Loading...

BIO305: Genetics

Unit 3: Extension of Mendelian Genetics  

Believe it or not, after Mendel published his groundbreaking work in 1866, his findings were forgotten for a few decades. It was not until 1900 that his work was rediscovered independently by Correns and de Vries. Additional research throughout the years would reveal that there are many types of gene inheritance and expression besides Mendelian inheritance. Thanks to advances in science and research, many of these types have been discovered and researched in detail. For example, we have learned about incomplete dominance, where a white flower mated with a red flower yields pink offspring. We have also learned about codominance, where there is more than one dominant allele, as there is in our blood type system (O, A, B, AB).
 
In this unit, we will discuss single and multigenic inheritance patterns that result in non-Mendelian phenotype distribution. In some cases, e.g., sex-linked genes and lethal alleles, a missing homologous chromosome or a missing homozygote (missing because it is lethal) cause the unexpected offspring phenotype distribution. Other inheritance patterns truly depart from Mendel’s recessive-dominant inheritance schemas, e.g., codominance allows two expressed allele traits and incomplete dominance results in an in-between phenotype. We will also discuss inheritance patterns where the recessive and dominant alleles do not matter at all. For example, in the case of imprinting, the only thing that matters is the origin of the allele; some genes are always maternal (it does not matter what allele the father contributes), while other genes are always paternal (it does not matter what allele the mother contributes). Finally, the ultimate departure from Mendel is epigenetic inheritance: the environment induced post-synthetic nucleic DNA modification results in phenotypes that are not written in the DNA sequence.

Unit 3 Time Advisory
This unit should take you approximately 13.75 hours to complete.
 
☐    Subunit 3.1: 1 hour
 
☐    Subunit 3.2: 3 hours
 
☐    Subunit 3.3: 0.5 hours
 
☐    Subunit 3.4: 1.5 hours
 
☐    Subunit 3.5: 1 hour
 
☐    Subunit 3.6: 0.25 hours
 
☐    Subunit 3.7: 0.25 hours
 
☐    Subunit 3.8: 1.5 hours
 
☐    Subunit 3.9: 2 hours
 
☐    Subunit 3.10: 2 hours
 
☐    Subunit 3.11: 0.75 hours

Unit3 Learning Outcomes
Upon successful completion of this unit, you will be able to: - predict the probability of affected offspring in X-linked inheritance; - compare and contrast as well as discuss Mendelian inheritance and codominance and incomplete dominance; - identify X-linked inheritance based on pedigree pattern; - predict the probability of offspring phenotype if a lethal allele is in play; - compare and contrast single and multiple gene determined phenotypes; - explain epigenetic inheritance; - compare and contrast as well as discuss multigenic inheritance and pleiotropy; - explain organellar inheritance; - characterize genetic imprinting; and - predict the probability of offspring phenotype during epistasis.

3.1 X-Linked Traits   - Reading: Massachusetts Institute of Technology: Professor Chris Kaiser’s “Lecture 5: Chromosomes and Sex Linkage” Link: Massachusetts Institute of Technology: Professor Chris Kaiser’s “Lecture 5: Chromosomes and Sex Linkage” (PDF)
 
Instructions: Select the PDF link for “Lecture 5: Chromosomes and Sex Linkage,” and read these lecture notes. These lecture notes briefly review meiosis and mitosis and explain the peculiar inheritance pattern of genes located on the X chromosome of organisms that are in the X-Y sex-determination system. X-linked genes are genes that are on the X chromosome. This text is technical, so please plan to read it several times for a full understanding.
 
Studying these lecture notes should take approximately 1 hour.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.2 X-Linked Genetic Disorders   - Reading: Lucile Packard Children’s Hospital at Stanford: “X-Linked Recessive: Red-Green Colorblindness, Hemophilia A” Link: Lucile Packard Children’s Hospital at Stanford: “X-Linked Recessive: Red-Green Colorblindness, Hemophilia A” (HTML)
 
Instructions: Read this article to ensure you understand the cause behind red-green color blindness and hemophilia. This should give you a practical understanding of some impacts of sex-linked disorders. This reading also covers the topic outlined in subunit 3.2.1.
 
Reading this article should take approximately 1 hour.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.2.1 Hemophilia   - Reading: National Institute of Health: “Explore Hemophilia” Link: National Institute of Health: “Explore Hemophilia” (HTML)
 
Instructions: First, read “What Is Hemophilia?” Next, study the following sections: “Other Names,” “Causes,” “Signs and Symptoms,” “Diagnosis,” “Treatments,” “Living with Hemophilia,” and “Clinical Trials.” You may access these sections by clicking on the link for each title in the table of contents on the left side of the webpage. Hemophilia is a group of disorders affecting blood clotting. Please note that hemophilia A is X-linked. It is also called The Royal Disease because of its high frequency in European royal families.
 
Reading this material should take approximately 1 hour and 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.2.2 Color Blindness   - Reading: US National Library of Medicine’s PubMed Health: A.D.A.M.: “Color Blindness” Link: US National Library of Medicine’s PubMed Health: A.D.A.M.: “Color Blindness” (HTML)
 
Instructions: Read this article. Note that color blindness is X-linked.
 
