Mutations

What is a population?

A group of organisms of the same species living together in a particular place at a particular time

What is a gene pool?

Sum of all alleles in a given population

What are allele frequencies?

How often each allele of a gene occurs in the gene pool for that population

What is a mutation?

DNA changed, resulting in a different variation of the trait. Some harmful, some are not.

What is a mutant?

An organism with characteristic resulting from a mutation.

What is a gene mutation?

Changes in a single gene (normal traits produced by gene destroyed/changed)

What is a chromosomal mutation?

All or part of a chromosome is affected

Which cells need to be affected for a mutation to be passed to offspring?

Gametes

What are mutagenic agents (mutagens)?

Mutations occur without any known cause, but a number of agents are known to increase the rate at which they occur.

What are some mutagenic agents (mutagens)?

• mustard gas

• formaldehyde

• sulfur dioxide

• some antibiotics

• ionising raditaion

  • x-rays

  • ultraviolet radiation

  • cosmic rays

Are pregnant women advised against X-rays?

For the 1st 3 months of pregnancy they are advised not to have X-rays as they can cause mutations in the development of the foetus.

e.g. intellectual disabilities, skeletal malformations, microcephalpy (small head to body)

What is albinism?

Absence of pigment from hair, skin, eyes, resulting from one missing protein

What are induced mutations?

Mutations caused by a mutagenic agent (mutant)

What are spontaneous mutations?

Random errors in a biological process such as mitosis or meiosis

What are somatic mutations?

A change in a gene in a body cell (somatic cells, not gametes). Only individual affected (individual dies = mutation dies).

e.g. Cancer

What are germline mutations?

Change in the DNA of gametes (egg/sperm cells) that becomes incorporated into the DNA of every cell in the body of offspring. Individual mutation occured in is unaffected (parent unaffected). Usually, natural abortion occurs if gametes are affected.

What are missense mutations?

Cause a change in the amino acid, changing proteing produced

What are nonsense mutations?

Alter a DNA base sequence so that a codon is changed into a stop codon. As a result, protein synthesis terminates prematurely, producing a shortened protein that is usually non-functional or unable to perform its normal role.

What are neutral mutations?

Cause a change in an amino acid but the amino acid is of the same type and does not change the strucutre of the protein enough to change its function.

What are silent mutations?

Do not cause any change in the amino acid, and therefore the protein produced. This is possible as most amino acids are coded for by more than one base sequence.

What codons code for the STOP codon?

• UAA

• UAG

• UGA

What are point mutations?

due to change in a single nucleotide

e.g. insertion, substitution, deletion

What is an insertion mutation?

A new nucleotide is added to the DNA strand

What is a substitution mutation?

Existing nucleotide replaced with another

What is a deletion mutation?

Nucleotide removed from DNA strand

What is a frameshift?

Occurs when bases added/removed (substitution/deletion mutations); affects the outcome for all DNA from that point on.

What arethe types of chromosomal mutations?

• duplication/insertion

• inversion

• deletion

• translocation

• non-disjunction

What is a duplication/insertion mutation? (chromosomal mutation)

A section of a chromosme occurs twice

What is a deletion mutation? (chromosomal mutation)

A piece of DNA is removed

What is an inversion mutation? (chromosomal mutation)

Breaks occur in a chromosome and broken piece join back, but the wrong way around (backwards)

What is a translocation mutation? (chromosomal mutation)

part of a chromosme breaks off and rejoins to the wrong chromosome

What is a non-disjunction mutation? (chromosomal mutation)

During meiosis: a chromosome pair do not seperate, one daughter cell has an extra chromosome and another one has one less.

What is aneuploidy?

A change in the chromosome number

Outline Duchenne muscular dystophy

• mutation in mother inherited by her sons

• mutation in male zygote so that the child develops the disease

• symptoms: wasting of leg muscles and later arms, shoulders, chest

• apparent ~3-5 years old

• life span ~20-25 years - failure in respiratory muscles = death

Outline cystic fibrosis

• mutation occurs on chromsome 7

  • gene mutated codes for 1480 amino acids that make up a protein that regulated the passage of Cl^- ions across cell membrane

• symptoms: salty skin, persistant coughing, wheezing or pneumonia, digestive problems

• revessive trait → inherited from both parents

• characterised by thick sticky mucous from mucous glands

  • clogs air passages, traps bacteria and increases infection chance => lung damage

  • pancreas - prevents secretion of digestiv enzymes creating problems with nutrition

What is tisomy?

• chromosmal mutation

• result of non-disjunction

  • failure of one or more chromatids to seperate in 2nd division of meiosis

  • eggs or sperm formed have +1 or -1 chromosome

• e.g. Down syndrome, Patau syndrome

Outline Down syndrome

• also known as trisomy 21

• child has 3 copies of chromosome 21 instead of the normal 2 copies

• increased chance for this to occur in children of older mothers

• characteristics: weak muscles, intellectual disability, characteristic facial expression

• increased change of birth defects (e.g. heart defects, digestive abnormalities)

Outline Patau syndrom

• extra chromosome 13

• characteristics: intellectual disability, microcephaly, +1 finger on each hand, cleft palate and/or cleft lip, eye and ear malformations

• occurs from either egg or sperm

• 1-5000 live births

• greater than 80% of children die within 1 month of birth

What is monosomy?

Individual missing a chromosome completely resulting in severe malformations and miscarriage or only part of a chromosome missing (partial monosomy).

What is cri-du-chat syndrome?

• missing portion of chromosome 5

• symptoms: infants sound like meowing kitten

• probels with larnyz and nervous system

• rare

What is Turner syndrome?

• chromosome set with only 1 X chrosome

• also called monosomy X

• symptoms: females short, lack secondary sexual characteristics, infertile

Are most mutations recessive or dominant?

Recessive => people are usually unaware of mutations, only known if person with recessive and another person with the same recessive have offspring => offspring with recessive condition

What occurs in lethal recessives?

Death of embryo or foetus by miscarriage or spontaneous abortion or early death of a child (if not masked by a dominant allele).

What is Tay-sachs disease (TSD)?

• inherited in an autosomal recessive pattern

• disorder of lipid metabolism

• caused by mutation in HEXA gene that codes for enzyme beta-hexosaminidase

  • responsible for breaking down toxic substances

    • e.g. GM2 ganglioside (fatty substance) in brain and spinal cord

      • accumulation => destroys neurons

• baby develops normal 2 months, then deteriorates (intellectual and physical disabilities)

• usually death occurs in early childhood

What is autosomal?

Any chromosome not a sex chromosome