1. What is the correct hierarchical order, from smallest to largest unit/structure:

Answer: nucleotide, gene, chromosome, genome Explanation: Nucleotides, also referred to as bases, are the building blocks of DNA. DNA is composed of just four nucleotides: Adenine, Thymine, Cytosine, and Guanine. Genes are discrete, working subunits of DNA. Genes contain the code for proteins. Chromosomes are the larger structural unit of DNA. They consist of DNA and proteins called histones. Humans normally have 23 pairs of chromosomes (46 total). Many genes are located linearly along the length of the chromosomes. Genome is the term used to describe all the genetic material in an organism. This refers to all the genes located on all the chromosomes. For an illustration of the relationship between these structures, go to DNA.

2. The human genome has approximately how many bases (or nucleotides)?

Answer: 3 billion. Explanation: It is estimated that only ~10% of the human genome consists of protein coding sequences (gene exons). The remainder of the sequence is non-coding sequence, introns and intragenic regions, frequently referred to as junk DNA. The functions of these sequences are unknown though some are likely to play regulatory roles.

3. How many genes do scientists estimate are in the human genome?

Answer: 30,000-40,000 genes. Explanation: Scientists intially estimated that there were 80,000-120,000 genes in the human genome. However, in February of 2001, researchers announced that the human had far fewer genes than predicted. Scientists now believe that there are approximately 30,000-40,000 genes in the human genome.

4. Every gene, in the human genome, is expressed in every cell of our body.

Answer: False. Explanation: The complete human genome is present in all our cells, except for red blood cells (they lack a nucleus), however, not all those genes are expressed. So while all the genes are there, they are not all active or turned on. The expression the various gene combinations is what distinguished different cell types (e.g. brain cell vs. skin cell).

5. Which of the following is NOT a type of genetic mutation?

Answer: Carryover Explanation: See Mutations for descriptions of different types of mutations.

6. An allele is

Answer: an alternate form of a gene. Explanation: A gene may have several variant forms. These different variants are referred to as alleles. Alleles often vary by only a single nucleotide difference in the sequence. Different alleles produce variations in characteristics such as eye color, or can result in variable protein function or efficiency.

7. If you inherit a mutation in the BRCA1 gene you will get Breast Cancer

Answer: False. Explanation: While a mutation in the BRCA1 gene increases a person's risk for breast cancer, it does not mean a person will definitely develop the disease. BRCA1 has a penetrance of 50-85%, meaning that only 50-85% of people who inherit a disease-causing mutation will get cancer.

8. Which of the following is an example of a condition caused by a mutation in a single gene?

Answer: Cystic fibrosis Explanation: Cystic Fibrosis is cause by a mutation in the CFTR gene. Cystic fibrosis is an autosomal recessive disease, thus both copies of the gene need to be mutated in order for the disease to develop. If a person has 1 mutant copy of the CFTR gene, they are not symptomatic and are called a carrier. Other examples of conditions caused by a mutation in a single gene are: Huntington Disease, Sickle Cell Anemia, Duchenne Muscular Dystrophy, and Acondroplasia (short-limbed dwarfism). Colon Cancer (as is most cancer) is caused by mutations in several genes and thus is called a multifactorial disease. Other examples of multifactorial conditions are heart disease, depression, Alzheimer's disease, etc. Down syndrome is caused by a chromosomal abnormality; individuals with Down syndrome have 3 copies of chromosome 21 instead of 2. Many genes are located on chromosome 21 Pneumonia is caused by a bacterial infection in the lungs.

9. How many chromosomes do humans typically have?

Answer: 46. Explanation: Humans typically inherit 23 chromosomes from each parent for a total of 46. Chromosomal abnormalities can lead to a total chromosome number that is more or less then this e.g. Down syndrome has 47, Turner syndrome has 45. To see a picture of human chromosomes, go to Karyotype Analysis.

10. A codon is

Answer: A sequence of 3 nucleotides which specify a specific amino acid. Explanation: Genes contain the code for proteins. The building blocks for genes are nucleotides, while the building blocks for proteins are amino acids. The DNA code is translated into the amino acid code to create proteins. Three consecutive nucleotides encode for 1 amino acid; those three nucleotides are called a codon. For a more detailed explanation, see Genetic Code.

11. A nonsense mutation results in

Answer: a shortened protein product Explanation: A nonsense mutation is a change in the genetic sequence which changes a codon from an amino acid to a stop codon. Because the mutation results in premature termination of protein production, the final protein is shorter than the normal copy and usually does not function normally.

12. Somatic gene therapy

Answer: results in a change in an individuals genetic make-up which is not passed on to offspring. Explanation: Gene therapy is a technique used to treat genetic diseases. The procedure involves replacing, manipulating or supplementing a nonfunctional gene with a healthy (functional) gene. Somatic gene therapy is when the procedure is applied to any cells in the body which are not reproductive cells. Since the healthy gene is not added to reproductive cells, that gene will not be passed onto offspring. In germline gene therapy, the healthy gene is applied to the reproductive cells of the body such as egg and sperm, any genetic alterations can be passed to offspring.

13. What governmental department initiated the Human Genome Project?

Answer: Department of Energy Explanation: After the atomic bomb was developed and used, the Department of Energy (DOE) wanted to examine the consequences of genetic mutations caused by radiation and chemical by-products of energy production. To do this, the DOE needed a reference sequence for comparison, and thus the Human Genome Project was proposed. The program is now run together by the NIH (NHGRI) and DOE.

14. Genetic polymorphisms

Answer: are variations in DNA sequence Explanation: The term polymorphism is usually used to describe naturally occurring variations in DNA sequence. Genetic polymorphisms are very common, occurring on average every 300-500 nucleotides. Genetic polymorphisms can cause observable changes in a trait, i.e. eye color, the ability of an individual to metabolize alcohol, etc. It is estimated that unrelated individuals probably differ in their genetic sequence at 3,000,000 bases, the majority of these differences are due to polymorphisms.

15. An exon is

Answer: a segment of a gene that contains directions for making a protein Explanation: Genes are composed of multiple exons, which all together contain the genetic code for a given protein. Exons are separated by intervening segments of DNA call introns. Introns do not contain the code for protein and are removed to produce messenger RNA (the intermediary between DNA and protein).