How Traits Change

How Traits Change

Middle School

​

Learning Objectives

• Describe how a gene's structure determines a protein's structure, affecting an organism's traits.

• Explain how gene mutations can alter proteins, leading to helpful, harmful, or neutral traits.

• Explain the differences between DNA replication, transcription, and translation.

• Contrast natural selection, driven by the environment, with artificial selection, driven by humans.

Key Vocabulary

​

Gene

A section of a chromosome that provides directions for a cell to assemble molecules that express traits.

​

Chromosome

A structure in a cell's nucleus that contains the genetic information, also known as DNA.

​

Protein

A molecule made of amino acids that performs a specific function in the body, determining traits.

​

Trait

An observable characteristic of an organism, influenced by both genes and the surrounding environment.

​

Mutation

A permanent change that occurs in the sequence of the DNA that makes up a gene.

​

Genetic Variation

The variety of different gene combinations that can exist within a given population of organisms.

Key Vocabulary

​

Natural Selection

Process where organisms with helpful traits are more likely to survive, reproduce, and pass on those traits.

​

Artificial Selection

The process where humans intentionally breed organisms together to get offspring with specific, desired traits.

​

DNA

Deoxyribonucleic acid, or DNA, is the molecule that carries the genetic instructions for an organism's development.

​

Replication

The biological process of producing two identical copies of a DNA molecule from one original DNA molecule.

​

Transcription

The process where a specific segment of DNA is copied into messenger RNA (mRNA) to make proteins.

​

Translation

The process where the genetic information from messenger RNA (mRNA) is used to create a specific protein.

​

​

The Structure of DNA

• Genes are segments of DNA on a chromosome that give instructions for traits.

• ​Its structure is a double helix, like a twisted zipper or ladder.

• It is made of nucleotides, which contain a base, sugar, and phosphate.

• The four bases pair up: adenine (A) with thymine (T) and cytosine (C) with guanine (G).

​

Multiple Choice

What are the three components of a nucleotide, the basic building block of DNA?

• A base, a sugar, and a phosphate

• A gene, a trait, and a chromosome

• An adenine, a thymine, and a guanine

• A double helix, a zipper, and a ladder

Multiple Choice

How are the two strands of the DNA double helix held together?

• Adenine always pairs with thymine, and cytosine always pairs with guanine.

• All four bases connect together in a long, single chain.

• The bases can pair with any other base in any order.

• The sugar and phosphate molecules determine the genetic code.

Multiple Choice

If one strand of DNA has the sequence A-T-C-G, what is the complementary strand?

• T-A-G-C

• A-T-C-G

• C-G-T-A

• G-C-A-T

​

​

From DNA to Protein

• Replication is the process where a DNA molecule makes an identical copy.

• Transcription creates messenger RNA (mRNA) from a DNA template in the nucleus.

• Translation occurs in ribosomes, reading mRNA codons to build a protein.

• A protein's amino acid sequence determines its 3D structure and function.

​

Multiple Choice

What is the overall purpose of the processes of transcription and translation?

• To make an identical copy of the cell's DNA.

• To build a protein using instructions from a DNA molecule.

• To break down proteins into amino acids.

• To store genetic information in the nucleus.

Multiple Choice

How do the processes of transcription and translation differ in terms of their location and final product?

• Transcription occurs in the nucleus to make mRNA; translation occurs in the ribosome to make a protein.

• Transcription occurs in the ribosome to make DNA; translation occurs in the nucleus to make mRNA.

• Both processes occur in the nucleus, but one makes mRNA and the other makes a protein.

• Both processes occur in the ribosome, but one copies DNA and the other builds a protein.

Multiple Choice

A specific protein is not functioning correctly. Based on the flow of genetic information, which of the following could be the most direct cause?

• The original DNA molecule was not able to replicate correctly.

• The ribosome failed to leave the nucleus after being made.

• The sequence of amino acids that makes up the protein was incorrect.

• The cell did not have enough energy for translation.

​

​

From Genes to Traits

• Genes on chromosomes contain the instructions for building specific proteins.

• A protein’s specific shape is essential for its proper function.

• The combined action of all proteins results in an organism’s traits.

• These traits include hair color, eye color, and other characteristics.

​

Multiple Choice

What is the primary function of genes located on chromosomes?

• To provide the instructions for building specific proteins.

• To create physical traits like hair color directly.

• To determine the shape and function of chromosomes.

• To store energy for the organism's cells.

Multiple Choice

How do proteins lead to an organism's traits, such as hair color?

• The combined action of many different proteins produces a specific trait.

• A single protein is solely responsible for every complex trait.

• Traits are physical characteristics, while proteins are instructions.

• Proteins are only responsible for internal traits, not visible ones.

Multiple Choice

Given that a protein's shape is essential for its function, what is the most likely consequence if a gene's instructions are changed, leading to a protein with a different shape?

• The protein's function would be altered, which would likely affect an organism's trait.

• The protein's function would remain the same, but its location would change.

• The organism's other genes would correct the protein's shape automatically.

• The chromosome would change shape to match the new protein.

What is a Mutation?

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

• Mutations can happen randomly or be caused by environmental factors called mutagens.

• Types of mutations include insertion, deletion, and substitution of nitrogen bases.

Multiple Choice

What is a mutation?

• A temporary change in a cell's structure.

