Natural Selection and Adaptations

Natural Selection and Adaptations

Middle School

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Learning Objectives

• Describe DNA's structure and how mutations cause genetic variation.

• Explain how natural selection changes the traits in a population.

• Describe adaptation as a response to environmental changes over time.

• Use math to explain how natural selection affects population trends.

• Compare natural selection, artificial selection, and genetic engineering.

Key Vocabulary

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Gene

A gene is a specific segment of DNA that carries the instructions for a particular trait.

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DNA

Deoxyribonucleic acid, or DNA, is the molecule that contains the genetic code for all living organisms.

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Mutation

A mutation is a permanent alteration in the DNA sequence that makes up a particular gene.

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Variation

Variation refers to the differences in genetic traits that exist among individuals within a certain population.

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Natural Selection

This is the process where organisms with favorable traits are more likely to survive and reproduce.

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Adaptation

An adaptation is an inherited characteristic that helps an organism survive and reproduce in its environment.

Key Vocabulary

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Distribution of Traits

Distribution of traits refers to how often a characteristic appears within a population of different organisms.

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Probability

Probability is a measure of the chance or the likelihood that a specific event will happen.

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Selective Breeding

Selective breeding is the process where humans choose organisms with desirable traits to reproduce for specific outcomes.

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Genetic Engineering

Genetic engineering involves the direct manipulation or modification of an organism's DNA.

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Camouflage

Camouflage is a type of structural adaptation that helps an organism blend in with its surrounding environment.

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Mimicry

Mimicry is a survival adaptation where one species evolves to look, sound, or act like another species.

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DNA Structure and Replication

DNA Structure

• DNA is our genetic material, with a structure resembling a twisted ladder called a double helix.

• The ladder's sides are made of sugar and phosphate, while the rungs are pairs of nitrogen bases.

• Base pairing rules are specific: Adenine (A) links with Thymine (T), and Cytosine (C) links with Guanine (G).

DNA Replication

• Replication is the process where a DNA molecule makes a perfect copy of itself before cell division.

• The DNA strand separates down the middle, much like a zipper unzipping to expose the bases.

• Each separated strand acts as a template to build a new strand, resulting in two identical DNA molecules.

Multiple Choice

Which statement best describes the basic structure of a DNA molecule?

• A single strand of sugars and bases.

• A double helix with sides of sugar and phosphate and rungs of base pairs.

• A braided rope of proteins and lipids.

• A circular molecule made only of nitrogen bases.

Multiple Choice

What is the relationship between the original DNA molecule and the new molecules created during replication?

• The DNA molecule coils up tightly to protect the genetic code.

• The DNA strand separates, and each side is used as a template for a new strand.

• The sugar-phosphate sides are completely replaced with new molecules.

• The entire DNA molecule is dissolved and a new one is built from scratch.

Multiple Choice

If a segment of a single DNA strand has the base sequence A-G-C, what would be the base sequence on the new complementary strand formed during replication?

• A-G-C

• T-C-G

• G-T-A

• C-G-T

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From DNA to Protein: Transcription and Translation

Transcription

• In the nucleus, a segment of DNA is used to create a messenger RNA (mRNA) molecule.

• RNA is single-stranded and contains uracil (U) instead of thymine (T), which is found in a DNA strand.

• The mRNA then carries the genetic instructions from the nucleus to the cytoplasm, where the next step will begin.

Translation

• In the cytoplasm, a ribosome reads the code on the messenger RNA (mRNA) to build a protein.

• A series of three nitrogen bases on the mRNA, called a codon, codes for one specific amino acid.

• Transfer RNA (tRNA) brings the correct amino acids to the ribosome, which links them together to make a protein.

Multiple Choice

What is the primary purpose of transcription?

• To create a messenger RNA (mRNA) molecule from a segment of DNA.

• To link amino acids together to build a complete protein.

• To carry amino acids to the ribosome for protein assembly.

• To copy the entire DNA strand into a new identical strand.

