[FMS] MCG - genetics and inheritance Flashcards by Sana Hashemi

what is a genotype

full complement of all the genes in the genome

How well did you know this?

Not at all

Perfectly

what is a phenotype

the functional consequence of a gene (or combination of genes)

How well did you know this?

Not at all

Perfectly

what is a monogenic disorder, give an example of a monogenic disorder

disorders associated with single gene
e.g. cystic fibrosis

How well did you know this?

Not at all

Perfectly

what is a polygenic disorder, give an example of a polygenic disorder

disorders associated with many different genes
e.g. Type II diabetes

How well did you know this?

Not at all

Perfectly

what is chromatin?

DNA + histones = chromatin

How well did you know this?

Not at all

Perfectly

how is DNA ‘packaged’

DNA is packaged in the nucleus in conjunction with positively charged histone proteins

DNA + histones = chromatin

Octamer of histones 2x (H2A, H2B, H3, H4) forms a core with the DNA around the outside

Histone octamer = nucleosome

H1 links nucleosome together

Nucleosomes form a chromatin fibre

Chromatin fibre loops out of a central nuclear matrix protein that create the individual chromosomes

How well did you know this?

Not at all

Perfectly

out of the 23 pairs of chromosmes, how many are autosomes and how many are sex chromosomes

22 pairs of autosomes
1 pair of sex chromosomes

How well did you know this?

Not at all

Perfectly

what are chromosomes stained with and where

stained at metaphase with giemsa dye

How well did you know this?

Not at all

Perfectly

what is cytogenics?

the study of the genetic component of a cell through the visualisation and analysis of chromosomes

How well did you know this?

Not at all

Perfectly

which chromsome is the largest and which is the smallest?

Chromosome 1 is largest and chromosome 22 is the smallest

How well did you know this?

Not at all

Perfectly

what is the normal female karyotype and male karyotype?

Normal female karyotype is 46 XX
Normal male karyotype is 46 XY

How well did you know this?

Not at all

Perfectly

describe the chromosome arms?

short (p)
^ hehe short peepee

long (q)

How well did you know this?

Not at all

Perfectly

how can the location of genes be specified?

based on the G-banding pattern and the arm of the chromosome

How well did you know this?

Not at all

Perfectly

how does the body prevent female cells from having double the amount of X-linked genes

X-chromosome dosage compensation - Female cells are 46 XX however only one of the X chromosome is active

How well did you know this?

Not at all

Perfectly

how is one of the X-chromsomes inactivated in x-chromosomes dosage compensation?

Early in embryology one of the X chromosomes inactivated randomly

A gene on the X-chromosome is transcribed as Xist ncRNA – this RNA triggers the transcriptional silencing of one of the X-chromosomes

How well did you know this?

Not at all

Perfectly

what region of Y is required for male development?

SRY gene

How well did you know this?

Not at all

Perfectly

what protein is encoded by the SRY gene?

testis-determining factor (TDF)

How well did you know this?

Not at all

Perfectly

what is euploidy?

normal number of chromosomes

How well did you know this?

Not at all

Perfectly

what is aneuploidy

irregular number of chromosomes

How well did you know this?

Not at all

Perfectly

what is aneuploidy caused by?

the failure of homologous chromosomes to separate properly during meiosis = non-disjunction

How well did you know this?

Not at all

Perfectly

which trisomies lead to live births?

13, 18, 21

How well did you know this?

Not at all

Perfectly

what is trisomy 13?

patau syndrome

47 XX +13 or 47 XY +13

Common abnormalities:
include heart defects
incomplete brain development

mean survival ~130 days

How well did you know this?

Not at all

Perfectly

what is trisomy 18?

Edward’s syndrome

47 XX +18 or 47 XY +18

Very rare live birth (95% die in utero) numerous

abnormalities: heart and intestinal development

10% survive for 12 months

How well did you know this?

Not at all

Perfectly

what is trisomy 21?

Down syndrome

47 XX +21 or 47 XY +21

abnormalities:
growth and development delay
cardiac abnormalities
increased risk of acute leukaemia

How well did you know this?

Not at all

Perfectly

which trisomy is downs syndrome

trisomy 21

which trismoy is pataus syndrome

trisomy 13

which trisomy is edwards syndrome

trisomy 18

when is amniocentesis carried out?

during weeks 15-20 of pregnancy

how do you check for chromosomal abnormalities?

Amniocentesis

when does the majority(95%) of non-disjunction occur?

during oogenesis ^ Spermatogenesis continues throughout life after puberty

how can you tell a disease is autosomal recessive from a pedigree?

