Section 1: Development and Physiology Part 1 Flashcards

Question

What is Budding?

Answer 1

e.g. “simple” invertebrate animals such as hydra can reproduce by budding. New individuals arise from outgrowths of existing ones

Answer 2

in this form of asexual reproduction the body can regrow from a fragment: If the body is broken/divided into pieces, all or some of the fragments can develop into new individuals by regeneration of lost body parts. This requires the presence of powerful “stem cells” throughout the body. Upon injury these stem cells can form a blastema of proliferating, undifferentiated cells that can be re-organised spatially to produce the correct differentiated cells, in the right order, the reform the missing part. Annelid worms, flat worms such as planaria, echinoderms such as the star fish and algae (e.g. Spyrogira) can asexually reproduce in this way.

Answer 3

– in this form of asexual reproduction the body can regrow from a fragment: If the body is broken/divided into pieces, all or some of the fragments can develop into new individuals by regeneration of lost body parts. This requires the presence of powerful “stem cells” throughout the body. Upon injury these stem cells can form a blastema of proliferating, undifferentiated cells that can be re-organised spatially to produce the correct differentiated cells, in the right order, the reform the missing part. Annelid worms, flat worms such as planaria, echinoderms such as the star fish and algae (e.g. Spyrogira) can asexually reproduce in this way.

Answer 4

this type of asexual reproduction is widespread in plants where the vegetative part of plant (leaves, stems and roots) can propagate without seeds. This happens naturally (for example underground roots that give rise to new plants) and is used widely in horticulture- e.g. “cuttings”

Answer 5

The vast majority of new complex organisms arise from a fertilised egg cell- also called a ZYGOTE. The fertilised egg cell has to give rise to many different cell types.

Answer 6

It allows genetic variation between individuals → genetic variation in the population. In asexual reproduction the offspring are genetically identical to the parent. ❖ Variation allows the population to adapt to changing conditions. ❖ Variation is the driving force for evolution ❖ And necessary for a healthy adaptive population

Answer 7

Meiosis and sexual reproduction only occur in a small number of lineages on the tree of life. e.g. ❖ Bacteria- only asexual reproduction ❖ Most algae, fungi and some land plants - asexual and sexual reproduction. Yeast- mostly by binary fission- but can undergo sexual reproduction- especially if under stress. ❖ Animals- mostly sexual reproduction but some exceptions- hydra can reproduce by budding. Even an exception among vertebrates- the guppy (fish).

Answer 8

- Germ cells contain a random distribution of half the chromosomes of the parent (n) - Fusion of germ cells restores the full compliment of genes (2n). - offspring share 50% of their genes with each of their parents- but which 50% is randomly determined - so siblings will each have 50% of the genes of each parent- but a different 50%. - siblings share on average 50% of their genes. But the shared genes between siblings could be as low as 0% or as high as 100%- 50% on average

Answer 9

the production of mature sperm is a continuous process in the adult male. It occurs in the seminiforous tubule of the testes. In the embryonic testes the primordial germ cells- or the stem cells that will give rise to all sperm, differentiate – these are called the spermatogonia. Mitotic divisions that make more of these stem cells continue throughout the life of the male. To form sperm the spermatogonia undergo two meiotic cell divisions –forming primary and secondary spermatocytes respectively. Both are produced in the seminiferous tubule with the more mature cells located closer to the lumen. Following meiosis the haploid spermatids then differentiate into mature, motile sperm released into the lumen. This last step is not a division but a differentiation- called spermiogenesis- distinct from spermatogenesis which is the whole process.

