ch 29: development and inheritence Flashcards
1
Q
what are the three periods (in order)
A
- gestation period
- prenatal period
- neonatal period
2
Q
when is the gestation period
A
fertilization to birth (38 weeks)
3
Q
what happens in the first week of development?
A
4
Q
what is sperm capacitation?
A
a series of functional changes.
Sperm need about 7 hours after ejaculation before its ready for fertilization
Occurs with the aid of secretions from the female reproductive tract
◦ Flagellum beats more rapidly
◦ Removal of cholesterol, proteins and glycoproteins from plasma membrane
near acrosome that prepare it for fusion with that of the oocyte
5
Q
define fertilization
A
= haploid sperm and secondary oocyte merge →
zygote with single diploid nucleus
6
Q
where and when does fertilization occur
A
Occurs in the uterine tube 12 to 24 hours post ovulation
◦ Oocyte viable in uterine tube for about 24 hours post-ovulation, sperm viable
for about 48 hours
7
Q
how many sperm enter the female and how do they get to where they need to go?
A
300 million sperm enter vagina at ejaculation → 2 million reach cervix → ~ 200
reach oocyte
* Sperm swims through vagina into cervical canal by whip-like movements of
flagella
* Muscle contractions of uterus and uterine tube keep sperm moving along
8
Q
what does a sperm need to do to fertilize the oocyte? how does this happen?
A
To fertilize an oocyte, a sperm must penetrate two layers around the oocyte:
The corona radiata and Zona pellucida
ZP3 is a glycoprotein in the zona pellucida
which acts as a sperm receptor
Upon binding to ZP3, sperm cells release
enzymes from acrosome, digesting a path
through the zona pellucida
9
Q
if multiple sperm reach the egg, why don[t more fuse with the oocyte?
A
Multiple sperm may bind to ZP3, but only the first sperm to make its way
through the entire barrier and reach the oocyte’s plasma membrane will fuse
with the oocyte
10
Q
what does the fusion of spem and oocyte cause
A
- Fast Block: Depolarization of the oocyte’s cell membrane
◦ Depolarized oocyte cannot fuse with another sperm
◦ Inactivates ZP3 molecules - Slow Block: Hardening of the zona pellucida
11
Q
Polyspermy is prevented by
a) depolarization of the oocyte
b) hardening of the zona pellucida
c) inactivation of ZP3
d) a and b
e) a, b and c
A
E
12
Q
describe fraternal twins
A
Fraternal twins (dizygotic)
◦ Independent release of 2 oocytes fertilized by 2 separate sperm
◦ Genetically as different as any 2 siblings
13
Q
describe identical twins
A
Identical twins (monozygotic)
◦ 2 individuals that develop from a single fertilized ovum
◦ Genetically identical (always the same sex)
◦ Separation of zygote must occur within 8 days post-fertilization
◦ If split before day 2, will develop separate placenta and separate amniotic sac
◦ If split between day 2 and 8, will share placenta but will have separate amniotic sacs
14
Q
events within the egg once the sperm enters
A
Sperm entry triggers oocyte to complete meiosis II
◦ It divides into a larger ovum and a polar body that
degenerates
Nucleus of sperm becomes male pronucleus
Nucleus of ovum becomes female pronucleus
Fusion of male and female haploid pronuclei produce
single diploid nucleus with 46 chromosomes
Fertilized ovum (2n) is called a zygote
15
Q
describe cleavage in a zygote
A
Rapid mitotic cell division of a zygote is called
cleavage
By day 4, has formed a solid ball of 32
blastomere cells called a morula
The morula is the same size as the original
zygote – blastomeres get smaller and smaller as
they divide
16
Q
A morula is a solid sphere of cells about the
size of the original zygote, and still
surrounded by the zona pellucida.
