Intro to Medical Genetics Flashcards
gene
a distinct sequence of nucleotides forming part of a chromosome, the order of which determines the order of monomers in a polypeptide or nucleic acid molecule which a cell (or virus) may synthesize.
genome
a distinct sequence of nucleotides forming part of a chromosome, the order of which determines the order of monomers in a polypeptide or nucleic acid molecule which a cell (or virus) may synthesize.
exome
the part of the genome that consists of exons
noncoding RNA
a functional RNA molecule that is transcribed from DNA but not translated into proteins. Epigenetic related ncRNAs include miRNA, siRNA, piRNA and lncRNA. In general, ncRNAs function to regulate gene expression at the transcriptional and post-transcriptional level.
precision medicine
Precision medicine is an approach to patient care that allows doctors to select treatments that are most likely to help patients based on a genetic understanding of their disease. This may also be called personalized medicine.
DNA transposon
A transposable element (TE, transposon, or jumping gene) is a DNA sequence that can change its position within a genome, sometimes creating or reversing mutations and altering the cell’s genetic identity and genome size. Transposition often results in duplication of the same genetic material.
retrotransposon
Retrotransposons represent a highly unique group of transposable elements and form large portions of the genomes of many eukaryotes (organisms with cells containing a clearly defined nucleus). Retrotransposons function by a “copy and paste” mechanism. Thus, they leave behind the original copy and generate a second copy that is inserted elsewhere in the genome. This process results in the insertion of repetitive sequences of DNA throughout the genome and is the mechanism responsible for the vast spread of transposable elements in many higher organisms.
epigenetics
the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.
The term “epigenetics” refers to inheritance of a phenotype not encoded directly in the
DNA sequence. The phenotype is due to a “change in gene expression” rather than a
Figure 3. The nucleosome is the
fundamental unit of chromatin.
Figure 4. The compaction of DNA
into chromosomes
INTRODUCTION TO MEDICAL GENETICS
[Block: Foundations | BEAR] [12 of 18]
change in a gene sequence. Epigenetic changes in gene expression may occur by
several mechanisms including reversible covalent chemical modifications in genomic
DNA (DNA methylation) or modifications in associated histones, and the transmission of
RNA from the parental cell to the daughter cell during cell division.
exons
a segment of a DNA or RNA molecule containing information coding for a protein or peptide sequence.
introns
intervening sequence
a segment of a DNA or RNA molecule which does not code for proteins and interrupts the sequence of genes.
repetitive DNA
DNA sequences that are repeated in the genome. These sequences do not code for protein
The sequences that account for 53% of nuclear genome are made up of repetitive DNA
- sequences that are repeated from tens to thousands of times. In some cases, these
repeated sequences occur in tandem arrays on a single chromosome. In other cases,
the repetitive sequences are dispersed on a single or multiple chromosomes.
Repetitive sequences may consist of long stretches of simple repeated sequences that
are only a few base pairs long, or the sequences may be repeats of hundreds or
thousands of base pairs, and can only be detected by a computer algorithm.
simple repeats
Some of the simple sequence repeats are associated with specific cellular functions.
The three most common are minisatellites, microsatellites and telomeres. They
derive their name from the fact that these DNAs were originally detected in the early
1950s in ultracentrifugation experiments where the DNA was located in small bands
above and below the bulk of genomic DNA because of their buoyant densities differing
from the other DNA due to their unique base compositions.
Other simple repetitive sequences occur within genes. These sequences are prone
to expansion and contraction due to DNA replication errors and unequal crossing over
during meiosis. Nucleotide repeat expansions in the germline DNA can lead to more
than 30 known diseases, including Huntington disease, fragile X syndrome, myotonic
dystrophy and Friedreich ataxia.
non-repetitive intergenic DNA sequences
In addition to regulatory sequences, the intergenic regions also contain pseudogenes
and gene fragments, which are inactivated remnants or nonfunctional duplications of
previously active genes. There are more than 5,000 pseudogenes and gene fragments
in the genome. Most pseudogenes and gene fragments normally lack the functional
regulatory sequences necessary for their expression or are missing important parts of
the coding regions such that non-functional transcripts are generated.
single gene disorders
Mendelian monogenic genetic diseases are characterized by mutations in single genes
or specific chromosomal aberrations, with a corresponding loss or gain of function of an
essential protein or multiple proteins. In most cases, the disease-causing mutation is
either dominant or recessive. Dominant mutations require that only one of the two
homologous chromosomes carry the gene mutation for the disease to occur, while
recessive mutations require that both homologous chromosomes carry a mutation in the
same gene. If the mutations are on the 22 autosomes, the mutation is said to be
autosomal, while mutations on the X or Y sex chromosomes are said to be sex-linked.
Common Mendelian monogenic diseases include Duchenne muscular dystrophy (Xlinked recessive), cystic fibrosis (autosomal recessive), and Huntington disease
(autosomal dominant).
chromosomal disorders
Chromosomal abnormalities, alterations and aberrations are at the root of many inherited diseases and traits. Chromosomal abnormalities often give rise to birth defects and congenital conditions that may develop during an individual’s lifetime. Examining the karyotype of chromosomes (karyotyping) in a sample of cells can allow detection of a chromosomal abnormality
Numerical: Aneuploidy refers to the presence of an extra chromosome or a missing chromosome and is the most common form of chromosomal abnormality. In the case of Down’s syndrome or Trisomy 21, there is an additional copy of chromosome 21 and therefore 47 chromosomes. Turner’s syndrome on the other hand arises from the absence of an X chromosome, meaning only 45 chromosomes are present.
Structural: Structural abnormalities occur when the chromosomal morphology is altered due to an unusual location of the centromere and therefore abnormal lengths of the chromosome’s short (p) and long arm (q).
