Chromosome Anomalies Flashcards Preview

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Flashcards in Chromosome Anomalies Deck (20):

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


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


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


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