DNA as a genetic material Flashcards
Mendelian laws of inheritence:
Mendel(1866)
Segregation: genes come in pairs, and individuals only pass on one of these to their offspring
Independent assortment: different genes are passed on separately from each other – inheritance of one does not depend on that of another
Dominance: an individual with two alleles of a gene will express the dominant form
Features of genetic material…
Replication of information
Storage of information
Expression of information
Variation by mutation
What did Sutton and Boveri (1902) study?
early development in 2 model organism using cytology and microscopy.
What organisms were used? why?
Sutton- grasshoppers
Boveri- Ascaris worms
Both has large but few chromosomes= easy to see
Finding:
Grouping in pairs and subsequent separation; reduction in chromosome number in gametes.
Destruction of chromosomes stopped normal development of embryos
Noticed that their observations were consistent with Mendel’s laws of heredity.
Suggested that different combinations of chromosomes could cause variation
Why are their findings referred to as a physical basis for Mendel’s independent assortment?
Chromosomes are required for embryonic development.
Chromosomes carry Mendel’s “factors” (Sutton used the term gene).
Chromosomes are linear structures with genes along them.
What did Griffith (1928) study?
transforming principle
Streptococcus pneumoniae, causes pneumonia in human and mice.
Describe both strains…
S strain - Smooth bacteria – polysaccharide coats – pathogenic
R strain – Rough bacteria – no polysaccharide coats – not pathogenic
-look different under the microscope
- different effects in vivo
Why is the S strain pathogenic?
Due to its polysaccharide coat, protecting it from the hosts immune system.
Griffiths method to test if these were fixed, or can be transformed from one strain to another?
- Kill S bacteria (heat)
- creates S extract (doesnt kill mouse) - Inject dead S with live R
-mouse is infectted - Is there a polysaccharide capsule?
-yes
What were Griffiths results?
-Inoculation with dead S bacteria + live R bacteria establishes infection.
- Bacteria taken from infected mice do have a polysaccharide capsule.
-R cells have undergone a “transformation”.
-Some sort of hereditary material has passed from the S bacteria to the R bacteria, changing the genotype.
-Griffith called this material the “transforming principle”.
What did Avery, MacLeod and McCarthy (1944) do?
Found which molecules were responsible for the transformation by systematically destroying each component of the S strain extract with enzymes, then combined with R to test.
What is required for the bacteria to be virulent?
DNA encoding for the enzymes to make the polysaccharide coat but not the polysaccharides themself.
