Genes and Heredity

Genes and Heredity

Middle School

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Learning Objectives

• Define the relationship between DNA, genes, and chromosomes.

• Explain how mutations can lead to variations in traits and affect an organism.

• Differentiate between artificial selection, genetic engineering, and cloning.

• Analyze a pedigree to trace the inheritance of a specific trait through generations.

• Describe how technologies like CRISPR, DNA sequencing, and DNA fingerprinting are used.

Key Vocabulary

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Gene

A segment of DNA on a chromosome that contains the instructions for a specific trait.

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Chromosome

A thread-like structure in the nucleus that contains DNA passed from one generation to another.

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Allele

One of the different forms of a gene found at the same place on a chromosome.

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Mutation

A change in the DNA sequence of a gene, which can alter an organism's traits.

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Pedigree

A model geneticists use to map the inheritance of traits across several family generations.

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Crossing Over

A process where chromosomes exchange segments, creating new gene combinations for the offspring.

Key Vocabulary

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Genetic Engineering

The process by which geneticists transfer a gene from one organism's DNA into another.

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Selective Breeding

The process where humans breed only those organisms with desired traits to produce the next generation.

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Clone

An organism that possesses the exact same genes as the organism from which it was produced.

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The Basics of Inheritance

• Genes on chromosomes determine your traits and are made of condensed DNA.

• Alleles are different forms of a gene; you get one from each parent.

• You are homozygous if alleles are the same, and heterozygous if they’re different.

• A dominant allele's trait shows, while a recessive allele may be hidden.

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Multiple Choice

What is the primary function of a gene?

• To determine an organism's traits

• To be a different form of a chromosome

• To hide recessive alleles

• To be made of different alleles

Multiple Choice

An organism is described as homozygous for a certain gene. What does this mean about its alleles?

• It has two identical alleles for the gene.

• It has two different alleles for the gene.

• It has only dominant alleles for the gene.

• It has only recessive alleles for the gene.

Multiple Choice

If an organism is heterozygous for a gene, what determines the trait that is physically expressed?

• The dominant allele, because its trait is the one that shows.

• The recessive allele, because it may be hidden.

• Both alleles, because they will blend together to form a new trait.

• The homozygous allele, because it is stronger than the heterozygous one.

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Chromosomes and Reproduction

• Human body cells have 46 chromosomes, while sex cells have 23.

• ​Fertilization combines 23 chromosomes from each parent, creating homologous chromosome pairs.

• During crossing over, these homologous chromosomes exchange small segments of genetic material.

• This process creates new gene combinations and increases genetic variation in offspring.

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Multiple Choice

What is the primary difference between human body cells and sex cells described in the context of reproduction?

• The type of genes they carry.

• The number of chromosomes they contain.

• The size of the cells.

• The location of the cells in the body.

Multiple Choice

What is the significance of homologous chromosomes exchanging genetic material during crossing over?

• It doubles the total number of chromosomes to 92.

• It creates new combinations of genes, leading to genetic variation.

• It reduces the number of chromosomes in the parents' cells.

• It ensures the offspring is identical to one parent.

Multiple Choice

Based on the process of fertilization, what can be concluded about the chromosomes of the resulting offspring?

• The resulting offspring would have 23 chromosomes from one parent.

• The resulting offspring would have 46 chromosomes, organized into 23 homologous pairs.

• The resulting offspring would have 46 chromosomes, but they would not be in pairs.

• The resulting offspring would have 92 chromosomes in total.

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Tracking Traits with Pedigrees

• A pedigree is a chart that tracks the inheritance of traits in a family.

• Geneticists use it to predict how traits might appear in future generations.

• Males are represented by squares and females by circles.

• Shaded shapes show an expressed trait; half-shaded shapes are carriers.

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Multiple Choice

What is the primary purpose of a pedigree chart?

• To track how traits are passed through a family and predict their appearance in the future.

• To change the genetic traits of future family members.

• To create a diagram of a family's social relationships.

• To identify the specific genes responsible for a trait.

Multiple Choice

In a pedigree chart, what does a shaded circle represent?

• A male who is a carrier of the trait.

• A female who expresses the tracked trait.

• A male who expresses the tracked trait.

• A female who is a carrier of the trait.

Multiple Choice

Why is it important to distinguish between individuals who express a trait (fully shaded) and those who are carriers (half-shaded)?

• It helps distinguish between male and female family members.

• It makes the chart more colorful and visually appealing.

• It allows geneticists to predict the likelihood of a trait being passed on, even if it is not expressed.

• It shows which individuals are older than others.

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Trait Variation and Chromosomes

Autosomal Chromosomes

• ​Humans have 23 pairs of chromosomes, with 22 of these pairs being autosomal chromosomes.

• ​​These chromosomes are homologous, with genes for the same traits in the same locations.

• ​Variations, or differences like eye color, can be helpful, harmful, or have no effect.

