Genetics

Genetics

How did Morgan’s research build upon Mendel’s observations?

Morgan used dihybrid crosses in fruit flies to study a new pattern of inheritance that revealed gene linkage in phenotypes.

His results did not always follow Mendel’s 9:3:3:1 pattern.

The probability that two genes on a chromosome will be inherited together is related to the_______ between them.

distance

Maps of the relative locations, or loci, of genes on a chromosome.

Linkage maps

What scientist discovered linkage maps? When?

Alfred Sturtevant, 1913

How can a linkage map be made from observations of traits?

By calculating the percentage of times phenotypes do not appear together in offspring of parents with known genotypes.

Summarize the importance of comparing wild type and mutant type fruit flies in genetic research.

The different types of flies were important in determining gene linkage because the different phenotypes were easily observed.

How is a linkage map related to cross-overs that take place during meiosis?

The higher the frequency of two genes crossing over separately, the farther they are from each other on a chromosome.

How are linked genes similar to sex-linked genes? How are they different?

Similar because both show a pattern of linkage in inheritance.

Different because linked genes are linked to each other on the same chromosome whereas sex-linked genes are linked to either the x or y chromosome

How can carriers differ between autosomal and sex-linked disorders?

Only females can be carriers of sex-linked disorders.

A chart that can help trace the phenotypes and genotypes in a family to determine whether people carry recessive alleles.

A pedigree chart

If approximately the same number of males and females have the same phenotype, then the gene is most likely on an _________.

autosome

If a phenotype is much more common in males the gene is likely on the ________ chromosome.

X

How are Pedigrees and Punnett squares different?

Punnett squares predict offspring phenotypes from known genotypes.

Pedigrees predict genotypes from phenotypes.

Punnett squares show a predicted outcome where Pedigrees show an actual outcome.

A picture of all of the chromosomes in a cell.Karyotype.

Why must many methods be used to study human genetics?

The human genome is huge…. Well…. Incredibly small….. But very complex.

How can Mendel’s principles be used to study human traits?

They apply to autosomal single-gene traits with dominant and recessive patterns in all sexually reproducing organisms.

Is a person who is homozygous recessive for a recessive genetic disease a carrier?

No, A carrier is someone who has a gene for the disorder but does not display the phenotype.

Suppose a colorblind male and a female with no recessive alleles for colorblindness have children. What is the probability they will have a colorblind son? A colorblind daughter?

Zero. Any son will inherit the normal allele from his mother.

Any daughter will have a normal phenotype but will be a carrier.

Under what circumstances could two individuals with no symptoms of a recessive genetic disease have children that do have the disease?

If the disorder is autosomal, both parents must be carriers (heterozygous). If the disorder is sex-linked, the mother must be a carrier.

Can a person merely be a carrier for a dominant genetic disorder?

No. If a person has just one allele for a dominant trait, that trait will be expressed.

Both men and women can be colorblind, but there are approximately 100 times more colorblind men than women in the world. Explain why men are more likely to be colorblind than women.

If a male has a recessive allele of a sex-linked gene, the allele is always expressed because males have only one X chromosome.

Females have 2 X Chromosomes and must have two copies of a recessive allele to express the trait.

Why are studies of identical twins important in helping understand interactions between environment and genotype?

Identical twins have the same genotype.Phenotype differences must be studied in

connection with environmental differences.

In 1928, Frederick Griffith was studying two forms of the bacterium that causes pneumonia. Describe the observable differences between the bacteria.

One form was surrounded by a coating of sugar molecules. He called these S because of their smooth appearance.

The second form had a rough outer appearance, so he called it R.

If Griffith’s 1982 experiment on pneumonia causing bacteria, which form killed the mice.

The S or smooth form.

In Griffith’s 1928 experiment, how did heat-killed S form bacteria affect the mice?

The mice survived.

In Griffith’s 1928 experiment, what happened to mice when they were injected with live R bacteria?

They survived.