Answer 10

Oogenesis begins already in the developing ovary of the female embryo, with the production of primordial germ cells or oogonia- these are produced by mitosis and are the stem cells of the future eggs. The oogonia give rise to the primary oocytes by initiating the first meiotic division but they arrest in prophase. These primary oocytes are present in the ovary of the female at birth, each contained within a protective follicle- they remain quiescent like this until puberty when hormonal release causes their maturation. In humans generally only one ovum continues to mature in each cycle- so normally only one offspring born- dizygotic twins would result from a double ovulation- animals with multiple births would of course mature and release multiple eggs simultaneously. At puberty then Follicle stimulating hormone periodically stimulates follicles to grow and induces the primary oocyte to complete meiosis I- this is an unequal division- producing a single secondary oocyte and extruding the extra genetic material in a polar body. the secondary oocyte arrests in metaphase of meiosis II and is released as an ovum during ovulation in this arrested state. In humans, meiosis II is not completed until a sperm fertilises the ovum at which point a second polar body containing the excess genetic material is extruded. In other animals the sperm may enter the ovum earlier, or later or at a similar stage to humans. The ruptured follicle is left behind after ovulation and degenerates.

Answer 11

1. Cytokenesis is unequal in meiosis- most cytoplasm going to a single daughter cell (oocyte)- goes on to form the ovum. The polar bodies degenerate. Why? -Cytoplasm is needed to support the future zygote. Eggs- largest cells in animal kingdom, In oviparous animals- e.g. frog- takes time to build up yolk and cytoplasm for embryo- 3years to sexual maturity 2. The cells from which sperm develop continue to be generated by mitosis through life of individual - not believed to happen in female. 3. Oogenesis marked by long resting periods whereas spermatogenesis is continuous.

Answer 12

Egg: The egg is full of molecules needed for nutrition, metabolism and development of the embryo Sperm: The sperm cell is specialised to move to the egg and penetrate it. The head of the sperm is tipped with a special body the acrosome- contains enzymes to help the sperm penetrate the egg. The sperm cell contains a large number of mitochondria to provide the energy (ATP) needed to move the tail or flagellum for motility. The sperm cell contains little else

Answer 13

❖ Brings male and females gametes together – produces diploid zygote ❖ It also activates the egg, triggering the beginning of embryonic development

Answer 14

a sea urchin. covered in lecture 2 notes.

Answer 15

POLYSPERMY: fertilisation by multiple sperm which would lead to an increased genetic compliment and in non-viable zygote]

Answer 16

1. Fertilisation is internal 2. Egg cloaked in follicle cells released with egg 3. Sperm undergoes capacitation in uterus- molecular changes that enable sperm to enter the egg 4. Egg has tough extracellular matrix called the zona pellucida - presents receptors for sperm binding. 5. Binding of the receptor leads to acrosomal reaction- entry through zona pellucida 6. No known fast block to polyspermy but similar cortical reaction for slow block 7. Whole sperm taken into the egg- base used to form centrioles for spindle 8. Nuclei do not fuse but both nuclear envelopes disperse- chromosomes align on spindle in cytoplasm. 9. First cell division slower- 12-36 hours

Answer 17

1. Cell division 2. Cell differentiation. 3. Morphogenesis.

Answer 18

Cell division and growth are both tightly regulated during development

Answer 19

A complex organism requires many hundreds of different cell types to form structures and carry out specific functions. For example, red blood cells are required to carry oxygen, muscle cells are required for movement, neurons are required to receive and transmit signals. The cells that arise by cell division from the zygote have to become different to each other over time.

Answer 20

Or “creation of form”. How the organism takes on a three dimensional shape with all the cells types in the right place to form structures and carry out functions

Answer 21

organogenesis involves more local interactions between cells and morphogenetic changes in tissue and cell shape- and in cell arrangement.

Answer 22

Induction:- the influence of one group of cells on neighbouring cells, changing the way in which the responding cells develop

Answer 23

the Spemann and Mangold experiment in 1924 elegantly demonstrated the ability of cells to influence each other / communicated with each other through Induction.

Answer 24

This means that the organiser cells from the donor could change the fate of the recipient cells. 1. Cells that form the secondary axis are not all derived from the graft (donor cells), a large proportion of cells are recruited from the recipient. This means that the organiser cells from the donor could change the fate of the recipient cells. 2. With time an almost complete second axis could be formed. This means that the organiser cells can set in motion a whole chain of events leading eventually to the production of a whole new body plan. This is why Spemann called the cells of the dorsal blastopore lip, the primary organiser.

