genetics 7 Flashcards
what is chromosome abnormalities the leading cause of
- pregnancy loss
- intellectual disabilities
-1:150 live births
what are the centromere positions
- metacentric - near the middle
- Acrocentric - near the tip
- submetacentric - between the middle and the tip
what is the karyotype
46XY or 46XX
how are chromosomes ordered
- size - largest first
- centromere position
what are the tips of chromosomes called
telomere
in metacentric what are the two arms called
- short arm = p
- long arm - q
what human chromosomes are acrocentric
13,14,15,21,22 and Y
what occurs with short arm in chromosomes
- fewer genes
- no essential genetic material
- nucleolus organising regions (NOR) - rDNA
what is important about Q/G bands
- A-T rich regions
- giemsa banding
- quinacrine-bright
what is important about R bands
- G-C rich
- hot phosphate buffer
- giemsa stain
- called a negative stain
what are the types of cytogenetic locations
chromosome –> arm–> region –> band –> sub-band
eg. 7q31.2
what does ploidy mean
- number of sets of chromosomes in a genome
what does the DNA content mean
- amount of DNA in a cell
what is a numerical abnormality
- abnormal number of chromosomes
- polyploidy - total chromsome copies
- aneuploidy - individual chromosomal copies
what are the types of polyploidy
- triploidy
- tetraploidy
what are the types of aneuploidy
- monosomy
- trisomy
- tetrasomy
what are structural abnormalities
- deletions, insertions, inversions
- translocations - reciprocal, robertsonian
- rings
- isochromosomes
what is triploidy
- 69 chromsomes
- caused by two sperm
- very high morbidity - 1:10,000 live births
what is tetraploidy
- 92 chromosomes
- caused by mitotic failure in early embryo
- few live births , very high morbidity
what is monosomy and what is an example
- only one copy of a chromosome
- very high morality
- turner syndrome (X)
what is trisomy and what is an example
- 3 copies of a chromosome
- less severe
- down-syndrome (cH21)
what is tetrasomy and what is an example
- four copies of a chromosome
- cat eye syndrome (Ch22)
what is turner syndrome and what are the symptoms and treatment
- monosomy of X chromosome
- short statue, normal intelligence, not mature during puberty, most infertile
- hormone therapy
what is klinefelter syndrome and what is the symptoms
- trisomy of sex chromosome
- taller than average, small testes giving slight feminine physique, infertile, learning disabilities, flat feet, curved little finger
what is Down syndrome and what are the symptoms
- trisomy of Ch21 - nondisjunction of egg cells
- intellectual disabilities, characteristic facial appearance, weak muscle tone, 50% heart defects
what is patau syndrome and what are the symptoms
- trisomy of Ch13
- 88% die in first year
- orofacial clefts, malformed eyes, wide nose, severe developmental issues
what is Edwards syndrome and what are the symptoms
- trisomy of Ch18
- slow growth before birth, small head, abnormally shaped jaw and mouth, overlapping fingers, heart defects
- many die before one month, 5-10% live past 1 year
what is nondisjunction
- unequal distribution of chromosome pair in cell division
- occurs in meiosis 1 and meiosis 2
what are the causes of structure abnormalities
- same number of chromosomes
- unequal crossing over during meiosis
- chromosomal breakage
what are the types of structural abnormalities
- balanced - no change in the amount of genetic material
- unbalanced - gain or loss of chromosomal material - serious consequences
what are the causes of DNA double strand breaks
- Reactive oxygen species
- Ionizing radiation
- Chemotherapeutic drugs (Clastogens)
- Meiosis
- Lymphocyte development
- Mobile genetic elements (viral)
what is reciprocal translocation
- between different chromosomes
- removal or addition of DNA - genetic duplication/ deletion
what is robertsonian translocation
- acrocentric chromsomes - centromere near the tip
what is the sex determining gene and where is it found
SRY gene
PAR1 - x and y chromosomes
how does the SRY gene create gender
gene crossover creating XX males and XY females
what is critical-du-chat syndrome and what are the symptoms
- deletion - single break terminal deletion
- characteristic cry, intellectual disability, small head
what is wolf-hirshhorn syndrome and what are the symptoms
- single break terminal deletion
- facial characteristics, cleft palate, delayed growth and development, intellectual disability and seizures
what is microdeletions
- <5 million bases
- need high resolution banding
- FISH and aCHG techniques
what is Prader-will syndrome and what are the symptoms
- 70% micro deletions of 15q11
- 50% of patients 15q11-q13
- due to imprinting
- Paternal microdeletion ch15 → Prader–Willi syndrome
Intellectual disability, short stature, obesity, hypotonia, characteristic facies, small feet
what is angel man syndrome
Maternally microdeletion ch15 → Angelman syndrome
Intellectual disability, ataxia (co-ordination, balance and speech), uncontrolled laughter, seizures
what are the causes of insertions
- offspring of person with reciprocal translocations
- unequal crossover during meiosis
what is an example of insertion
- x-linked colour blindness
what is charcot-marie-tooth disease and what are the symptoms
- progressive damage to peripheral nerves
- high arches, flat feet or curled toes
what are the causes of inversions
- reinsertion of double break
- wrong orientation
- balanced
what is pericentric inversions
- centromere inverted
what are paracentric inversions
- no centromere involved
what is an example of inversions
- servere hemophillia A
- interruption of factor VII gene
what causes ring chromosomes
- breakage at both tips —> ends fuse
- usually de novo
- rarely inherited
- most common Ch 14 and 22
what is an example of ring chromosomes
Female ring X chromosome 46,X,r(X)
what are isochromosomes
- chromosomes divided along wrong axis
- chromosomes with two p or q arms or robertsonian translocation of Ch21q
what are the 3 types of Edward syndrome and what are the symptoms
Full Edwards’ syndrome - Trisomy Ch18
- Severe, high mortality before birth
Mosaic Edwards’ syndrome - Extra Ch18 in some cells
- Milder effects
- May live to 1 year or adulthood
Partial Edwards’ syndrome – Extra sections of Ch 18
