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Question 1

Define heredity.

Answer 1

The transmission of traits from one generation to the next.

Question 2

Define character. Give an example.

Answer 2

A heritable feature that varies among individuals within a population.

EXAMPLE: Flower colour in pea plants, eye colour in humans.

Question 3

Define trait. Give an example.

Answer 3

A variant of a character found within a population.

EXAMPLE: Purple flowers in pea plants, blue eyes in people.

Question 4

Define hybrid. Give an example.

Answer 4

The offspring of parents of two different species or of two different varieties of one species; the offspring of two parents that differ in one or more inherited traits; an individual that is heterozygous for one or more pairs of genes.

EXAMPLE: Offspring that would result if plants with purple flowers and plants with white flowers were cross-fertilized.

Question 5

Define monohybrid cross. Give an example.

Answer 5

A mating of individuals that are heterozygous for the character being followed.

EXAMPLE: Pp x Pp.

Question 6

Define genotype. Give an example.

Answer 6

The genetic makeup of an organism.

EXAMPLE: PP, Pp, or pp.

Question 7

Define phenotype. Give an example.

Answer 7

The expressed traits of an organism.

EXAMPLE: Purple or white flowers.

Question 8

Define locus. Give an example.

Answer 8

The particular site where a gene is found on a chromosome. Homologous chromosomes have corresponding gene loci.

EXAMPLE: P, a, B, or b.

Question 9

Define dihybrid cross. Give an example.

Answer 9

A mating of individuals differing at two genetic loci.

EXAMPLE: Rr x Yy.

Question 10

Define testcross. Give an example.

Answer 10

The mating between an individual of unknown genotype for a particular character and an individual that is homozygous recessive for that same character.

EXAMPLE: B_ x bb (e.g., to find genotype of black lab, cross with chocolate lab homozygous recessive bb)

Question 11

Define wild-type traits. Give an example.

Answer 11

A trait most commonly found in nature.

EXAMPLE: The absence of freckles (ff) is more common than their presence FF or Ff).

Question 12

Define recessive disorders. Give an example.

Answer 12

The genetic conditions caused by recessive alleles.

EXAMPLE: Albinism.

Question 13

Define dominant disorders. Give an example.

Answer 13

The genetic conditions caused by dominant alleles.

EXAMPLE: Dwarfism.

Question 14

Who was the first person to analyze patterns of inheritance? What plant did he primarily use in his studies? Please list 3 reasons why he used this plant.

Answer 14

Gregor Mendel used garden peas to study inheritance for the first time because they were easy to grow and came in many readily distinguishable varieties. For example, one variety has purple flowers, and another variety has white flowers.

Question 15

What is a gene compared to an allele?

Answer 15

A gene is a portion of DNA that determines a certain trait. An allele is a specific form of a gene.

Question 16

Please list and explain two of Mendel’s laws.

Answer 16

Law of Segregation states that the two alleles in a pair segregate (separate) into two different gametes during meiosis.

Law of Independent assortment states that when gametes form during meiosis, each pair of alleles for a particular character segregates (separates) independently of each other pair.

Question 17

Please list and explain Mendel’s 4 hypotheses.

Answer 17

(1) There are alternative versions of genes that account for variations in inherited characters. These alternative versions of a gene are now called alleles.
(2) For each character, an organism inherits two alleles of a gene, one from each parent. An organism that has two identical alleles for a gene is said to be homozygous for that gene (and is called a homozygote for that trait). An organism that has two different alleles for a gene is said to be heterozygous for that gene (and is a heterozygote).
(3) If an organism has two different alleles for a gene, one allele determines the organism’s appearance and is called the dominant allele; the other allele has no noticeable effect on the organism’s appearance and is called the recessive allele.
(4) A sperm or egg carries only one allele for each inherited character because the two alleles for a character segregate (separate) from each other during the production of gametes. This statement is called the law of segregation.

Question 18

Please list and explain 3 variations on Mendel’s laws. Provide an example for each.

Answer 18

(1) Incomplete Dominance: A type of inheritance in which the phenotype of a heterozygote (Aa) is intermediate between the phenotypes of the two types of homozygotes (AA and aa). E.g., A red snapdragon and a white snapdragon producing a pink snapdragon.
(2) Codominant: Expressing two different alleles of a gene in a heterozygote. E.g., the AB blood type.
(3) Pleiotropy: The control of more than one phenotypic character by a single gene. E.g., sickle-cell disease.
(4) Polygenic inheritance: The additive effect of two or more genes on a single phenotypic character. E.g., skin colour and height.

