Genetics Flashcards by Emily Christie

What are the stages of the cell cycle?

G1
S phase
G2
M phase

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What happens during S phase?

The DNA is replicated

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What happens in G1 phase?

Cells increase in size and the cell contents are duplicated

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What happens in mitosis?

One diploid parent produces 2 identical diploid daughter cells

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What happens in meiosis?

Gametes are produced

One diploid parent produces 4 haploid daughter cells

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What are the parts of a chromosome?

Telomere
Centrosome
Short arm (p)
Long arm (q)

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What techniques can be used to analyse chromosomes?

FISH
Array CGH
PCR
NGS - next generation sequencing

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What does FISH stand for?

Fluorescent in-situ hybridization

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What can FISH be used to determine?

Whether there is extra or missing material

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What can NGS do?

Sequence the whole genome or all known exons

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What does array CGH do?

Analyses the whole genome BUT cannot detect a balanced arrangement - only unbalanced

The patient’s DNA is compared to a reference sample

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What is aneuploidy? - Give examples

A whole extra or missing chromosome

Trisomy 21 = downs syndrome
Trisomy 18 = Edward’s syndrome

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What does balanced mean?

All the chromosomes are present however they may be rearranged

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What is Robertsonian translocation?

Two chromosomes get stuck together

Note: all the genetic material is still present so there is no disease BUT offspring will be affected

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What does trisomy 14 cause?

Miscarriage

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What is reciprocal translocation?

When segments of material are exchanged between different chromosomes

This means 50% of offspring will have normal chromosomes or a balanced translocation
The other half will be unbalanced

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What is a polymorphism?

A variation in the human genome that occurs in >1% of the population

Therefore it doesn’t cause disease in it’s own right but it may predispose you to specific diseases

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What does SNP stand for and what effect does it have?

Single nucleotide polymorphism

Most have no effect

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What are CNVs?

Copy number variations

They are extra or missing stretches of DNA

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What is a mutation?

A gene change that causes a disease

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What are Mandelian disorders?

They are caused by a change in a single gene and are high penetrance

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What is penetrance?

The likelihood of having a disease if you have the mutation

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What is non-mandelian inheritance? Give examples

Multi-factorial

Methylation and mosaicism

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What is mosaicism?

When different cells have different genetic material

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A type of Mandelian inheritance is autosomal dominant, what does this mean, for offspring too?

Only one copy of the gene is needed to cause the disease. Meaning offspring have a 50% chance of getting the disease if parent is affected - so seen in all generations and independent of gender

What does autosomal recessive mean and what does it mean for offspring?

This means two copies of the gene are needed to get the disease. Meaning the offspring of a carrier has a 25% chance of having the disease if parents are carriers and 50% chance will be carriers. If one parent has the condition and the other is normal then children 100% chance of being carrier

What is X-linked recessive? (Also Mandelian inheritance)

2 recessive mutations on the X chromosome. Since males only have one X chromosome they will always have the disease (if mother is carrier), but will never be carriers but can pass onto daughter to be carrier(as need two affected X) Females will be carriers or affected or fine and will not show major features of disease

What are oncogenes?

Involved in cancer and promote cell division

What are tumour suppressors?

They stop cells dividing

What is methylation and where does it usually occur and what does it do?

The addition of a methyl group. Occurs on cytosone bases just before guanine bases Leads to modification of histones that stop transcription

what are the stages in the cell cycle?

G1 -> S -> G2 -> M -> G1

at which stage does DNA synthesis occur?

s phase

define mitosis.

one diploid parent become 2 identical diploid daughters

define meiosis.

on diploid parent become 4 haploid daughter cells

what sequence variation can you get within a gene?

changes in promoter sequence | changes in exon sequence

what sequence changes can you get in DNA between genes?

SNPs | larger deletions or duplications

do polymorphisms cause disease?

no, but may predispose to a common disease

what is a polymorphism?

a genetic variation prevalent in population which, in itself doesn't cause disease.

what is multifactorial disease caused by?

multiple polymorhisms

what is aneuploidy?

whole extra or missing chromosome

what is translocaiton?

rearrangement of chromosomes

what translocation results in miscarriage?

trisomy 14

what translocation results in Edward syndrome?

trisomy 18

what is a normal male and female?

46XX or 46XY

what is 45X?

turner syndrome

What is 47XXY?

Klinefelter syndrome

what is Robertsonian translocation caused by?

Two acrocentric chromosomes stuck end to end

what is the first line chromosome test?

microarray CGH

what is microarray CGH used for?

to detect any missing or duplicated piece of chromosome and to find polymorphisms

what is mosaicism?

different cells having a different genetic make up (could be a chromosome abnormality or point mutation etc)

What does gonadal mosaicism cause?

a recurrence risk for autosomal dominant conditions even if parent unaffected

what is somatic mosaicism?

all cells suffer mutations as they divide, repair mechanisms exist

what does a tumour suppressor do?

prevent cells dividing

what does an oncogene do?

initiate cell division

what is first line for paediatric referral which checks for deletions/duplications?

aCGH = microarray comparative genomic hybridisation

what do promotor and splice site sequence mutations cause?

Stop transcription or cause abnormal splicing

What will a mutation resulting in changing a base result in?

potentially amino acid change, causing change in protein sequence. May reduce function of protein

what is a mendelian disorder?

an umbrella term for a disease that is caused by a change in a single gene

what is X-linked dominant and how are offspring affected?

One dominant mutation on X chromosome is needed. So homo and heterozygote dominant females affected (XD XD or XD Xd) Males be affected. Males only pass onto daughters (X comes from mother for son) Females pass equally to offspring.

What type of inheritance is Huntington's disease?

autosomal dominant

give an example of x-linked dominant disease.

fragile-X- syndrome

what type of inheritance is cystic fibrosis?

autosomal recessive

what type of inheritance is haemophilia?

X-linked recessive