Biology 1002B Lecture Notes - Lecture 15: Histone H2B, Noncoding Dna, Chromatin

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Published on 15 Apr 2013
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Lecture 15: Epigenetics Identical Twins are Not
Clicker: Which of the following signals in DNA is “understood” by the cell through protein
binding to nucleic acid?
o Polyadenylation signal is a site that cuts the mRNA off so it is understood
Gets recognized by protein to get cut after it gets transcribed into mRNA
o Operator
o Enhancer
Know figure 14.6, in the textbook
Clicker: if identical twin sisters each have a son with identical twin brothers, the kids will be
identical
o False , gametes are different, sexual recombination
Clicker: what does more than 50% heritability of schizophrenia mean for Alice? (identical twins)
o Over 50% means, over that 50% variability attributed from genes, so that if they’re
identical, she has a very high chance of getting schizophrenia
What is different about identical twins
o They make different gametes
o Gene expression might be different (might have same gene but different expression)
o There are mutations within them because from 1 to trillions of cells there bound to be
mistakes within replication, random mutations
Environmental mutagens
o Only females: different active X in different tissues
o
Random X chromosome inactivation creates genetic mosaics
o Rainbow was a cat, and they cloned the cat and they look very different because the
inactivation of X
Same genotype, different phenotype
o At about 100 cells the both X chromosomes are active but then the cells undergo
inactivation. The cells will inactivate paternal X or maternal X, at random, so that they’re
all at random, mosaics
o All the descends of the cells will keep the same inactive X, the cell line will all keep the
same inactive X, so there are about 100 cell lines and each with random inactive X
That’s why they’re mosaic
Xist RNA binds along the inactive X chromosome, silencing most genes
o Very condensed X chromosome called bar body
o Xist -> X inactive specific transcript
o They keep the X chromosome inactive
o It codes the chromosome and keep it away from replication machineries to make it
inactive
Stable through the cell’s entire cell line
o This is called epigenetics, binding of the non-coding DNA
Xist and tsix genes are transcribed in opposite direction at same locus
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Document Summary

Clicker: which of the following signals in dna is understood by the cell through protein binding to nucleic acid: polyadenylation signal is a site that cuts the mrna off so it is understood. Gets recognized by protein to get cut after it gets transcribed into mrna: operator, enhancer. Clicker: if identical twin sisters each have a son with identical twin brothers, the kids will be identical: false , gametes are different, sexual recombination. Environmental mutagens: only females: different active x in different tissues. Random x chromosome inactivation creates genetic mosaics: rainbow was a cat, and they cloned the cat and they look very different because the inactivation of x. Same genotype, different phenotype: at about 100 cells the both x chromosomes are active but then the cells undergo inactivation. Xist rna binds along the inactive x chromosome, silencing most genes: very condensed x chromosome called bar body, xist -> x inactive specific transcript, they keep the x chromosome inactive.

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