(5) Epigenetic inheritance: Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence of a genome; frequently involves chemical modification of DNA bases
and/or histone proteins.

Question 19

Define sex-linked genes. Provide an example.

Answer 19

A gene located on a sex chromosome. For example, red-green colour blindness.

Question 20

Please compare and contrast the structure of DNA and RNA.

Answer 20

Both are polymers of nucleotides (a sugar + a nitrogenous base + a phosphate group). In RNA, the sugar is ribose; in DNA, it is deoxyribose. Both RNA and DNA have the bases A, G, and C, but DNA has T and RNA has U.

Question 21

What is the function of DNA? How is DNA replicated?

Answer 21

DNA contains the instructions needed for an organism to develop, survive, and reproduce. DNA replication begins on a double helix at specific sites, called origins of replication. Replication then proceeds in both directions, creating what are called replication “bubbles”. The parental DNA strands open up as daughter strands elongate on both sides of each bubble. Eventually, all the bubbles merge, yielding two completed double-stranded daughter DNA molecules.

Question 22

Please explain the 3 steps in transcription. How are the products from transcription processed before translation?

Answer 22

Step (1) The promoter signals to “start transcribing”. Initiation is the attachment of RNA polymerase to the promoter and the start of RNA synthesis.

Step (2) In elongation the RNA grows longer.

Step (3) In termination the RNA polymerase reaches the terminator. It signals the end of the gene.

The RNA transcribed functions as messenger RNA (mRNA). With capping, tailing, and splicing completed, the “final draft” of eukaryotic mRNA is ready for translation.

Question 23

Please explain the structure and function of mRNA, tRNA and ribosomes.

Answer 23

mRNA: Cap, start & end of genetic message, tail as a nucleotide strand. mRNA, produced by transcription, is required by translation.

tRNA: tRNA is the site where an amino acid will attach and another that is the three-nucleotide anticodon where the mRNA will attach. A tRNA molecule is made of a single strand of RNA that twists and folds upon itself forming several double-stranded regions in which short stretches of RNA base-pair with other stretches. tRNA molecules (1) pick up the appropriate amino acids and (2) recognize the appropriate codons in the mRNA.

Ribosomes: A ribosome has two subunits, and each subunit is made up of proteins and a considerable amount of ribosomal RNA (rRNA). A fully assembled ribosome has a binding site for mRNA on its small subunit and binding sites for tRNA on its large subunit. One of the tRNA binding sites, the P site, holds the tRNA carrying the growing polypeptide chain, while another, the A site, holds a tRNA carrying the next amino acid to be added to the chain. The anticodon on each tRNA base-pairs with a codon on the mRNA. The subunits of the ribosome act like a vise, holding the tRNA and mRNA molecules close together. The ribosome can then connect the amino acid from the tRNA in the A site to the growing polypeptide.

Question 24

Please explain the 3 steps in translation.

Answer 24

Step (1) In initiation, the ribosome assembles around the mRNA to be read and the first tRNA (carrying the amino acid methionine, which matches the start codon, AUG).

Step (2) Elongation is the stage where the amino acid chain gets longer. In elongation, the mRNA is read one codon at a time, and the amino acid matching each codon is added to a growing protein chain.

Step (3) Termination is the stage in which the finished polypeptide chain is released. It begins when a stop codon (UAG, UAA, or UGA) enters the ribosome, triggering a series of events that separate the chain from its tRNA and allow it to drift out of the ribosome.

Question 25

Please list and explain the 3 types of mutations. Are mutations good or bad? Explain.

Answer 25

A mutation is any change to the genetic information of a cell or virus. Occasionally, a base substitution leads to an improved protein or one with new capabilities that enhance the success of the mutant organism and its descendants. More often, though, mutations are harmful.