Answer 25

* It sets aside the cells for and forms the rudiments of the entire nervous system. * It is the first event in organogenesis. GO TO LECTURE #4

Answer 26

this is a fluid-filled cavity which forms by splitting the mesoderm- it is by definition surrounded by mesoderm on all sides. Many of the organs as they form will push into this space- although contained within the peritoneum

Answer 27

are mesoderm cells that form into blocks on either side of the neural tube (see figure below). These are transitory structures that later dissociate to form different cell types. 1. The muscle blocks of the body and muscles attached to the skeleton 2. The vertebrae of the back-bone. The cells from within the somite that will form the vertebrae (blue on lower diagram) leave the somite and migrate around the notochord and neural tube. The notochord later degenerates; the only remnants forming the “disks” between the vertebrae.

Answer 28

The entire embryo will form from one cell layer- the epiblast

Answer 29

Gastrulation involves cells from the epiblast moving underneath through a line at the midline of the disk called the primitive streak.

Answer 30

GO TO LECTURE # 4

Answer 31

Reptiles, including birds, and mammals left an aquatic life and must produce their young on dry land. Their eggs and embryos have special characteristics that reflect this- they are AMNIOTES

Answer 32

1. Evolution of a protective egg shell on externally laid eggs (reptiles, birds and a few mammals (monotremes) or 2. Evolution of a uterus and placenta to facilitate internal development inside the mother’s body in mammals.

Answer 33

- surrounds the embryo, forms fluid filled sac that bathes the embryo. Made from ectoderm and mesoderm

Answer 34

outer membrane- exchanges gasses between embryo and surrounding air. O2 and CO2 diffuse freely across the egg shell.

Answer 35

encloses the yolk- blood vessels develop in the yolk sac to bring nutrients to the embryo. The first site of blood production.

Answer 36

waste disposal sac- metabolic wastes. Also performs gas exchange.

Answer 37

Viviparity- giving birth to live young

Answer 38

Consider that the embryo is like transplanted foreign tissue within the body of the mother. This is not fully understood but the placenta also acts as a barrier for the immune response

Answer 39

The inner cell mass (ICM) will give rise entirely to the embryo and most extra-embryonic membranes

Answer 40

Amnion- encloses the embryo in a fluid filled sack- this ruptures just before birth (referred to as breaking of waters) Chorion- contributes to the placenta in humans- outer membrane. Yolk sac- no yolk but retains the name from its ancestral role- this structure is said to be “homologous” to the structure in birds (see explanation of term homologous below). It is similar in another of its functions across the group- it is the site of first blood production. Allantois- incorporated into the umbilical cord.

Answer 41

“[W]e come to know [truths] by the power of our own native intelligence, without any sensory experience” – René Descartes

Answer 42

Concepts of Memory & Knowledge 1. Knowledge originates in a foreign entity 2. Knowledge is an innate and essential property of the human mind 3. Knowledge is built up systematically through interactions of the mind with the world (3 is accepted)

Answer 43

- Mind is non-physical - Brain may control movement - Mind and consciousness exist in a non-physical world - Body is determined by the physical world, mind is not

Answer 44

The Brain is a Network of Electrochemically Active Nerve Cells - Billions of brain cells (neurons) - Trillions of synaptic connections

Answer 45

All organisms can move, but only some have coordinated movement

Answer 46

- A behaviour is an action carried out by muscles under control of the nervous system - Behaviors and the anatomical structures related to their performance are subject to natural selection - all behaviour has a function

Answer 47

1. Causation (stimulus AND mechanism) 2. Survival Value (adaptive function) 3. Ontogeny (how it is built in development) 4. Phylogeny (evolutionary history)

Answer 48

Innate Behaviour - Present in all members of a given species - Develops independently of environmental context - Often present at birth - Almost always long-lasting - Slightly modifiable