In Griffith’s 1928 experiment, what happened to the mice that were injected with heat-killed S bacteria and live R bacteria?

The mice died.

In Griffith’s 1928 experiment, when mice were injected with live R bacteria they survived. When they were injected with heat-killed S bacteria, they survived. When mice were injected with both, they died. Why?

Some material (DNA) must have been transferred from the heat-killed S bacteria to the live R bacteria. The once harmless R bacteria was changed into a harmful form of bacteria. This became known as ‘the transforming principle’.

From 1934 to 1944, what was Oswald Avery and his team trying to determine?

They were trying determine if the transforming principle was casual by DNA or protein.

In 1944, when Avery and his team presented their evidence that DNA caused the transforming principle, why did some scientists continue to harbor doubts?

Some scientists insisted that his extract must have contained protein.

In 1944, what evidence did Oswald Avery and his team present that pointed to DNA as causing the transforming principle?

1.) Standard tests showed that DNA was present in their extract but not protein.

2.) A chemical analysis showed that the proportions of elements in the extract modeled DNA.

3.) Transformations failed to occur when an enzyme was added to destroy DNA.

What is a bacteriaophage and what does it do?

It is a type of virus.It takes over a bacterium's genetic machinery

and directs it to make more viruses.

What is an elemental difference between protein and DNA? How did Hershey and Chase make use of this difference?

Protein contains sulfur but little phosphorus

DNA contains phosphorus but no sulfurThey radioactively tagged phages in

cultures with sulfur or phosphorus.

Describe Hershey and Chase’s first experiment over the transforming principle.

Bacteria was infected with phages that had radioactive sulfur atoms in their protein molecules.

They then separated the bacteria from the phages that were outside of the bacteria. (The phages would have injected material into the bacteria.)

After examining the bacteria, no significant radioactivity was found.

This meant that the bacteriophage was not injecting protein into the bacteria to make copies of itself.

Describe Hershey and Chase’s second experiment over the transforming principles.

They tagged the phages’ DNA with radioactive phosphorus.

Radioactivity was clearly present in bacteria.

Their findings proved that genetic material is DNA, and not protein. (Proven in 1952)

DNA is composed of four types of _________.Nucleotides

The small units, or monomers, that make up DNA are called __________.

Nucleotides.

What are the three parts of a nucleotide?A phosphate group, A ring-shaped sugar

called deoxyribose, and a nitrogen containing base.

How do nucleotides differ from one another?Only in their nitrogen-containing bases.

What are the four bases of DNA?CytosineThymineAdenineGuanine

What hypothesis was the key reason that scientists were not convinced that DNA could be genetic material?

Scientists hypothesized that DNA was made up of equal amounts of the four nucleotides.

This means that the DNA in all organisms would be exactly the same. Identical molecules could not carry out different instructions across all organisms.

In 1950, how did Erwin Chargoff change how scientists viewed DNA?

He found that the proportion of the four nitrogen bases differs from organism to organism.

Describe Chargoff’s rule.The amount of cytosine roughly equals the

amount of guanine.The amount of adenine roughly equals the

amount of thymine.

What did Watson and Crick develop and present in 1953?

An accurate model of DNA’s 3D structure.The double helix model. It also explained

Chargoff’s rule by showing how Cytosine combines with guanine and adenine combines with thymine.

What type of bond holds the DNA helix together between the bases in the middle?

A hydrogen bond.

What type of bond connects the sugar of one nucleotide to the phosphate of the next nucleotide?

A covalent bond.

Which part of a DNA molecule carries the genetic instructions that are unique for each individual: the sugar-phosphate backbone or the nitrogen-containing bases?

The backbone is the same in all DNAThe nitrogen bases contain the unique

instructions.

The DNA of all organisms on this planet contains the same four bases. What might this indicate about the origin of life on Earth?

It suggests that the wide diversity of life that we see might have stemmed from a common ancestor.

What was one of the most powerful implications of the Watson and Crick model of DNA?

