sex and reproduction 2 Flashcards
1
Q
what do sex hormones affect
A
growth, development, reproductive cycles and sexual behaviour
2
Q
what are the sources of sex hormones
A
gonads and the adrenal glands
3
Q
what are the 3 types of steroid hormone secreted by the gonads
A
androgens, oestrogen and progesterone
4
Q
what is the most important oestrogen in the female reproductive system
A
oestradiol
5
Q
what is progesterone involved in
A
preparation and maintenance of tissues of the uterus required for the support and growth of an embryo
6
Q
what is synthesis of gonadal hormones usually controlled by
A
two gonadotropins from the anterior pituitary - FSH and LH
7
Q
what is gonadotropin secretion controlled by
A
secretion of GnRH from the hypothalamus
8
Q
what is AMH
A
it is released from the testes along with testosterone and promotes the degeneration of female ducts
9
Q
what is the bipotential gonad
A
it either forms testes or ovaries - it is the structure present in the embryo before sexual development occurs
10
Q
what is DES
A
synthetic oestrogen prescribed to women at risk of pregnancy complications
it can alter the reproductive system of the fetus and is now recognised as an endocrine disrupter (a foreign molecule that interrupts the normal function of a hormone pathway)
11
Q
what happens in asexual reproduction of aspen trees
A
all trees in a groove have developed from the roots of one founder tree - the grove is a somatic clone
12
Q
what describes the sexual rituals of lizard mating even though parthenogenesis is occurring
A
pseudo mating
13
Q
how doo bananas breed
A
asexually - they are all clones of the buds forming from the main plant - similar to aspen trees
14
Q
what is fertilization
A
the fusion of gametes to form a zygote
15
Q
what would happen if polyspermy were too occur
A
the entry of multiple sperm cells into the egg nuclei - the resulting abnormal number of chromosomes would be lethal to the embryo
16
Q
what is an acrosomal reaction
A
the discharge of hydrolytic enzymes from the acrosome, a vesicle at the tip of the sperm, when the sperm approaches or contacts an egg
17
Q
what is an acrosome
A
a vesicle at the tip of a sperm that contains hydrolytic enzymes and other proteins that help the sperm reach the egg
18
Q
what do the hydrolytic enzymes of the acrosome of a sperm do during the acrosomal reaction
A
they partially digest the jelly coat of the egg enabling a sperm structure called the acrosomal process to form elongate and penetrate the coat
19
Q
what do the protein molecules on the tip of the acrosomal process do
A
they bind to specific receptor proteins in the egg plasma membrane
20
Q
what happens after the sperm has bound to the receptor proteins on the egg in the acrosomal reaction
A
the sperm nucleus enters the egg cytoplasm as ion channels open in the eggs plasma membrane.
sodium ions diffuse into the egg causing depolarization which acts as a fast block to polyspermy
21
Q
how is the slow block to polyspermy established
A
- once the sperm binds to the egg, vesicles called cortical granules fuse with the egg plasma membrane
- the contents of the cortical granules are released into the space between the egg plasma membrane and the surrounding vitelline layer
- enzymes and other granule contents then trigger a cortical reaction which lifts the vitelline layer away from the egg and hardens the layer to protect the fertilization envelope that has just been formed
22
Q
what are the steps in the acrosomal reaction and the cortical reaction
A
- contact - the sperm contacts the eggs jelly coat
- acrosomal reaction - hydrolytic enzymes are released from the acrosome making a hole in the jelly coat. the acrosomal process protrudes from the sperm head, penetrates the jelly coat and binds to receptors in the egg plasma membrane
- contact and fusion of sperm and egg membranes - fusion triggers depolarization of the membrane which acts as a fast block to polyspermy
- cortical reaction - cortical granules fuse with the plasma membrane. the secreted contents clip off sperm binding receptors and cause the fertilization envelope to form. this acts as a slow block to polyspermy
- entry of the sperm nucleus
23
Q
what does formation of the fertilization envelope require
A
high concentrations of calcium ions in the egg
24
Q
what signal transduction pathway is activated when the sperm binds to the egg
A
- a signal transduction pathway that triggers the release of calcium ions into the cytosol from the ER
- the resulting increase in calcium ion concentration causes the cortical granules to fuse with the plasma membrane
25
fertilization initiates and speeds up the metabolic reactions that bring about the onset of ……………...
