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DNA segregation contd
Nature of Alleles and their products
Dominance vs Recessiveness
Pedigrees for Single Gene traits
Direct Detection of Segregation of DNA using different methods
RFLP- Restriction fragment length polymorphisms
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Below, these are based upon use of PCR
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[RFLP (Detect restriction
fragments by using Southern Analysis); Cleaved Amplified Polymorphism;

CAPS - cleaved amplified polymorphisms
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Very Similar to RFLP
First PCR amplify gene or DNA of interest , from all individuals then digest
with restriction enzyme, then run on agarose gel and stain the gel
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Ends up with hundreds of amplifications of just the region of interest
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Then put in a restriction enzyme and cut that
gene
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Don’t need probe and transfer on to a membrane because many copies
present and can see it on the gel
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Heterozygotes display additive patters on the gel
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doesn’t matter how many fragments
there are, heterozygotes will always be additive
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Only see 1 homozygous pattern and 1 heterozygous pattern on the gel
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• PCR amplify the gene of interest from each genotype
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Run the
DNA on a non-denaturing polyacrylamide gel
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Since the DNA
is single stranded, under the particular gel running conditions, the single
stranded DNA folds up depending on its sequence, and then runs
through the gel as a function of the way it has been folded
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• Make it single stranded and see 2 bands on the gel for AA, because 2 strands
complimentary to each other
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Small aa, runs differently
because its folded a different way
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• Don’t need to know what the sequence is except for the gene of interest in
order to amplify it and is not very widely used
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• Can detect one nucleotide difference using very small amounts of DNA
on the gels
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Tend to show dominance
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Not required to know for this course
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Should
segregate in a mendellion way
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bk]
• Alleles can differ by one base pair at the DNA level or one or more
nucleotides
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• Silent mutation- mutation that has no effect whatsoever on the individual
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Different codon but still code for the
same amino acid
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Example
Leucine and Isoleucine
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Some mutations close to
the end of an intron may cause differences in how they are cut out but
greater probability that there won’t be any effect on the protein
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Changes in the amino acid that causes the enzyme not
to work or mutation that inserts a stop codon and therefore stops
translation due to the pre-mature stop codon causing the protein to be
made to be non-functional
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If you have a mutation there, it
may affect whether the protein is expressed or not
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The gene that is
involved in this disease that causes it has an enzyme that converts the
normal functioning gene from phenyalanine to tyrosine
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When the enzyme is blocked, there is a
buildup of phenylalanine which then has other enzymes that convert it to
phenylpyruvic acid which is a neurotoxin
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• Figure 2
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Gene
will never be turned on and so will be non-functional
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Silentmutation may be occurring in a part of the protein that causes on
effect and doesn’t change the structure or function of the protein
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Dominance vs Recessiveness [refer to n
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Which means having just one copy of the
gene that is sufficient to allow you to carry out the biochemical function of
the gene
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[PP, Pp] In a haploid form Pp, can still carry out there biochemical
function since they are haplosufficient
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• The opposite would then be haploinsufficient
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This is because a haploinsufficient
gene that has only one copy of the functional gene cannot produce
enough product
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Sex linked Inheritance
• Thomas Hunt Morgan first discovered sex linked inheritance
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Could see the difference in chromosomes between X and Y
and was perfectly correlated to the genotypes seen

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