Chromosomal Aberrations Flashcards
What is non-disjunction?
Failure of chromosomes to move to opposite poles
When does non-disjunction occur?
Anaphase of Meiosis 1 and meiosis 2, oogenesis, spermatogenesis
What happens if there is a complete absence of the x chromosome?
will die
How is it possible for a sperm cell to carry 2 y chromosomes?
Because or non-disjunction at anaphase 2
How do you write a karyotype?
Total no. of chromosomes, sex, what chromosome is extra eg. for down syndrome 47, XY, +21
Breast enlargement in males
Gynecomastia
A disorder where it occurs in 1 in 2000 newborn females, no masculinization, is sterile, and some with normal intelligence 45, XO
Turner syndrome
Has a frequency of 1/1200, is taller than average, mostly with normal sexual development, increased risk of learning disabilities, delayed motor skills, hypotonia, behavioral and emotional difficulties
Metafemales or triplo x
Has a frequency of 1/2000, and is named after Dr. Patricia Jacobs, characters include unusually tall, has tendency for subnormal intelligence, and tendency for personality disorder or aggressive behavior (has a karyotype of xyy)
Jacobs syndrome
Who proposed to screen newborn infants for xyy karyotype in 1968 at the boston hospital for women?
Stanley walzer and park gerald
What was the prison where Dr. Patricia Jacobs had karyotyped 315 males?
Scottish maximum security prison in 1965
What are the types of aberrations?
Variation in chromosome number and structural aberrations
The types of variation in chromosome number
Aneuploidy and euploidy
This is the change in the number of one or a few chromosomes but not a complete set eg. 2n+1
Aneuploidy
This is the change in the number of complete sets of chromosomes eg. 3n
Euploidy
What are the types of structural aberrations?
Deletions, duplications, inversions, translocations, fragile sites
How may aneuploidy arise?
1 loss of centromere leading to acentric chromosome, 2 loss of the small chromosome generated thru a robertsonian translocation, 3 non-disjunction
What are the types of aneuploidy?
Nullisomy, monosomy, trisomy, tetrasomy
This is the loss of both members of a homologous chromosome making it non-viable
Nullisomy
What is an example of nullisomy?
Loss of sex chromosomes, or pair of autosomes
What is monosomy?
Loss of a single chromosome eg. 2n-1 XO Turner’s syndrome
This is the gain of a single chromosome eg. 2n+1, xxy, xxx, xyy
Trisomy
What are examples of trisomy?
Sexual trisomy: Kleinfelter, metafemale, jacobs note: there are also autosomal trisomy
What is 2n+1+1?
Double trisomy
This is the gain of 2 homologous chromosomes eg. 2n+2, xxxx, xxxy
Tetrasomy
What is 2n-1-1?
Double monosomy which is an aberration at 2 chromosome locations
What are the types of autosomal trisomy?
Trisomy 21, trisomy 18, trisomy 13
What is trisomy 21?
Down syndrome
What is trisomy 18?
Edwards syndrome
What is trisomy 13?
Patau syndrome
Characterized by mental retardation, congenital heart defects, 1/100 risk of leukemia, short broad skull, cataracts, life expectancy is 30 yrs but 25% live up to 50 yrs also known as mongolism
Down syndrome
What is the probability of getting child with down syndrome at the age of 20?
1/2000
What is the probability of getting child with down syndrome at the age of 30?
1/900
What is the probability of getting child with down syndrome at the age of 40?
1/100
What is the probability of getting child with down syndrome at the age of 50?
1/12
What are the characteristics of edward syndrome?
1/8000 live births, severely retarded, elfin appearance, receding lower jaw, low set ears, short neck, deformed teeth, clenched fingers, heart problems
This usually affects females with a mortality of 80% at 2 yrs old
Edwards syndrome
1/15000 live births, severe mental retardation, small head, sloping forehead, small eyes, cleft lip and palate, polydactyly
Patau syndrome
Half of children die within the 1st month and 95% die by age 3
Patau syndrome
Why does monosomy and trisomy not common for other autosomes?
Because deformation is so severe it leads to spontaneous abortion
Why does euploidy occur?
Because of polyspermy
This is common in plants where 40% occurs in flowering plants and about 70-80% occurs in grasses and thus is agriculturally important
Polyploidy
All chromosome sets are from a single species
Autopolyploidy
Even no. of polyploids have______ survival and fertility than odd no. of polyploids
Greater
There is _______ fertility in genetically unbalanced daughter cells
Reduced
This is when chromosome sets are from 2 different species
Allopolyploidy
9A9B in f2 generation
Amphidiploid or allotetraploid
What are the significance of polyploidy?
Increase in chromosome number causes increase in cell size, many polyploids have bigger flowers, fruits, leaves, and seeds or sometimes no seeds
female horse x male donkey
Mule
male horse x female donkey
Hinny