embryonic development
26
what causes egg activation
the rise in calcium ion concentration
27
artificial fertilization is possible even if the nucleus has been removed from the egg - what does this suggest
the proteins and mRNAs required for activation are already present in the cytoplasm of an unfertilised egg
28
what marks the end of the fertilization stage
it is complete once the egg and sperm nuclei have fused and the first cell division has taken place
29
what is a key difference between sea urchin and human fertilization
sea urchins eggs have already completed meiosis once they are released from the female whereas human eggs are arrested at metaphase II until a sperm binds
30
terrestrial animals fertilise their eggs internally/externally
internally
31
in mammals what surrounds the egg before and after ovulation
a layer of follicle cells - support cells
32
in mammals what is the zona pellucida
the extracellular matrix of the egg
33
where on the egg does the binding of sperm result in initiation of the acrosomal reaction
the sperm receptor
34
what does sperm binding to the egg trigger
the cortical reaction
35
In mammals what happens in the cortical reaction
- sperm binding triggers the release of enzymes from the cortical granules to the outside of the cell
- the enzymes catalyse changes in the zona pellucida which acts as the slow block to polyspermy
36
do mammals have a fast block to polyspermy like sea urchins
no - they only have the slow block that results from the cortical reactions
37
what is the next stage of development after fertilization
cleavage
38
the nucleus in a newly fertilised egg has too little DNA to synthesis enough …………… to meets the cells need for new proteins
mRNA
39
initial development is carried out by proteins and mRNA deposited in the egg during which process
oogenesis
40
what is cleavage
a series or rapid cells divisions during early development
41
during cleavage the cell cycle consists mainly of which 2 steps
M (mitosis) and S (DNA synthesis)
| the G1 and G2 phases are skipped and little or no protein synthesis occurs
42
what is the result of little or no protein synthesis occurring in cleavage
the cell doesn't increase in mass
43
what is the result of cleavage
it partitions the cytoplasm of the large fertilised egg into many smaller blastomeres
44
what is the need for blastomeres
because they are smaller the DNA is able to produce enough RNA to make the proteins the cell requires for programming further development
45
what do the first 5-7 cleavage divisions produce
hollow balls of cells (blastula) surrounding a fluid filled cavity called the blastocoel
46
what are the 4 steps of cleavage in sea urchins
1. fertilized egg - zygote surrounded by the fertilization envelope
2. four cell stage - cells have completed the second cleavage division
3. early blastula - after further cleavage divisions the embryo is a multicellular ball that is still surrounded by the fertilisation envelope. the blastocoel has begun to form in the centre of the cells
4. later blastula - a single layer of cells surround a large blastocoel and the fertilisation envelope is still present
47
in the eggs of frogs and many other animals, stored nutrients called ………….. are concentrated to one pole called the ……….. pole and away from the ………. pole
yolk
vegetal pole
animal pole
48
what results from the asymmetrical distribution of yolk in the eggs of frogs
it give the animal and vegetal hemispheres different colours and influences the pattern of cleavage divisions
49
when an animal cell divides an indentation called a …….…….……………. forms in the cell surface as cytokinesis divides the cell in half
cleavage furrow - forms a small groove in line with the old metaphase plate and on the cytoplasmic side contains a contractile ring of actin and myosin that interact to pinch the cell in 2
50
in the frog embryo where do the fist cleavage furrows form
parallel to the line connecting the 2 poles
51
what happens as a result of the yolk having slow cytokinesis
the fist cleavage furrow is still dividing the yolky cytoplasm in the vegetal hemisphere when the second cell division begins
52
what is the result of the first two cleavage divisions
four blastomeres of equal size extend from the animal pole to the vegetal pole
53
what happens during the third cleavage division in frog embryos
- the yolk begins to affect the relative size of the cells produced in the 2 hemispheres
