Mutations and Genetic Disorders

Group 3: Mutations and Genetic Disorders

Mutations and causes

  • A change in genetic material, specifically in the nucleic acids DNA and RNA 

  • Anything that has DNA/RNA can have mutations

  • Many mutations can be neutral in affect, which means that a mutation can happen but processes still carry out as normal, called “Silent” Mutations

    • For example, the coding for a protein called Leucine in RNA is CUU, however a mutation can result in the code being CUC, but the Leucine is still coded from that so the mutation is neutral

  • Mutations can be either harmful or helpful as well

  • Mutations are random, but there can be factors that make mutations more likely to occur: external factors like radiation or chemicals or internal factors such as a mistake in DNA replication in interphase 

  • There are two types of mutations:

  • Gene mutations

    • DNA makes up genes that code for proteins that influence different traits

    • The types of gene mutations are substitution (wrong base is matched), insertion (an extra base(s) are added in), and deletion (a base is removed)

    • Insertions and deletions are especially dangerous because bases are read in threes and if you add or remove a base, the number of bases total is changed, and everything read after the mutation is different - this is called a Frameshift Mutation


  • Chromosome mutations (*also look at the notes from Group 1)

    • Chromosomes are made up of DNA and protein and are highly organized, they have genes on them

    • The human body has 46 chromosomes (23 from each parent)

    • Some examples of chromosomal mutations are duplication (where extra copies of genes are generated), deletion (where some of the extra genetic material is broken off), inversion (when a broken chromosome segment gets inversed and put back on the chromosome), translocation (when a fragment of one chromosome gets broken off and put on another chromosome) (although there are more) 

  • There are times when mutations are more likely to occur like meiosis or DNA replication

    • In Meiosis sometimes the chromosomes don’t separate completely and this is called Nondisjunction (this can cause too many or too few chromosomes)

  • If a parent has a mutation they can pass it down to their offspring if the mutation is included in the sperm or egg

  • Fruit flies are used for experiments to research about mutations since they are pretty reflective of what it's like for humans


Human genetic diseases including chromosomal analysis

  • One example of a genetic disease is sickle cell anemia

    • Hemoglobin is a protein in red blood cells that helps carry oxygen  

    • In the disorder the gene that codes for hemoglobin is mutated

    • If you inherit two copies of the gene (you must carry TWO genes, if you only carry one than you are a carrier) than you will have the disorder

    • Fun fact: Carriers seem to have a protective factor against malaria, they seem to have less severe symptoms

    • Makes it hard for red blood cells to carry oxygen since the shape is changed 


  • Chromosomal analysis

    • The microscopic examination of chromosomes in the metaphase stage of the cell cycle

    • This analysis detects changes in the chromosome model number and within the chromosome structure 

    • It’s done to diagnose or rule out certain genetic conditions, or to understand the cause of certain health problems

    • It involves taking a sample of blood, tissue, or fluid and then looking at the chromosomes under a microscope

    • It can only detect certain types of changes in chromosomes 

    • Karyotyping is a type of chromosomal analysis but there are other ways to do it 



Variation of Traits 

  • Heredity is about how traits are passed down from parents to offspring 

  • Traits are things like patterns on body or size and they are coded by the DNA

  • Traits can be influenced by the environment such as amount of food present can affect size

    • Another famous example is during the Industrial Revolution when a lot of bark was coated with coal, moths adapted because moths with light colored wings died because they couldn’t camouflage while the dark colored moths survived and had offspring 

  • DNA is in the nuclei of all cells and is inherited from the parents

  • In asexual reproduction, an organism inherits its DNA from the one parent

  • DNA in humans can code for height (short, tall, average), eye color (blue, brown, black, green), hair color (black, brown, red, blonde), and even risk of certain diseases

  • That’s why criminals can be caught just by leaving a hair: since all cells have DNA so they can use the DNA from the hair to find the person 

  • Traits are determined by genes which are specific segments of DNA

  • Changes in DNA called mutations can introduce new variations in traits (good or bad)

Why do living things have different versions of the same characteristic?

  • Living things have different versions of the same characteristic because they have different versions of genes. Genes are like recipes for making living things. They contain instructions for building all the different parts of a living thing, like its eyes, its fur, and its wings.

  • Genes can have different versions, called alleles. Alleles are like different versions of a recipe. For example, there is a recipe for blue eyes and a recipe for brown eyes.

  • When living things reproduce, they pass on their genes to their offspring. This means that offspring can inherit different combinations of alleles from their parents. This is why siblings can look different from each other, even though they share the same parents.

How do these differences get passed down from parents to offspring?

  • Differences in traits are passed down from parents to offspring through genes. Genes are passed down from parents to offspring during reproduction.

  • During sexual reproduction, each parent contributes one set of chromosomes to their offspring. Chromosomes are made up of DNA, which contains genes. This means that offspring inherit half of their genes from each parent.

  • The combination of genes that offspring inherit from their parents determines their traits. This is why offspring can look like a combination of their parents.

How does the environment affect these differences?

  • The environment can also affect the differences between living things. For example, if one plant gets more sunlight than another plant, it might grow taller.

  • The environment can also affect how genes are expressed. For example, some genes are only turned on at certain temperatures. This means that two living things with the same genes might look different if they live in different environments.



Pedigrees

  • A pedigree is like a family tree, it can show an inherent trait passed down from generations 

  • Circles represent females

  • Squares represent males

  • Roman numerals on the side represent generations

  • Lines connecting two shapes together are marriage lines

  • A line from the marriage line branches out into the next generation which signifies a couple’s children

  • Shaded shapes represent that the trait is there

  • There are different types of pedigrees

  • You can use a pedigree chart to determine what kind of pedigree it is and therefore what kind of disease it is

  • When listing possibilities of genotypes list all POSSIBLE genotypes, even though one may seem more likely

  • For autosomal, write the concluded genotypes above the shape, while for sex-linked, you write either XX or XY depending male/female

  • Autosomal Dominant: 

    • Every person with the allele will show symptoms of the disease and only one allele needs to be inherited

    • Every affected individual must have an affected parent and the trait often appears in every generation

    • Pattern is called vertical inheritance pattern, as in from top to bottom of the pedigree

    • However it is possible for other kinds of inheritance to have affected individuals in every generation so don’t rule the other ones out just because this is the case

    • Males and females are affected in roughly equal proportions

    • Affected individuals can pass it on to their children

  • Autosomal recessive:

    • Require that both parents of an affected individual carry at least one copy of the disease allele

    • Many individuals in the pedigree can be CARRIERS but may not necessarily be affected

    • There are often fewer affected individuals in the pedigree

    • Sometimes the disease “skips” generations

    • The main thing that separates autosomal recessive and dominant is that unaffected individuals can have AFFECTED offspring

    • Affect both males and females equally 

  • X-linked dominant

    • All daughters of a male who has the trait will also have the trait

    • There is no male to male transmission, the trait follows the inheritance of the X chromosome (since the father gives the Y chromosome)

    • Sons can have the trait only if their mother also has the trait

    • Same inheritance pattern as autosomal dominant in human females 

  • X-linked recessive

    • Sons of a carrier mother and an unaffected father have a 50% chance of being affected, while the daughter will not be affected but have a 50% chance of being carriers

    • Sons of an affected mother will all be affected

    • No father-to-son transmission of X-linked traits