Answer 49

Learned Behaviour - Modification of a behaviour with experience - Can be short or long-lasting - Highly modifiable - Different for each individual

Answer 50

An innate behaviour - Central pattern generators (CPGs) are biological neural circuits that produce rhythmic outputs in the absence of rhythmic input. - CPGs have at least two interacting components to allow rhythmic activity -Examples of CPGs include: ◦ Breathing ◦ Chewing ◦ Swallowing ◦ Swimming ◦ Escape reflex

Answer 51

An innate behaviour - A fixed action pattern is a sequence of unlearned acts directly linked to a simple stimulus - Fixed action patterns are unchangeable and, once initiated, usually carried to completion - A fixed action pattern is triggered by an external cue known as a sign stimulus

Answer 52

It is an innate behaviour (minnow example lecture 10)

Answer 53

It is a learned behaviour - Imprinting is the establishment of a longlasting behavioral response to a particular individual or object - Imprinting can only take place during a specific time in development called the sensitive period ◦ For example, in gulls, the sensitive period lasts one to two days ◦ Offspring and parents must bond with each other during this time or the parent will reject the offspring

Answer 54

It is a learned behaviour - Spatial learning is the establishment of a memory that reflects the environment’s spatial structure - Tinbergen showed how digger wasps use landmarks to find nest entrances - A cognitive map is an internal representation of spatial relationships between objects in an animal’s surroundings

Answer 55

It is a learned behaviour - In associative learning, animals associate one feature of their environment with another ◦ For example, a blue jay will avoid eating monarchs and similar-looking butterflies after an experience with a distasteful monarch butterfly - Classical conditioning is a type of associative learning in which an arbitrary stimulus is associated with a reward or punishment ◦ For example, a dog that repeatedly hears a bell before being fed will salivate in response to the sound of a bell in anticipation of a meal

Answer 56

Pavlovian (classical) Conditioning and Operant Conditioning

Answer 57

- Operant conditioning is a type of associative learning in which an animal learns to associate one of its behaviors with a reward or punishment - Also called trial-and-error learning ◦ For example, a rat that is fed after pushing a lever will learn to push the lever in order to receive food

Answer 58

it is learned behavoiur (examples in lecture 10)

Answer 59

- Cognition is a process of knowing that involves awareness, reasoning, recollection, and judgment - It was once thought that only primates and certain marine mammals exhibit cognition, but other groups including insects use abstract thinking ◦ For example, honeybees can distinguish “same” from “different” and distinguish between human faces - Some bird species, particularly corvids, demonstrate complex problem solving ◦ For example, ravens can obtain food suspended by a string by pulling up the string

Answer 60

- Bees innate communicate angle and distance to food sources -Distance as number of waggles - Angle from sun as direction

Answer 61

Experimental Psychology and Ethology

Answer 62

Behaviour + Biology = Neuroscience

Answer 63

Homeostasis requires cooperation between multiple organ systems

Answer 64

42 L (60% of body mass) - total body water 28 L - intracellular fluid 14 L - extracellular fluid 3 L - plasma + 11 L - interstitial = extracellular (Volumes in L are those of average 70kg adult male human. In females, TBW is 50%)

Answer 65

Normal daily inputs (variable) Ingestion Fluid (1.25 litres) Food (1 litre) Metabolism (350 ml) [Remember metabolism yields CO2 and H2O] total 2.6 litres

Answer 66

Normal daily outputs (variable) Gut (Faeces 100 ml) Urine (1.5 litres) Breathing/Skin (900 ml) Sweating (100 ml) total 2.6 litres

Answer 67

Abnormal inputs Clinical – Injection/infusion Excessive drinking (‘polydipsia) Abnormal inputs Clinical – Injection/infusion Excessive drinking (‘polydipsia)

Answer 68

External environment Temperature O2 CO2 water, food in environment Light Noxious stimuli/predators Etc.

Answer 69

Internal environment Composition of body fluids Temperature Metabolites Blood pressure O2 and CO2 in tissues Etc.

