Genetics Flashcards
(38 cards)
what is the Difference between constitutive and regulated gene expression?
Constitutive :Products made by all cells all the time - often called ‘housekeeping’ genes. Expression is constant.
Regulated: Time (developmental), place (cell type), amount, in response to signals. Can be under very tight control

~20,000 genes but many more (millions??) proteins. Protein diversity is increased and can occur because?
Many genes have more than one promoter.
Alternative splicing
mechanisms for chromatin remodelling using epigenetic marks (5)?
o histone modifications (acetylated in euchromatin; methylated or hypo-methylated depending on histone variant).
o DNA methylation (NB methylation of CpGs (often around promoters)lead to silencing of genes).
o nucleosome positioning.
o non-coding RNAs.
o nuclear location of chromatin.
Differences between euchromatin and heterochromatin?
eu = open, relaxed. Hetero = closed, condesned
what percentage of the human genome is responsible for protein coding seqeunces
1-2%
Factors involved in basal gene expression (3)?
open chromatin, RNA polymerase, basal transcription
factors that interact with promoters (DNA) and various proteins.
Factors involved in regulated gene expression (6)?
same as above (open chromatin, RNA polymerase, basal transcription factors that interact with promoters (DNA) and various proteins.) + enhancers/silencers (DNA), more
transcription factors, long non-coding RNAs
• Basic steps in gene expression
open conformation of chromatin. Transcription. Post-transcription processing. Translation. Post Translation processing. Protein targeting and transport.
what does biallelic mean?
gene is expressed from both maternal and paternal copy
consequenes of monoallelic expression?
for some genes its sufficient. Others its not. Some it IS ESSENTIAL (X inactivation)
Inactivation of genes on the X chromosome and genomic imprinting is mostly determined by epigenetic mechanisms. name them (3)
Histone modifications, DNA methylation and Non-codingRNAs
what is the inactived X chromosome called
Barr Body
describe X chromosome inactivation
occurs in early embryogenesis and starts with expression of Xist – a long non-coding RNA, leading to heterochromatin formation spreading along the chromosome; DNA methylation also plays a role.
is the whole chromosome switched off in x inactivation
no, Some genes on the X chromosome escape X inactivation because they need to be expressed biallelically
definition of genomic imprinting
a phenomenon by which certain genes can be expressed in a parent-of-origin-specific manner
Genomic imprinting involves which epigenetic mechanisms (3)?
DNA methylation, Chromatin condensation (including histone modifications), Non-Coding RNAs
• Mechanisms that can give rise to disorders of imprinting (4)
Deletion or duplications of regions of imprinted genes (Loss of Heterozygocity). Uniparental Disomy (UPD) - both chromosomes from mother or father. Epimutations - loss of imprinting DNA mutations in imprinted genes
how does UPD occur (4)?
1: Meiotic non- disjunction in both gametes (egg has 2 chromosome and sperm has none. or vice versa).
2: Meiotic non- disjunction in one gamete followed by duplication in zygote (egg has 1 chromosome, sperm has none and egg is duplicated. or vice versa).
3: Loss of one chromosome in zygote and duplication of other chromosome.
4: Meiotic non-disjunction in one gamete followed by loss of chromosome in zygote (egg has 2 chromosome, sperm has one, sperm is lost in zygote. or vice versa).
what is BW syndrome? what is the majority of causes?
Beckwith-Weidemann syndrome is an imprinting disorder linked to imprinted genes on chr 11p15.5.
Majority caused by epimutations on maternal allele.
what are PW syndrom and Angelmann syndrome? what are their causes.
are imprinting disorders linked to imprinted genes on chr 15q. PWS due to deficiency of paternally expressed genes (P or paternal). AS essentially due to a deficiency of maternally expressed genes
pattern of inheritance for Mutations in an active paternal/inactive maternal?
male carriers and affected males can have affected children but not carrier children.
Female carriers and affected females can have carrier children but not affected children
Pattern of inheritance for Mutations in an active maternal/inactive paternal?
female carriers and affected females can have affected children but not carrier children.
Male carriers and affected females can have carrier children but not affected children.
what percentage of babies have a birth defect?
4%
what are the most common autosomal and sex chromosomal defects respectively?
Trisomy 21 and Klinefelter Syndrome (XXY).