Types of Mutations: (a) Base substitution. A substation is the replacement of one nucleotide and its base-pairing partner with another nucleotide pair. Because genetic code is redundant, some substitution mutations have no effect at all. For example, a silent mutation can result when two codons both code for the same amino acid. A missense mutation is when a single nucleotide does change one amino acid to another. Some change the final product, and some have little or no affect. Nonsense mutations, another type of substitution, change an amino acid into a stop codon. The result will be a prematurely terminated protein, which will probably not function properly. (b) Nucleotide deletion. When a nucleotide is deleted, all the codons from that point on are misread. The resulting polypeptide is likely to be completely non-functional. (c) Nucleotide insertion. As with deletion, inserting one nucleotide disrupts all codons that follow, most likely producing a non-functional polypeptide.
• A frameshift mutation is when the number of nucleotides is not a multiple of three, all nucleotides will be regrouped into different codons.

Question 26

What are phages? Please explain the 2 reproductive cycles of phages.

Answer 26

Bacteriophages: A virus that infects bacteria; also called a phage.

Lytic Cycle: A viral reproductive cycle resulting in the release of new viruses by lysis (breaking open) of the host cell.

Lysogenic Cycle: A bacteriophage reproductive cycle in which the viral genome is incorporated into the bacterial host chromosome as a prophage. New phages are not produced, and the host cell is not killed or lysed unless the viral genome leaves the host chromosome.

Question 27

What are viruses? Please explain the reproductive cycle of an animal virus.

Answer 27

Virus: A microscopic particle capable of infecting cells of living organisms and inserting its genetic material. Viruses have a very simple structure and are generally not considered to be alive because they do not display all the characteristics associated with life.

(1) The viral envelope fuses with the cell’s membrane, allowing the protein-coated RNA to enter the cytoplasm.
(2) Enzymes then remove the protein coat.
(3) An enzyme that entered the cell as part of the virus uses the virus’s RNA genome as a template for making complementary strands of RNA. The new strands have two functions:
(4) They serve as mRNA for the synthesis of new viral proteins, and
(5) they serve as templates for synthesizing new viral genome RNA.
(6) The new coat proteins assemble around the new viral RNA.
(7) Finally, the viruses leave the cell by cloaking themselves in plasma membrane. In other words, the virus obtains its envelope from the cell, budding off the cell without necessarily rupturing it.

Question 28

Please explain how HIV infects a cell. What does HIV infection cause?

Answer 28

(1) uses the RNA as a template to make a DNA strand and then
(2) adds a second, complementary DNA strand.
(3) The resulting double-stranded viral DNA then enters the cell nucleus and inserts itself into chromosomal DNA, becoming a provirus. Occasionally, the provirus is
(4) transcribed into RNA
(5) and translated into viral proteins.
(6) New viruses assembled from these components eventually leave the cell and can infect other cells. This is the standard reproductive cycle for retroviruses.

HIV infects and eventually kills several kinds of white blood cells that are important in the body’s immune system. The loss of such cells causes the body to become susceptible to other infections that it would normally be able to fight off. Such secondary infections cause the syndrome (a collection of symptoms) that eventually kills AIDS patients.

Question 29

Please define gene expression. Please explain how the human body has different cells although every somatic cell in the body has identical genetic instructions.

Answer 29

Gene expression: The process whereby genetic information flows from genes to proteins; the flow of genetic information from the genotype to the phenotype: DNA -> RNA -> protein.

Cells with the same genetic information can develop into different types of cells through gene regulation, mechanisms that turn on certain genes while other genes remain turned off. Regulating gene activity allows for specialization of cells within the body.

Question 30

Please define promoter.

Answer 30

A specific nucleotide sequence in DNA, located at the start of a gene, that is the binding site for RNA polymerase and the place where transcription begins.

Question 31

Please define operator.

Answer 31

In prokaryotic DNA, a sequence of nucleotides near the start of an operon to which an active repressor can attach. The binding of a repressor prevents RNA polymerase from attaching to the promoter and transcribing the genes of the operon.

Question 32

Please define repressor.

Answer 32

A protein that blocks the transcription of a gene or operon.

Question 33

What is an operon? How does the lac operon of E. coli work in the absence of lactose? In the presence of lactose? You may use diagram to supplement your answer.

Answer 33

Operon: A unit of genetic regulation common in prokaryotes; a cluster of genes with related functions, along with the promoter and operator that control their transcription.