Sex Chromosomes

• ​The 23rd pair of chromosomes are the sex chromosomes, which determine the biological sex of an individual.

• ​​Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

• ​The X chromosome is much larger and contains more genes than the much smaller Y chromosome.

Multiple Choice

What is the primary function of the 22 pairs of autosomal chromosomes?

• To carry the genes that determine an individual's traits, such as eye color.

• To determine the biological sex of an individual.

• To ensure that all traits in a person are identical.

• To exist only in female cells.

Multiple Choice

What is the key difference between the function of autosomal chromosomes and sex chromosomes?

• Autosomal chromosomes determine general traits, while sex chromosomes determine biological sex.

• There are more sex chromosomes than autosomal chromosomes in a human cell.

• Only sex chromosomes can have variations in the genes they carry.

• Autosomal chromosomes are found in males, while sex chromosomes are found in females.

Multiple Choice

Which statement provides the best explanation for why a female's 23rd chromosome pair contains more genetic information than a male's?

• Females have two large X chromosomes, while males have one large X and one smaller Y chromosome.

• Males have more total genetic information on their sex chromosomes because the Y chromosome is unique.

• The Y chromosome contains more genes for traits than the X chromosome does.

• Biological sex cannot be determined by looking at the 23rd pair of chromosomes.

Genetic Mutations

• A mutation is a change in the DNA of a gene or chromosome.

• Types of mutations include deletion, addition, and substitution of a DNA base pair.

• Mutagens are environmental factors like UV rays that can cause DNA mutations.

Multiple Choice

What is a genetic mutation?

• A change in the DNA of a gene or chromosome.

• A type of cell that exists in the body.

• The process of creating new genes.

• A factor that prevents changes in DNA.

Multiple Choice

What is the relationship between mutagens and DNA mutations?

• They are the different types of mutations.

• They are environmental factors that can cause DNA mutations.

• They are sections of a chromosome that contain DNA.

• They are changes that are beneficial to an organism.

Multiple Choice

If a person experiences high exposure to UV rays, what is a potential consequence for their genetic material?

• The person's DNA would be protected from all future changes.

• A base pair in the person's DNA could be deleted or substituted.

• The person's chromosomes would become a type of mutagen.

• The structure of the DNA would remain unchanged.

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Genetic Technologies: Selection and Engineering

Artificial Selection

• Humans select organisms with specific traits to breed for the next generation.

• This process, also known as selective breeding, is guided by human choice, not nature.

• The selected traits benefit humans but may not help the organism survive in the wild.

Genetic Engineering

• Scientists directly modify an organism's DNA by inserting a gene from another species.

• This creates new traits that are not possible to achieve through traditional breeding.

• Bacteria are engineered with a human gene to produce insulin for people with diabetes.

Multiple Choice

What is the primary guiding factor in artificial selection?

• The choices made by humans.

• The natural survival needs of the organism.

• The random mutation of genes.

• The organism's ability to adapt to its environment.

Multiple Choice

What is a key difference between genetic engineering and artificial selection?

• Genetic engineering involves modifying DNA by inserting a gene from another species, while artificial selection works with existing traits within a species.

• Artificial selection is performed by scientists in a lab, while genetic engineering happens in nature.

• Genetic engineering creates traits that only benefit humans, while artificial selection benefits the organism.

• Artificial selection creates entirely new traits, while genetic engineering only enhances existing ones.

Multiple Choice

Scientists needed to produce insulin for people with diabetes by using bacteria. Why would they use genetic engineering instead of artificial selection for this task?

• Because bacteria do not naturally have the gene for producing human insulin, so it had to be inserted into their DNA.

• Because artificial selection would cause the bacteria to become resistant to medicine.

• Because breeding bacteria is a much slower process than genetically engineering them.

• Because the traits from artificial selection may not help an organism survive in the wild.

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Advanced Genetic Technologies: Gene Therapy and Cloning

Gene Therapy

• Gene therapy involves changing a gene to treat a medical disease, such as a genetic disorder.

• This process can replace a faulty or absent gene with a normal, fully functional one.

• A tool called CRISPR can cut a harmful mutation from DNA and insert a normal sequence.

Cloning

• A clone is an organism that has the exact same genes as the original parent organism.

• This is done by placing a body cell nucleus into an egg cell without a nucleus.

• Cloning reduces genetic diversity, making populations more vulnerable to diseases.

Multiple Choice

What is the primary purpose of gene therapy?

• To alter a gene in order to treat a medical disease.

• To create an organism with the exact same genes as its parent.

• To increase the genetic diversity of a population.

• To study the effects of harmful mutations on an organism.

Multiple Choice

How does the process of cloning differ from the process of gene therapy?

• Cloning involves transferring a whole nucleus, while gene therapy alters a specific DNA sequence.

• Cloning reduces genetic diversity, while gene therapy increases it.