a) True
b) False
A
true
17
Q
development of the blastocyst
A
morula enters the uterine cavity by ~day 5
fluid enters morula, separates blastomeres
and forms the blastocyst cavity
a blastocyst is a ball of cells filled with fluid
◦ outer covering is the trophoblast – will
develop into the chorion
◦ embryoblast (inner cell mass) – will
develop into the embryo
18
Q
how and when does the blastocyst escape from the zona pellucida
A
After ~ 5 days, blastocyst escapes from zona pellucida by digesting a small hole
in it using an enzyme, and then squeezing through the hole
◦ Must do so in order to implant
19
Q
describe implantation
A
The attachment of a blastocyst to the endometrium
occurs ~6 days after fertilization and is called implantation
The embryoblast is oriented to face the endometrium
Cells of trophoblast also secrete human
chorionic gonadotropin (hCG), which
rescues corpus luteum from degeneration
Allows sustained secretion of estrogens
and progesterone, preventing
menstruation
20
Q
describe an ectopic pregnancy. Why can it happen? How to treat
A
development of an embryo outside of the uterine cavity
normally happens in the uterine tubes
◦ due to scarring caused by previous infection
◦ destruction of cilia (smoking)
◦ defect in peristalsis
◦ abnormal tubal anatomy
can also occur in ovaries, abdominal cavity or uterine cervix
unless removed, developing embryo will cause rupture of uterine tube and
death will follow because of hemorrhage
21
Q
All the following statements about a
blastocyst are true EXCEPT
a) Develops about 5 days after fertilization
b) Surrounded by the zona pellucida
c) Still about the size of the original zygote
d) Organized as embryoblast and trophoblast
A
B
22
Q
Identical twins:
a) Share a placenta
b) Do not share a placenta
c) Sometimes share a placenta
d) Can be opposite sexes
e) Are caused by multiple ovulation events
A
C
23
Q
describe the development of the trophoblast
A
Trophoblast cells in contact with
endometrium rapidly multiply and divide into
2 layers
Syncytiotrophoblast - outermost layer
secretes enzymes that allows blastocyst to
push through epithelial cells lining uterus
◦ Blastocyst burrows into endometrium
◦ Epithelial cells cover gap
24
Q
what is the endometrium called when zygot implants and what are the 3 parts?
A
Endometrium now called decidua and has 3 parts:
1. Decidua basalis is endometrial layer between
embryo and stratum basalis
◦ Provides glycogen & lipids
◦ Later becomes maternal portion of placenta
2. Decidua capsularis is thin layer between embryo
and uterine cavity
3. Decidua parietalis is remaining endometrium
lining uterine cavity
25
The trophoblast
a) becomes part of the chorion
b) secretes enzymes which help penetration of the uterine lining by
the blastocyst
c) secretes estrogen and progesterone
d) a and b
e) a, b and c
D
26
describe the development of the embryoblast
Inner mass cells differentiate about 8 days after
fertilization into 2 layers:
Hypoblast- layer of cuboidal cells
Primitive endoderm (lining of GI and resp. tract)
Epiblast - layer of columnar cells
Primitive ectoderm (epidermis and nervous
system)
Bilaminar embryonic disc cells of hypoblast and
epiblast form flat disc
Amniotic Cavity
◦ Small cavity appears within epiblast and eventually
will enlarge
27
what is the amnion? What are its functions and what is it made of?
Amnion - membrane which develops from the epiblast
Creates amniotic cavity filled with amniotic fluid, which eventually
surrounds the entire embryo
Functions of the amniotic fluid
◦ Absorbs shock , regulates body temperature, and prevents
adhesions with surrounding structures
Fluid is filtrate of mother’s blood + fetal urine
May be examined for embryonic cells (amniocentesis)
28
describe the umbilical vesicle and its functions
Still on day 8, cells from hypoblast migrate over inner surface of blastocyst wall
Flatten and form thin exocoelomic membrane
◦ This membrane and the hypoblast forms the wall of the umbilical vesicle
Functions:
1. During the 1st and 2nd week, the umbilical vesicle supplies nutrients to the embryo
(then the endometrium takes over)
2. Contains primordial germ cells that will migrate to developing gonads to become
spermatogonia or oogonia in 3rd week
3. Also, site of blood cell formation during 3rd to 6th weeks of life (then liver takes over)
4. Forms part of gut in 4th week
29
describe the development of the chorion
Extraembryonic mesoderm develops from umbilical vesicle and forms a layer of
CT that surrounds umbilical vesicle and amnion
Extraembryonic mesoderm together
with trophoblast will form chorion =
embryonic contribution to the placenta
The chorion surrounds the embryo/fetus
Secretes hCG and suppresses the
mother’s immune system
Bilaminar disc connected to trophoblast by band of extraembryonic mesoderm
called connecting stalk
◦ Will become umbilical cord
30
The bilaminar embryonic disc is formed
from the
a) Outer cell mass
b) Amnion
c) Embryoblast
d) Syncytiotrophoblast
C) embryoblast
31
The _________ supplies nutrients to the embryo
and is the source of blood cells during early
embryonic development.