Reading this article should take approximately 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.3 Codominance and Incomplete Dominance   - Lecture: YouTube: Brian Bennett’s “Sex-Linked Traits and Incomplete Dominance” Link: YouTube: Brian Bennett’s “Sex-Linked Traits and Incomplete Dominance” (YouTube)
 
Instructions: Watch this video, which first reviews X-linked traits and then explains incomplete dominance from the 4:30-minute mark to the end.
 
Watching this video and pausing to take notes should take approximately 15 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Lecture: YouTube: Brian Bennett’s “Codominance and Multiple Alleles” Link: YouTube: Brian Bennett’s “Codominance and Multiple Alleles” (YouTube)
     
    Instructions: Watch this video, which first explains codominance in general and then explains the codominance of A and B alleles in human AB blood type, starting at the 2:55-minute mark.
     
    Watching this video and pausing to take notes should take approximately 15 minutes.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.4 Epistasis   - Reading: BioMed Central: Journal of Biology: Frederick Roth, et al.’s “Question & Answer: Epistasis” Link: BioMed Central: Journal of Biology: Frederick Roth et al.’s “Question & Answer: Epistasis” (HTML)
 
Instructions: Read this series of questions and answers about epistasis. Note that, in the case of epistasis, an allele of another gene masks the expression of a trait. For example, the fur color of a rodent is predicted based on the presence of alleles that are responsible for the pigment production; however, the pigments must be delivered to the hair, and this process is controlled by another gene. The second gene has an allele that does not allow pigment delivery to the hair; thus, this allele masks the pigment-dependent phenotype. Enlarge and study all of the figures on this webpage.
 
Reading this text should take approximately 1 hour and 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.5 Polygenic Traits and Heritability   - Reading: Dr. John W. Kimball’s Biology Pages: “Continuous Variation: Quantitative Traits” Link: Dr. John W. Kimball’s Biology Pages: “Continuous Variation: Quantitative Traits” (HTML)
 
Instructions: Read this article. Note that polygenic inheritance typically results in continuous phenotype. If alleles of only one gene determine a phenotype, then the phenotype has discrete values – e.g., Mendelian inheritance, incomplete dominance, and complete dominance. Epistasis also results in discrete values of a phenotype.
 
Reading this article should take approximately 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: Memorial University: Dr. Steven M. Carr’s “Quantitative Genetics” Link: Memorial University: Dr. Steven M. Carr’s “Quantitative Genetics” (HTML)
     
    Instructions: Read this article. Note that not only the genes but the environment can also influence certain phenotypes. It is important to understand this reading well before you move on to the next resource.
     
    Reading this article should take approximately 30 minutes.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: Proceedings of the National Academy of Sciences: Or Zuk’s “The Mystery of Missing Heritability: Genetic Interactions Create Phantom Heritability” Link: Proceedings of the National Academy of Sciences: Or Zuk’s “The Mystery of Missing Heritability: Genetic Interactions Create Phantom Heritability” (PDF)

    Instructions: Select the link titled “Full Text (PDF).” Read this optional article for a demonstration of how heritability is used in science. This article comes from the Proceedings of the National Academy of Sciences (PNAS) and is considered a premiere journal that scientists/authors strive to publish in. Do not get discouraged if you need to read the article a couple of times; most scientific articles can have some concepts that are difficult to understand if you are not a scientist. Just do your best to get an idea of how research is focusing on the application of heritability.
     
    Reading this optional article should take approximately 4 hours.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: PLOS One: Barbara Ballentine and Russell Greenberg’s “Common Garden Experiment Reveals Genetic Control of Phenotypic Divergence between Sweet Sparrow Subspecies That Lack Divergence in Neutral Genotypes” Link: PLOS One: Barbara Ballentine and Russell Greenberg’s “Common Garden Experiment Reveals Genetic Control of Phenotypic Divergence between Sweet Sparrow Subspecies That Lack Divergence in Neutral Genotypes”(HTML) 

    Instructions: Read the “Background,” “Introduction,” and “Discussion” sections of this optional peer reviewed population study.
     
    Reading this optional article should take approximately 1 hour.
     
    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.6 Pleiotropy   - Reading: YouTube: Ben Paulson’s “Genetics – Complex 1” Link: YouTube: Ben Paulson’s “Genetics – Complex 1” (YouTube)
 
Instructions: Watch this video, which introduces pleiotropy.
 
Watching this video and pausing to take notes should take approximately 15 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.7 Recessive Lethal Alleles   - Lecture: YouTube: California Lutheran University: David Marcey’s “Mendelian Genetics, Extended” Link: YouTube: California Lutheran University: David Marcey’s “Mendelian Genetics, Extended” (YouTube)
 
Instructions: Watch this video from the 12:38-minute mark to the 18:25-minute mark. You will see scanning electron microscopic images of the heads of wild type and mutant fruit flies on black background. The mutant has legs in the place of its antennae. In this example, the Antp/Antp homozygote is absent in the offspring population. The Ant allele is homozygous lethal. Please note that a lethal allele can result in divergence of the Mendelian phenotypic ratios.
 
