Mutations

🧬 Mutations: Changes in DNA

Mutations are changes in DNA, which can affect the messenger RNA transcribed from it, and subsequently alter the proteins produced. These changes can have varying effects on an organism.

🍪 Mutations as Recipe Changes

Mutations can be analogized to changes in a recipe, such as the Nestle Tollhouse Chocolate Chip Cookie recipe.

• Point Mutation Example 1: Changing "stiqks" to "sticks" of butter. This small change likely won't ruin the cookies.

• Point Mutation Example 2: Changing one teaspoon to nine teaspoons of baking soda would result in awful-tasting, alkaline cookies.

• Large-Scale Mutation Example: Moving the oven temperature instruction to the end of the recipe would result in dough instead of cookies.

💥 Causes of Mutations

Mutations can arise in two primary ways:

• Spontaneous Mutations: These occur during DNA replication or gamete formation due to errors like strand slippage, where the parent and daughter strands misalign.

• Induced Mutations: These are caused by environmental factors.

  • Example: Radiation causing skin cancer.

  • Example: Chemicals in cigarettes, such as benzo a pyrene, fitting into the DNA double helix and causing mutations, potentially leading to cancer by affecting cancer-suppressing genes.

📍 Point Mutations

These are mutations at a single point in the DNA sequence.

• Substitution: Replacing one base with another (e.g., adding a C instead of a T).

  • Cells have repair mechanisms that can detect mismatches (e.g., A bonded to C).

  • Enzymes can cut out the incorrect base and replace it.

  • There's a 50% chance the repair mechanism will replace the wrong letter.

  • If this occurs within a gene that codes for amino acids, it can significantly impact protein structure.

• Insertion: Adding a new nucleotide.

  • Radiation or chemicals can cause DNA to break.

  • When the DNA is repaired, a new letter might be added.

  • This extra letter can shift all subsequent letters, disrupting the entire protein sequence.

• Deletion: Removing a nucleotide.

  • Chemicals or radiation can cause a nucleotide to be lost.

  • During DNA repair, the strand may fold on itself.

  • Copying the damaged strand results in a missing letter or a large portion of the gene.

масштабна Large-Scale Mutations

These involve significant changes affecting large portions of a chromosome. They can occur during mitosis or meiosis.

• Deletion: Losing a large segment of a chromosome, potentially containing hundreds or thousands of genes.

• Duplication: A segment of a chromosome is copied, resulting in multiple copies of those genes during the S phase.

• Inversion: A segment of a chromosome is flipped upside down.

• Insertion: A segment from one chromosome is inserted into another chromosome.

• Translocation: A segment from one chromosome is moved to another, and vice versa.

🧬 Mutation Types

🧬 Mutations: Changes in Genetic Material

Types of Organisms that Can Have Mutations

• Mutation: A change in genetic material, specifically within a nucleic acid (RNA or DNA).

• Organisms that can have mutations:

  • Animals (including humans)

  • Plants

  • Fungi

  • Protists

  • Bacteria

  • Archaea

  • Viruses

Effects of Mutations

• Neutral mutations: Have no effect. Example: A silent mutation where a base is altered, but the codon still codes for the same amino acid (e.g., leucine).

• Mutations can be harmful or helpful.

• Mutations are random. Organisms cannot "will" themselves to get a specific mutation.

• Factors that can make mutations more likely:

  • External factors: Certain chemicals, excessive radiation

  • Internal factors: Problems with DNA replication during interphase

Gene Mutations

• Gene mutations: Changes in one or more DNA bases that can lead to the production of different proteins, affecting an organism's traits.

• Examples of gene mutations:

  • Substitution: The wrong base is matched.

  • Insertion: An extra base (or bases) is added.

  • Deletion: A base is removed.

• Frameshift mutation: An insertion or deletion that changes the total number of bases. This can alter the reading frame and affect all codons downstream.

  • Bases are read in threes during protein synthesis. Adding or removing a base shifts the reading frame, affecting subsequent codons.

  • Can lead to multiple amino acid changes.

Chromosomal Mutations

• Chromosomes: Made of DNA and protein and contain many genes.

• Human chromosome number: 46 (23 from egg, 23 from sperm).

• Fruit fly chromosome number: 8 (4 from egg, 4 from sperm).

• Types of chromosomal mutations:

Mutations During Meiosis

• Vulnerable times for mutations: During DNA replication and meiosis.

• Nondisjunction: Chromosomes don't separate completely during meiosis.

  • Results in egg or sperm cells with too many or too few chromosomes.

Inheritance of Mutations

• Asexual reproduction (e.g., in protists): Daughter cells can inherit the same mutation.