a) trophoblast
b) hypoblast
c) epiblast
d) bilaminary embryonic disc
e) umbilical vesicle
E
32
describe the third week of development
During the third week, the three primary germ layers are established and lay
the groundwork for organ development in weeks 4-8
During the process of induction, one tissue (inducing tissue) stimulates the
development of an adjacent unspecialized tissue (responding tissue) into a
specialized one
33
during gastrulation the bilaminar disc will form 3 primary germ layers. What are they?
Bilaminar disc will form 3 primary germ layers:
1. Endoderm will become lining of G.I. tract, respiratory tract and other
organs
2. Mesoderm will become muscle, bone, connective tissue, peritoneum
3. Ectoderm will become skin epidermis, and nervous system
Endoderm and ectoderm are tightly packed epithelial cells
Mesoderm much looser connective tissue
34
describe gastrulation
Gastrulation involves the
rearrangement of cells from the
bilaminar disc
◦ Epiblast becomes ectoderm
◦ Hypoblast becomes endoderm
◦ In between is mesoderm (new, red)
~ Day 16, mesoderm cells migrate towards head
◦ Form hollow tube = notochordal process
~ Days 22-24, tube forms solid cylinder = notochord
Induction drives notochord to secrete substances that
induces nearby unspecialized mesoderm cells to start to
become vertebral bodies
◦ Notochord ends up as nucleus pulposus of
intervertebral discs
Small depressions at dorsal head
and tail form oropharyngeal
membrane & cloacal membrane
◦ 4th week oropharyngeal
membrane becomes oral cavity
◦ 7th week cloacal membrane
becomes openings for anus and
urinary/reprod. tracts
35
describe neruolation
Thickening of the ectoderm above mesoderm is called neural plate
Plate folds inward and forms a longitudinal neural groove
The raised edges of the neural plate are called neural folds
Neural folds increase in height and meet to form the neural tube
Neural tube cells will eventually
develop into brain and spinal cord
36
describe the development of somites
About day 17, mesoderm near the notochord & neural tube form paired
longitudinal columns
This mesoderm will break up into chain of cube-shaped blocks of tissue =
somites
Somites differentiate into:
◦ Myotomes – skeletal muscle of neck, trunk, limbs
◦ Dermatomes – dermis & connective tissue
◦ Sclerotomes – vertebrae
37
development of the cardiovascular system
can’t provide enough nutrients
◦ Development of new blood vessels = angiogenesis
Blood vessels and blood plasma begin to develop outside the embryo from
angioblasts
(precursors to blood cells and blood vessel cells) in the umbilical
vesicle, connecting stalk, and chorion = extraembryonic
Blood formation begins within the embryo at about the 5th week in the liver,
and the 12th week in the spleen, red bone marrow and thymus
Angioblasts aggregate to form isolated masses of cells
referred to as blood islands
◦ Angioblasts form the walls of the blood vessels
◦ Spaces in the blood islands form the lumen of blood
vessels
The heart develops from the mesoderm in the third
week.