It (the model) suggested how DNA could be copied.

The process by which DNA is copied during the cell cycle.

Replication.

How does replication ensure that cells have complete sets of DNA?

It doubles the amount of DNA so that both of the daughter cells resulting from mitosis have their own complete set of DNA.

Does DNA actually copy itself?No. Enzymes and proteins do the work of

replication. DNA merely stores information.

Enzymes that form bonds between nucleotides during replication.

DNA polymerases.

Describe the steps in the replication process.1.) Enzymes unzip the helix at numerous

places. H bonds are broken. Bases are exposed. Process proceeds in 2 directions at the same time.

2.) Free floating nucleotides pair with exposed bases. DNA polymerases bond the nucleotides.

3.) Two identical molecules of DNA result.

Why is DNA replication called semiconservative?

One old strand is conserved.One new strand is made.

Roughly, how often do errors in replication occur?

1 error per 1 billion nucleotides.

Why does a cell need to replicate its DNA quickly?

Our cells have a large amount of DNA. It must be copied quickly enough to keep up with the demand for cell division and to enable the cell to carry out its normal functions.

How do cells help insure that DNA replication is accurate?

Certain types of DNA polymerases have a built in proofreading function that connects most mispaired nucleotides.

What is the central dogma, defined by Francis Crick for molecular biology?

Information flows in one direction…. From DNA to RNA to proteins.

What are the three processes of Francis Crick’s central dogma?

Replication, Transcription, Translation.

The process that converts a DNA message into an intermediate molecule, called RNA.

Transcription.

Interprets an RNA message into a string of amino acids, called a polypeptide.

Translation.

In __________ cells, replication, transcription, and translation all occur in the cytoplasm at approximately the same time.

Prokaryotic.

In ______ cells, where DNA is located inside the nuclear membrane, these processes are separated both in location and time.

Eukaryotic

In ______ cells, replication and transcription occur in the nucleus, while translation occurs in the cytoplasm.

Eukaryotic.

The __________ in eukaryotic cells goes through a processing step before it can be transported out of the nucleus.

RNA

RNA is a temporary copy of ____________ that is used and then destroyed.

DNA

How do RNA and DNA differ?1) The sugar in RNA is ribose, which has one

oxygen atom more than DNA2) RNA has the base Uracil in place of

thymine. 3) RNA is a single strand of nucleotides.

The single stand structure allows RNA to form complex 3D shapes. Because of its structure, RNA can catalyze reactions like an enzyme.

The process of copying a sequence of DNA to produce a complementary strand of RNA.

Transcription.

Just as replication is catalyzed by DNA polymerase, transcription is catalyzed by ___________.

RNA polymerase.

Describe the first step in transcription for a eukaryotic cell.

RNA polymerase recognizes the start of a gene.

RNA polymerase and other proteins assemble on the DNA strand and unwinds the DNA molecule.

Describe the second step in transcription.RNA polymerase, using only one strand of

DNA as a template, strings together a complementary strand of RNA nucleotides.

The growing RNA strand hangs freely as it is transcribed, and the DNA helix zips back together.

Describe the third step in the transcription process.

Once transcribed, the RNA strand detaches from the DNA segment.

How RNA recognizes the end of the genes is complicated. It varies with each type of RNA.

What are the three major types of RNA produced by transcription?

mRNA messenger RNArRNA ribosomal RNAtRNA transfer RNA

An intermediate message that is translated to form a protein.

Messenger RNA (mRNA)

Forms part of ribosomes, a cells protein factory.

Ribosomal RNA (rRNA)

Brings amino acids from the cytoplasm to a ribosome to help make growing proteins.

Transfer RNA (tRNA)

Why must transcription occur in the nucleus of eukaryotes?

DNA is located in the nucleus of eukaryotes, so processes involving DNA, such as transcription, must occur there as well.

Why does transcription produce more errors than replication?

Unlike DNA polymerase, RNA polymerase cannot proofread the transcript being formed.