• Cloning is used to treat diseases, while gene therapy is used to create new organisms.

• Cloning requires an egg cell, while gene therapy requires a body cell.

Multiple Choice

A large population of potatoes is grown by cloning them from a single parent plant. If a new potato disease appears, what is the most likely outcome?

• The population would be highly vulnerable to the disease due to a lack of genetic diversity.

• The population would be completely immune to the disease because they are genetically identical.

• Only the original parent organism would be affected by the disease.

• The population would quickly develop a new gene to fight the disease.

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Understanding Our Genome

DNA Sequencing

• DNA sequencing is the process of determining the precise order of nitrogen bases in an organism's DNA.

• The Human Genome Project was a research effort that successfully mapped the entire human genetic code.

• This helps scientists study gene functions, understand diseases, and learn how humans have evolved over time.

DNA Fingerprinting

• DNA fingerprinting is a technology used to identify an individual based on their unique DNA pattern.

• It involves breaking DNA into fragments and then separating them by size to create a unique pattern.

• This is used in forensics to connect a person to a crime or to identify family relationships.

Multiple Choice

What is the main purpose of DNA sequencing?

• To determine the precise order of nitrogen bases in DNA.

• To create a unique pattern for identifying individuals.

• To break DNA into smaller fragments for analysis.

• To connect a person to a crime scene using DNA.

Multiple Choice

How do the primary goals of DNA sequencing and DNA fingerprinting differ?

• DNA sequencing determines the order of bases, while DNA fingerprinting identifies unique patterns.

• DNA sequencing is used for forensics, while DNA fingerprinting is used to study evolution.

• DNA sequencing maps the entire genome, while DNA fingerprinting only looks at specific genes.

• DNA sequencing breaks DNA apart, while DNA fingerprinting puts it back together.

Multiple Choice

A forensic scientist needs to determine if a hair sample found at a crime scene belongs to a particular suspect. Which of the following describes the best approach?

• Use DNA fingerprinting to see if the unique pattern from the sample matches the suspect's.

• Use DNA sequencing to determine the function of the genes in the sample.

• Use the Human Genome Project to compare the sample to the entire human genetic code.

• Use DNA sequencing to study how the suspect may have evolved over time.

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Ethics of Genetic Technologies

Genetic Privacy

• The use of genetic technologies has led to public debate about the privacy of genetic information.

• The Genetic Information Nondiscrimination Act (GINA) was passed to protect people from this.

• GINA makes it illegal for health insurers or employers to discriminate based on genetic information.

GMO Controversy

• Genetically Modified Organisms (GMOs) are organisms whose DNA is changed to express desired traits.

• Pro: Farmers can increase crop yields with plants engineered to resist pests and weeds.

• Con: Some people fear unknown health and environmental impacts, like cross-breeding with wild organisms.

Multiple Choice

What is the primary purpose of the Genetic Information Nondiscrimination Act (GINA)?

• To protect people from being treated unfairly by employers or health insurers based on their genetic information.

• To set safety standards for the creation of genetically modified organisms.

• To ensure that all genetic research is kept private from the public.

• To fund the development of new genetic technologies for farmers.

Multiple Choice

Which statement best explains the controversy surrounding Genetically Modified Organisms (GMOs)?

• The benefits of creating pest-resistant crops are debated against the potential for unforeseen health or environmental consequences.

• Farmers are unable to grow enough food without using genetically modified seeds.

• Cross-breeding between modified and wild organisms has been proven to be beneficial for the environment.

• Health insurers can legally deny coverage to people who consume genetically modified foods.

Multiple Choice

A company develops a genetically modified salmon that grows twice as fast as wild salmon. Which of the following scenarios represents a likely ethical concern related to this new organism?

• A concern that the modified fish could escape and disrupt wild ecosystems by cross-breeding.

• A violation of the company's genetic privacy under the GINA law.

• An effort by farmers to increase their crop yields using pest-resistant plants.

• A debate over whether employers can access the genetic information of the fish.

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Common Misconceptions

Misconception	Correction
All mutations are harmful.	Mutations can be harmful, helpful, or neutral, sometimes helping an organism survive.
Dominant traits are always the most common in a population.	Dominance does not determine how common a trait is in a population.
Humans evolved from the chimpanzees that exist today.	Humans and chimpanzees share a common ancestor but did not evolve from each other.
An organism can develop a trait because it ‘needs’ it to survive.	Variations come from random mutations, not from an organism's needs or wants.

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Summary

• DNA holds life's instructions in genes, which are located on chromosomes.

• Alleles, crossing over, and mutations all contribute to genetic variation.

• Pedigrees track inherited traits through generations.

• Humans influence inheritance through selective breeding and genetic engineering.

• Technologies like CRISPR and cloning have powerful applications.

• The use of GMOs and other genetic technologies raises ethical questions.

Poll

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

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