Mutations

Compiled by Siti Sarah JumaliRoom 14, Level 3

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Changes in Heredity- Mutations

Nothing is perfect…Mutation – any changes (alterations) in the

sequence of DNA that affects genetic information and the appearance of offspring.

Caused by: UV Light, X-Rays, etc.

Types of MutationsGene mutation – a mutation that occurs in a

single gene and affects one trait.Ex: Eye color, Sickle cell Anemia,

Hemophilia

Chromosome mutation – a mutation that occurs in many genes and affects many traits at once.

Ex: Down Syndrome (an extra 21st chromosome)

How Can Mutations Affect an Organism?

Body cell mutations can cause cancer.

- only the individual is affected.Gamete cell mutations affect the egg and the sperm.

- all offspring of the individual can be affected.

Gene ExpressionAn individual’s trillions of body cells all come

from one cell (zygote).In differentiation the cells become different

tissues. (ex: skin, muscle, organ)Certain cells will “turn on” or activate only the

genes they need. This is called gene expression.

Factors that Affect Gene Expression

The internal and external environment of a cell can influence which genes are “turned on”.

Ex: - Hormones can “tell” a cell to activate a specific gene.

- Outside temperature changes fur color in rabbits.

End of Today, You Should Know:What is a mutation?What are some examples of harmful

mutations?Neutral Mutations are…What are some examples of beneficial

mutations?

What is a Mutation?Abrupt, heritable changes in a single gene or

a region of a chromosome, can also include alterations in chromosome number

Mutations are the fuel for evolution and are the basis for the variation in population.

What is a Mutation?Can be when one letter is switched -

accidentally copied incorrectly within the DNA.

When one section of the DNA, sometimes an entire gene, is not properly connected to the rest of the DNA; sometimes it even reconnects to another chromosome

One section of DNA, sometimes an entire gene, appears more than once

What is a Mutation?Will only get passed on to offspring when the

sex cells contain the mutationCan be caused after birth by environmental

factors like radiation and chemicals, which can alter a person’s DNA, even in their sex cells, causing their offspring to have disorders

Mutation..Affects molecular changes in the DNA sequence of

a geneAlter the coding sequence within a geneCauses permanent change in DNA sequenceInvolve insertion or removal of 1 or more base pairsPoint mutation is a change in single base pair

within DNA sequencesBase substitution changes is in pair2 types of changes

Transition (within same group AT and GC)Transversion (between 2 groups)

Transition vs Transversion

Changes in coding sequenceSilent mutation –does not alter the amino acid

sequence of the polypeptide although the nucleotide sequence was changed

Missense mutation- base substitution causes change in amino acid eg sickle cell anemia (Glu to Val)

Nonsense mutation – change from normal to stop codon. Translation is termination in abrupt producing truncated protein

Frameshift mutation – additional or deletion of a number of nucleotides that will not be realized if 3 nucleutides because 3 bases code for 1 aa. But if it is not in multiple 3, will be very dangerous, changes the whole aa sequence

Missense mutation

Nonsense mutation

Silent or neutral mutationSilent mutation can result in enhancing new

protein, but all other mutations reduce the function

Missense mutation generally affect mutation, it is also known as neutral mutation

Silent mutation

Frameshift mutation

Frameshift mutation

Some Mutations Cause Disorders…

Down’s Syndrome• Offspring receives 3 copies of 21st

chromosome90% of the time the extra chromosome comes

from the motherAffects 1 in 800 live births

Effects of Down’s SyndromeDifferent in each personDoes not usually pass this onto childrenCommon effects include

Learning DisabilitiesHeart defects (can usually be corrected with

modern technology)

Turner’s Syndrome45 (instead of 46) chromosomesoffspring are born with one X chromosome

(no Y; only one X)only affects womenIn about 80% of cases the X comes from the

mother and the father’s sperm has no YAffects 1 in 2500 live births

Effects of Turner’s Syndrome• Sometimes a lack of ovarian development• Can have more masculine qualities

(stronger), although are femaleIn some cases:

Webbed neckArms that turn in at the elbowLow hairline on the back of the head

Klinefelter’s Syndrome• Offspring inherit a Y chromosome and two X

chromosomesBecause there is a Y all offspring are maleSometimes the extra X comes from the egg

and sometimes it comes from the spermOccurs in 1 out of every 500 – 1000 live births

Effects of Klinefelter SyndromeSparse facial and body hairUnderdeveloped musclesWide hipsTall heightLong legs & armsHigher-pitched voice

AlbinismCaused by a recessive geneCauses genes to release unusual amounts of

melanin (chemical that provides color)Affects 1 in 17,000 peoplePeople of all races are susceptibleAll animals are susceptible

Effects of AlbinismLight skinLight hairReddish or violet eyes (in some albinos)Lack of eye pigment leads to vision problemsSkin cancer – especially in third world

countries

                                                          

                                          

                                           

     

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There are MANY other mutations…

Not all Mutations Are Bad…

Mutations Can Be NeutralThey may have little or no effect on the

survival of an organism or on its ability to reproduce.

They may result in the same kind of organism - meaning that the change still tells the cell to do what it should, so there is no difference.

It is estimated that the average human has 50-100 mutations within their DNA - most (if not all) are neutral or beneficial

Mutations Can Be BeneficialBacterial resistance to antibiotics

Insecticide resistance in bugs

Rapid mutation rates in virus’s proteins allowing them to adapt to new “hosts”

Mutations Can Be BeneficialIn humans, it can be a different set of

circumstances… Here’s an example:Sickle-Cell Anemia is a genetic disorder

in which there is a defect in the structure of red blood cells. This leads to fatigue and anemia when not treated.

However, it has been found that people who are carriers for Sickle-Cell Anemia also has some genetic protection against another disease, malaria.

Mutations Can Be Beneficial• In evolutionary studies, scientists have

connected the presence of a brain chemical microcephalin (a proposed mutation) with the human’s development of art, music, and complex tool-making practices

• This same research indicates that the human brain is still evolving and becoming more and more capable of more complex tasks

• Some humans have been found to have mutations that protect them from other diseases, such as AIDS