Because most genes are transcribed many times, a few defective copies of mRNA, and thus protein, usually cause no harmful effects. These errors are not transmitted to the next generation because the DNA is not affected.

Why must the DNA strand unwind and separate before transcription can take place?

The bases must be exposed so that free nucleotides can pair with them.

In the second step of transcription how does the base sequence of the RNA transcript being formed compare with the sequence on the template strand?

It is complementary

How is transcription similar to replication?1.) Both occur in the nucleus of eukaryotic cells.2.) Both are catalyzed by large, complex

enzymes.3.) Both involve unwinding of the DNA double

helix. 4.) Both involve complementary base pairing to

the DNA strand. 5.) Both processes are highly regulated by the

cell.

How do transcription and replication differ?Replication ensures that each new cell will

have one complete set of genetic instructions. Replication occurs only once during each

round of the cell cycleTranscription can make hundreds or

thousands of proteins.

The process that converts, or translates, an mRNA message into a polypeptide.

Translation

One or more polypeptides make up a ____________.

Protein.

Just as the ‘language’ of DNA uses C,G,T,A….. The ‘language’ of proteins uses _________ _________.

Amino acids.

The four nucleotides of DNA code for _________ amino acids.

20

A 3-nucleotide sequence that codes for an amino acid.

Codon.

The root of transcribe is “___ _______”The root of translate is “___ ________”To writeTo transfer

Signals the end on an amino acid chain.Stop codon

Signals the start of translation.Start codon

The order in which a series of three nonoverlapping nucleotide codons are read.

Reading frame

A set of three nucleotides that is complementary to an RNA codon.

Anticodon.

Where does translation occur?In the cytoplasm of both prokaryotic and

eukaryotic cells.

Explain the different roles of the large and small ribosomal sub units.

The small sub unit holds onto the mRNA transcript.

The large subunit has three sites where the tRNA molecules can dock; it helps form the peptide bond between the amino acids and helps break the bond between the amino acid and its carrier tRNA molecules.

Explain the connection between a codon and an amino acid.

A codon is a sequence of three nucleotides that specifies a particular amino acid.

Each tRNA molecule binds to a specific amino acid and has an anticodon that binds to a specific codon.

Suppose a tRNA molecule had the anticodon AGU. What amino acid would it carry?

The tRNA molecule would recognize the mRNA codon UGA, so it would carry the amino acid serine.

The DNA of eukaryotic cells has many copies of genes that code for rRNA molecules. Suggest a hypothesis to explain why a cell needs so many copies of these genes.

rRNA is critical for making ribosomes to carry out protein synthesis. rRNA must be made in sufficient quantities to keep up with a cell’s demand for various proteins.

Prokaryotic cells turn genes on and off by controlling ___________.

Transcription.

The regulations of gene expression allows prokaryotic cells, such as bacteria, to _____________.

Better respond to stimuli.Conserve energy and materials.

A DNA segment that allows a gene to be transcribed…. by helping RNA polymerase find where a gene starts.

Promoter.

A promoter interacts with proteins that increase the rate of __________ or block __________ from occurring.

Transcription, transcription.

Bacteria have much less DNA than do eukaryotes, and their genes tend to be organized into ___________.

Operons.

An ___________ is a region of DNA that includes a promoter, an operator, and one or more structural genes that code for all the proteins needed to do a specific task.

Operon.

Humans have an estimated 20,000 to 25,000 genes. Why wouldn’t you expect all these genes to be transcribed and translated at the same time?

What might be an analogy to this in your own life?The cell would run out of energy and raw

materials (amino acids and nucleotides).Proteins would accumulate in the cell if they were

not needed. Eating all of the food in the house at once Everyone in the class talking at the same time

(imagine that)

Why is the lac operon an advantage to a bacterial cell?

The cell does not waste energy making enzymes to digest lactose when lactose is not present.

What happens when sonic hedgehog is missing in a fruit fly?

The embryos fail to form normal body segments.