- as each of the 4 blastomeres begin the division, yolk near the vegetal pole displaces the mitotic apparatus and the cleavage furrow from the egg equator towards the animal pole
- the result of this is smaller blastomeres in the animal hemisphere than the vegetal hemisphere
- the division is equatorial - perp. to the line connecting the poles - and produces an 8 cell embryo
54
what causes the blastocoel to form entirely in the animal hemisphere
the displacing effect of the egg yolk on the mitotic apparatus and the cleavage furrow persists in subsequent divisions after the third division of cleavage
55
cleavage in amphibian development is said to be holoblastic, what does this mean
complete - the cleavage furrow still passes right through the egg even though the yolk affects where it divides it
56
describe the cleavage in animals whose eggs contain little yolk e.g. humans
it is holoblastic
the blastocoel forms centrally
the blastomeres are generally of similar size
57
give examples of animals whose volume of yolk is so large that the cleavage furrow cannot pass through it
birds, reptiles, many fish and insects
58
what happens if the volume of yolk is so great that the cleavage furrow cannot pass through it
only the region of the egg lacking yolk undergoes cleavage - this is called meroblastic cleavage
59
for chickens the part of the egg that we call the yolk is not actually the yolk, what is it
the entire egg cell
60
in early development of drosophila, multiple rounds of replication occur without cytokinesis - what does this account for
no cell membranes form around the early nuclei
the nuclei spread throughout the yolk and later migrate to the outer edge of the embryo
after further mitosis the plasma membrane forms around each nucleus
the embryo is now the equivalent of a blastula
61
what occurs over the last 2 stages of embryonic development
morphogenesis
62
what are the last 2 stages of embryonic development
gastrulation and organogenesis
63
what are the stages of embryonic development in order
fertilization
cleavage
gastrulation
organogenesis
64
give an overview of gastrulation
sets of cells at or near the surface of the blastula move to an interior location, cell layers are established and a primitive digestive tube is formed
65
give an overview of organogenesis
the formation of organs
66
gastrulation id the dynamic reorganisation of the hollow blastula into a 2 or 3 layered embryo called a …….…..
gastrula
67
only the embryos of animals …………...
gastrulate
68
what are the cell layer produced in gastrulation called collectively
germ layers
69
in the gastrula, …………….. forms the outer layer and …….…….…. forms the lining of the digestive tract
ectoderm - outer
| endoderm - inner
70
what are diploblasts
animals that only form ectoderm and endoderm layers in gastrulation - occurs in radially symmetric animals
71
what are tripoblasts
a third germ layer is formed between the ectoderm and endoderm in gastrulation - occurs in bilaterally symmetric animals
72
what does gastrulation typically begin with
invagination
73
what is invagination
the infolding of a sheet of cells
74
describe invagination
1. at the end of cleavage single cells cover the surface of the blastula
2. a group of cell buckle into the blastocoel forming a shallow depression
3. continued invagination forms a blind ended tube, the archenteron
4. the open end of the archenteron is called the blastopore
5. the tip of the archenteron reaches the embryo surface completing formation of the primitive gut of the embryo, now a gastrula
75
at the end of embryogenesis each germ layer gives rise to what
specific tissues and organs
76
what are the major derivatives of the ectoderm (outer layer)
- epidermis of the skin and its derivatives
- nervous and secretory systems
- pituitary gland and adrenal medulla
- jaws and teeth
77
what are the major derivatives of the mesoderm (middle layer)
- skeletal and muscular systems
- circulatory and lymphatic systems
- excretory and reproductive systems (except germ cells)
- dermis of the skin
- adrenal cortex
78
what are the major derivatives of the endoderm (inner layer)
- epithelial lining of the digestive tract and associated organs
- epithelial lining of the respiratory, excretory and reproductive tracts and ducts
- thymus, thyroid and parathyroid glands
79
when does embryo development begin in humans
when the embryo makes its way down the oviduct to the uterus
80
what are the 4 steps of embryonic development gastrulation in humans (detailed)
