Mutations: The Basis of Genetic Change Hurray for Chromosomes

Mutation – a change in the structure or amount of genetic material of an organism, can be caused by damage or copying incorrectly

Mutations can occur naturally during the cell cycle when DNA is not copied correctly, be inherited from a parent or developed due to the environment (such as those caused by radiation or chemicals). Mutations can be expressed differently and affect differing amounts of DNA based on what the mutation actually is. A mutation can only be as small as one piece of DNA long or an entire chromosome (or more!).

Mutations can have many possible effects Mutations can have many possible effects. They could be small and have no effect, they could harm your cells, or they could help your cells. Everyone carries many recessive mutations that are not always expressed or harmful Inbreeding can cause them to get expressed! Mutations that occur in gametes (sex cells) are the only ones that get passed on to the offspring.

Different Types of Mutations Inserting – when extra DNA is added to the sequence Deleting – when DNA is deleted (removed) from the sequence Substituting – one segment of DNA replaces another

All of these types of mutations will be passed on to every cell that develops off of the mutated cell. BUT remember mutations that occur in non-sex cells WON’T be passed on to the next generation (offspring).

How can we identify mutations? We can analyze small pieces of DNA but replicating them and running them through gel electrophoresis. We can analyze whole chromosomes by looking at karyotypes.

Karyotype – is an organized profile of a person’s chromosomes Karyotype – is an organized profile of a person’s chromosomes. Chromosomes are arranged and numbered by size (from largest to smallest). This genetic picture makes it easy to recognized chromosomal mutations.

http://learn.genetics.utah.edu/content/begin/traits/karyotype/

Let’s review quick: A normal human has how many chromosomes total? How many DIFFERENT chromosome pairs does a normal human have? Homologous Pair of Chromosomes – have the same genes in the same location Each organism gets one chromosome from their mother, one from their father to make up the pair.

Male Chromosome Karyotype

Female Chromosome Karyotype

Chromosomal Mutation Disorders: Down Syndrome – also know as, trisomy 21, an individual with Down Syndrome has 47 chromosomes because instead of having only two 21st chromosomes they have 3 Children who have down syndrome often have mental disabilities and distinct facial features

Down Syndrome Karyotype

Chromosomal Mutation Disorders: Turner’s Syndrome – an individual with Turner’s syndrome only has 45 chromosomes, because they are lacking an entire sex chromosome these girls only have one X and experience abnormalities such as non-working ovaries, webbed necks, short stature, broad chests, low ears and often many additional internal abnormalities

Turners Syndrome

Chromosomal Mutation Disorders: Klinefelter’s Syndrome – an individual who has 47 chromosomes because they are a male with two X chromosomes instead of one (XXY), those affected with the syndrome tend to have small sexual organs and reduced fertility (this is actually the most common sex chromosome disorder, the condition exists in roughly 1 out of 1000 males but every 1 in 500 males has an extra X and for some reason it is repressed and they don’t express the disorder)

Gene Mutation Disorders: Sickle Cell Anemia (autosomal recessive) Caused by genes coding for a defective protein (hemoglobin) Cells are sickle shape, stiffer and sticky. They tend to block blood flow in the blood vessels of limbs and organs

Hemophilia (X-linked recessive) Caused by genes coding for a defective protein (autoantibody) Bleeding disorder that slows the blood clotting process

Cystic Fibrosis (autosomal recessive) Caused by genes coding for a defective protein (channel protein that lets chloride out of cells) Causes a buildup of thick, sticky mucus that can damage organs