• A permanent change in the DNA sequence.

• The process of a cell dividing into two.

• A chemical message sent between cells.

Multiple Choice

What is the role of a mutagen?

• A random change that happens during cell division.

• An environmental factor that can cause a mutation.

• A type of mutation that only adds nitrogen bases.

• The result of a permanent change in the DNA.

Multiple Choice

If a DNA sequence is altered by removing one nitrogen base, which statement best describes the change?

• An insertion, because a new nitrogen base was added.

• A substitution, because one base was swapped for another.

• A deletion, because a nitrogen base was removed.

• A random event, because it happened without a cause.

The Effects of Mutations

​

Harmful Mutations

• These negatively affect an organism's ability to survive and reproduce.

• Many genetic disorders, like Cystic Fibrosis, are caused by harmful mutations.

• These mutations often result in the creation of defective proteins.

​

Beneficial Mutations

• These provide an advantage, increasing chances of survival and reproduction.

• An organism with a beneficial mutation is more likely to thrive.

• An example is a mutation giving an insect pesticide resistance.

​

Neutral Mutations

• These do not have a significant effect on an organism's survival.

• They change a trait but are neither helpful nor harmful to survival.

• An example is the mutation that causes blue eyes in humans.

Multiple Choice

What is the primary factor that determines if a mutation is classified as harmful, beneficial, or neutral?

• Its effect on an organism's survival and reproduction.

• The specific gene in which the change occurs.

• Whether the mutation results in a visible physical change.

• The type of organism in which the mutation happens.

Multiple Choice

How can a harmful mutation lead to a negative effect on an organism, such as a genetic disorder?

• By causing the creation of a defective protein.

• By preventing the organism from ever reproducing.

• By changing a trait that is neither helpful nor harmful.

• By providing a clear advantage in a specific environment.

Multiple Choice

A species of moth lives on dark-colored tree bark. A mutation occurs that changes the wing color of a moth from light to dark, making it harder for birds to see. How would this mutation be classified and why?

• Beneficial, because it increases the moth's chances of survival from predators.

• Neutral, because it only changes a physical trait.

• Harmful, because any change to an organism's proteins is negative.

• Neutral, because a change in color does not affect reproduction.

​

​

Natural Selection

• Genetic variation describes the gene differences between individuals in a population.

• These variations are caused by mutation and sexual reproduction.

• The environment selects for individuals with traits best suited for survival.

• Over generations, these advantageous traits become more common in the population.

Multiple Choice

Which statement best defines the process of natural selection?

• The process where the environment selects traits that are advantageous for survival and reproduction.

• The process where individuals change their traits to better fit their environment.

• The process where all individuals in a population eventually become identical.

• The process where organisms consciously choose the best traits for their offspring.

Multiple Choice

What is the role of genetic variation in the process of natural selection?

• It provides the different traits within a population that natural selection can act upon.

• It ensures that all individuals in a population have an equal chance of survival.

• It causes individuals to develop new traits during their lifetime.

• It stops the environment from having any effect on the population.

Multiple Choice

Based on the principles of natural selection, what is the most likely outcome for a population when a specific inherited trait provides a survival advantage?

• The frequency of the advantageous trait will increase in the population over time.

• The environment will change to favor a different trait.

• All individuals in the population will immediately develop the advantageous trait.

• The population size will decrease regardless of any traits.

​

​

Artificial Selection (Selective Breeding)

• Artificial selection is when humans pick which organisms reproduce to keep wanted traits.

• People choose parents with certain genes so offspring inherit traits, practiced for thousands of years.

• Examples include breeding gentle guide dogs, high-yield crops, and dairy cows producing more milk.

• Modern tools like genetic modification let humans change traits more directly and quickly.

​

Multiple Choice

What is the definition of artificial selection?

• A process where humans choose which organisms reproduce to get desired traits.

• A natural process where the strongest organisms survive and reproduce.

• A method for changing an organism's traits during its lifetime.

• A technique for creating entirely new species in a laboratory.

Multiple Choice

How does artificial selection lead to offspring inheriting wanted traits?

• By changing the environment to cause new traits to appear.

• By selecting parents that have the specific genes for those traits.

• By training organisms to develop the traits that people want.

• By only using modern genetic modification tools on the offspring.

Multiple Choice

A dairy farmer wants to increase the milk production of her herd over time. Based on the principles of artificial selection, what is the most effective strategy?

• Feed all the cows a special diet to increase their milk.

• Select the cows that produce the most milk and breed them together.

• Use modern genetic tools to change the milk of all the cows.

• Mix different breeds of cows together randomly and hope for the best.

​

Common Misconceptions

Misconception	Correction
All mutations are harmful.	Mutations can be harmful, beneficial, or neutral.
Traits are determined only by genes.	The environment also influences an organism's final traits.
Individuals can choose to adapt to their environment.	Natural selection acts on existing genetic variation in a population.
An organism can pass on any trait it acquires.	Only genetic traits in egg or sperm cells are inherited.

​

Summary

• A gene's DNA sequence determines a protein, which in turn determines an organism's traits.

• A gene mutation can alter a protein, causing harmful, beneficial, or neutral effects.

• The environment favors advantageous traits through natural selection, leading to population change over time.

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

Poll

On a scale of 1-4, how confident are you about explaining how traits can change?

• 1

• 2

• 3

• 4