Answer 70

Temperature Osmolarity pH Gas partial pressures (O2 and CO2) Electrolyte (ion) concentration Metabolite concentration (glucose etc.) All of these variables are physiologically regulated (GO TO LECTURE 8 -Homeostasis- for Ionic composition of major body fluid compartments diagram)

Answer 71

Mechanisms of homeostasis moderate changes in the internal environment For a given variable, fluctuations above or below a set point serve as a stimulus; these are detected by a sensor A control center then generates output that triggers a response The response returns the variable to the set point Example: temperature in mammals (or thermostatically controlled central heating) – but every variable is homeostatically regulated

Answer 72

Homeostasis in animals relies largely on negative feedback, which helps to return a variable to a normal range (eg temperature regulation, blood glucose regulation). (diagram lecture 8)

Answer 73

Positive feedback amplifies a stimulus and only contributes to homeostasis in animals in a small number of functions (childbirth, blood clotting, electrical impulses in nerves). (diagram lecture 8)

Answer 74

Feedforward: anticipatory responses to expected change (eg increased heart rate in anticipation of exercise; increased secretion of insulin before food is digested to yield glucose; stimulation of gastric secretions due to thought/smell of food). (diagram lecture 8)

Answer 75

Bioenergetics: subject to homeostatic regulation Energy-containing molecules from food are usually used to make ATP, which powers cellular work After the needs of staying alive are met, remaining food molecules can be used in biosynthesis Biosynthesis includes body growth and repair, synthesis of storage material such as fat, and production of gametes O2 consumed, CO2 produced (diagram lecture 8)

Answer 76

homeostasis is regulated by nervous and endocrine systems

Answer 77

The nervous system is a network of specialized cells—neurons—that transmit signals along dedicated pathways * Hard-wired * Fast acting (milliseconds) * Electrical and chemical signaling * Local cellular response * Rapid response by target cell

Answer 78

Chemical signaling by hormones is the function of the endocrine system * Hormones transported in blood * Slower acting (minutes, hours, days) * Chemical signaling, often involves changes in gene expression * Slower and often long-lasting responses of target cell

Answer 79

Brain Spinal cord

Answer 80

Cranial nerves Ganglia outside CNS Spinal nerves

Answer 81

Gray matter, white matter, ventricles The brain and spinal cord contain: ◦ Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons ◦ White matter, which consists of bundles of myelinated axons

Answer 82

Acetlycholine Amino acids glutamate GABA Glycine Neuropeptides Substance P Met-enkephalin (an endorphin) Gases Nitric oxide Biogenic amines Dopamine seretonin norepinephrine

Answer 83

- Sensation leads to perception - Travels from the PNS to the CNS - Processing of sensory information can occur before, during, and after transmission of action potentials to the central nervous system (CNS) - Integration often begins as soon as the information is received - Perceptions are the brain’s construction of stimuli Stimuli from different sensory receptors travel as action potentials along dedicated neural pathways - The brain distinguishes stimuli from different receptors based on the path by which the action potentials arrive (lecture 12 has diagram)

Answer 84

- Action potentials travel from motoneurons - Activate muscles through neuromuscular junction (NMH) (lecture 12 has diagram)

Answer 85

sensory reception, transduction, transmission, perception, response (lecture 12 has diagram)

Answer 86

- Receptor cells for taste in mammals are modified epithelial cells organized into taste buds, located in several areas of the tongue and mouth - Most taste buds are associated with projections called papillae - Any region with taste buds can detect any of the five types of taste Taste receptors are of three types: - The sensations of sweet, umami, and bitter require specific G protein-coupled receptors (GPCRs) - The receptor for sour belongs to the TRP family and is similar to the capsaicin and other thermoreceptor proteins - The taste receptor for salt is a sodium channel

Answer 87

- Phenyl-beta-D-glucopyranoside (PBDG) - Bitter to humans - Mice are indifferent because they have no receptor to sense it - Genetically engineered mutant mice to express the human PBDG receptor in sweet or bitter taste receptor cells - Examined mouse behaviour for consuming PBDG or water (choice) at varying concentrations

