Download Basics in Genetics

Basics in Genetics
a. DNA--> RNA--> protein
DNA=genes=instructions for making proteins=stored information
Proteins=gene products=machinery with which cell carries out all necessary tasks.
eg. make energy (ATP), synthesize other proteins, sense environment, regulate "gene
expression"
In general- one gene makes one protein.
Chromosomes= very large molecules of DNA, each carrying many, many genes.
Transcription—process of making mRNA from DNA
b. Brief review of Mendelian genetics.
All cells have 2 copies of each chromosome, 1 from mother, 1 from father.
Therefore have 2 copies of each gene.
Genotype= genes you have. Phenotype= Consequences of those genes for cells or for
animal.
Normal gene= wild type = + i.e. makes normal functional protein.
Alter gene--> alter protein = mutation. Mutant protein usually less functional or nonfunctional
Individual carrying mutation= mutant
Example= cystic fibrosis gene = CFTR. Makes pump that pumps chloride ions
Homozygous= both copies of gene the same
e.g. homozygous mutant= mutation / mutation
Heterozygous= two copies of gene different e.g. mutation / +
Recessive mutation= mutation / + = wild type; Dominant mutation= mutation / + =
mutant
Usually either copy can make enough protein product i.e. mutation / + = wild type
phenotype
Thus most mutations recessive!!
Null mutation= makes no protein or totally non-functional protein.
Weak or Hypomorphic mutation= makes protein that retains some but not all function.
Loss of function mutation vs. Gain of function mutation
c. One gene has different alleles. Normal allele = wild type.
Different changes in gene sequence --> different changes in protein = different alleles.
Different alleles can have different phenotypes
d. Wild type = + or e.g. CFTR+.
e. In addition to subtly altering single genes, mutations can also result
from large scale changes in chromosome structure, which can affect multiple genes.
Deletions (Deficiencies)= deletion of DNA, from several basepairs
to large portions of a chromosome.
Duplications= extra copy of part of the DNA, again from several basepairs
to large portions of a chromosome. Usually moved to a new chromosomal location.
Inversions= Rearrangement of the order of the genes along the chromosome.
eg. Original gene order might be A B C D E F: New gene order A D C B E F
Results from breakage and rejoining of DNA in incorrect way.
Translocations= DNA rearrangment that involves 2 different chromosomes
Also results from breakage and rejoining of DNA in incorrect way.
eg. Chromosome 2= genes A B C D E F; Chromosome 3= gene S T U V W X Y
Translocation--> new combined chromosomes A B C D W X Y and S T U V E F
These sorts of DNA rearrangements frequently found in tumor cells