Genetics & Inheritance Flashcards
What is a MONOGENIC disorder?
Name an example.
A disorder associated with X1 Gene.
E.g. Cystic Fibrosis
Sickle-cell Anaemia
What is a POLYGENIC disorder?
Name an example.
A disorder associated with multiple genes.
E.g. Type-II Diabetes
Rheumatoid Arthritis
Genotypes can determine if you are resistant to a disease.
What gene affects an immunity from HIV-1.
CCR5 Chemokine Receptor (a protein on the surface of leukocytes). HIV uses these as a way of entering and infecting host cells.
Genes can determine responses to drugs.
Which enzyme is responsible for Codeine metabolism (& approx 25% of metabolism of all clinically used drugs)?
CYP2D6 - a member of the cytochrome P450 class of enzymes.
It converts Codeine into its active form (Morphine).
What is a gene?
A sequence of DNA nucleotides which encodes for a specific protein.
Explain the structure of chromosomes, beginning at the DNA level.
DNA - wrapped twice around X8 histone proteins = X1 nucleosome.
Multiple nucleosomes form chromatin.
When chromatin condenses chromosomes are formed.
What is a normal human karyotype?
46, XX (female)
or
46, XY (male)
How many pairs of autosomes does a normal person have?
X22
How many pairs of sex chromosomes does a normal person have?
X1
What is the implication of females having no Y chromosome?
That it contains no genetic information essential for the viability of humans.
What is the name given to the patterns of bands on chromosomes?
G-banding
Name the three locations the centromere can be found on sister chromatids.
Metacentric - two arms are almost equally (P-arm slightly smaller)
Submetacentric - shorter P-arm and longer Q-arm
Acrocentric- P-arm only exists as a satellite held on by a small stalk
Name the two arms of chromosomes.
P & Q arms.
What are the characteristics of MITOTIC daughter cells?
X2 daughter cells.
Each are diploid (X2 copies of each gene).
What are the characteristics of MEIOTIC daughter cells?
X4 daughter cells.
Each are haploid (X1 copy of each gene).
What is the name of the region on the Y chromosome that determines sex?
SRY Region - sex determining region.
What two genotype combinations can exist whereby the karyotype does NOT match the individuals gender?
XX Males (one X chromosome has the SRY region on its P-arm).
XY Females (Y chromosome is missing SRY region).
What percentage of spontaneous abortions are due to chromosome abnormalities?
And what percentage of these are due to trisomies?
50%
50% (therefore 25% overall)
What is the name given to a normal human karyotype with one EXTRA chromosome?
Trisomy.
What is the name given to a normal human karyotype with one LESS chromosome?
Monosomy.
What is Aneuploidy?
A karyotype of chromosomes other than 46.
What is Euploidy?
A karyotype of 46 chromosomes (full set).
What is Trisomy 21?
46, XX or XY +21
Down Syndrome
What are some of the clinical signs of Down syndrome?
Simians crease
Eyes lower than Earline
Wide nose bridge
What is Trisomy 13?
46, XX or XY +13
Patau Syndrome
What is Trisomy 18?
46, XX or XY +18
Edward’s Syndrome
Which Syndrome does a karyotype of 47, XXY indicate and what are some of its symptoms?
Klinefelter Syndrome
Infertility
Small testes
Which Syndrome does a karyotype of 47, X indicate and what are some of its symptoms?
Turner Syndrome
No growth spurt
Short in stature
Amenorrhoea (no menstrual cycle)
What is the name of the only monosomy born?
Turner’s Syndrome
What is the cause of aneuploidy?
Non-disjunction (failure of sister chromatids to separate during cell division) during oogenesis.
What procedure on the amniotic fluid can test for chromosomal abnormalities?
Amniocentesis.
Why does increases in age increase the risk of a trisomy?
Oogenesis is completed at birth and suspended in meiosis 1 therefore the ova are as old as the mother.
What are the X5 modes of Mendelian inheritance?
Autosomal recessive Autosomal dominant X-linked recessive X-linked dominant Mitochondrial
Give an example or an autosomal recessive disease?
Cystic Fibrosis.
What chromosome and gene are responsible for cystic fibrosis?
Chromosome 7
CFTR gene (Cystic fibrosis transmembrane conductance regulator)
Give an example of an autosomal dominant disease?
Huntington’s disease
Explain Huntington’s disease.
It is a mutation at the HD locus on chromosome 4 which causes an increase in the number of CAG repeats (glutamine) forming a longer than normal polyglutamine tract.
Normal <28 repeats
Abnormal >36 repeats which is a cytotoxic protein aggregation.
What is cystic fibrosis?
Increased viscosity (thickness) of mucus due to a lack of expression of CFTR channels, which normally pump out Cl- which is followed by water. A lack of this makes the mucus more viscous leading to increased infections.
What is genetic anticipation, as shown by conditions such as Huntington’s?
Whereby a condition becomes more severe or appears earlier in successive generations.
Why do heterozygous individuals suffering with Huntington’s still get the disease.
Even if the wild-type allele will not produce excessive CAG repeats, the one mutant copy of the allele will which is enough to cause them to aggregate.
What is meant by the term progeny?
Offspring.
What is meant by diploid?
Each cell has X1 copy of each gene.
What is meant by haploid?
Each cell has X2 copies of each gene.
Give an example of an X-linked recessive disease.
Haemophilia A
Duchenne muscular dystrophy
What is affected in haemophilia A?
A mutated gene for clotting factor VIII (8)
Give an example of an X-linked dominant disease.
Vitamin D resistant rickets
What are the two types of twins?
Monozygotic (X1 sperm / X1 egg)
Dizygotic (X2 individual conceptions)
What is meant by twin concordance?
The extent to which twins possess the same same trait.
Higher concordance in monozygotic twins indicated genetics plays a larger role in that condition.
