5. Principles of Genetic Inheritance Flashcards
Where would you find the centromere in a metacentric chromosome?
What about a submetacentric chromosome?
What about an acrocentric chromosome?
What is special about acrocentric chromosomes?
The center
“just off” from center
Very close to one end, such that very little material is above/below it.
You can lose the genetic material on one side and still be ok (in some cases).
What is the normal human karyotype?
46,XX or 46,XY
In the karyotype: 46,XX, t(4,13)(q12:q14)
What is the underlined section?
The location of a translocation (in this case from chromosome 4 to 13)
Define “Lyonization”
The random choice of which X chromosome will be activated.
More commonly called X-Inactivation
Define Robertsonian Translocation
Where the long arm of TWO acrocentric chromosomes kicks off their tiny short arms and combine into one long chromosome.
Chronic Myelogenous Leukemia is associated with what specific translocation?
What is the name of the resulting chromosome?
What type of translocation is that?
t(9:22) placing BCL and ABL together
The Philadelphia Chromosome
Reciprocal
What is an inactivated X chromosome called?
A Barr Body
Define Mosaicism
When, in a given patient, one of their cells has one set of genes, and another cell in their body has a different set of genes - or more or fewer genes.
What is the genotype for a patient with Turner Syndrome?
What are the basic symptoms?
45,XO (Absent Y, so femaie)
- Short stature
- Many do not undergo puberty without HRT
- Ovarian hypofunction
- Webbed neck
- CV defects
What is the genotype for a patient with Klinefelter Syndrome?
What are the primary symptoms?
47,XXY
Gynecomastia
Tall stature
Infertility
Low muscle mass
For Down’s Syndrome
What is the basic cause?
What translocation can cause this disease?
What is the most common karyotype?
Autosomal Trisomy (possibly non-disjunction)
Robertsonian translocation can cause the disease (extra 21st chromosome material comes from the long arm of another chromosome sticking on, not a whole other chromosome.)
47,XY +21 (The +21 means an extra 21’s chromosome; trisomy 21. The other chromosomes are normal)
Some genes are only expressed when they come from your mother or your father. What makes this happen?
When does this tag get put on?
Methylation of the genetic material - Called Genomic Imprinting
When you make a gamete. (The tags from your mother and father are taken off, and your new tags (father if you’re male, mother if you’re female) are put on.)
Prader-Willi and Angelman syndromes are both due to the same deletion on Chromosome 15. What determines which disease a patient gets?
It depends on which gene is expressed.
Paternal Chromosome 15 deletion is Prader-Willi
P is for Paternal and Prader-Willi
Maternal Chromosome 15 deletion is Angelman
Mommy’s little angel
Note: due to imprinting, different genes would have been expressed by the paternal vs maternal regions, therefore it’s a net loss of different genes.
Define pleiotropy
Individuals with the same genotype having different phenotypes.
Define Proband
The first person in a pedigree to have a disease / trait.
What is the recurrent risk for an autosomal dominant disease?
How would you identify it on a pedigree? (3)
What example of this was given?
50%
Equal in males and females, present in every generation, and an unaffected person can not transmit the disease.
Postaxial Polydactyly
What is the recurrent risk for an autosomal recessive disease, if both parents are carriers?
How would you identify it on a pedigree? (3)
What example of this was given?
What special consideration increases risk?
25%
Unaffected parents can transmit the disease, skips generations, affects females and males equally.
Tyrosinase negative albinism
Consanguinity (First cousins mating)
What is the transmission pathway for X-linked recessive?
How would you identify it on a pedigree? (3)
What example of this was given?
Female carriers transmit the disease allele to 50% of sons and daughters both. The sons are affected. An affected male will pass the allele to all of his children.
Half of female offspring of a carrier will be carriers. No females will be affected - except in crazy rare cases where an affected male mates with a carrier female.
Duchenne’s Muscular Dystrophy
What is the pattern of recurrance for X-Linked Dominant Disease?
How would you identify it on a pedigree? (3)
What example of this was given?
Males pass the disease on 100% of the time to female children, and 0% to male children. Females pass the disease on 50% of the time.
Using the above information. Practically everyone is affected.
Hypophosphatemia
What example was given for reduced penetrance?
Retinoblastoma
What example was given for variable expressivity?
Neurofibromatosis
What example was given for Locus Heterogeneity?
Osteogenesis Imperfecta
If you have a mutation for a mitochondrial disease, you might still not present symptoms. What has to be reached before symptoms present?
The disease threshold.
What is the example given for multifactorial inheritance?
Is it more common in women or men?
Is it more likely to be transmitted by a woman or a man?
Pyloric Stenosis
5x more common in men (Women have a higher risk threshold)
Women are more likely to pass it on. (“The recurrance risk is higher if the proband is a member of the less affected sex.”)
