MODULE 6. GENETIC CHANGE Flashcards
definition - mutagens
environmental agents which damage DNA
definition - mutations
permanent changes to the structure and sequence of DNA
effect of mutations
mutations produce new genetic variations via forming new possible alleles
definition - electromagnetic radiation sources
waves which carry electromagentic energy
high EM radiations cause…
atoms to vibrate and lose electrons - this breaks bonds, damaging DNA
EM radiation sources-
The sun - emits infrared, Uv light - causes mutations e.g. skin cancer
radioactive elements- e.g. uranium 236 - releases gamma rays as they decay - made in chemistry labs, nuclear bombs
medical imaging machines e.g. X-ray, PET scanner
How can chemicals cause mutations
chemicals can accidentally incorporated into DNA, instead of proper nucleotides. e.g. 5-bromodeoxyuridine
DNA polymerase accidentally incorporated 5-BDU into DNA
Chemical insert itself into the DNA. e.g. actinomycin D. creates a bulge in the DNA which prevents replication
chemical makes gaps in the DNA e.g. dimethyl suphate . breaks the bond base and sugar
naturally occurring mutagens occur in:
microbe
plant
animals
naturally occurring mutagens: MICROBES
mycotoxins are poisonous chemicals produced by fungi e.g. aflatoxin B1 - inserts itself into DNA and distorts it
naturally occurring mutagens: PLANT
cyasin is a mutagenic chemical, found in cycad plants
naturally occurring mutagens: animal
Dimethyl nitrosamine is produced in the stomach when nitrate is consumed.
defintion - point mutation
point mutations involve a change within a gene in which one base pair in the DNA sequence is altered.
Addition, deletion, or substitution occurs
what are point mutations a result of?
mistakes made in DNA replication
however they also occur through X-rays or UV radiations
Point mutations may involve:
- base subsitiution: one pair of nucleotides (e.g. A-T) is substituted for another pair
Frame shift - extra bases are added to or deleted form a strand of DNA, changing the whole sequence of nucleotides
types of base subsitiution (point mutations)
SILENT - there is no change to amino acid sequence in the polypeptide - no effect
MIS-SENSE - there is a change to the amino acid sequence in the polypeptide - effect= incorrect polypeptide
NONSENSE - there is a premature stop codon, which shortens the polypeptide and so usually results in a non-functional protein, effect= shorter and incorrect polypeptide chain-produces a stop codon
what are frame shift mutations
extra bases are added to or deleted from a strand of DN, changing the whole sequence of nucleotides - effect = incorrect polypeptide
e.g.s of point mutations
SICKLE CELL ANAEMIA - recessive disorder caused by a single substitution in the gene that creates haemoglobin. When people have two copies of this mutation, it results in thin sickle-shaped blood cells that sometimes cannot carry oxygen properly
CYSTIC FIBROSIS - results in the loss of amino acid and causes an incorrectly folded protein (this deletion is not a frameshift mutation because three bases next to each other are deleted, and all the other amino acids in the chain remain the same)
what does chromosomal mutations involve
Chromosomal mutations involve structural or numerical changes to chromosomes. They differ from gene mutation and in many cases creates a more dangerous affect
chromosomal mutations: numerical abnormalities
- Numerical abnormalities, when an individual has an extra chromosome or is missing a copy of a chromosome. E.G. down syndrome.
chromosomal mutations: structural abnormalities
chromosomal mutations: chromosomes having chunks deleted, duplicated or translocated from one chromosome to another, or chromosome being inverted to face the opposite direction.
processes that occur in chromosomal mutations
duplication
inversion
deletion
translocation
chromosomal mutations: duplication
a process of the chromosome is duplicated resulting in extra genetic material
effect =pushes all nucleotides out of order - incorrect polypeptide
E.G. downsyndrome - a disorder related to physical growth delays, characteristic facial features and often intellectual disability due to the presence of an extra chromosome 21
chromosomal mutations: inversion
a portion of the chromosome has broken off, turned upside down, and reattached within itself, therefore genetic material is inverted
effect = incorrect nucleotide order
chromosomal mutations: deletion
A portion of the chromosome is missing or deleted.
–> occurs from errors in crossover in meiosis
effect= shorter polypeptide
E.G. partial deletion in the short arm of chromosome 4 causes wolf-Hirschhorn syndrome that causes a distinct craniofacial phenotype and intellectual disability
chromosomal mutations: translocation
a portion of one chromosome de-attaches and is transferred to another chromosome
effect= changes in nucleotide sequence of chromosome = incorrect functioning
what are germ line mutations
Occur in germ cells which become gametes and affects offspring of the individual
what are somatic mutations
Occur in body cells during mitosis and only affects the individual
effect of germ-line mutation
Mutate offspring and introduce new alleles into a population.
Often results in sterility as they are in the sex cells
effect of somatic mutations
Error in DNA = more susceptible to developing cancer, but are not passed on to the next generation
what is the function of coding DNA
codes for and produces amino acids and polypeptides
what is the function of non-coding DNA
Does not code for amino acids and polypeptides but is essential for proper cell functioning.
what happens if there is a mutation in coding DNA
Genetic diseases
what happens if there is a mutation in non-coding DNA
Mutations in non-coding DNA have been linked to development disorders such as isolates Pierre Robin sequence, which is caused by changes in enhancer elements that control the activity of the SOX9 gene.
Non-coding DNA mutations have also been associated with several types of cancer
what % of DNA is non-coding
98%
what are the 3 causes of genetic variation
mutation
meiosis
fertilisation
causes of genetic variation: mutation
This provides a source of new variation, either somatic or germ line mutation introduce new alleles.
The changes cause genetic variation in a number of ways including:
- Adding or removing parts of gene creates defective protein or might create a less functioning protein with a deviant structure.
- Silencing genes that can eliminate a particular trait.
- Adding, deleting, translocating chromosomes causing disorders in organisms, some of which are untreatable and lethal.
- Mutations can also produce different products from similarly sequenced mRNA transcripts.
causes of genetic variation: meiosis
Crossing over is the process by which the allele of different gene on the same chromosome are recombined during meiosis.
Variation is further increased when cells divide during meiosis, where homologous chromosomes are randomly distributed, separating independently of each other. This is called independent assortment. It results in gamete that have unique combinations of chromosomes.
Independent assortment of genes during meiosis shuffles them.
causes of genetic variation: fertilisation
during fertilisation a zygote receives half of the genotype from the mother and the other half from the father - the way their genes interact can determine the production of traits
this involves the random fusing of genetically recombined gametes during fertilisation increasing genetic variation