A lac operon in “off” mode, its status when there is no lactose available:
Transcription is turned off because (1) a protein called a repressor binds to the operator and (2) physically blocks the attachment of RNA polymerase to the promoter.
A lac operon in “on” mode when lactose is present:
The lactose interferes with attachment of the lac repressor to the operator by (1) binding to the repressor and (2) changing the repressor’s shape. Altering the repressor’s shape changes how it acts and the repressor cannot bind to the operator, and the operator switch remains on. (3) RNA polymerase is no longer blocked, so it can now bind to the promoter and from there (4) transcribe the genes for the lactose enzymes into mRNA. (5) Translation produces all three lactose enzymes.

Question 34

Please explain 4 ways that eukaryotes can regulate genes (turned on/off).

Answer 34

The regulation of DNA packing: DNA packing tends to prevent gene expression by preventing RNA polymerase and other transcription proteins from binding to the DNA.

Initiation of transcription: To do its job, RNA polymerase requires the assistance of proteins called transcription factors. Transcription factors bind to noncoding DNA sequences called enhancers and help RNA polymerase bind to the promoter. Genes coding for related enzymes, may share a specific kind of enhancer, allowing these genes to be activated at the same time. Repressor proteins may bind to DNA sequences called silencers, inhibiting the start of transcription.

RNA processing and breakdown: RNA processing includes the addition of a cap and a tail, the removal of introns, and RNA splicing. Thanks to alternative RNA splicing, an organism can produce more than one type of polypeptide from a single gene.

The initiation of translation: The process of translation (in which an mRNA is used to make a protein) offers additional opportunities for control by regulatory molecules.

Protein activation and breakdown: The final opportunities for regulating gene expression occur after translation. Another control mechanism operating after translation is the selective breakdown of proteins. This regulation allows a cell to adjust the kinds and amounts of its proteins in response to changes in its environment.

Question 35

Please define homeotic genes. What happens to the organism if there are mutations in these genes? Please provide an example.

Answer 35

A master control gene that determines the identity of a body structure of a developing organism, presumably by controlling the developmental fate of groups of cells. (In plants, such genes are called organ identity genes.) For example, one set of homeotic genes in fruit flies instructs cells in the midbody to form legs. Elsewhere, these homeotic genes remain turned off, while others are turned on. Mutations in homeotic genes can produce bizarre effects. For example, fruit flies with mutations in homeotic genes may have extra sets of legs growing from their head.

Question 36

What is nuclear transplantation?

Answer 36

A technique in which the nucleus of one cell is placed into another cell that already has a nucleus or in which the nucleus has been previously destroyed. The cell is then stimulated to grow, producing an embryo that is a genetic copy of the nucleus donor.

Question 37

Please fully explain how reproductive cloning works. What are some practical applications of reproductive cloning?

Answer 37

Reproductive cloning: Using a body cell form a multicellular organism to make one or more genetically identical individuals.
In agriculture, farm animals with specific sets of desirable traits might be cloned to produce identical herds. In research, genetically identical animals can provide perfect “control animals” for experiments. The pharmaceutical industry is experimenting with cloning animals for potential medical use.

Question 38

Please fully explain how therapeutic cloning works. What are some practical applications of therapeutic cloning?

Answer 38

Therapeutic cloning: The cloning of human cells by nuclear transplantation for therapeutic purposes, such as the replacement of body cells that have been irreversibly damaged by disease or injury.
• Nuclear transplantation: A technique in which the nucleus of one cell is placed into another cell that already has a nucleus or in which the nucleus has been previously destroyed. The cell is then stimulated to grow, producing an embryo that is a genetic copy of the nucleus donor.

Question 39

Please define pluripotency.

Answer 39

The capacity of individual cells to initiate all lineages of the mature organism in a flexible manner directed by signals in the embryo or cell culture environment.

Question 40

Please define oncogene, proto-oncogene and tumor-suppressor gene. How do these terms relate to the progression of a cancer?

Answer 40

Oncogene: A cancer causing gene; usually contributes to malignancy by abnormally enhancing the amount of activity of a growth factor made by the cell.
Proto-oncogene: A normal gene that can be converted to a cancer-causing gene.
Tumor-suppressor gene: A gene whose product inhibits cell division, thereby preventing uncontrolled cell growth.

Question 41

Define carcinogens.

Answer 41

A cancer-causing agent, either high-energy radiation (such as X-rays or UV light) or a chemical.
Although some cases of cancer occur spontaneously, most often a cancer arises from mutations that are caused by carcinogens, cancer-causing agents found in the environment. Mutations often result from decades of exposure to carcinogens.