Lecturea 2-4

Question 1

how does a new multi cellular organism arise

Answer 1

an aggregation of many single cells.

Question 2

cellular slime molds

Answer 2

these form multicellular aggregates in which cells are separated by their membranes

Question 3

example of cellular slime mold

Answer 3

dictyostelium discoideum

Question 4

fruiting body

Answer 4

fungal structures that contiain spores

Question 5

asexula reproduction

Answer 5

bacteria and simple animals such as hydra can reproduce by budding.

Question 6

mechanisms of asexual reproduction

Answer 6

fission - (separation of an organism into two or more individuals of approx equal size)

Question 7

fission

Answer 7

fission - (separation of an organism into two or more individuals of approx equal size)

Question 8

budding

Answer 8

budding - new individuals arise from existing ones. (found only in invertebrates0

Question 9

fragmentation

Answer 9

two step process, breaking of the body into pieces, all or some of which develop into adults, followed by regeneration. (regrowth of lost body parts (annelid worms)

Question 10

parthenogenesis

Answer 10

females produce offspring from unfertilised eggs (mainly invertebrates )
bees wasps and ants

Question 11

zygote

Answer 11

a fertilised egg cell

Question 12

driving force behind evolution

Answer 12

variation

Question 13

general principles of development

Answer 13

cell division, cell differentiation, morphogenesis

Question 14

gametogenesis

Answer 14

Spermatogenesis- the production of mature sperm is a continuous process in the adult
male. Sperm structure is very consistent throughout the animal kingdom.
Oogenesis, the development of a mature egg, is a prolonged process

Question 15

why dont we study development in humans

Answer 15

Observation is difficult
• Morally and ethically- no experiments on human embryos (following implantation).
• We wouldn’t want to (nor could we) breed humans to look at effects of gene mutations
on embryos.
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Question 16

model organism

Answer 16

an organism who has very similar developmental mechanisms to the organism being studied

Question 17

aspects to be considered when choosing a model organism

Answer 17

1. biological considerations
2. practical considerations
3. historical considerations

Question 18

organism for observing development and morphological analysis

Answer 18

Advantages in this case would be large eggs, accessible embryos, short development
time, and easy to keep in the lab. So the organisms of choice for this kind of work would be
the amphibian (frog) and the chicken. Arabidopsis in the case of plants.

Question 19

for manipulating the embryo (experimental biology)

Answer 19

larg accesible embryos, robust embryos that can tolerate manipulation.
can be grown in a dish, in culture.

frog or chick

Question 20

vertebrate

Answer 20

The frog Xenopus laevis (Chp 46 – first page)
Advantages
•Ease of access and manipulation of the egg and embryo
allowing experimental manipulation, assay inductive interactions
•Robust embryos, can tolerate manipulation in relatively simple lab facilities.
•Parts of the embryo can easily be cultured.
•Rapid development, 4 days to a free swimming tadpole.
•A well-established system
Disadvantages
•No genetics. Complex, uncharacterised genome.
•Animals cannot be bred for multiple generations in the lab.
The mouse Mus musculus has a long history as a mammalian model of development.
Advantages
•Much is known about its biology, including its genes.
•The genome is well characterized and almost completely sequenced
•Sophisticated and elaborate techniques exist to manipulate mouse genes:
transgenic mice and
mice in which particular genes are “knocked out” by mutation.
Disadvantages:
Mice are complex animals with a genome as large as ours, and their embryos develop in the
BYU11102 Organisms to Ecosystems: Multicellularity and Development
Dr. Rebecca Rolfe – Lecture 2
mother’s uterus, hidden from view.
•The embryo develops in utero and is inaccessible.
-we are restricted to snap shots of development
•Embryo culture is difficult and limited.
•The generation interval is long (3 months)
•Difficult to find genes by mutational screens, because of the above.
But the mouse is still an important model system because we want to be able to study
development in a mammal. It serves as a good model for human development.