• Sexual reproduction (e.g., in fruit flies): A mutation can be passed to offspring if it's in the sperm or egg cell's genetic material.

🍎 Fruit Flies in Mutation Studies

• Fruit flies are frequently studied to understand mutations and their inheritance.

Sickle Cell Anemia: A Human Gene Mutation Example

• Hemoglobin: A protein in red blood cells that carries oxygen.

• Sickle cell anemia: A disorder caused by a mutation in the gene that codes for hemoglobin.

  • Inheriting two copies of the mutated gene leads to the disorder.

  • The mutated hemoglobin protein affects the shape of red blood cells, impairing their ability to carry oxygen, leading to anemia and other problems.

  • Treatment has improved, but there is currently no cure.

• Carriers: Individuals who inherit only one copy of the mutated gene.

  • Usually do not have symptoms.

  • Appear to have a protective factor against malaria, with less severe symptoms if infected.

  • Malaria is caused by a protist transmitted by mosquitoes.

Genetic Counseling

• Studying mutations and genetic disorders is a large and important field.

• Genetic counselors help families that may be affected by genetic disorders.

🧬 Mutations

Mutations are changes that occur in the genetic material or DNA. A mutation occurs when a change happens in a base sequence.

• Example: a 'G' changing to a 'T' or a 'T' changing to an 'A'.

🤔 What Causes Mutations?

Mutations can be spontaneous or induced.

• Spontaneous mutations: Mutations that happen normally, often during DNA replication when mistakes are made.

• Induced mutations: Mutations caused by certain factors.

☢ Factors That Induce Mutations

⚡ High-Energy Radiation

High-energy radiation can increase the rate of mutations in DNA. Examples include:

• Ultraviolet (UV) radiation from the sun

• X-ray radiation

🧪 Mutagenic Chemicals

Mutagenic chemicals are substances that can cause mutations in DNA.

🔥 High Temperature

Very high temperatures can cause mutations in DNA.

📝 Summary of Factors

🧬 Mutation Outcomes

Mutations are usually bad or deleterious, causing a negative impact on cells. However, sometimes mutations can lead to an advantage, which is key to evolution. Spontaneous mutations are inevitable and unavoidable, often occurring during DNA replication.

Mutations and Evolution 🧬

Types of Mutations

• A mutation is a change in the genetic code.

• Mutations are often copying errors that happen during DNA replication.

• Most mutations have no effect on the organism.

• Some mutations alter important genes, harming the organism and decreasing chances of survival.

• Some mutations alter genes, giving rise to a new trait that gives the organism an advantage.

• Mutations are the ultimate source of variations in life on Earth.

Mutations That Cannot Lead to Evolution 🚫

• Some mutations only affect the individual carrying the mutation.

• These mutations occur in body cells.

• Mutations in body cells that happen during an organism's lifetime can only be passed on through mitosis to new body cells.

• The mutation will only be present in the cells that develop from the cell with the original mutation.

• An acquired mutation has no effect on evolution, even if the mutation is beneficial.

• Body cell mutations cannot be passed on to offspring.

Mutations That Can Lead to Evolution ✅

• The only way for a mutation to influence the gene pool is if it can be passed on to the next generation.

• For this to happen in sexual reproduction, the mutation must be present in the gametes.

• Mutations in gametes are inherited by the offspring's first cell through fertilization.

• As every cell originates from the zygote, this mutation would be present in all cells of the offspring.

• If the mutation gives the organism an advantage and they survive and reproduce successfully, they may pass on this gene to their offspring as well.

• Beneficial mutations through natural selection may increase in frequency from one generation to the next.

Evolution Defined ✍

• Evolution is the change of a gene pool over time, thus affecting the traits and survival of individuals in a population.

🧬 Point Mutations and Genetic Information

Genetic Information Overview

• Genetic information is contained within a stretch of DNA or RNA called a gene.

• Genes determine the size, shape, and behavior of living creatures.

• Humans have over 20,000 genes that instruct cells to build and maintain bodies.

• All living things on Earth evolved from a common ancestor with less genetic information than organisms today.

🧫 Point Mutations Defined

• Point mutation: Any change that affects a single pair of nucleotides (letters) in the genetic code.

  Point mutations often occur during cell reproduction and appear to be mostly random.

• In humans, each newborn has roughly 70 unique point mutations.

• Most mutations are neutral, but some can negatively affect survival and reproduction. Natural selection removes these.

🧪 Examples of Beneficial Point Mutations

E. Coli Experiment

• Researchers in Dr. Richard Lenski's lab observed mutations in bacteria.

• A beneficial point mutation occurred in E. coli where an A was replaced with a T in its code.

