body plan development

Question 1

what is morphogenesis and what is it controlled by

Answer 1

the regulation of the pattern of anatomical development controlled by homeotic genes

Question 2

what controls the growth and development of DIFFERENT living forms

Answer 2

the SAME small group of genes

Question 3

why are fruit flies useful for investigating mutations and discovering that the same group of genes control the growth of different life forms

Answer 3

they’re small, easy to keep and have a short life cycle

Question 4

what are homeobox genes

Answer 4

group of regulatory genes that contain a homeobox

Question 5

what is a homeobox

Answer 5

a section of DNA that is 180 base pairs long coding for a protein (60 amino acids long) that is highly conserved in plants, animals and fungi

Question 6

what is the protein thats coded for by a homeobox

Answer 6

a homeodomain

Question 7

what is a homeodomain

Answer 7

binds to DNA and switches other genes on/off. it acts as a transcription factor

Question 8

what is the structure of a homeodomain

Answer 8

two alpha helices connected by 1 turn

Question 9

what is Pax 6

Answer 9

a homeobox gene

Question 10

what happens when Pax 6 is mutated

Answer 10

it causes a form of blindness (due to underdevelopment of the retina) in humans.

Question 11

which organism have the Pax 6 gene

Answer 11

mice and fruit flies. disruption of this gene leads to blindness in these organisms which suggests Pax 6 is involved in eye development

Question 12

what are hox genes

Answer 12

a group of homeobox genes that are only present in animals. its responsible for correct positioning of body parts

Question 13

in animals, hox genes are found in gene clusters. how many clusters do mammals have

Answer 13

4 clusters on different chromosomes

Question 14

1) how many Hox genes do humans have
2) where have they arisen from
3) what have they accumulated over time

Answer 14

1)39
2) likely to have arisen from one ancient homeobox gene by duplication
3) accumulated mutations over time

Question 15

function of Hox genes

Answer 15

regulates development of embryos along the anterior-posterior (head-tail) axis. controls when body parts grow where. active during early embryonic development and expressed in order along anterior-posterior axis

Question 16

the order in which the genes appear along the chromosome is….

Answer 16

… the order in which their effects are expressed in the organism

Question 17

what is colinearity

Answer 17

sequential and temporal order of gene expression corresponds to sequential and temporal development of various body parts

Question 18

what do hox genes encode for

Answer 18

encode homeodomain proteins that act as transcription factors in the nucleus and activate genes involved in mitotic cell divisions, apoptosis, cell migration and regulation of the cell cycle

Question 19

how are body plans represented

Answer 19

as cross sections through the organism showing arrangements of tissue layers

Question 20

what is special about the layout of animals

Answer 20

they are segmented - segments have multiplied over time and are specialised to form different functions

Question 21

what do hox genes in the head control development of

Answer 21

mouthparts

Question 22

what do hox genes in the thorax control development of

Answer 22

wings, limbs or ribs

Question 23

what have individual vertebrae and associated structures developed from

Answer 23

segments in embryos called somites

Question 24

what are somites directed by

Answer 24

directed by hox genes to develop in a particular way depending on their position in the sequence

Question 25

what are hox genes regulated by

Answer 25

gap genes and pair rule genes. these genes are regulated by maternally supplied mRNA from the egg cytoplasm

Question 26

what does the body shape of most animals show

Answer 26

symmetry

Question 27

what is radial symmetry and where is it seen

Answer 27

seen in diploblastic animals like jellyfish. they have no left or right sides only a top and bottom

Question 28

what is bilateral symmetry and where is it seen

Answer 28

seen in most animals. the organisms have both left and right sides and a head and tail rather than a top and bottom

Question 29

what is assymetry and where is it seen

Answer 29

seen in sponges and has no line of symmetry

Question 30

what is mitosis

Answer 30

cell division and proliferation

Question 31

what is apoptosis

Answer 31

programmed cell death

Question 32

how does mitosis lead to growth and what is it regulated by

Answer 32

regulated by homeobox and hox genes. increases the number of cells leading to growth. it ensures each new daughter cell contains the full genome and is a clone of the parent cell

Question 33

what happens during differentiation

Answer 33

some genes are switched off and not expressed

Question 34

what is the Hayflick constant

Answer 34

normal body cells divide around 50 times before dying

Question 35

how is apoptosis different from cell death due to trauma

Answer 35

cell death due to trauma involves hydrolytic enzymes apoptosis removes unwanted cells/tissues to shape different body parts.

Question 36

process of apoptosis

Answer 36

- enzymes break down cell cytoskeleton - the cytoplasm becomes dense with tightly packed organelles - the cell surface membrane changes and small protusions form (blebs) - chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments - the cells break into vesicles that are ingested by phagocytic cells so that cell debris does damage any other cells/tissues - very quick process

Question 37

how can cells undergoing apoptosis stimulate mitosis

Answer 37

cells undergoing apoptosis can release chemical signals which stimulate mitosis leading to remodelling of tissues

Question 38

what signalling molecules are released

Answer 38

cytokines, hormones, growth factors and nitric oxide

Question 39

how do the signalling molecules induce apoptosis

Answer 39

by making inner mitochondrial membrane more permeable to H+ ions and dissipating the protein gradient. proteins are released into cytoplasm and bind to apoptosis inhibitor proteins and apoptosis occurs

Question 40

why is apoptosis important

Answer 40

- prevents extensive proliferation of cell types. - causes digits to separate during limb development - removes ineffective or harmful T-lymphocytes during immune system development

Question 41

how many cells apoptose per day in 8-14 year old children

Answer 41

20-30 billion cells

Question 42

how many cells apoptose per day in adults

Answer 42

50-70 million cells

Question 43

why should the rate of cells dying due to apoptosis equal the rate of cells produced by mitosis

Answer 43

not enough apoptosis leads to formation of tumours too much apoptosis leads to cell loss and degeneration

Question 44

what is stress

Answer 44

condition produced when homeostatic balance within an organism is upset

Question 45

what external factors affect expression of regulatory genes

Answer 45

change in temperature, light intensity

Question 46

what internal factors affect expression of regulatory genes

Answer 46

hormones, psychological stress

Question 47

what was thalidomide initially used for

Answer 47

treating morning sickness

Question 48

what was the problem with thalidomide

Answer 48

it prevented the normal expression of Hox genes so babies were born with shortened limbs

Question 49

why is thalidomide now used in cancer treatments

Answer 49

it prevents formation of the network of capillaries necessary for tumours to grow