Flashcards in Genetics Deck (27)
What is a karyotype?
The number and appearance of all the chromosomes in a cell. Usually presented as a picture of the mitotic (wound up into x-shape) chromosomes.
How big does a mutation have to be in order to be seen on a karyotype?
At least 4 mb (megabases)
What is an ideogram?
A diagram of the banding pattern of a chromosome
What are the parts of a chromosome?
Long arm (q)
Short arm (p for petite)
How many pairs of autosomes and how many sex chromosomes do humans have?
22 pairs of autosomes and two sex chromosomes
How do the medical and general usage of the word "gene" differ?
General: any functional unit of a chromosome
Medical: strictly the protein-coding sequences
What is a locus?
The exact physical location of a gene on a chromosome, its address.
Includes the chromosome number, long or short arm (p or q) and the number giving its position.
What are alleles?
Variants of a gene that are present in the population. They're the different options for that gene.
For example, in sickle cell disease you have a normal allele and the mutated allele that produces the disease, so there are two alleles for that gene in the population.
What is the difference between genotype and phenotype?
Genotype: which alleles you have for a particular trait
Phenotype: the observable trait
Example: I have Factor V Leiden. For the gene Factor V, I have a heterozygous genotype (one dominant allele, one recessive). My phenotype is a propensity to develop blood clots.
What is a SNP?
Single Nucleotide Polymorphism
A single nucleotide difference between two homologous sequences of DNA.
Example: I have Factor V Leiden, a mutation in the gene for clotting factor V. The difference between the mutated gene and the normal gene is a SNP.
List the ways autosomal dominant and autosomal recessive modes of inheritance differ.
Autosomal means the locus is on an autosome
Dominant: Only one copy of the abnormal allele is needed in order for the trait to be expressed (heterozygous genotype produces the phenotype)
Every generation is affected.
Recessive: Two copies of the abnormal allele needed for expression (homozygous recessive genotype produces the phenotype)
Every OTHER generation is affected.
What are the five points of control for gene expression?
(memorize for boards)
Chromatin stage (unwinding the DNA)
Post translational control into cytoplasm
Post translational modification
Which parent do you inherit mitochondrial DNA from?
What are the genetic principles of pleiotropy, aneuploidy, and anticipation?
Pleiotropy: A single disease-causing mutation affects multiple organ systems. Common feature of genetic diseases. Ex: Marfan syndrome, makes fibrillin stretchy.
Aneuploidy: Having an abnormal number of chromosomes (either extra copies or missing copies). All autosomal aneuploidies are inconsistent with life except trisomy 21 (Down syndrome)
Anticipation: the propensity of later generations with a genetic disease to develop the disease earlier in life than prior generations. This is due to extra copies of the gene (repeats) inserted in the chromosome.
For X-linked recessive inheritance, who is affected and who is a carrier?
In X-linked inheritance, the gene of interest is located on the the X chromosome.
Women carry the disease but usually do not express it, because the copy with the mutation is silenced.
Men express the disease in all cases because there is no second X chromosome to mask the mutated one.
Additionally, all of affected males' daughters will carry the mutation.
Why are females more likely to get an X-linked dominant disease than males?
Females are twice as likely to get the disease because they have two X chromosomes--twice as many chances as males.
What are the major features of Turner syndrome, and why is it called a mosaic disease?
Features: short stature, ovarian dysgenesis, neurocognitive problems
Mosaic: different populations of cells have different numbers of X chromosomes (one, two, or three). Think of the coloring of a calico cat.
Why is fragile X syndrome called "fragile"? What are its major features?
Due to an unstable CGG repeat on the X chromosome which makes it breakable.
Broad forehead, elongated face, large ears
Crossed eyes, hyperextensible joints
self-abuse, indented chest, hypotonia, flat feet
What is the difference between imprinting of the X chromosome and imprinting of autosomes?
Imprinting ensures that only one of the inherited alleles (the non-imprinted one) is ever expressed in the individual, and it's dependent on the parent it comes from.
Imprinting on the X chromosome results in total silencing of an entire chromosome.
Imprinting on autosomes results in silencing of individual genes.
Silencing means that the gene is permanently turned off and will not be transcribed.
Prader-Wili and Angelman syndrome are examples of this epigenetic disease process.
Microdeletions, specifically on chromosome 15.
These are examples of imprinting: Prader-Willi results from microdeletion on the paternal chromosome, Angelman syndrome from microdeletion on the maternal chromosome.
Why does DNA naturally wrap around histones, and what epigenetic changes can occur to histone tails to encourage winding/unwinding?
DNA is negatively charged, histones are positively charged.
Histone methylation: may up- or downregulate transcription
Histone acetylation: upregulates transcription
DNA methylation: downregulates transcription
Why should we consider sex chromosome aneuploidies as traits, rather than diseases?
They don't result in dysfunction.
What is a promoter region, and why are they generally not methylated?
The promoter is a region upstream of the gene where the transcription complex binds. They aren't methylated because it results in gene silencing.
What is a non-mutagen epigenetic carcinogen?
Compounds that result in increased incidence of tumors, though their effects result in epigenetic changes rather than genetic mutations.
How do HAT-HDAC drugs work?
HAT and HDAC are chromatin remodelers that normally work together to control gene transcription.
Deregulated HAT and HDAC plays a role in the development of cancers, so inhibitors of these enzymes can work as anticancer agents.
Are all genes possible proto-oncogenes?
No. Proto-oncogenes are typically involved in accelerating the cell cycle, so that when they become mutated they promote out of control replication.