Watching this segment of the lecture and pausing to take notes should take approximately 15 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.8 Expressivity and Penetrance   - Reading: National Institute of Health’s Genetics Home Reference: “What Are Reduced Penetrance and Variable Expressivity?” Link: National Institute of Health’s Genetics Home Reference: “What Are Reduced Penetrance and Variable Expressivity?” (HTML)
 
Instructions: Read this article on penetrance and expressivity. Make sure you read the section titled “For More Information about Penetrance and Variable Expressivity” and then click on the suggested links. This information builds on what you have learned so far and uses some of the genetic terminology of the scientific realm. You should be familiar with a lot of these terms, and most if not all of these extra readings should make sense to you.
 
Reading this article should take you approximately 1 hour and 30 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.9 Genomic Imprinting   - Reading: University of Utah’s Genetic Science Learning Center: “Genomic Imprinting” Link: University of Utah’s Genetic Science Learning Center: “Genomic Imprinting” (HTML)
 
Instructions: Read this article, which discusses genomic imprinting, an example of non-Mendelian inheritance.
 
Reading this article should take approximately 2 hours.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.10 Mitochondrial Inheritance   - Reading: BioMed Central: Human Genomics: Ryan R. Parr and Luis H. Martin’s “Mitochondrial and Nuclear Genomics and the Emergence of Personalized Medicine” Link: BioMed Central: Human Genomics: Ryan R. Parr and Luis H. Martin’s “Mitochondrial and Nuclear Genomics and the Emergence of Personalized Medicine” (HTML)
 
Instructions: Read this article carefully. Subunits 3.1-3.10 describe non-Mendelian inheritance patterns of nuclear DNA. In this subunit, you will learn about extra-chromosomal inheritance. Note that mitochondrial DNA is inherited only from the mother; thus, mitochondrial inheritance pattern is always maternal. Plastids of plants and protists are also maternally inherited.
 
Reading this article should take approximately 2 hours.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

3.11 Environment and Gene Expression   - Reading: Massachusetts Institute of Technology: Professor Patricia Christie’s “Lecture 6: Epigenetics” Link: Massachusetts Institute of Technology: Professor Patricia Christie’s “Lecture 6: Epigenetics” (PDF)
 
Instructions: Select the PDF link for “Lecture 6: Epigenetics,” and read these lecture notes. These lecture notes describe the effect of the environment on gene expression. This text is technical, so please plan to read it several times for a full understanding.
 
Reading these lecture notes should take approximately 15 minutes.
 
Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Lecture: YouTube: University of California, Berkeley: Professor Haim Cedar’s “Biology 1A - Lecture 25: Human Genetics and Epigenetics” Link: YouTube: University of California, Berkeley: Professor Haim Cedar’s “Biology 1A - Lecture 25: Human Genetics and Epigenetics” (YouTube)
     
    Instructions: Watch this lecture beginning at the 35:56-minute mark, when Professor Cedar starts to talk about epigenetics. You can find the exact start of the epigenetics section with the help of the text on the blackboard: “Epigenetic Inheritance – a heritable trait that maps to a position on a chromosome – but does not involve a change in the DNA sequence.”
     
    Watching this portion of the lecture and pausing to take notes should take approximately 30 minutes.
     
    Terms of Use: Please respect the copyright and term of use displayed on the webpage above.

  • Reading: BioMed Central: Clinical Epigenetics: Takeo Kubota, Kunio Miyake, and Takae Hirasawa’s “Epigenetic Understanding of Gene-Environment Interactions in Psychiatric Disorders: A New Concept of Clinical Genetics” Link: BioMed Central: Clinical Epigenetics: Takeo Kubota, Kunio Miyake, and Takae Hirasawa’s “Epigenetic Understanding of Gene-Environment Interactions in Psychiatric Disorders: A New Concept of Clinical Genetics” (HTML)
     
    Instructions: Read this optional article. This article discusses an influence of epigenetic patterns on the onset of psychiatric disorders. Epidemiological studies have shown that famine and nutrition change the epigenome.
     
    Reading this optional article should take approximately 2 hours.
     
    Terms of Use: Please respect the copyright and term of use displayed on the webpage above.

  • Assessment: The Saylor Foundation’s “Family Pedigree” Link:The Saylor Foundation’s “Family Pedigree” (HTML)
     
    Instruction: Complete this multiple choice assessment. You will find links to five pedigrees on this page. You will be asked to determine if the highlighted trait in the pedigree follows dominant, recessive, or sex-linked inheritance. Clicking on an answer will bring you to another page: If your answer is correct, then it is acknowledged with a short explanation. If your answer is wrong, you will be taken to a tutorial page. Study the tutorial page carefully. At the end of the tutorial page, you will be prompted to return to the assessment to try it again. Note that family pedigrees are indispensable in medical counseling.
     
    Completing this assessment should take approximately 1 hour.