Testosterone and Anti-Mullerian
68
Define testosterone
A steriod male sex hormone produced by the testis
69
Define Anti-Mullerian hormone
Hormone produced by developing testis that causes breakdown of Mullerian (female) ducts in the embryo
70
What does an embryonic gonad develop as?
An ovary
71
What happens in the absence of testosterone?
The Wolffian duct system degenerates
72
What happens in the absences of MIS?
The Mullerian duct system forms female reproductive system
73
What is the function of hormones called Androgens?
They are secreted by the testis to control later stages of male sexual differentiation such as: i) Testosterone ii) Dihydrotestosterone (DHT) iii) Androstenedione
74
What is Androgen Insensitivity Syndrome (AIS)?
Androgen Insensitivity Syndrome (AIS) is a genetic condition in which an individual with XY chromosomes cannot respond to androgens (male hormones), leading to female or partially female physical traits despite having testes.
75
What is pseudohermaphroditism?
A condition where a person has one biological sex (based on gonads) but looks like the other sex on the outside.
76
What is 46, XX Intersex?
A person with XX chromosomes who develops some male physical traits, usually due to extra male hormones.
77
What is 46, XY Intersex?
A person with XY chromosomes who develops female or mixed physical traits, usually because the body can’t respond to male hormones.
78
In sex-influenced and sex-limited inheritance, the sex of the individual affects...
Whether the trait is expressed and the degree to which the trait is expressed
79
How do sex hormone levels affect autosomal and sex-linked genes?
Sex hormone levels modify expression of these genes, giving rise to altered phenotypic ratios
80
What is pattern baldness?
Due to sex-influenced genes increase in Androgens / Androgen receptors
81
How does a balding scalp occur?
Increased concentration of testosterone via 5a-reductase increased production of DHT which leads to an increase of androgen receptors
82
What is the function of Finasteride?
Inhibits 5a-reductase
83
What is an example of loci that produce a phenotype in only one sex?
Precocious puberty in heterozygous males but not in heterozygous females
84
What is an example of a trait being expressed only in females because males die before reproductive age?
Male-lethal X-linked dominant traits, such a focal dermal hypoplasia
Human Genetics
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