Answer 88

- The simplest animals with nervous systems, the cnidarians, have interconnected neurons arranged in nerve nets - More complex animals have nerves, in which the axons of multiple neurons are bundled together - Bilaterally symmetrical animals exhibit cephalization, the clustering of sensory organs at the front end of the body (lecture 12 has diagram)

Answer 89

- The spinal cord conveys information to and from the brain and generates basic patterns of locomotion - The spinal cord also produces reflexes independently of the brain

Answer 90

A reflex is the body’s automatic response to a stimulus ◦ For example, a doctor uses a mallet to trigger a knee-jerk reflex

Answer 91

- The PNS transmits information to and from the CNS and regulates movement and the internal environment - In the PNS, afferent neurons transmit information to the CNS, and efferent neurons transmit information away from the CNS - The PNS has two efferent components: the motor system and the autonomic nervous system (MUST LOOK AT DIAGRAM IN LECTURE 12!!)

Answer 92

- The motor system carries signals to skeletal muscles and can be voluntary

Answer 93

- The autonomic nervous system regulates breathing, heart rate, urination, sexual arousal

Answer 94

- The enteric nervous system exerts direct control over the digestive tract, pancreas, and gallbladder

Answer 95

forebrain midbrain hindbrain

Answer 96

- The forebrain has activities including processing of olfactory input, regulation of sleep, learning, and any complex processing

Answer 97

- The midbrain coordinates routing of sensory input

Answer 98

- The hindbrain controls involuntary activities and coordinates motor activities

Answer 99

- Comparison of vertebrates shows that relative sizes of particular brain regions vary - These size differences reflect the relative importance of the particular brain function - Evolution has resulted in a close match between structure and function

Answer 100

- The midbrain and part of the hindbrain form the brainstem, which joins with the spinal cord at the base of the brain - The rest of the hindbrain gives rise to the cerebellum - The forebrain divides into the diencephelon, which forms endocrine tissues in the brain, and the telencephalon, which becomes the cerebrum

Answer 101

- The cerebrum controls skeletal muscle contraction and is the center for learning, emotion, memory, and perception - Outer layer of the cerebrum is called the cerebral cortex and is vital for perception, voluntary movement, and learning - A thick band of axons called the corpus callosum enables the right and left cerebral cortices to communicate - The cerebellum coordinates movement and balance and helps in learning and remembering motor skills - The hypothalamus constitutes a control center that includes the body’s thermostat and central biological clock

Answer 102

- The brainstem consists of the midbrain, the pons, and the medulla oblongata (or medulla) - The midbrain receives and integrates sensory information and sends it to specific regions of the brain - A major function of the pons and medulla is to transfer information between the PNS and the midbrain and forebrain - The medulla is also in control of several automatic functions such as breathing, heart and blood vessel activity, swallowing, vomiting, and digestion

Answer 103

- Broca’s area is essential for language production - Wernicke’s area is essential for language comprehension (spoken and written)

Answer 104

- Generation and experience of emotions involve many brain structures, including the amygdala, hippocampus, and parts of the thalamus - These structures are grouped as the limbic system - Amygdala is emotional centre

Answer 105

- Damaged orbitofrontal cortex and amygdala - steel rod through the brain and survived

Answer 106

H.M. Suffered from Epilepsy - Surgery in 1953 (bilateral medial temporal lobe removed) - IQ left in normal range - Surgery caused severe anterograde amnesia for explicit episodic memories, including memories for people, words, shapes, sounds places, events - Amnesia demonstrated through free recall tests and recognition tests - Short-term memory intact

Answer 107

- Neuronal plasticity describes the ability of the nervous system to be modified after birth

Answer 108

Synaptic plasticity means the strengthening or weakening of synaptic junctions

Answer 109

- In the vertebrate brain, long-term potentiation (LTP) involves a lasting increase in the strength of synaptic transmission - LTP involves a presynaptic neuron that releases the neurotransmitter glutamate - LTP involves two types of glutamate receptors on the receiving cell – NMDA receptors being central - The receptors on the postsynaptic membrane change in response to a stimulus - Agents that disrupt LTP seem to disrupt memory