By the end of the third week, the primitive heart begins
to beat
◦ Joins blood vessels in other parts of the embryo,
connective stalk, chorion and yolk sac to form a
primitive cardiovascular system
38
describe the development of the placenta
As embryonic tissue invades the uterine wall,
maternal uterine vessels are eroded
Forms spaces called lacunae that fill with
maternal blood
Chorionic villi develop as outgrowths of the
chorion that project into the endometrial wall
By the end of the third week, blood capillaries
develop in the chorionic villi
◦ These vessels connect to the embryonic
heart by the umbilical arteries and vein
The fetal blood capillaries within the chorionic villi project into the lacunae →
unite to form the intervillous spaces
◦ Bathe the chorionic villi with maternal blood
Maternal and fetal blood vessels do NOT join
Maternal and fetal blood does NOT mix
Oxygen, nutrients & wastes diffuse between the capillaries
39
describe placentation, chorionic villi, decidua basalis and the functions of the placenta
Placentation = process of forming the placenta (continues until 12th week)
Formed from two separate individuals
◦ The chorionic villi of the chorion form the fetal portion of the placenta
◦ The decidua basalis forms the maternal portion
Functions of the placenta:
1. Allows nutrient/waste exchange between mum and fetus
◦ Stores nutrients (e.g., carbohydrates, proteins, calcium, iron)
◦ Produces hormones needed to sustain pregnancy
2. Acts as barrier to most microorganisms (some viruses can cross - HIV,
rubella, polio…)
****Drugs, alcohol pass easily through****
40
describe the connection between placenta and embryo. What happens after birth to the placenta
connecting stalk)
◦ 2 umbilical arteries → carry deoxygenated fetal blood to placenta
◦ 1 umbilical vein → carries oxygenated blood into fetus
Afterbirth – placenta detaches from
uterus following birth
Umbilical cord is cut and area where
cord was attached becomes scar tissue
called umbilicus (naval)
41
The muscles, bones, other connective tissues,
and the peritoneum are all derived from the
a) Endoderm
b) Mesoderm
c) Ectoderm
d) Chorionic villi
B
42
The neural plate, neural folds, and neural
tube form through the process of
a) Gastrulation
b) Neurulation
c) Invagination
d) Induction
B
43
The placenta forms from the chorionic villi of
the mother and the decidua basalis of the
embryonic endoderm.
a) True
b) False
false
44
what happens during the fourth week of development?
During the 4th week, dramatic changes in shape and size happen
◦ Embryo almost triples in size
◦ Embryonic folding – process which involves taking a flat embryonic disc &
folding it into a 3-D cylinder
◦ Ectoderm (blue) on outside
◦ Endoderm (yellow) in center
◦ Mesoderm (red) in between
Embryo now has distinct superior/inferior, left/right, anterior/posterior
◦ Overall, series of folding causes embryo to curve into a C-shape
During remainder of 1st trimester → Organogenesis
◦ Formation of body organs and systems
45
describe organogenesis
Pharyngeal (branchial) arches develop during 4th week
◦ 5 pairs
◦ Found either side of head & neck
◦ Made of endoderm, mesoderm, ectoderm
◦ Within each are an artery, a cranial nerve, cartilage &
muscle tissue
◦ Become various head/neck structures
Otic placode (ectoderm) appears
◦ Future ear
Lens placode (ectoderm) appears
◦ Future eye
Upper and lower limb buds form
◦ Mesoderm covered by ectoderm
Heart prominence forms – distinct projection on ventral surface
Embryo still has a tail at end of 4th week
46
describe fourth through eigth weeks of development
During the fifth week there is rapid brain development and considerable head
growth.
During the sixth week the head grows larger in relation to the trunk, there is
substantial limb growth, the neck and trunk begin to straighten, and the heart
is now four-chambered
During the seventh week the various regions of the limbs become distinct and
the beginnings of digits appear
By the end of the eighth week, all regions of the limbs are apparent, the digits
are distinct, the eyelids come together, the tail disappears, and the external
genitals begin to differentiate
47
Limb buds develop as outgrowths of
mesoderm covered by ectoderm.
a) True
b) False
True
48
when does the fetal period begine?
begins at 9 weeks post-fertilization
49
describe fetus during fetal period
At 9 weeks, the fetus (5.5 cm) has human
characteristics
Has all organs and body parts with a disproportionate
head
Muscles and bone are forming
Limb buds are formed into arms and legs with fingers
and toes
Can now move, turn, make motions with mouth
Sex is evident and heartbeat can be detected
All structures developed in the embryonic period are
growing and differentiating
◦Very few structures appear during the fetal period
~6cm in length at 14 weeks
~19cm at 20 weeks, 1lb
Fetus is very active
By the end, eyes can open, and teeth are forming
50
describe the fetal period from 28 weeks to birth
Rapid growth, gain of strength
Changes in the circulatory and respiratory system to
prepare for air breathing
Maintains its own body temperature
Hardening of bone
Thickened muscles
Head changes proportions
~50cm and 2.7-4.5kg at birth
51
what are teratogens and what can they cause
Agent or influence that causes developmental defects in the embryo
Alcohol is the most common fetal teratogen.