1. at the end of cleavage the embryo is called a blastocyst (mammalian name for blastula). at one end of the blastocyst is the inner cells mass which will develop into the embryo proper
2. implantation of the embryo is initiated by the trophoblast (the outer epithelium of the blastocyst). enzymes secreted by the trophoblast breakdown the endometrium allowing invasion by the blastocyst. the trophoblast also extends finger like projections that cause capillaries in the endometrium to spill out blood so it can be captured by the trophoblast tissues. during implantation the inner cells mass forms a flat disc with an inner layer of cells (epiblast) and an outer layer (hypoblast)
3. as implantation is completed, gastrulation begins. some epiblast cells remain as ectoderm on the surface while others move inwards through a primitive streak and form the mesoderm and endoderm. after implantation, the trophoblast continues to expand into the endometrium and 4 new membranes appear (extraembryonic membranes). the membranes arise from the embryo but they enclose structures located outside the embryo
4. by the end of gastrulation the embryonic germ layers have formed. extraembryonic mesoderm and extraembryonic membranes now surround the embryo. cells of the trophoblast, epiblast and endometrial tissue all contribute to the formation of the placenta
81
what part of the blastocyst is the source for the embryonic cell lines
the inner cell mass
82
the human embryo develops almost entirely from epiblast/hypoblast cells
epiblast
83
what are the four stages of embryonic development and gastrulation in humans (short)
1. blastocyst reaches uterus
2. blastocyst implants
3. extraembryonic membranes start to form and gastrulation begins
4. gastrulation has produced a 3 layered embryo with 4 extraembryonic membranes: amnion, chorion, yolk sac, allantois
84
what is the basic process of organogenesis
regions of the 3 embryonic germ layers develop into the rudiments of organs
85
what is neurulation
the early steps in the formation of the brain and spinal chord in vertebrates
86
what does cell migration in embryonic development involve
the cytoskeleton and the extracellular matrix
87
what can happen in metamorphosis from larval to adult form
programmed cell death (apoptosis) of structures no longer required
88
what defines a cells development fate
where it resides, how it appears and what it does
89
what is meant by determination
the process by which a cell or group of cells becomes committed to a particular fate
90
what is meant by differentiation
the specialization in structure and function
91
every diploid cell formed during development has the same genome except from which cells
mature immune cells
92
how do cells have different fates if they all have the same genome
they undergo gene expression so that only the genes required for their specialised functions are expressed
93
what are fate maps
diagrams showing structures arising from each region of an embryo
94
describe bilateral symmetry
body plan exhibits symmetry along the dorsal-ventral and anterior-posterior axes
95
in the frog when is the position of the anterior-posterior axes determined
during oogenesis
96
why is asymmetry apparent in the frog egg
because it forms 2 distinct hemispheres: dark melanin granules are embedded in the cortex of the animal pole, whereas the yolk fills the vegetal hemisphere
97
the animal-vegetal asymmetry dictates where …………………. axis forms in the embryo
anterior-posterior
98
how is the dorsal-ventral axes of the frog embryo determined
at random - wherever the sperm enters in the animal hemisphere determines where the dorsal-ventral axis forms
99
what is a cortex
the outer layer
100
what are the steps in axis establishment in an amphibian
1. the polarity of the egg determines the anterior-posterior axis before fertilization (animal-vegetal poles)
2. after fertilization, the pigmented cortex slides over the underlying cytoplasm towards the point of sperm nucleus entry. this rotation exposes a region of lighter-coloured cytoplasm, the gray crescent which is a marker of the future dorsal side
3. the first cleavage division bisects the gray crescent. once anterior-posterior and dorsal-ventral axes are defined so is the left-right axis
101
once the 16 cell stage is reached, mammalian cells are determined to form the ………….or the inner cell mass
trophoblast
102
how do twins result
when cells or groups of cells from a single embryo become separated
103
in general the tissue specific fates of cells are fixed in the late …………...