Answer 110

1. Cell division 2. Cell differentiation. 3. Morphogenesis.

Answer 111

Morphogenesis refers to how the organism and its parts are shaped. In trying to understand morphogenesis, we talk about pattern formation, which is the spatial organisation of differentiation events and other cellular changes so that the cells, tissues and organs are all in characteristic places. Morphogenesis is the outcome of correct pattern formation

Answer 112

By receiving information (molecular signals and cues) that indicates their relative positions within the embryo: this is called positional information. So positional information is therefore the molecular signals and cues experienced by the cells according to position.

Answer 113

By co-ordinates along 3 axes You have seen already that at the end of gastrulation, the frog and chick embryos have an overall 3D body plan with head and tail ends, dorsal and ventral sides and left and right sides.

Answer 114

two possible ways in which cells can receive positional information: 1. localisation of cytoplasmic determinants 2. Induction

Answer 115

The ultimate effect of signaling at the cell surface is a change in gene expression in the nucleus. So cell signaling is the basis of induction. Signaling molecules are produced by the inducing cells and are detected by the responding cells, leading to a series of changes inside the responding cell and ultimately a change in the gene expression pattern within.

Answer 116

This means: 1. That some cells will not respond at all to a signal (if they don’t have a receptor). 2. That two different cells can respond in different ways to the same signal (if they possess different receptors for the same signal) This is referred to as competence; the cells in case 1 above are called non-competent and the cells in case 2 show different competencies to the same signal.

Answer 117

1. The signaling molecules 2. The receptors 3. The molecules that effect the changes inside the responding cell, e.g. transcription factors

Answer 118

* Three classes of floral organ identity genes are represented by the A, B C hypothesis * The ABC hypothesis addresses how floral organ identity genes direct the formation of the four types of floral organs (LOOK BACK AT THE FLOWER LAB)

Answer 119

The answer depends on the group of vertebrate animals being considered. Although subsequent development is very similar across vertebrates, the earliest steps differ. (LOOK AT LECTURE 6 for info)

Answer 120

A morphogen is the name given to a substance (a chemical or molecule) involved in pattern formation where cells have a graded response depending on the level of the signal (morphogen) they are exposed to.

Answer 121

Vulval development in the nematode illustrates several important developmental concepts. 1. Sequential inductions drive the formation of organs. 2. The effect of an inducer can depend on its concentration -it acts as a morphogen. 3. Inducers produce their effects via signal-transduction pathways. 4. The response is often the activation (or inactivation) of genes → establishes the pattern of gene activity characteristic of that particular cell type (cellular differentiation).

Answer 122

-Change its gene expression and differentiate or -Divide but it might also respond by -Changing its shape -Moving about (migrating) -Or even by dying (programmed cell death or apoptosis).

Answer 123

The cytoskeleton is also important in cell movement- allows cells to “crawl”- by extending and retracting processes: lamellipodia (sheets) or filipodia (spikes)

Answer 124

The ECM is made up of secreted glycoproteins lying outside the cell membrane. The exact makeup of the ECM can help to guide cell movement so that some environments are attractive to moving cells and other environments are repulsive. For example fibronectin is attractive and is present inside the blastocoel where cells will crawl during gastrulation

Answer 125

among the glycoproteins that may be present on the surface of the cells are Cell Adhesion Molecules (CAMs). These influence how tightly the cells bind to neighbouring cells (other CAMs on the surface).

Answer 126

The last type of cell change considered as important in morphogenesis was Programmed cell death. One very striking example of programmed cell death (apoptosis) playing an important role in sculpting the shape of the embryo is in removal of the region between the future digits of the hands and feet. In the early embryo the hands and feet develop as paddles, digits are formed by the cells between the future digits being removed very precisely by cell death.