Clinical Genetics

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  • Created by: amh4
  • Created on: 15-02-17 13:48
Down Syndrome
Trisomy 21, 47,**,+21, caused by meiotic non disjunction or roberstonian translocation (14/12), possible mosaicism.
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Down Syndrome features
Epicanthic folds and upwards slanted eyes, single palmular crease, learning and physical disabilites, large and protruding tongue, short stature,
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Down syndrome Health Problems
Risk of seizures increasing with age, hypothyroidism in 50% of adults, eye and hearing problems, increased risk of leukemia in children, 40% born with congential heart disease, 12% born with gastrointestinal issues, risk of alzhiemers
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Edwards Syndrome
Trisomy 18,47,**,+18, non disjunction or translocation. Risk increases with maternal age, Only 10% of babies live past age 1.
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Edwards Syndrome Health Problems
kidney malformations, heart defects, intestines protruding from outside the body, ID and DD, slow growth and feeding and breathing difficulties
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Edwards Syndrome features
Microcephaly, low set ears, small jaw, clenched fists, cleft lip, clubfoot, webbed toes, wide spaced eyes
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Klinefelter Syndrome
47 XXY, Decreased IQ, passive behaviour, hypogonadism, infertility, gynaecomastia, tall, wide hips, poor facial hair growth
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Turner Syndrome
45 X, short stature, renal abnormalities, missing X usually paternal copy, nuchal translucency, neck webbing, lymphoedema, gonadal dysgenesis, infertility, decreased IQ speech language delay
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Quadrivalent
Meisosis 1 heterozygote pairing, formation of a cross shaped configuration most clearly seen at pachytene. No mechanism to ensure equal distribution of material between daughter cells.
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Alternate segregation
Alternate chromosomes with different centromeres goes alternately to one or other gamete. Always results in BALANCED gametes
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Adjacent 1 segregation
Adjacent chromosomes with nonhomolous centromeres travel to the same daughter cell. Trisomy for one translocated segment and monosomy for the other
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Adjacent 2 segregation
Adjacent chromosomes with homologous centromeres go to the same daughter cell. Trisomy for one centric segment and monosomy for the other.
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3:1 segregation
Form gametes with 24 and 22 chromosomes, 47 and 45. Two catagories - interchange and tertiary.
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Types of genomic disorders
Gene dosage, gene interruption, gene fusion, position effect, unmasking recessive allele or transvection effect
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3 mechanisms for Genomic disorders
Non allelic homologous recombination, non-homologous end joining,fork stalling and template switching
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Low copy repeats
DNA blocks of 10-400kb with >97% sequence identity, 5-10% of human genome sequence, predominate in subtelomeric and pericentromeric regions
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LCRs align at meiosis and mitosis
Recombination at allelic LCRS will result in only minor alterations, misalignment of non allelic LCRs and subsequenct recombination results in major alterations to DNA sequence - NAHR
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NAHR can occur...
Between repeats on the same chromosome (interchromosomal), two sister chromatids, different chromosomes and different regions on the same chromatid (intrachromatidal)
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Heritability is ..
Heritability is the proportion of population phenotypic variance for a quantitative trait that is attributable to genetic factors.
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The multifactorial threshold heritability model is used for
binary or ordinal traits
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Define linkage
genetic loci are linked when they are sufficiently close together on the same chromosome (syntenic) to be coinherited more than 50% of the time
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Define haplotype
A haplotype is the arrangement of alleles along an individual chromosome
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Crossing over
a reciprocal event between a pair of homologous chromosomes at the pachytene stage of prophase I
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Recombination
The process or act of exchanges of genes between chromosomes, resulting in a different genetic combination and ultimately to the formation of unique gametes with chromosomes that are different from those in parents.
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Penetrance
Penetrance in genetics is the proportion of individuals carrying a particular variant (or allele) of a gene (the genotype) that also express an associated trait (the phenotype).
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DNA polymorphisms on the Y chromosome and on mtDNA have been used extensively to study the history in humans
1. No recombination 2. paternal or maternal inheritance 3. high copy number for mtDNA
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What is satellite DNA?
Repetitive non-coding sequences, some of which contain centromeres. DNA sequences forming separate fraction when genomic DNA is separated along a density gradient due to distinct buoyant density; predominantly localised in telomeres and centromeres
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What are tandem repeats?
Repeats of a chromosomal region that lie adjacent to each other in either the same or reverse order
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What are long interspersed nuclear elements (LINEs)?
They are non-Long Terminal Repeat retrotransposons. LINEs typically encode a reverse transcriptase and may encode an endonuclease H. They are transcribed and then the LINE RNA can be reverse transcribed and encoded elsewhere in the genome.
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What are variable number tandem repeats?
A tandem repeat is a short sequence of DNA that is repeated at a specific chromosomal locus. Tandem repeats are interspersed throughout the human genome. Some sequences are found at only one site -- a single locus.
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What is RFLP?
Restriction fragment length polymorphism, he DNA sample is broken into pieces and (digested) by restriction enzymes and the resulting restriction fragments are separated according to their lengths by gel electrophoresis
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Other cards in this set

Card 2

Front

Epicanthic folds and upwards slanted eyes, single palmular crease, learning and physical disabilites, large and protruding tongue, short stature,

Back

Down Syndrome features

Card 3

Front

Risk of seizures increasing with age, hypothyroidism in 50% of adults, eye and hearing problems, increased risk of leukemia in children, 40% born with congential heart disease, 12% born with gastrointestinal issues, risk of alzhiemers

Back

Preview of the back of card 3

Card 4

Front

Trisomy 18,47,**,+18, non disjunction or translocation. Risk increases with maternal age, Only 10% of babies live past age 1.

Back

Preview of the back of card 4

Card 5

Front

kidney malformations, heart defects, intestines protruding from outside the body, ID and DD, slow growth and feeding and breathing difficulties

Back

Preview of the back of card 5
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