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 sulfur • They 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 bacteriophagewas 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? • Cytosine • Thymine • Adenine • Guanine
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 beexactly 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 DNA • The 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.