Trait is rare in pedigree Trait often skips a generation

in autosomal recessive diseases which sex is affected more?

neither, affects both

do the parents of affected individuals with autosomal recessive diseases have the disease?

no - Parents of affected individuals do not have the disease

give an example of an autosmal recessive disease?

what is CF caused by?

mutation of the Cystic fibrosis transmembrane conductance regulator (CFTR) gene most common is CFTRD508 (deletion of codon 508)

what is a normal, functional allele called?

wild type allele

can you give a biological explanation as to how CF is recessively inherited? why carriers are unaffected?

CFTR pumps Cl- out of cells and leads to water exiting the cell by osmosis Normally 50% of the CFTR is produced from the paternal allele and 50% from the material allele When an individual inherits a single mutant allele the cell only produces 50% of the normal amount of CFTR This 50% is sufficient to provide the function that is needed in the cell It is also possible there is upregulation of the normal allele to compensate

biologically explain what happens when an individual has CF

the mutant CFTR does NOT exit the endoplasmic reticulum as usual = loss of cl- = thicker mucus

how can you tell a disease is autosomal dominant in a pedigree?

Trait is frequent in pedigree Individuals are affected in each generation.

are males and females affected equally or unequally in an autosomal dominant pedigree?

Trait affects males and females equally Trait is transmitted by either sex

in an autosomal dominant pedigree do the parents have the phenotype?

yes

give an example of an autosomal dominant disease?

Huntington’s disease (HD)

what is huntingtons caused by

Caused by mutations at HD locus Mutant HD gene has MORE THAN 36 repeats of CAG sequence instead of ~28

biologically explain how someone has HD

A patient who is a heterozygote with a single mutant allele (Hh) develops the disease Mutant huntingtin protein with the pathologically expanded polyglutamine region also causes the normal protein to aggregate leading to neurotoxicity This is a gain of **negative function**

what are 2 explanations for dominant/ recessive inheritances for other syndromes

**haploinsufficiency** – means the reduction to 50% of the normal protein is insufficient for the normal function to occur **Somatic second hit** – often in cancer predisposition syndromes , patients inherit one mutant allele and a second mutation occurs somatically leading to cancer

how do you know if a diseases is x-linked recessive from a pedigree?

Trait is rare in pedigree Trait skips a generation

which sex does x-linked recessive inheritence occur most in?

males

do parents of x-linked recessive disease have the disease?

Parents of affected individuals DO NOT have the disease

which parent cannot transfer x-linked recessive disease to their sons

**Fathers** can not transmit it to their **sons**

example of x-linked recessive disease

haemophilia A

what is haemophilia A disease

haemophilia A is a blot clotting disorder

what is the cause of hameophilia A

mutation in the factor **VIII** (8) gene on **X chromosome**

is haemophilia A dominant or recessive inheritance?

recessive

what does it mean when most human characteristics are polygenic

are controlled by genes **at more than one locus** e.g. height

what does it mean if a disease is multifactorial?

both polygenic and influenced by the environment

what are the 3 polygenic diseases

obesity diabetes cardiovascualr disease

what is a Monozygotic MZ twin

genetically identical

what is a Dizygotic DZ twin

not genetically identical

if a disease is principally controlled by the environment, which twin would you see it more in: MZ or DZ

BOTH

How much of the Y chromosome confers maleness?

Two chromosomal abnormalities suggest that a small region at the end of the short arm of the Y is all that is needed to confer maleness

What is the function of PAR on a Y chromosome

PAR = pseudo autosomal regions its at both end of chromosomes and have equivalent DNA sequence to X chromosome which allows X to pair to Y during meiosis

what is function of MSY in Y chromosome

MSY = Male specific region this section does not form pair with X chromosome

what are 3 diseases caused by sex chromosome abnormalities

klinfelters syndrome turners syndrome XYY syndrome

what is klinfelters syndrome

47 XXY ^ remember the K looks like an X, therefore has 2 X's = XXy - can appear normal - causes small testes + limited development of secondary sexual characteristics = infertility

what is turners syndrome

45 X - diagnosis during adult life - no adolescent growth spurt, no periods = infertility

what is XYY syndrome

47 XYY ie known as super male syndrome because of the extra Y so have more male characteristics - asymptomatic = no symptoms - increased growth - above average height

Explain Mendelian inheritance.

- The simplest genetic characters are those that depend on the genotype at a single locus. - Diseases caused by these factors are referred to as monogenic disorders. - They display Mendelian inheritance patterns.

What is Mendel’s law?

- Every individual possesses a pair of alleles for a given trait, one of which is passed on to its offspring. - Genes for different traits assort independently of each other (unless they are linked).

Define locus and allele.

- Locus: chromosomal location (position of gene) - Allele: variant of a gene

what can proteins be labelled with

35 S

what can DNA be labelled with

32 P

theres no sulphur in what?

DNA

theres no phosphorus in what?

Protein

what is the composition of the human genome

Describe (metacentric,submetacentric and acrocentric)