gastrula
104
as embryonic development continues cells influence each others fate by …………….
induction
105
inductive signals play a major role in ………………...
pattern formation
106
what is pattern formation
a process governing the arrangement of organs and tissues in their characteristic places in 3D space
107
what are the molecular cues that control pattern formation called
positional information - these tell a cell where it is with respect to the body axes
108
what do vertebrate limbs begin as
limb buds - bumps of mesodermal tissue covered by a layer of ectoderm
109
how do non motile cilia function in development
they act as antenna on the cell surface receiving signals from proteins. the cilia are responsive to particular signals. when cilia are defective, signalling is disrupted
110
how do axis formation and pattern formation differ
axis formation establishes the location and polarity of the 3 axes that provide the coordinates for development
pattern formation positions particular tissues and organs in 3D space defined by the coordinates from axis formation
111
there is never more than one ………… in one genus
asexual species
112
how can aspen reproduce
sexually and asexually
asexually - trees develop from the root system of a founder tree - slow mutation rate
sexual - variation produced
113
how do dandelions reproduce
they are obligate asexual reproducers by apomixis
| - diploid ovules become seeds and they are disseminated in the wind
114
in parthenogenic lizards how are eggs produced
by mitosis
115
what is the relative hormone concentrations of the lizard on top in pseudo sex
low level of oestradiol
high levels of progesterone
small ovary
116
what is the relative hormone concentrations of the lizard on the bottom in pseudo sex
high oestradiol
low progesterone
increase in ovary size --> ovulation
117
giving up sex is an evolutionary …………..
dead end
118
explain how bananas being genetic clones was disadvantageous
when panama disease came about it was able to infect a banana host and so it was able to infect every gros michel banana because they are identical
a new strain evolved and was then able to exploit cavendish bananas too
if a virulent pathogen arises that can affect one host of a single genotype species then it can affect them all
119
which race of the panama disease is cavendish resistant to
race 1
| but is sensitive to race 4
120
is different virulence of a pathogen in one species common
yes - but only if they reproduce sexually to introduce variation
with asexual reproduction the genotypes are the same without mutations so pathogens have similar virulence in each species
121
what is the red queen hypothesis
when the evolution of the host drives the evolution of the pathogen - coevolution
continual evolution is required to maintain relative fitness compared to the other evolving system
122
..……….. in host species reduces the likelihood of a pathogen wiping out an entire population
genetic diversity
123
give examples of red queen arm races
predator/prey
| host/pathogen
124
explain how sexual selection can be an evolutionary arms race
sexual preference in one gender drives the physical or behavioural functions in the other gender
e.g. peacock tail - why they are always perfect
125
is a male human heterogametic or homogametic
heterogametic - 2 sex chromosomes
126
why in XXY does Y still promote maleness
because the Y chromosome has the SRY gene which is dominant
127
how do XX males occur
if a region of Y translocates onto X
128
how do XY females arise
by rare Y chromosome deletions
129
which sex is the default sex
female
130
what does SRY control
the mammalian switch that controls mammalian sex determination
131
how does SRY work
it triggers a regulatory cascade of other genes and their encoded proteins
- the SRY gene encodes a protein that is a transcription factor
- transcription factors regulate gene expression by binding to specific DNA sequences adjacent to genes
132
what is the indifferent gonad
the bipotent gonad
A gonad in an embryo that has not differentiated into a definitive testis or ovary. An indifferent gonad becomes a testis if the embryo has a Y chromosome, but if the embryo has no Y chromosome, the indifferent gonad becomes an ovary.
