Compiled by Siti Sarah Jumali Room 14, Level 3 06-4832123 Mutations Compiled by Siti Sarah Jumali Room 14, Level 3 06-4832123

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 Mutations Gene 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 Expression An 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 mutation Can 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 gene Alter the coding sequence within a gene Causes permanent change in DNA sequence Involve insertion or removal of 1 or more base pairs Point mutation is a change in single base pair within DNA sequences Base substitution changes is in pair 2 types of changes Transition (within same group AT and GC) Transversion (between 2 groups)

Transition vs Transversion

Changes in coding sequence Silent 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 mutation Silent 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 chromosome 90% of the time the extra chromosome comes from the mother Affects 1 in 800 live births

Effects of Down’s Syndrome Different in each person Does not usually pass this onto children Common effects include Learning Disabilities Heart defects (can usually be corrected with modern technology)

Turner’s Syndrome 45 (instead of 46) chromosomes offspring are born with one X chromosome (no Y; only one X) only affects women In about 80% of cases the X comes from the mother and the father’s sperm has no Y Affects 1 in 2500 live births

Effects of Turner’s Syndrome • Sometimes a lack of ovarian development • Can have more masculine qualities (stronger), although are female In some cases: Webbed neck Arms that turn in at the elbow Low hairline on the back of the head

Klinefelter’s Syndrome • Offspring inherit a Y chromosome and two X chromosomes Because there is a Y all offspring are male Sometimes the extra X comes from the egg and sometimes it comes from the sperm Occurs in 1 out of every 500 – 1000 live births

Effects of Klinefelter Syndrome Sparse facial and body hair Underdeveloped muscles Wide hips Tall height Long legs & arms Higher-pitched voice

Albinism Caused by a recessive gene Causes genes to release unusual amounts of melanin (chemical that provides color) Affects 1 in 17,000 people People of all races are susceptible All animals are susceptible

Effects of Albinism Light skin Light hair Reddish or violet eyes (in some albinos) Lack of eye pigment leads to vision problems Skin cancer – especially in third world countries

                                                          

                                          

                                                

                                                   

                                          

There are MANY other mutations…

Not all Mutations Are Bad…

Mutations Can Be Neutral They 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 Beneficial Bacterial resistance to antibiotics Insecticide resistance in bugs Rapid mutation rates in virus’s proteins allowing them to adapt to new “hosts”

Mutations Can Be Beneficial In 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