• Bacteria with this mutation reproduced faster and outcompeted non-mutant siblings in the lab.

Salmonella Mutation

• In 1976, scientists found a mutation in Salmonella, later classified by Dr. Michael Behe as a rare gain-of-function mutation.

• The mutation enabled the microbes to detect and consume a rare sugar called D-arabinose.

🐶 Point Mutations in Animals

Fur Length in Dogs

• A study of over 700 dogs compared their DNA to that of wolves.

• Scientists discovered a single point mutation on the FGF5 gene (changing an AG to a T).

• This mutation is largely responsible for the long fur in breeds like Shih Tzus, Collies, and Pomeranians.

🐸 Point Mutations in Wild Plants and Animals

Resistance to Toad Toxins

• Cane toads produce a milky toxin that kills animals that try to eat them.

• Animals like lizards, snakes, and hedgehogs have independently undergone point mutations.

• These mutations modify the shape and stickiness of transporter proteins, preventing toad toxins from attaching. Mutants become immune to the poison.

📝 Summary of Point Mutations

• Point mutations can provide new genetic information to a population.

• Dog populations now have information for both short and long fur due to a point mutation.

• Point mutations typically edit existing information rather than increasing the total amount.

• For an individual, gaining new information through point mutations often means losing old information.

🧬 Evolution of New Genes

As previously discussed, a gene is a long DNA sequence encoding information, usually for a protein or protein group. Point mutations can alter small sections within a gene, modifying the resulting protein. While these edits are significant for evolution, comparing genes across species reveals that some species possess entirely novel genes absent in others.

🧩 The limits of Point Mutations

The presence of unique genes across different organisms prompts the question: How do entirely new genes evolve? Point mutations alone are insufficient to explain this phenomenon.

👯 Gene Duplication and Mutation

Scientists have discovered that one common mechanism for the evolution of new genes involves a duplication event followed by further mutations.

Duplications occur naturally and can range from small nucleotide sequences to entire genes. Subsequent mutations in the duplicated gene can lead to new genetic information that codes for proteins with novel functions.

Duplication events have been directly observed in the lab. Scientists can now analyze genetic code, identify signatures of past duplication events, and understand how specific genes likely evolved.

🐶 Dachshund Legs: A Case of Duplication

The unique short legs of dachshunds are not a disability but an adaptation for digging and entering small burrows.

• Researchers discovered that their leg structure resulted from a duplication event of the FGF4 gene.

• The duplicated gene produces protein that interacts with bone growth, reshaping the legs.

• Humans selectively bred dogs with this trait, leading to new breeds.

• This demonstrates that even unusual mutations can be beneficial in the right environment.

🐒 Leaf-Eating Monkeys: Specialized Digestion

Certain Asian monkey species, such as the Duke langur, consume primarily leaves, which presents digestive challenges. These monkeys have adapted to this diet through various mechanisms, including gene duplication.

• RNase1 is a protein that helps cells fight viruses and breaks down genes from food in the intestines.

• In humans, the pH level in the intestines is similar to that of cells, allowing RNase1 to function effectively in both environments.

• Leaf-eating monkeys have more acidic intestines, which aids in breaking down leaf cell walls but impairs RNase1 function.

• A duplication of the RNase1 gene in these monkeys has led to the evolution of a version that functions better in acidic conditions.

  Gene	Function
  Original gene	Produces protein to fight infections
  New gene	Functions effectively in acid to digest

This example illustrates how a duplicated gene can specialize to perform different tasks.

🐍 Snake Venom: A Deadly Adaptation

Venomous snakes produce venom in their saliva glands, which is a complex mixture of proteins that can kill prey.

• Saliva in most creatures contains proteins that initiate the breakdown of food.

• Venomous snakes have evolved this process further to produce deadly venom.

• Blood clots are formed through chemical reactions, facilitated by the factorX protein.

  • Normally, factorX is dormant until activated at the site of an injury, initiating clot formation.

• The saliva of the Australian rough-scaled snake contains pre-activated factorX.

  • When injected, this causes rapid clotting throughout the victim's body, often leading to death.

• Analysis of the snake's DNA reveals that the gene coding for factorX was duplicated.

  Gene	Function
  Original factorX	Functions in blood clotting for healing
  Duplicated factorX	Mutated to produce activated factorX in venom glands, leading to deadly venom

This shows that a gene originally used for healing can evolve to kill through duplication and mutation.

📝 Summary: Gene Duplication and Evolution

In summary, new genes evolve through the duplication of existing genes followed by the accumulation of new mutations. These processes, along with other mutations, occur naturally, leading to a variety of new genetic information, traits, and species.