In eukaryotes ________ are nucleotide segments that code for parts of the protein. ________ are nucleotide segments that intervene, or occur, between _________.

Exons, introns, exons

Which parts of a gene are expressed as protein: introns or exons?

Exons.

In eukaryotic cells, genes each have a specific combination of regulatory DNA sequences. How do these combinations help cells carry out specialized jobs?

These combinations help a cell turn on only specific genes. Based on the different genes that are turned on or off, a cell has a unique set of proteins that enable it to carry out certain functions

Suppose a bacterium had a mutated repressor protein that could not bind to the lac operator. How might this affect regulation of the operator.

The operon could never be turned off. The genes would be continually

transcribed.

A change in a organism’s DNA.Mutation.

Generally, mutations that affect a single gene happen during __________, whereas mutations that affect a group of genes or an entire chromosome happen during __________.

Replication, meiosis.

A mutation in which one nucleotide is substituted for another.

Point mutation.

Mistakes during the replication process are usually corrected by ____________.

DNA polymerase

The insertion or deletion of a nucleotide in the DNA sequence. It usually affects a polypeptide much more than does a substitution. It is a change that throws off the reading frame, which results in codons that code for different amino acids.

Frameshift mutation

A type of chromosomal mutation in which a chromosome has two copies (or more) of a gene as a result of crossing over.

Gene duplication

A type of chromosomal mutation in which a piece of one chromosome moves to a nonhomologous chromosome.

Translocation

In a mutation of a chromosome, what may be the results of a substituted amino acid?

It could affect protein folding or the function of the protein itself. It could also cause a premature stop codon.

A mutation that does not affect the resulting protein is called _____________.

silent

What is the difference between a mutation in a germ cell and a mutation in a body cell?

Mutations in body cells only affect that specific organism. Mutations in germ cells are passed on to offspring.

Mutations may be a significant cause of ____________.

aging

Agents in the environment that can damage DNA.

Mutagens

Why do frameshift mutations have a greater effect than point mutations?

Point mutations typically affect only one codon. A frameshift mutation affects all of the codons in a gene that follow it.

If GUA is changed to GUU, will the resulting protein be affected? Explain.

No, they both code for the amino acid valine.

Explain how mutagens can cause genetic mutations in spite of your body’s DNA repair enzymes.

Mutagens may produce so much damage that the repair enzymes cannot keep up with the repairs.

Some genetic mutations are associated with increased risk for a particular disease. Tests exist for some of these genes. What might be the advantages and disadvantages of being tested?

Advantages: You would know to look for symptoms and prepare for treatment.

Disadvantages: There may be no cure. Having a gene does not mean you will get the disease.

How could a mutated gene produce a shorter protein than that produced by the normal gene?

A frameshift or a point mutation may have changed one of the codons to a stop codon.

What are some situations or circumstances in which DNA testing could help identify someone or something?

Human remains are found that cannot be identified by other means.

People may need to determine parentage.

DNA may be left at a crime scene.

How might biotechnology help to repopulate the Galapagos Islands with native tortoise species?

Scientists could identify members of the tortoise species that are native to the islands by using DNA fingerprinting and then selectively breeding those tortoises. DNA could also identify family members so they are not used as breeding pairs.

Enzymes that cut DNA molecules at specific nucleotide sequences.

Restriction enzymesAlso called endonuclease

The sequence of nucleotides that is identified and cut by a restriction enzyme.

Restriction site

Why are endonuclease also called restriction enzymes?

They restrict, or decrease, the effect of a virus on a bacterial cell.

What is the difference between a ‘sticky end’ of DNA and a ‘blunt end’ of DNA?

A blunt end is a straight cut across the two strands of a DNA molecule. A sticky end is a staggered cut that leaves tails of free DNA bases exposed.

Fragments of DNA are separated and sorted according to their sizes by a technique called _____ __________.

Gel electrophoresis

A map showing the lengths of DNA fragments between restriction sites in a strand of DNA.