◦ Fetal Alcohol Syndrome (FAS)= mental retardation, slow growth (b/f and a/f
birth), defective heart and other organs, malformed limbs, genital
abnormalities, CNS damage, hyperactivity, extreme nervousness, reduced
ability to concentrate, no sense of cause-and-effect relationship
Other teratogens
◦ LSD, cocaine, cigarette, certain viruses, pesticides, industrial chemicals, some
hormones, antibiotics, some anticoagulants, anticonvulsants, antitumor
agents, thyroid drugs and many other prescription drugs.
52
estrogen and progesterone during pregnancy
Produced by corpus luteum in first 3-4 months of pregnancy to maintain the
lining of the uterus and prepare mammary glands
◦ From 3rd-4th month through the remainder of pregnancy, placenta provides
higher levels of estrogens and progesterone – corpus luteum no longer required.
53
describe hCG hormone during pregnancy
Secreted by the chorion (which becomes placenta)
◦ Stimulates continued production of estrogens and progesterone by the corpus
luteum - necessary for the continued attachment of the embryo / fetus to the
lining of the uterus
◦ Can be detected in blood and urine 8 days after fertilization, peaks at week 9,
decreases in 4th-5th month and levels off until birth
54
hormones secreted by the placenta
Progesterone & Estrogen by 4th month
Relaxin (first by corpus luteum, then by placenta until birth)
◦ increases flexibility of pubic symphysis and ligaments around pelvis (sacroiliac and
sacrococcygeal joints)
◦ helps dilate uterine cervix during labour
Human placental lactogen (hPL)
◦ Helps prepare mammary glands for lactation
◦ Decreases glucose use from mother so that more glucose is available for fetus
(mother uses fatty acids for ATP)
Corticotropin-releasing hormone (CRH)
◦ establishes timing of birth (high levels=premature, low levels = after due date)
◦ Increases secretion of cortisol which is important for lung development and
surfactant production
55
what happens to the uterus during pregnancy
The uterus continuously enlarges,
filling first the pelvic and then the
abdominal cavity, displacing and
compressing several structures
56
physical changes during pregnancy
Weight gain; increased protein, fat, and mineral storage; marked breast
enlargement; and lower back pain.
*Increase in stroke volume by approximately 30%, rise in cardiac output by
approximately 20-30%
*Increase in heart rate by 10-15%, and increase in blood volume up to 30-50%
(mostly during the latter half of pregnancy
57
where is all the extra weigh from pregnancy coming from
Baby—~8 pounds (4 Kg)
Placenta—2-3 pounds (1 Kg)
Amniotic fluid—2-3 pounds (1 Kg)
Breast tissue—2-3 pounds (1 Kg)
Blood supply—4 pounds (2 Kg)
Stored fat for delivery and breastfeeding—5-9 pounds (4 Kg)
Larger uterus—2-5 pounds (1 Kg)
Total—25-35 pounds (~ 14 Kg)
These numbers are the normal average figures
58
changes in things to do with breathing
Increased tidal volume (30-40%)
*Decreased expiratory reserve volume (by up to 40%)
*Increased minute volume of respiration (by up to 50%), decreased airway
resistance in the bronchial tree (by up to 36%)
*Increase in total body oxygen consumption (by 10-20%).
59
changes in digestive system
*GI tract compressed causing heartburn & constipation
Decreased motility can result in constipation and delayed gastric emptying.
Nausea, vomiting, and heartburn also occur.
*Increase in appetite
*Pressure on bladder causing changes in frequency & urgency
*Glomerular filtration rate rises up to 40%.
