Chapter 13- Chromosomes Flashcards
Cytogenetics
Study of chromosomes and their abnormalities
Karyotype
Displays chromosomes by their size and structure
Used for clinical diagnosis
Telomeres
DNA Repeats on chromosome ends
Protects ends of DNA information
Shorten every cell division in absence of telomerase
Centromere
Site of spindle fiber attachment
Specialized heterochromatin with DNA and proteins
Telocentric chromosomes
Centromere at the tip of chromosomes
Acrocentric chromosomes
Centromere close to the end
Submetacentric chromosomes
Centromere off-center
Metacentric chromosomes
Centromere in the center
Amniocentesis
Collecting fetal cells from the amniotic fluid at 16-20 weeks to test for chromosomal and biochemical defects
Recommended for older women or history of chromosomal abnormalities
Chorionic Villi Sampling (CVS)
Collect chorionic villi (placental projections) trans-vaginally
Earlier results but less accurate and higher chance of miscarriage
Euploidy
Correct chromosome number
Polyploidy
Cells with entire extra sets of chromosomes
Triploid- 69 chromosomes
Tetraploid- 92 chromosomes
Aneuploidy
Gain or loss of individual chromosomes
Non-disjunction
Failure of paired homologs to separate properly during segregation
Occurs in meiosis I or II
Causes aneuploidy
Monosomy
2n-1 condition, loss of one chromosome
Lethal very early in embryogenesis
Trisomy
2n+1 condition, gain of one chromosome
Varying lethality depending on chromosome repeated
Trisomy 21- Down Syndrome
95% due to nondisjunction in meiosis I from ovum
Distinctive facial and physical problems
Predisposition for leukemia, alzheimer’s, and heart defects
Varying developmental disability
Trisomy 18- Edward’s Syndrome
Survival less than 4 months
Most common in stillbirths
Associated with advanced maternal age
Trisomy 13- Patau Syndrome
95% miscarry
Death within 3 months
Many growth, developmental, and anatomical defects
XO- Turner Syndrome
Female phenotype
99% die in utero
Loss of one X chromosome from ovum or sperm
Short, infertile, many medical problems
Failure to develop secondary sex characteristics
Only viable monosomy in humans
XXX- Triple X Syndrome
Little phenotypical change from normal females
Majority never diagnosed
XXY- Klinefelter Syndrome
Many X with at least 1 Y chromosomes
Male phenotype
Tall, large limbs
Hypogonadism, sterile
Gynecomastia
XYY- Jacob’s Syndrome
Male phenotype
96% normal development
Great height
Acne
Speech and reading disabilities
Translocation of Chromosomes
Transfer a piece of chromosome to non-homologous chromosome
Balanced
Robertsonian Translocation
Breakage of acrocentric chromosomes and fusion of two distinct long arms into hybrid chromosome
No clinical significance for carrier
Produce unbalanced gametes
Reciprocal Translocation
Breakage of two non-homologous chromosomes with exchange of fragments
Balanced
Normal phenotype with risk for unbalanced gametes
Burkitt Lymphoma
Translocation of pronto oncogeme c-myc into immunoglobulin heavy chain
Leads to tumor development
Chromosomal Deletions
Missing genetic segments
Arise de novo from chromosome breaks
Hemizygous expression- Only copy remaining will always be expressed
Chromosomal Duplications
Part of chromosome is copied, leading to extra genetic material
Occurs during meiosis due to unequal crossing over
Tandem or dispersed repeats
Chromosomal Inversions
Chromosome segment with flipped orientation
May lead to health problems or reduced fertility
Balanced- Both copies flip
Unbalanced- Only one copy flips- Causes issues in crossing over
Isochromosomes
Chromosome with two identical arms
2p arms- Short
2q arms- Long
Tetrasomy 18
Isochromosomes of chromosome 18 lead to low birth weight and developmental abnormalities
Ring Chromosomes
Chromosome ends break and fuse to one another, forming ring
Arise with telomere loss
Occur with or without disrupting genetic material
Uniparental Disomy
One parent contributes both copies of a chromosome
Loss during trisomy zygote
Non-disjunction in both parents on same chromosome
Robertsonian Down Syndrome
5% of cases
Robertsonian translocation of chromosomes 21 and 14
Offspring has chance to inherit hybrid chromosome or normal copies from carrier
Cause trisomy 21
Cru du Chat Syndrome
De novo deletion on chromosome 5
Delete CTNND2 and HTERT gene
Defects in telomerase and nerve cell development
High pitched cry, intellectual and developmental impairment, low birth weight