Restriction maps

What do the bands represent on a gel? (in gel electrophoresis)

The length of the DNA fragment

List four different ways in which scientists can manipulate DNA.

DNA can be cut, copied, sequenced, and changed.

What determines how DNA will be cut by a restriction enzyme?

The number and location of restriction sites recognized by the restriction enzyme.

How does gel electrophoresis separate DNA fragments from each other?

The DNA sample is loaded into a gel through which an electrical current flows. The negatively charged DNA fragments are pulled toward the positive electrode. The largest molecules move slowest, and the smallest move quickest.

Suppose you cut DNA. You know that you should find four DNA fragments on a gel, but only three appear, and one fragment is very large. Explain what happened.

This might indicate a mutation. One of the restriction sites may have been deleted or changed by the mutation, resulting in one very large fragment where there should have been two.

What is the relationship between restriction sites and a restriction map?

A restriction map reveals the lengths of DNA fragments between restriction sites. The more restriction sites there are, the more fragments there will be on the map.

How do scientists get an amount of DNA that is large enough to be studied and manipulated?

They copy the same segment of DNA over and over again using a technique called PCR (polymerase chain reaction)

What enzymes unwind and separate DNA molecules?

helicases

A short segment of DNA that acts as the starting point for a new strand.

primer

A representation of parts of an individual’s DNA that can be used to identify a person at the molecular level.

DNA fingerprint

A genetically identical copy of a gene or of an organism.

clone

The altering of an organism’s DNA to give the organism new traits.

Genetic engineering

DNA that contains genes from more than one organism.

Recombinant DNA

Closed loops of DNA that are separate from the bacterial chromosome and that replicate on their own within the cell.

plasmids

An organism that has one or more genes from another organism inserted into its genome.

transgenic

What is the greatest concern of genetically engineering crops?

All organisms in a transgenic population have the same genome. A decrease in genetic diversity could leave crops vulnerable to new diseases or pests.

Why is the offspring of asexual reproduction a clone?

The offspring of asexual reproduction are genetically identical to the parent.

What are plasmids, and how are they used in genetic engineering?

Plasmids are closed loops of bacterial DNA. New genes can be incorporated into plasmids, and the bacteria will produce the proteins coded for by genes.

The study of genomes.Genomics

By studying genomics, biologists who study evolution can learn when closely related species __________ from each other.

diverged

All studies of genomics begin with _____ __________, or determining the order of DNA nucleotides in genes or in genomes.

Gene sequencing

The two main goals of the Human Genome Project were to ……….

1) map and sequence all of the genes within the sequence.

2) identify all of the genes within the sequence

The HapMap project is working to ……….study how DNA sequences vary among

people.

The use of computer databases to organize and analyze biological data.

bioinformatics

Tools that allow scientists to study many genes, and their expression, at once.

DNA microarray

The study and comparison of all the proteins that result from an organism’s genome.

proteomics

Describe the difference between gene sequencing and DNA fingerprinting.

Gene sequencing finds the DNA sequence; a DNA fingerprint shows a number of repeated DNA sequences.

How is the study of specific genes different from the study of a genome?

Genomics studies all genes.

How might genomics and proteomics help researchers predict how a medical treatment might affect cells in different tissues?

By knowing about how genes and their products interact, researchers could be able to predict how one drug will affect many different areas of the body. They could tailor a treatment to target a specific gene or protein in order to avoid damaging others.

The process of testing DNA to determine a person’s risk of having or passing on a genetic disorder.

Genetic Screening

Why might genetic screening raise ethical concerns about privacy?

Genetic information may be used to discriminate against a person in some way.

The replacement of a defective or missing gene, or the addition of a new gene, into a person’s genome to treat a disease.

Gene Therapy

How is gene therapy similar to, and different from, making a transgenic organism?

They both involve inserting a new gene into an organism, but gene therapy replaces a defective gene with a normal gene in an adult organism; a transgenic organism has genes from more than one species.