*Compression of vena cava causing varicose veins & edema in the legs
60
During pregnancy, the placenta secretes human
chorionic gonadotropin (hCG), which suppresses
estrogen and progesterone production
a) True
b) False
false
61
Progesterone is required during pregnancy to
a) stimulate the corpus luteum
b) ensure relaxation of the uterine myometrium
c) increase the flexibility of the pubic symphysis
d) decrease glucose usage by the mother while making it more
available to the fetus
e) help establish the timing of labor and delivery
B
62
A chang occurring in a pregnant woman
that is indicative of a potential disorder is
a) increased metabolic rate.
b) 30% to 40% increase in cardiac output.
c) increased oxygen consumption.
d) increased urinary protein
D
63
Varicose veins may occur during pregnancy
because of the
a) hormonal changes experienced during pregnancy.
b) decreased venous return due to compression of the inferior vena
cava.
c) increased blood volume required by the mother.
d) increased cardiac output by the mother.
e) inability to exercise normally during pregnancy.
B
64
The shift of blood flow from the uterus to the
muscles and skin during exercise may result in an
inadequate blood supply to the placenta.
a) True
b) False
False
65
describe labor
A decrease in progesterone levels and elevated levels of estrogens,
prostaglandins, oxytocin, and relaxin are all involved in the initiation and
progression of labor.
Progesterone inhibits uterine contractions
◦ levels must therefore drop
A rise in estrogens overcomes this inhibition
66
dilation stage of labor
* 6 to 12 hours
* Regular contractions of the uterus
* Rupture of amniotic sac
* Complete dilation of cervix (10cm)
67
expulsion stage of labor
From complete cervical dilation
to delivery of baby
* 10 minutes to several hours
* Baby moves through birth canal
68
placental stage of labor
After delivery until placenta is expelled
* 5-30 minutes
* Afterbirth is expelled by uterine
contractions
* Forceful contractions constrict blood
vessels that were torn, reducing the
possibility of hemorrhage
69
For labor to begin…
a) oxytocin must be released
b) estrogen levels must rise
c) the effects of progesterone must be inhibited
d) A and B are correct
e) A, B, and C are correct
E
70
puerperium
After delivery of the baby and placenta, there is a period called the puerperium:
◦ lasts about six weeks after delivery
◦ reproductive organs and maternal physiology return to the prepregnancy
state
◦ uterus undergoes involution (reduction in size)
◦ uterine discharge (lochia) of blood and serous fluid for two to four weeks
after delivery
71
adjustments of respiratory system of infant at birth
*After cord is cut, increased CO2 levels in blood
*Respiratory center in the medulla oblongata is stimulated
*Causes contractions of muscles of inhalation (diaphragm & external intercostal
muscles) → first breath
*Breathing rate begins at 45/minute for the first 2 weeks & declines to reach
normal rate (~12 breaths/minute)
72
adjustments of cardiovascular system at infant birth
Foramen ovale closes at moment of birth
◦ diverts deoxygenated blood to the lungs for the first time
Ductus arteriosus & umbilical vein close by muscle contractions & become
ligaments (within 3 months)
At birth, pulse is high (120-180 beats/min) due to low levels of RBC
◦ after birth, O2 demand increases, which stimulates erythropoiesis
◦ after RBC count is higher, pulse goes down
73
physiology of lactation
Prolactin, from anterior pituitary, increases during pregnancy; for secretion of milk
◦ progesterone inhibits effect of prolactin until delivery
◦ just before delivery, progesterone levels drop
Suckling activates stretch receptors which send nerve impulses to hypothalamus –
stops release of prolactin-inhibiting hormone (PIH), and stimulates secretion of
prolactin-releasing hormone (PRH)
If suckling stops, milk secretion stops
Oxytocin causes ejection of milk from mammary ducts
Stimulated by touch receptors on nipples (impulse sent to hypothalamus)
74
physiology of lactation during late pregnancy and first few days after birth
During late pregnancy and the first few days after birth, the mammary glands
secrete a cloudy fluid called colostrum.
◦ not as nutritious as true milk (less lactose and no fat) but serves adequately
until the appearance of true milk on about the fourth postpartum day.
Colostrum and maternal milk contain antibodies and immune cells that protect
the infant during the first few months of life.
Breast milk contains several molecules (antibodies, antimicrobial agents,
proteins, essential fatty acids) beneficial to the child, either immediately or later
in life.
