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Flashcards in Medical Genetics- Intro Deck (24)

Berg and Boyer's contributions to genetics

Developed tools that allows scientists to manipulate DNA to more deeply understand their functions and to mass product drugs generated through recombinant technology (i.e.: insulin)



A tightly wound pieces of DNA, house genes



An individual's chromosomes profile can be analyzed using this technique

This process stains metaphase chromosomes with a Geimsa dye that will stain heterochromatin in distinct, AT-rich banding patterns, sometimes referred to as G-bands

The stained chromosomes are then visualized, organized according to size and matched with its chromosome homolog



Segregation errors in meiosis

Can lead to germ cells carrying too many or two few copies of affected chromosomes


What happens if Nondisjunction occurs during meiosis one?

End up with two cells with no chromosomes
And two cells with each cell having two sister chromatids (2 chromosomes in each cell)


What if Nondisjunction happens at the end of meiosis 1?

One cell with nothing
One cell with two sister chromatids (same ones)
Two cells normal with one sister chromatids each


Turner syndrome

If a germ cell missing a copy of an X chromosome were to fuse with another germ cell carrying it normal X chromosomal content, the result would be a human with a single X chromosome.


Where can mutations occur?

Coding region, promoter region, intron-exon junction


Recessive allele

When the mutation eliminates or reduces normal activity of the gene, also known as a loss-of-function mutation

Will only result in a specific phenotype or observed trait when the second copy of the gene is also a recessive allele or when no second copy exists


Dominant allele

Increased activity of the gene leading to a gain in [toxic] function


linked genes

If two genes are very close to each other on the chromosome, they can be inherited together and can only be separated during recombination in meiosos


incomplete dominance

each genotype will show a different phenotype because of differences in gene dosage (ie: flower example)


Codominant alleles

each allele can contribute to the phenotype regardless of the presence of absence of any other alleles

ie: blood type


Incomplete penetrance

a particular genotype does not manifest itself in the expected phenotype 100% of the time

can be due to either environmental influences or interactions of a particular gene with an individual's genetic background


Modifier Loci

alternate genes in the genome that can affect a particular phenotype associated with a different gene

can influence or prevent phenotypic manifestation of a particular genotype



individuals can expose themselves to an environmental factor that phenotypically mimics a condition present in the family



When many systems are adversely affected by a single genetic defect (b/c genes have multiple functions in various tissues)


Multifactorial inheritance

Joint actions of a large number of genes and outside stimulus in a particular phenotype (can produce a spectrum of observed phenotypes)


Acetylation of lysines

Histones have lysines, add acetyl group to the tails to neutralize the positive charge on the lysines --> makes chromatin more open because negative DNA backbone not attracted anymore

associated with open conformation


Where does methylation occur on DNA?

cytosine residues of CpG dinucleotides

can be found in promoter regions of the genes and are known at CpG islands


What is the methylated state associated with?

Closed conformation and gene silencing


Can DNA methylation be propagated?


1) replication
2) maintenance of methylation



genes whose expression is determined by the parent that contributed them

The process begins during gamete formation when

in males certain genes are imprinted in developing sperm and
in females, others are imprinted in the developing egg.

All the cells in a resulting child will have the same set of imprinted genes from both its father and its mother EXCEPT for those cells ("germplasm") that are destined to go on to make gametes. All imprints — both maternal and paternal — are erased in them.


What happens to methylation during gametogenisis?

methylation marks on promoters are erased --> resets the epigenetic status in germ cells