Bi Sc 002 Exam 2
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What is intermediate Inheritance?
aka co-dominance where the phenotype of an individual shows the affects of both alleles- shows third phenotype
What is sickle cell anemia and what is it an example of?
rbc cant carry oxygen as well. since sickle cell allele is dominant, theres a third phenotype possible- which gives you a milder survivable case sickle cell anemia even if your heterozygous
What does it mean to have mulitple alleles in the population?
That there are many different versions of a gene in the population, even though a person only has two
Whats an example of Multiple alleles being in the population?
- ABO gene which determines blood type
- has three alleles (A B and O)
Which alleles have dominance in the ABO gene?
- A and B are co-dominant
- - AB, AO (A) BO(B) AA BB OO=O most common in pop.
what is the most common case in a phenotype?
Having multiple genes working together to give you a trait
22 out of 24 types of chromosomes and contains both members of homologous pair and carry all the genes for that particular chromosome tye
- 23rd pair of type of chromosomes- some genes may be missing from one member
- X and Y chromosomes
- Y is smaller
What two chromosomes make a girl? a boy?
How do embryos start out in respects to phenotype
they start out girl and the Y turns on to make a guy- acts to alter this tendency
Organs that develop first and develop into ovaries or testes if testosterone is produced
Produce both estrogen and testosterone during development
how are intersex people created?
too much testosterone is made during development
what happens to females after 16 days of development to chromosomes?
- one gets turned off or inactive becomes Barr Body
- this shrivels up because all the genes necessary are there on the X chromosome
- the inactivation is random in different cells
example of inactivation of X chromosome
tortoise shell cats- gene for fur color is on X so depending on which X gives black or orange color
what gene is on the Y chromosome that isnt on the X? and what is it?
- SRY gene- sex determining region Y
- transcription factor which turns genes on and off in gonads to develop testes
Whats the problem with SRY gene?
its near the end of the Y chromosome so it can easily break off and connect to the X chromosome which then can be passed down and can have an XX individual thats a boy
what determines the sex of the offspring?
which chromosome is carried by the sperm because all eggs have X
odd number of sex chromosomes- three chromosomes results in Klinefelter's syndrome
resulted from three sex chromosomes - XXY- is more male than female but has underdeveloped testes and is usually sterile and has increased risk of speech and reading dificulties
what are sex-linked traits?
- traits or characteristics that are more often seen in males- not related to reproduction- genes only on X chromosome
- Because males only get one X from their mother and if that allele is mutated then they have the trait
example of sex linked trait that mostly males get because females have two chances to get good allele when males only have one
- problem clotting blood- high mortality at early age
- result of problem on X-sex linked trait
- two alleles - normal is dominant and usually passed on by heterozygous women to sons because males usually die before they can reproduce and sons only have one chance of getting a good allele
How can you compare DNA?
by matching all the base sequences of the whole genome
Instead of looking at every base in DNA fingerprinting you look at...?
Loci or locus
Loci or Locus
- particular part of DNA or spot of DNA where there is likely to be many alleles in the population
- usually found in non-coding regions
Why are loci usually found in non-coding regions?
- because mutations in these regions have no effect so over time there are lots of different mutations in the population which creates many alleles - areas between DNA
- Usually sequences where bases are repeated
Types of repeated bases used in DNA fingerprinting
- STRs- short tandem repeats- 2-6 repeats
- VNTRs- variable number tandem repeats- 7-20or30 repeats
Short tandem repeats-- 2-6 bases
Variable number tandem repeats 7-30 repeats
What represents allele in non-coding DNA
number of Repeats
what is the length of DNA in STRs/VNTRs directly related to?
number of repeats
How do you find out the length of DNA
by cutting out regions with enzymes that cute at specific sequences then separate using gel electrophoresis
- 1. Add fragments to one end of a gel
- 2. Apply electric current so that far end of the gel has a positive pole
- 3. DNA fragments that were cut usuing restriction enzymes move through the mesh towards the positive pole bc negative charge
- 4. position of fragment when done determines how long because shorter fragments go faster
- having only one version of a gene- one allele in all cells
- only on X cells in males
how to find fragments in the gel...
- could dye the DNA to see all the fragments
- but usually we just wanna see the fragment with the variable repeats
- so we can use probes to find those DNA repeats
has a specific base sequence that compliments the base sequence we are looking for
Two sources of DNA when we need lots of copies of a given locus
- blood sample
- PCR- polymerase chain reaction
Polymerase Chain Reaction (PCR)
- can copy one strand of DNA and make thousands of copies
- doubles the number of copies with each round of PCR
- Quick and Cheap and powerful- only need one copy and dont need cells
- requires knowledge of sequence being copied
Comparing Alleles for DNA fingerprinting
if enough alleles are the same length with same repeats at all the loci then its probably the same person
DNA fingerprinting is used to determine...
paternity. if child has alleles from alleled father then the child is likely to be the child of the father
Why is it important to test to determine presence of genetic abnormalities?
