L7-8: Eukaryotic Organisms

Question 1

What are ideal characteristics of model organisms?

Answer 1

Rapid rate of development
Easily manipulates
Short life span
Readily available
Large numbers offspring per generation

Question 2

Why is E.coli a good model?

Answer 2

Simple & free-living, gram negative rod shaped bacterium, easy to grow, easy to genetically manipulate and transform

Question 3

What is a homologue?

Answer 3

A gene related to another gene by descent for a common ancestral DNA sequence (relationship between genes in different species or event of genetic duplication)

Question 4

What is an orthologue?

Answer 4

Genes in different species that evolved from a common ancestral gene, retain the same/similar function in the course of evolution

Question 5

What is a paralogue?

Answer 5

They are genes generated by a duplication event

Question 6

What is a gene knockout?

Answer 6

Gene sequences are completely or partially removed and gene expression is completely eliminated

Question 7

What is gene knockdown?

Answer 7

Techniques that reduce/interfere with the expression of the gene

Question 8

What are the 2 major yeast genetic models?

Answer 8

Saccharomyces cerevisiae (budding) and Schizosaccharomyces pombe (fission)

Question 9

Why is yeast a good model?

Answer 9

Small size and simple growth and storage conditions, rapid growth rate, exist as diploid or haploid

Question 10

What are advantageous genetic factors of yeast?

Answer 10

Sexual cycle enables large scale genetic crosses, construction of gene knockouts and gene knock-ins is trivial, easily transformable with plasmids, large mutant collections and genetic crosses and screening may be automated

Question 11

What are advantageous characteristics of Drosophilia melanogaster?

Answer 11

Small (large numbers cheaply maintained), small life cycle with lots of offspring produces,

Question 12

What are advantageous genetics of Drosophilia melanogaster?

Answer 12

Easy to cross, huge number of mutants available, phenotypic markers, mature larvae allow genetic mapping, transformable using P element transposon, create both deletion and insertion mutations and can do tissue specific knockdowns or deletions

Question 13

What biological processes has Drosophila helped understand?

Answer 13

Cell signalling
Development
Neurological diseases

Question 14

What are some advantageous characteristics in Caenorhabditis elegans?

Answer 14

Small, transparent, feed on bacteria so cheaply maintained, short life cycle, short lifespan (2-3 wekks), extremely fecund (hermaphrodites can produce ~300 offspring)

Question 15

What are some advantageous genetics in Caenorhabditis elegans?

Answer 15

Easy to perform genetic crosses, many mutants available, transformable, genes can be knocked down using RNA interference

Question 16

What are advantageous characteristics of zebrafish?

Answer 16

Sexually mature by 3-4 months old and have transparent embryos

Question 17

What are advantageous genetics of zebrafish?

Answer 17

Sturdy 1mm embryos, possible to make mutants by random mutagenesis, methods for manipulation genomic DNA, knockdown of expression of specific genes is possible using morphlinos

Question 18

What are advantageous mouse characteristics?

Answer 18

Most closely related to humans

Question 19

What are advantageous mouse genetics?

Answer 19

2 month breeding cycle, inbreeding (identical genetic composition), manipulations of embryonic stem cells (transgenic mice), production of mouse knockouts

Question 20

What are the advantages and disadvantages of mouse disease models?

Answer 20

Pros: powerful approach understanding the role of a particular gene in a model and its role in disease
Cons: Production of knockouts is very expensive and time consuming (ethical implications too)

Question 21

What are characteristics of eukaryotic nuclear genomes?

Answer 21

Split into linear set of chromosomes, have at least 2 chromosomes, have multiple origins of replication

Question 22

What are the names of the staining patterns in chromosomes?

Answer 22

G-banding (dark AT rich), R-banding (dark GC rich), Q-banding (dark AT rich) and C-banding (dark constitutive heterochromatin)

Question 23

What do decondensed chromosomes do when not undergoing division?

Answer 23

They occupy a specific territory within the nucleus

Question 24

What are centromeres?

Answer 24

Where sister chromatids are held together

Question 25

Where are centromeres located?

Answer 25

At the assembly site for a protein complex called the kinetochore (used in chromosome division)

Question 26

What are the 4 different positions the centromere can have?

Answer 26

Metacentric, submetacentric, acrocentric and telocentric

Question 27

What are telomeres?

Answer 27

They are composed up of hundreds of copies of repeated motif and associated with a specific set of proteins

Question 28

What are the 2 major functions of telomeres?

Answer 28

1. Allow a cell to distinguish a real chromosome end from an unnatural end
2. They solve problems that the cell has replicating the ends of linear chromosomes

Question 29

What is the end replication problem and how is it fixed?

Answer 29

3’ terminal cannot be copied so it is degraded which shortens the chromosome, the overhang is recognised by telomerase which adds repeats so it is not degraded

Question 30

What is replicative cell senescence?

Answer 30

When telomerase is turned off in nearly all somatic cells which allows chromosome ends to degrade and end up damaged to a point they can no longer survive

Question 31

How is all of the DNA packaged into cells?

Answer 31

DNA is associated with histones which it is wrapped twice around an octamer of forming a nucleosome which is the basic repeating unit of chromatin

Question 32

What are the 2 different types of chromatin and what do they do?

Answer 32

Euchromatin: relatively uncondensed associated with active genes
Heterochromatin: condensed, associated with repetitive gene poor regions that are inactive

Question 33

What are different unusual chromosome types?

Answer 33

Minichromosomes (short rich in genes), B chromosomes (additional chromosomes), holocentric chromosomes (do not have single centromere but multiple kinetochores) and polytene chromosomes (giant chromosomes)