75
The hormone released from the posterior
pituitary during the milk ejection reflex is
a) Gonadotropin
b)Prolactin
c) Vasopressin
d)Oxytocin
D
76
Which hormone is the most important for
establishing the timing of birth?
a) Estrogen
b) DHEA
c) Progesterone
d) ACTH
e) CRH
E
77
true or false within the human population we all have the same genes
True
78
what are alleles
Each gene can come in different “versions”, called alleles
◦ A gene can have many different alleles within the human population
However, no matter how many alleles a gene can have, every individual will
only carry a maximum of two alleles of a given gene
That’s because we are diploid = 2 sets of chromosomes
79
genotype vs phenotype
The set of alleles a person carries is known as their “genotype”
◦ “Homozygous” = 2 identical alleles
◦ “Heterozygous” = 2 different alleles
◦ Note: an individual cannot simply be a homozygote or a heterozygote. An
individual is homozygous or heterozygous at a specific “locus” (or for a
specific gene)
The visible traits created by the genotype are known as that person’s
“phenotype”
80
Assuming that this karyotype is from my cells:
which of the following is TRUE regarding the
location of the gene P53?
a) P53 is found at that location in my cells only
b) P53 is found at that location in my cells, as
well as in the cells of some people in this
room
c) P53 is found at that location in my cells, as
well as in the cells of most people in this
room
d) P53 is found at that location in everybody’s cells
d
81
Which of the following is NOT correct?
a)
b)
c)
d)
a gene can only have 2 different alleles
a gene can only have 2 different alleles in a single individual
an individual is heterozygous for most genes
a person’s entire genome cannot be homozygous
A
82
The BRCA1 gene is found only in some
individuals with breast cancer
a) TRUE
b) FALSE
B, mutation causes cancer
83
dominant vs recessive gene
When a defective allele is dominant, only
one defective allele is necessary for the
disease to show
When a defective allele is recessive, both
alleles must be defective for the disease to
show up in an individual
84
A person who is heterozygous for a recessive
gene will
a) show the recessive phenotype.
b) possibly have a child who shows the recessive phenotype.
c) have two identical alleles.
d) A and B
e) A, B and C
B
85
For an autosomal dominant disease
a)
b)
c)
d)
e)
a homozygous genotype (aa) shows as an affected phenotype
a homozygous genotype (aa) shows as a normal phenotype
a heterozygous genotype (Aa) shows as an affected phenotype
a and c
b and c
C
86
In general, a XX zygote develops as female, and a XY
zygote develops as male.
What do you think determines the “male sex”?
a)
b)
The absence of multiple X chromosomes = male
Presence of the Y chromosome = male
B
87
screening and prenatal diagnosis
Quad screen is performed at 15-20 weeks' gestation
◦ maternal blood is tested for abnormal levels
◦ AFP (alpha-fetoprotein) produced by fetus
◦ hCG (human chorionic gonadotropin) produced by placenta
◦ estriol produced by fetus and placenta
◦ inhibin-A produced by placenta and ovaries
abnormal levels may indicate neural tube defects, trisomy 21, trisomy 18 or
other types of chromosomal abnormality
88
amniocentesis
Usually done at 14-16 weeks to detect suspected
genetic abnormalities
Fetal cells from amniotic fluid are examined for
genetic defects
takes about 2 weeks to get results
* Needle through abdominal wall and uterus
* Chance of spontaneous abortion is 0.25-0.5%
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Chorionic Villi Sampling
Withdrawal of chorionic villi for
chromosomal analysis.
◦ can be done earlier than amniocentesis
(at 8-10 weeks)
◦ results are available more quickly
* Placental tissue removed by suction through cervix
(transvaginal) or with needle through abdomen
* Chance of spontaneous abortion is 1-2%
90
Non-invasive prenatal test (NIPT)
Screening method where blood sample
is collected from the mom and cfDNA
(fetus DNA) is amplified for the
detection of chromosomal aneuploids
and microdeletions
NIPT cannot
:
*detect aneuploidy other than chromosomes 13, 18, 21, X and Y
◦ some companies are now adding screening for other trisomies and certain
microdeletion syndromes
*detect single gene conditions
*detect congenital anomalies
*completely rule out aneuploidy
91
Genetic disorders in a fetus can be detected
through
a) Amniocentesis
b) Chorionic villi sampling
c) Ultrasonography
d) A and B
e) A, B and C
E