Multiple Choice

What is a key difference between the processes of transcription and translation?

• Transcription happens in the nucleus, while translation happens in the cytoplasm.

• Transcription uses ribosomes to create mRNA, while translation uses the nucleus.

• Transcription builds proteins, while translation builds mRNA molecules.

• Transcription involves tRNA, while translation involves codons.

Multiple Choice

If a cell were unable to produce transfer RNA (tRNA), what would be the most likely outcome?

• The ribosome would not be able to build the protein because the tRNA would not deliver the correct amino acids.

• The mRNA molecule would not be able to leave the nucleus to begin translation.

• The DNA would fail to create an mRNA molecule during transcription.

• The codons on the mRNA would code for the wrong type of protein.

Genetic Mutations: The Source of Variation

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Deletion

• A mutation is a permanent change in the sequence of DNA.

• In a deletion, one or more DNA bases are left out.

• The effects of a mutation can be negative or even neutral.

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Insertion

• Mutations are the source of all genetic variation in a population.

• In an insertion, one or more DNA bases are added in.

• The effects of a mutation can sometimes be positive for an organism.

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Substitution

• A substitution happens when one DNA base is replaced by another.

• Only mutations in reproductive cells can be passed on to offspring.

• These mutations are essential for the long-term evolution of a species.

Multiple Choice

What is the fundamental role of genetic mutations within a population?

• They are the source of all genetic variation in a population.

• They only cause negative effects in an organism.

• They prevent the long-term evolution of a species.

• They only occur in the body cells of an organism.

Multiple Choice

If a single DNA base in a gene is swapped for a different one, what specific type of mutation has happened?

• A substitution, where one DNA base is replaced by another.

• A deletion, where one or more DNA bases are left out.

• An insertion, where one or more DNA bases are added in.

• A neutral mutation, which has no effect on the organism.

Multiple Choice

A mutation in an organism's body cell results in a positive trait. Why is this change unlikely to contribute to the long-term evolution of the species?

• The mutation must occur in a reproductive cell to be passed on.

• Only mutations with negative effects can be passed on.

• Evolution happens too quickly for the mutation to be included.

• All mutations are permanent and cannot be passed on.

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Natural Selection and Probability

• Natural selection explains how populations change over time through inherited traits.

• Individuals with helpful traits have a higher probability of surviving and reproducing.

• For instance, a bird with a thick beak can easily eat hard-shelled nuts.

• Over time, more birds in the population will have this advantageous trait.

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Multiple Choice

What does the principle of natural selection primarily explain?

• How individual animals learn new behaviors.

• How populations of species change over time.

• How the environment remains stable.

• How animals choose their mates.

Multiple Choice

In the context of natural selection, what is the main advantage of having a helpful trait?

• They guarantee that an individual will live longer.

• They make an individual stronger than all others.

• They increase the likelihood of surviving and reproducing.

• They are developed by an individual through practice.

Multiple Choice

If a bird population's main food source shifts to hard-shelled nuts, what is the most probable long-term outcome for the population?

• The birds will learn to find a different food source.

• All birds in the population will immediately develop thicker beaks.

• The proportion of birds with thick beaks in the population will likely increase.

• The population of birds will decrease because the nuts are too hard to eat.

Types of Adaptations

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Structural

• ​These are physical features of an organism that help it survive.

• A polar bear's thick fur helps it to stay warm in arctic.

• A bird's beak is shaped to help it get specific food.

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Behavioral

• ​These are the actions an organism takes to increase its survival chances.

• Birds migrating south during the winter is a common behavioral adaptation.

• A squirrel burying nuts for the winter is another example.

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Functional

• ​These are internal processes that help an organism to survive.

• A snake producing venom is a key functional adaptation for defense.

• The ability of a cactus to store water in its stem.

Multiple Choice

A physical feature of an organism, like a polar bear's thick fur, that helps it survive in its environment is what type of adaptation?

• Structural adaptation

• Behavioral adaptation

• Functional adaptation

• Environmental adaptation

Multiple Choice

What is the key difference between a structural adaptation and a behavioral adaptation?

