Genetics & Genetic diseases Flashcards
(28 cards)
What is a karyotype?
the complete set of chromosomes in a species, or an individual organism. Homo sapiens are the only primates with pairs of 22 autosomes
what is an ideogram? (remember that mutations have to be larger than 4mb to be seen on a karyotype)
a graphic symbol that represents an idea or concept
What are the parts of a chromosome (long arm, short arm, etc.)?
p= short arm, q= long arm, centromere = links sister chormatids
How may pairs of autosomes, and how many sex chromosomes do humans have?
humans have 22 pairs of autosomes (non-sex chromosomes) and 2 sex chromosomes (XX or XY)
How does the medical and general usage of the word “gene” differ?
medical usage of “gene” = only those sequences that code for proteins
general usage of “gene”= any functional unit of a chromosome
What is a locus?
the exact physical location of a gene on a chromosome. they are marked by “p” or “q” followed by a number
what are alleles?
used when there are 2 or more variations of a gene in a population. Ex: normal vs sickle would be the two types of alleles in a population
What is the difference between genotype and phenotype?
genotype refers to the particular combination of alleles that a person has for some locus. That genotype is then reflected as their phenotype. Phenotype is any observable trait
What is a SNP?
single-nucleotide polymorphism (SNPs) - a DNA sequence variation occurring when a single nucleotide (A, T, C or G) differs between members of a species or paired chromosomes in an individual. The genomic distribution of SNPs is not homogenous, SNPs usually occur in non-coding regions more frequently than in coding regions.
List the ways autosomal dominant and autosomal recessive modes of inheritance differ?
autosomal dominant inheritance: the locus is on autosomal chromosome (1-22) and only one mutant allele is required for expression of the phenotype. The disease is typically observed in sequential generations.
autosomal recessive inheritance: the locus is on an autosomal chromosome and both alleles must be mutant alleles to express the phenotype. In contrast to autosomal dominant disease, autosomal recessive disease are typically seen in only one generation of a pedigree (do skip generations!)
Which parent do you inherit your mitochondrial DNA from?
inheritance only through maternal lines. Affected males do not pass on the genes.
What are the genetic principles of pleiotropy?
Marfan syndrome is an AD disease that affects 1/10000. It is caused by a mutation in the gene that encodes fibrillin (causes CT to be stretchy). Pleiotropy= single disease causing mutation affects multiple organ systems
What are the genetic principles of aneuploidy?
aneuploidy is a deviation from the euploid number (a cell that has a multiple of 23 chromosomes) by chromosome gain or loss. Monosomy- loss of a chromosome
trisomy- gain of a chromosome
What are the genetic principles of anticipation?
refers to a pattern of inheritance in which individuals in the most recent generations of a pedigree develop a disease at an earlier age or with greater severity than do those in the earlier generations
For X-linked recessive inheritance, who is affected and who is a carrier (i.e. male vs. female)?
X-linked recessive disease in males, because males only have one X chromosome, a male can have a recessive X-linked disease even though he only has one copy of the gene. This is because in only having one chromosome, he does not have another good copy to “hide” the effect of that mutation. Therefore men are affected and women are more likely to be carriers
Why are females more likely to get an X-linked dominant disease than males?
heterzygous females are affected. Because females have two X chromosomes and thus two chances to inherit an X-linked disease causing mutation and males have only one. X-linked dominant disease are seen about twice as often in females as in males.
What are the major features of Turner syndrome, and why is it called a mosaic disease?
only monosomy consistent with life (because its NOT autsomal). 45,X encompasses several conditions in human females, of which monosomy X (absence of an entire sex chromosome) is most common (50% of cases). In some cases, the chromosome is missing in some cells but not others, a condition referred to as mosaicism (46. XX and 47,XXX).
Arising from x-chromosome monosomy, Turner’s syndrome results in marked short stature (improved with growth hormone), ovarian dysgenesis, and neurocognitive problems.
Why should we consider many sex chromosome aneuploidies as traits, and not diseases as they have been classified in the past?
because it is simply a deviation from standard chromosomal number and not necessarily indicative of disease processes (such as Klinefelter’s syndrome and Aliens 3 syndrome) - also it alienates individuals
Why is fragile X syndrome called “fragile,” and what are some of its major features?
fragile due to unstable CGG repeat at Xq27. A portion of chromosome X is dangling by a thread. The severity of the disease correlates with # of CGG repeats. It is THE most common inherited form of mental retardation (1/1000 males). Expansion from pre- to full mutation only occurs through female meiosis
What is the difference between imprinting of the X chromosome, and imprinting of the autosomes?
imprinting refers to the fact that a small number of genes are transcriptionally active only when transmitted by one of the two sexes. The homologous locus in the other parent is rendered transcriptionally inactive. For imprinted loci it is normal to have only the maternal or only the paternal active
Prader-Wili and Angelman syndrome are examples of this epigenetic disease process ______? (the answer is in the previous question)
imprinting
Prader-Willi - microdeletion on paternal chromosome 15
Angelman syndrom - microdeletion on maternal chromosome 15
There are 5 points of control for gene expression? The one most studied in terms of epigenetic influence is what stage?
- Chromatin stage (most studied?)
- Transcriptional stage
- Translational stage
- Post translational control into cytoplasm
- Post translational modification
Why does DNA naturally wrap around histones, and what epigenetic changes can occur to histone tails to encourage or discourage winding/unwinding?
The negative charge of DNA is attracted to the positive charge of the histones and wraps around it to become more compact. Methylation of Cytidine (CpG) down regulates transcription and stimulates transcription (CAN DO BOTH!), acetylation inhibits DNA from becoming condensed and active transcription is thus encouraged.
What is a promoter region on a gene, and why are promoter regions generally not methylated?
A promoter is a region of DNA that initiates gene transcription. Promoter regions are generally not methylated because hypermethylation is one of the major epigenetic modifications that repress transcription via promotor region of tumor suppressor genes. Methylation in a CpG island can change the nucleotide from C to T and cause problems- ex: turns off tumor suppressor genes (want these to fight off tumors!) or can turn a proto-oncogene into an oncogene
