Chromosome Anomalies Flashcards
What is Mendel’s Law
Structure of chromosome determines inheritance
Genes inherited in blocks
What is the difference between dark and light bands on the chromosome
Light bands = Replicate early. Less condensed chromatin. Protein coding genes
Dark bands = Replicate late. Condensed chromatin. Structural Proteins
What is flourescent in situ hybridisation
Flourescent probes that bind to parts of chromosome with high degree of sequence similarity
What is array
Can be used to hybridise RNA from tumours to determine patterns of gene expression
Does patient have more of some type of DNA
What type of chromosomal anomaly is Down Syndrome. How is it caused?
Triosomy 21
3 copies of 21
Robertsonian translocation
Mosaicism
How does 3 copies cause down syndrome
Gene Dosage Effect = 1.5x amount of specific gene products
Amplified developmental instability = overall effect of imbalance
What is Edwards Syndrome
Triosomy 18
Multiple malformations
Clenched hands with overlapping fingers
What is Patau Syndrome
Triosomy 13
Multiple malformations
Affects midline structures
What is Klinefelter Syndrome
47, XXY
Poorly developed secondary sexual characteristics
Infertile
What is Turner’s Syndrome
45, X
Primary Amernorrhoea
Congenital Heart Defect
Webbed Necks
What is non-disjunction
Failure of chromosomes to separate during meiosis 1 or 2
Result in nullisomic (no chromosome) or disomic (2 instead of just 1)
Why the association with maternal age
Lengthy interval between onset & completion of meiosis
Accumulating effect on primary oocyte, wear and tear on cell division machinery
What are the different types of triploidy
YYX = Large cystic placenta. Severely growth retarded foetus
XXY = Small + Underdeveloped Placenta
XXX
How does organism identify paternal/maternal genes
Some human genes behave differently depending from which parent
Small number of genes are imprinted. Some expressed in paternally inherited chromosome, others in maternally
What is Robertsonian translocation
Involve only chromosome 13,14,15,21,22 (Acrocentric)
Breakage of chromosome at/close to centromere with subseqeunt fusion of their long arms-short arms
Correct number of genes but location altered
Can be balanced = normal phenotype/unbalanced = deletion/addition
Reduce number of chromosomes to 45
What is reciprocal translocation
Breakage along short/long arm of 2 non-homologous chromosomes with exchange of fragments
Balanced = clinically normal
Un-balanced = harmful
What is mosaicism
2 population of cells with different genetic constitutions
Can be somatic/gonadal
What do we know about the Y chromosome
Apart from tip of p arm, no recombination with homologous chromosome
Sext determining region Y determines male-ness
How does translocation affect the next generation
Balanced translocation carriers are at greater risk of creating gametes with an unbalanced translocation
What is the difference between Robertsonian and reciprocal translocation
Robertsonian occur in the five acrocentric chromosomes (e.g., chromosomes in which the short (p) arm is so short, it is very difficult to observe) 13, 14, 15, 21, and 22. Reciprocal translocations typically occur between chromosomes 13 and 14, 13 and 21, and 21 and 22, where the long (q) arms fuse at the centomere and the short arms of each chromosome disappear