• One is a physical feature, while the other is an action.

• One happens inside the body, while the other is a physical feature.

• One is a choice, while the other is an instinct.

• One is for finding food, while the other is for defense.

Multiple Choice

A snake uses venom to neutralize its prey and camouflage to hide from predators. How would these adaptations be classified?

• The snake's venom is a functional adaptation, while its camouflage is a structural adaptation.

• The snake's venom is a structural adaptation, while its camouflage is a behavioral adaptation.

• Both the venom and the camouflage are functional adaptations.

• Both the venom and the camouflage are structural adaptations.

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Modeling Natural Selection

• Scientists use mathematical models like graphs to show natural selection.

• ​A chart could show the distribution of traits like bird beak sizes.

• After a drought, the average beak size in the population increases.

• Models visualize how survival traits become more common over generations.

Multiple Choice

What is the primary purpose of using mathematical models in the study of natural selection?

• To represent how traits in a population change over time.

• To track the life cycle of a single animal.

• To prove that all mutations are helpful.

• To change the environment of a population.

Multiple Choice

How can a tool like a bar chart be used to show the effects of natural selection on a population of birds?

• It can show how the frequency of different beak sizes in a population changes.

• It can show the exact age of each individual bird.

• It can show why a single bird's beak changes color.

• It can show the total number of birds in the world.

Multiple Choice

A scientist creates a graph showing that the average beak size in a bird population has steadily increased over 30 years. What is the most likely conclusion supported by this model?

• The trait for longer beaks has become more common because it improves survival.

• All birds in the population now have long beaks.

• Individual birds are growing longer beaks during their lifetime.

• Shorter beaks will become more common in the next generation.

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Artificial Selection and Genetic Engineering

• Humans use artificial selection to breed organisms with specific desired traits.

• This process is useful for selectively breeding organisms for desired traits over multiple generations.

• Genetic engineering is the technique used to directly change the arrangement of desired DNA that makes up a gene.

• It helps in creating pest-resistant or herbicide-resistant crops, developing bacteria to produce human insulin, and producing golden rice for enhanced nutrition.

Multiple Choice

Which statement best defines artificial selection?

• A process where humans choose organisms with specific traits to reproduce.

• A process where an organism's DNA is directly changed using scientific methods.

• A process that occurs in nature without any human influence.

• A process used to create medicines like insulin using bacteria.

Multiple Choice

What is the primary difference between artificial selection and genetic engineering?

• Genetic engineering directly changes an organism's DNA, while artificial selection relies on choosing organisms for breeding.

• Artificial selection is used only for plants, while genetic engineering is used only for animals.

• Genetic engineering occurs naturally, while artificial selection requires human intervention.

• Artificial selection is a faster process than genetic engineering.

Multiple Choice

A scientist wants to create bacteria that can produce human insulin for medicine. Why is genetic engineering the most effective method for this specific goal?

• It allows for the insertion of human DNA into the bacteria's DNA.

• It is the only method that can be used on microorganisms like bacteria.

• It is a modern version of the breeding techniques used to create different dog breeds.

• It ensures that the bacteria will be resistant to all types of pests.

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Common Misconceptions

Misconception	Correction
An individual organism can adapt during its lifetime.	Individuals cannot change their genes. Adaptations are inherited traits that appear over generations.
All mutations are harmful.	Mutations can be harmful, beneficial, or neutral, sometimes helping survival.
Natural selection is a predictable and guaranteed process.	Natural selection is based on probability, not a predictable guarantee of survival.

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Summary

• DNA's structure allows copying; mutations during this process create genetic variation for evolution.

• Natural selection favors adaptations, which are helpful traits that become common in a population.

• Mathematical models help track how natural selection changes the distribution of traits over time.

• Humans influence traits through artificial selection and genetic engineering.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1 (Not confident)

• 2 (A little confident)

• 3 (Mostly confident)

• 4 (Very confident)