133
for the first 6 weeks of gestation in humans what is important to notice
sex development has not begun - at this point all embryos express the same genes
134
what does the indifferent gonad develop from
the genital ridge
135
which two types of cells do the gonads contain
germ cells and somatic cells
136
where do the somatic cells develop
in the genital ridge
137
where do the germ cells migrate from
they migrate from the hind gut to the genital ridge
138
what do the indifferent gonads develop into
the testes or the ovaries
139
in XX embryo what do the Mullerian ducts differentiate into
the oviduct
140
in an XX female what happens to the Wolffian duct
it degenerates
141
what happens to the Wolffian and Mullerian ducts in the XY embryo
each Wolffian duct differentiates to form and epididymis, vas deferens and seminal vesicle and the Mullerian ducts degenerate
142
what are the structures found in the indifferent gonad
- mesonephros - embryonic kidney (distinct from adult kidney) - contributes ducts to the males and female reproductive organs
- metanephric - kidney - persists as an adult
- ureter - persists in adults
gonads
- gonads
- Wolffian duct
- Mullerian ducts
143
what happens to the cloaca in the indifferent gonad
it becomes 2 openings: urethral and anal
| it later becomes 3 in females - vaginal
144
how does the indifferent gonad develop into a penis
genital swellings fuse together - to form the penis
145
how does the indifferent gonad develop into the female reproductive organs
the genital swellings stay separate forming the labia majus and the glans become the clitoris
146
what are the 4 transcription factors central to mammalian sex determine
SF1 - expressed in somatic gonadal precursor genital ridge cells. it is required for proper gonad development in males and females
SRY - making the sex decision
SOX9 - needed in males for the full male phenotype
DMRT - needed in females for the full male phenotype
147
describe the path of sex development form the indifferent gonad
- SF1 expressed in the indifferent gonad
- DMRT on NO SRY - pre-female
- DMRT stays on
- ovary and female
- SF1 expressed in the indifferent gonad
- DMRT on SRY on pre-male
- DMRT off SOX9 on
- male and teste
(DMRT is only transiently expressed and is turned off by the presence of SRY)
(SRY turns on SOX9)
148
describe the path in the production of testosterone
1. MALES: SRY expressed in somatic gonadal precursor cells of genital ridge, SOX9 activated & DMRT off, cells differentiate into Sertoli cells.
2. Sertoli cells secrete Anti-Mullerian Hormone (AMH).
3. AMH promotes Leydig cell differentiation in gonad.
4. Leydig cells produce testosterone.
5. Testosterone promotes the male phenotype
149
why can men continue to produce sperm throughout their life
because the spermatogonium continually divides
150
what are the basic steps in the ovarian cycle
1. primary oocyte within follicle
2. growing follicle
3. mature follicle
4. ruptured follicle
5. ovulated secondary oocyte
7. corpus luteum formation
8. corpus luteum degenerates
151
what is the oocyte surrounded by
follicle cells
152
which hormone increases with follicle cell growth
oestradiol
153
what happens in ovulation
the follicle ruptures and ovum released into the oviduct
154
what does the corpus luteum develop from
the remnants of the follicle
155
what does the corpus luteum release
progesterone and oestradiol
156
where are corticosteroids made
adrenal glands on the top of the kidney
157
where are sex steroids made
the gonads or the placenta -they are synthesised from cholesterol
158
what are the roles of corticosteroids
• Regulate various aspects of homeostasis, blood pressure, water retention, salt balance, immune system & inflammation
159
where are sertoli cells found
the seminiferous tubules
160
where are the Leydig cells found
in between the seminiferous tubules
161
a large follicle synthesises high levels of what
| what does this stimulate
oestradiol - which in high levels stimulates the hypothalamus to produce GnRH which stimulates the anterior pituitary to produce FSH and LH
162
what happens to the levels of progesterone and oestradiol when the corpus luteum degenerates
they decrease removing the inhibition on the hypothalamus
163
what inhibits the anterior pituitary
low levels of oestradiol
164
what are the 3 steps in the ovarian cycle
1. follicular phase
2. ovulation
3. luteal phase
165
what do progesterone and oestradiol promote
the thickening of the endometrium
166
when are the oestradiol and progesterone levels low
early in the follicular phase and in the menstrual flow phase
167
what happens in the menstrual flow phase
bleeding
168
what happens in the proliferative phased
build-up of endometrium
169
when are hormone levels high
in the secretory phase
| need high levels of hormones for the uterus to be able to receive an embryo.