Question 21

invertebrate

Answer 21

INVERTEBRATE
The nematode worm Caenorhabditis elegans normally lives in the soil but is easily
grown in petri dishes.
•Only a millimeter long, it has a simple, transparent body with only a few cell types and
grows from zygote to mature adult in only three and a half days.
•Its genome has been sequenced.
•It is easy to identify mutant animals: Because individuals are hermaphrodites, it is easy to
detect recessive mutations: Self-fertilization of heterozygotes will produce some homozygous
recessive offspring with mutant phenotypes.
•The huge advantage is its simplicity: every adult C. elegans has exactly (only) 959 somatic
cells. These arise from the zygote in virtually the same way for every individual.
•By following all cell divisions with a microscope, biologists have constructed the
organism’s complete cell lineage, a type of fate map.
A fate map traces the development of an embryo – Cell lineage analysis. (

Question 22

For Developmental genetics:

Answer 22

Advantages would be ease of breeding in the laboratory, short generation interval (time
from fertilisation to sexual maturity), simple or small genome and ease of observing embryos
to see mutant effects. Organisms that have been widely used for this are the fruit fly
(Drosophila), the zebrafish (Danio), the nematode worm (Caenorhabditis elegans), The plant
Arabidopsis thaliana, the mouse (despite major disadvantages, see below).

Question 23

transcription factors

Answer 23

In molecular biology, a transcription factor is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence

Question 24

actin and myosin

Answer 24

In summary, myosin is a motor protein most notably involved in muscle contraction. Actin is a spherical protein that forms filaments, which are involved in muscle contraction and other important cellular processes

Question 25

neuroreceptors

Answer 25

in neurons receive cell signals

Question 26

globulin genes

Answer 26

make haemoglobin which carry oxygen

Question 27

repressor in prokaryotes

Answer 27

a repressor is encoded by the lacl gene which binds to the operator which prevents RNA polymerase from binding to the promoter and transcribing the genes downstream

Question 28

promoter

Answer 28

a regulatory sequence at the start of the coding sequence that are needed for the transcriptional machinery to assemble and begin to transcribe the DNA sequence into an RNA message or transcript

Question 29

promoters in eukaryotes

Answer 29

much more complicated in eukaryotes, often has upstream control elements called enhancers which can influence prooter function.
can be either proximal or distal, or upstream or downstream or placed within an intron

Question 30

general transcription factors

Answer 30

these control transcription initiation by binding to the enhancers.
form a transcription initiation complex

Question 31

cell-specific transcription factors

Answer 31

also known as activators.
these influence the efficiency with which the general transcription factors assemble on the promoter sequence and initiate the expression of a gene.

Question 32

determination

Answer 32

irreversibly commits a cell to become a particular cell type

Question 33

MyoD protein

Answer 33

capable of starting a cascade of events that changes non-muscle cells into muscle cells

Question 34

master regulatory genes

Answer 34

the genes that encode transcription factors that control cellular differentiation

Question 35

gene expression analysis

Answer 35

allows researchers to examine where a particular gene is expressed in the embryo

Question 36

plant gene expression and cellular differentiation

Answer 36

funtions based on gene expression
however, in plants gene activation depends on the cell to cell communication

eg. arabidopsis root epidermis forms root hairs or hairless cells depending and the number of cortical cells it is touching.
GLABRA - 2 gene

Question 37

maternal affect gene

Answer 37

Maternal-effect genes are transcribed in the mother and their mRNA influences development of oocytes and embryos.

one source of early information in fertilised egg cells is proteins and transcription factors. this information is transcribed by genes known as maternal affect genes

Question 38

differential gene expression

Answer 38

the specialisation of cells thorugh gene regulation - the turning on and off of genes to allow them to specialise.
the cells take on characteristics appropriate to their location within the embryo and their ultimate function within the cell

Question 39

three types of genes

Answer 39

structural genes
housekeeping genes
regulatory genes

Question 40

developmental mutants

Answer 40

organisms in which genes have been altered

Question 41

feasability of a mutant screen

Answer 41

space to house a large number of animals

short generation time

does the mutation show in the phenotype

Question 42

two ways developmental mutants have been classically identified

Answer 42

spontaneous mutations

large scale mutant screens

Question 43

maternal effect genes

Answer 43

genes that are active in the mother not the embryo

the gene product is supplied to the egg/early embryo by the mother

Question 44

bicoid gene

Answer 44

forms the front half of the embryo

in the absence of bicoid, embryos with no head,and posterior structures at both ends are formed

Question 45

morphogen

Answer 45

a gene that establishes body plan according to a graded concentration