- presence of genetic abnormalities can lead to genetic disease
- first step in predicting risk of the diseases
Finding mutated genes requires
- large numbers of copies of gene - need to use PCR if we dont have enough copies
- you can use early stage embryo cells
Why do we need thousands of copies of DNA for gel electrophroesis?
because you need to be able to see it.. one copy with one probe wont be enough to see it in the gel
Methods of testing for presence of genetic abnormalities
- Karyotyping from abnormality in chromosome number
- if not that key is to know location of gene and sequence of gene
- If the mutation changes sequences at restriction sites then we can cut the DNA and if the fragments are longer than it has a mutation
- if its inbetween restriction sites use probes to find the mutated sequence
- photograph chromosomes
- physically cut out of paper chromosomes
- arrange them by type based on size
- look for extras
- good with down syndrome and klinefelter's
Example of restriction site enzyme
Eco R1- cuts at sequence CTTAAG
Huntington's Disease (reading Fate)
- Chromosome number 4, important in brain development, produces protein called huntingtin which needs to be removed, if not removed it accumulates - fatal
- Number of repeats determines time to die- 39 or more is fatal
- theres no doubt that you will die when you get tested for it
- and theres no cure so your fate is held in the results
Venezuelan Woman (fate)
- asked doctors if she had the gene but doctors didnt have a test
- were certain she had it but said maybe
- changed her fate of killing herself but probably died from huntington's
Why would you get tested for Huntington's?
- protect your kids
- know your fate
- it effects families- parents who have it 50% of kids get it also.
(Knowledge that can Save you) what genes are involved in breast cancer? does it explain it?
- BRCA1 or BRCA2 genes- certain alleles that give you more risk of developing breast or ovarian cancer or prostate cancer (in males too)
- its a mutation in cell division makes cells divide uncontrollably
- No it explains about 10% of cases
Does the risk of getting cancer increase if you have BRCA?
- yes 6-10x increase risk for breast cancer (50%-80%)
- and 10-20x risk for ovarian cancer (27%-40%)
Similarities and differences between BRCA testing and Huntington's testing
- Similarities- test for specific alleles of specific genes and testing for life threatening conditions
- Differences- Not 100% outcome there are ways to decrease risks
Ways to decrease risk of getting Breast cancer with BRCA genes
- Double mastectomy- remove breast tissues
- Oophorectomy- remove ovaries
- Mammogram- most common of the three- early detection and increased survival
Concerns about testing for BRCA
- Family dynamics- brother has it, sister may have it also
- 50% chance if parent is heterozygous
Genetic Engineering is
moving DNA/genes from one organism to another- even accros species lines
What is need for Genetic Engineering?
- Huge number of copies of gene
- start with huge numbers of cells and use restriction enzymes to cute DNA
- or use polymerase chain reaction
- in genetic engineering-
- cuts DNA at specific sequence cuts in a way to leave short single strand ends which can then match up with the DNA from different sources cut with the same restriction enzymes and will compliment and match up
What is the ideal situation to deliever genes to the cells? (theory)
- if the gene of interest can be returned to the cell withough being degraded by enzymes in the cell then cells will replicate the inserted gene with every cell division and will make desired protein product
- but usually short linear pieces of DNA are degraded by enzymes
- DNA that are used to deliver desired DNA to cells.
- DNA is cut and inserted into vector DNA with the same restriction enzyme
- product is called recombinant DNA
DNA from two sources
- circles of DNA that hold 5 to 20 genes
- easily removed from cells to paste desired genes in
- make recombinant plasmids in test tubes
How do you return Plasmids to the cells
- 1. mechanical injection using tiny needles
- 2. Microprojectiles
- 4. Agrobacterium
- put the plasmids into a very tiny gold particle because gold is a dense metal and it will punch through things and isnt reactive
- put into a gene gun and fire it into cells
- treat cells to make the outer part of the cell a little bit leaky
- now the cell can absorb the plasmid DNA
- type of bacterium that natrually affects plant cells
- naturally delivers Ti plasmid
- naturally inserts DNA into plant chromosome
- We can insert genes into Ti plasmid and manipulate natrual happenings by inserting our genes into the plant
- good for deliver genes into plant and animal cells
- some types naturally insert DNA into nucleus
- For Genetic Engineering- remove certain viral genes so that the virus doesnt replicate itself
- then paste in genes of interest
The fate of DNA thats delievered by Virus vectors
- depends on virus vector type
- some form circles outside chromosomes- chromosomal circle
- some insert DNA into chromosomes
- would be used in gene therapy
Bacteria and yeast are used as...?
- protein factories - you can grow huge numbers of cells after transferring genes to these organisms
- put into bacteria using leaky cells
Transfer of genes to plants
- more complicated
- usually will be used with crop species because you can make money off of them
- creates genetically modified crops
- transfer of genes into humans
- goal is to add a good gene or allele to make a good protein
- doesnt remove defective alleles
- uses virus vectors to deliver
Problems with using virus vectors in humans
- the immune system recognizes its a virus and may attack the good DNA
- much more difficult to do inside body (liver) white blood cells are easier to do becasue can take them out of the body
problems with gene therapy
- have to "fix" millions of cells to make a difference
- delivery methods are often very inefficient often only a few cells are going to be affected
- poor regulation causes too much protein or too little protein
Hasty Decisions (reading) What is OTC deficiency and why is it toxic?
- OTC enzyme prevents build up of ammonia from use of amino acid- toxic if you cant get rid of them
- most babies dont live through first year but if they pass the first year they dont usually live much longer
Problems with gene therapy fixing OTC deficiency
- difficult to fix cells in liver because cant take them out of the body
- Adenoviruses are efficient at delivering DNA to cells but set off strong immune system response
- monkeys died when trying to do same procedure
Problems with jesse's case (OTC Hasty reading)
- ethics- didnt tell him everything about the risks
- money from investments pushed the doctors to go ahead with operations
- they wanted to be the first so they hurried through
- made some adjustments but didnt test them
- textbook exampleof how things go wrong.
consent given when all the information about the risks and procedures are presented
What would you like to do?
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