BI 3: Genetic Errors

Genetic Errors
Impacts of genetic errors:
changes to DNA sequence of an organism resulting in changes to the polypeptide coded for by that DNA
these changes can cause:
no noticeable effect
variation in traits
serious disease/disorder or death
failure of cell/individual to develop
DNA Mutations
Chromosomal Alterations
Non-Disjunction Events
mutation - change in the nucleotide sequence of an organism resulting in genetic diversity
1. Point Mutations
2. Frameshift Mutations
silent (no effect) - change to DNA sequence does not result in a change in the amino acid coded for because of wobble (repetitive nature of codons - some code for same amino acids)
missense mutation - change in DNA results in different amino acid being put into polypeptide
nonsense mutation - change in DNA causes premature STOP codon and results in shorter polypeptide
mutagen - physical or chemical agent that interacts with DNA to cause mutations
ex: X-rays, ultraviolet (UV) light
reading frame - triplet grouping of bases on mRNA that is read during translation (determined by location of START codon)
frameshift mutation - addition or removal of a number of nucleotides that is not a multiple of three
insertion - addition of nucleotide pairs in a gene sequence
deletion - removal of nucleotide pairs in a gene sequence
normal DNA sequence
ex: sickle cell anemia - condition caused by a single base pair missense mutation resulting in abnormally shaped red blood cells
ex: Down syndrome (Trisomy 21) - inheritance of extra 21st chromosome; characterized by defined facial features, short stature, heart defects, mental retardation
ex: chronic myelogenous leukemia - cancer of white blood cells caused by reciprocal translocation between chromosomes 9 and 22
chromosomal alterations - breakage of large sections of chromosomes causing change in chromosome structure and arrangement of genes
deletion - removal of a chromosome segment
duplication - repeat of a chromosome segment
inversion - reversal of order of a chromosome segment
translocation - movement of a segment of one chromosome onto a non-homologous chromosome
non-disjunction - failure of homologous chromosomes (during meiosis I) or sister chromatids (during meiosis II) to separate during gamete formation
aneuploidy - inheritance of an abnormal number of chromosomes caused by non-disjunction during egg or sperm production
karyotype - ordered display of chromosome images from longest to shortest; used to diagnose aneuploidies