16 R

16.1 Talking Glossary: Recessive

https://www.genome.gov/genetics-glossary/Recessive

Abstract: “Recessive is a quality found in the relationship between two versions of a gene. Individuals receive one version of a gene, called an allele, from each parent. If the alleles are different, the dominant allele will be expressed, while the effect of the other allele, called recessive, is masked. In the case of a recessive genetic disorder, an individual must inherit two copies of the mutated allele in order for the disease to be present.”

Image: https://www.genome.gov/sites/default/files/tg/en/illustration/recessive.jpg

Transcript: Recessive refers to a type of allele which will not be manifested in an individual unless both of the individual’s copies of that gene have that particular genotype. It’s usually referred to in conjunction with a Punnett square, other types of Mendelian genetics, and frequently contrasted with a dominant pattern of inheritance wherein if one has one copy of the gene, regardless of what the other copy is, that dominant allele will show itself. In the case of a recessive allele, the individual will show the trait which corresponds to that genotype only if both alleles are the same and have that particular recessive characteristic. Now, that recessive characteristic can be one of no functional consequence. This results in differences between individuals such as in eye color or hair color, but it can also refer to a disease. For instance, in cystic fibrosis, which is a very common Mendelian disorder, that disease exists only when there’s a malfunction of both genes that correspond to cystic fibrosis. If there is only one mutation, then that recessive mutation can be compensated for by the normal allele. However, when the function of both are lost, then the disease manifests itself as a recessive disease where there is a loss of function and therefore observable disease.

Christopher P. Austin, M.D.

16.2 Talking Glossary: Recombinant DNA (0.5 min)

National Human Genome Research Institute https://www.genome.gov/genetics-glossary/Recombinant-DNA

Introduction: “Recombinant DNA (rDNA) is a technology that uses enzymes to cut and paste together DNA sequences of interest. The recombined DNA sequences can be placed into vehicles called vectors that ferry the DNA into a suitable host cell where it can be copied or expressed.”

Audio: https://www.genome.gov/sites/default/files/tg/en/narration/recombinant_DNA.mp3

Transcript: “Pieces of DNA, such as human DNA, can be engineered in a fashion that allows them to be copied, or replicated, in bacteria or yeast. This involves attaching appropriate elements to a piece of DNA and then transferring into a bacterial or yeast cell, with those elements then instructing the bacterial or yeast cell to copy this DNA along with its own. This process is known as DNA cloning, with the resulting cloned DNA often referred to as recombinant DNA.”

Eric D. Green, M.D., Ph.D.

16.3 Talking Glossary: Repressor (1 min)

Abstract: “A repressor is a protein that turns off the expression of one or more genes. The repressor protein works by binding to the gene’s promoter region, preventing the production of messenger RNA (mRNA).”

Audio: https://www.genome.gov/sites/default/files/tg/en/narration/repressor.mp3

Transcript: “A repressor is a protein that has a negative effect on gene expression. So these usually are proteins that bind to DNA, and they either prevent the RNA transcription machinery from getting in there and transcribing that DNA, or they just slow it down. So repressors are present in cells where you don’t want a particular gene expressed. So if the repressor cell recognizes a sequence in that gene, it will travel to there and keep that gene off in that cell. And this is how you prevent hemoglobin from being expressed in neurons, and how you would prevent liver enzymes from being expressed in red blood cells. Repressors are very difficult to study because it’s much easier to study things that give you more of what you’re looking for. But I think as we go along we’re going to find they play as important a role in gene regulation as the activating proteins.”

David M. Bodine, Ph.D.

16.4 Talking Glossary: Restriction Enzyme (0.5 min)

National Human Genome Research Institute

https://www.genome.gov/genetics-glossary/Restriction-Enzyme

Intro: “A restriction enzyme is an enzyme isolated from bacteria that cuts DNA molecules at specific sequences. The isolation of these enzymes was critical to the development of recombinant DNA (rDNA) technology and genetic engineering.”

Audio: https://www.genome.gov/sites/default/files/tg/en/narration/restriction_enzymes.mp3

Text “Restriction enzymes are proteins that bind to DNA in a very specific manner. So they actually recognize the base pairs within the DNA. And typically they will bind to a palindromic sequence, for instance, a sequence that is a mirror copy of itself–AGCCGA.”

Stacie Loftus, Ph.D.