170
what does low progesterone promote
the proliferative phase
171
what happens in the follicular phase
the new follicle is developing
172
what do the hydrolytic enzymes in the acrosome do
digest carbohydrate bonds
digest peptide bonds
sperm receptor for egg protein
173
what is capacitation
- occurs in female tract as sperm swims out of seminal fluid into female tract secretions
- acrosome membrane fuses with sperm cell membrane which exposes sperm receptor for egg protein
- sperm now ready to fuse with the egg
174
what happens to the egg when a sperm penetrates it
Extracellular matrix is changed by enzymes so that it Is no longer permeable to sperm. All the sperm receptor proteins on the membrane are also destroyed. By this process it is ensured that triploids are not produced
175
cells progressively lose …………... when they commit to specific cell fates
totipotency
176
Terrestrial embryos have true embryonic tissue PLUS …………………….. that helps surround the embryo in a reservoir of fluid - the amnion or amniotic sac.
extraembryonic tissue
177
does the trophoblast contribute to the embryo
no - only thee placenta
178
what does the trophoblast secrete
human chorionic gonadotropin (hCG) (a hormone). Acts like LH – maintains the corpus luteum which continues to secrete oestradiol and progesterone. Maintains endometrium (no menstrual bleeding).
179
what are the steps in gastrulation
hypoblast cells displaces by inward migrating epiblast cells - internal epiblast become endoderm, outer ectoderm
more epiblasts squeeze between ecto and endo and becomes the mesoderm
180
The ……………….. genes specify regional identity to body segments and work by work by regulating the expression of other genes to control differentiation.
Homeotic - they contain HOX which encode transcription factors
181
expression of ............. proteins is global positioning giving regional identity in animals
HOX - shorts for homeotic box containing genes
182
what is an enucleated egg
an egg with its nucleus removed
183
describe gurdons experiment
- he used UV light to destroy the nucleus of tadpole egg cells
- he transplanted either a cell from a tadpole embryo or an intestinal cell from a fully developed tadpole into an enucleated egg
- the results showed that the embryo cell when transplanted into the egg was able to regenerate an entire organism whereas the intestinal cell test stopped developing before tadpole stage
184
what do homeotic genes determine
the special arrangement of structures about the body axes
185
the products of which class of homeotic genes provides positional information in an embryo
HOX genes - prompts cells to develop into structures appropriate for a particular location
186
when expressed what does the ubx HOX gene suppress
leg formation
187
what are three major parts of a fruit fly
head, thorax (midbody where wings and legs extend), abdomen
188
what is the anterior-posterior axis of a fruit fly
head to tail
189
what is the dorsal-ventral axis of a fruit fly
back to belly
190
what does much of the genetic variation of humans seem to be in the from of
SNPs - single nucleotide polymorphisms - single base pair mutations
191
what are CNVs
when people have more or lees than the standard 2 copies of a gene - copy number variants
192
what is a homeobox
a 180 nucleotide sequence within homeotic genes that is widely conserved in animals
193
do all homeobox containing genes act as homeotic genes
no - the ones that don't act as homeotic genes do not directly control the identity of body parts
194
what do homeobox encoded homeodomains do
they bind to DNA and function as a transcription factor regulating gene expression
195
the luteal phase of the ovarian cycle is coordinated with what phase of the uterine cycle
secretory
196
the follicular phase of the ovarian cycle is coordinated with what phase of the uterine cycle
proliferative phase
197
what are the 2 key apoptosis genes in C. elegans
ced-3 and ced-4 - apoptosis occurs when their proteins are present in inactive forms - this results in ced-9 releasing the "brake" on apoptosis and the apoptotic pathway activates proteases and nucleases that cut up the proteins and DNA of the cell
198
when cytochrome c is released from the mitochondria what does it act as
a cell death factor
