Non-Mendelian Genetics Notes PDF

Republic of the Philippines Northwest Samar State University Calbayog City Name of Reporters: Campesinio, Aprilyn Mancol, Joshua Rey Ygrubay, Jerry...

Republic of the Philippines Northwest Samar State University Calbayog City Name of Reporters: Campesinio, Aprilyn Mancol, Joshua Rey Ygrubay, Jerry Gentallan, Lorens Lopar, Rodelyn Geocadin, Richie Grimpula, Ivy Topic: Non - Mendelian Genetics 1. Incomplete Dominance 2. Codominance 3. Multipple Alleles 4. Sex - Linked Traits 5. Sex - Influenced Traits 6. Pleiotropy 7. Epistasis 8. Genetic Background and Environment Name of Instructor: Mr. Reymark Merino School Year/Semester: 2024 - 2025 / First Semester Subject: Bio 1 - Pronciples of Genetics Program/Year: Bachelor of Science in Agriculture - Second Year Introduction This presentation is all about how traits get passed down from parents to their kids, but it goes beyond the simple rules we learned from Gregor Mendel, a famous scientist who studied pea plants. Mendel's rules, like dominant and recessive genes, are a good starting point, but they don't explain everything. This dives into the world of "non-Mendelian genetics," which is like a whole new set of rules for how traits work. Imagine you're mixing colors. Sometimes, you get a blend like mixing blue and yellow to make green (that's like "incomplete dominance"). Other times, both colors show up clearly, like red and white flowers making a red-and-white spotted flower (that's "codominance"). And sometimes, there are more than just two colors to choose from, like a whole rainbow of possibilities (that's "multiple alleles"). Then there are traits that depend on whether you're a boy or a girl, like some genes that work differently in males and females (that's "sex-linked traits" and "sex-influenced traits"). Sometimes, one gene can control many different things, like a master switch that turns on lots of different lights (that's "pleiotropy"). And sometimes, genes can interact with each other, like one gene turning another gene on or off (that's "epistasis"). But it's not just about genes; the environment can also play a role in how traits are expressed. Think of a plant: it might have genes for being tall, but if it doesn't get enough sunlight or water, it might stay short. It is all about exploring these complex and interesting ways that traits are passed down and expressed, going beyond the simple rules of Mendel and showing us the fascinating diversity of life. What is Non - Mendelian Genetics? Non-mendelian genetics does not follow the iconic Mendel’s Laws and can be defined as any inheritance pattern that fails to follow one or more laws of Mendelian genetics. When scientists began exploring more and more test crosses, they observed that there are several traits that do not match up with Mendel’s laws. Non-mendelian traits are not determined by dominant or recessive alleles. They can involve more than one gene leading to a complex pattern of inheritance. Some traits exhibited blending where the organisms’ offspring had two separate traits from the parent, meaning that certain alleles were not dominant. 1.) INCOMPLETE DOMINANCE After Gregor Mendel discovered inheritance laws, the term ”incomplete dominance” was proposed by the German botanist, Carl Correns (1864–1933). Carl Correns continued research and conducted an experiment on four o’clock flowers. This experiment leads to the discovery of incomplete dominance. Incomplete dominance is the phenomenon in which two true-breeding parents crossed to produce an intermediate offspring (also known as heterozygous) in which a heterozygous individual doesn’t show a dominant allele but rather shows an intermediate phenotype of the phenotypes of the dominant and recessive alleles. It is also referred to as partial dominance or intermediate inheritance. In incomplete dominance, the variants (alleles) are not expressed as dominant or recessive; rather, the dominant allele is expressed in a reduced ratio. Example: Remember! "With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits." 2.) CODOMINANCE Codominance is a form of inheritance wherein the alleles of a gene pair in a heterozygote are fully expressed. As a result, the phenotype of the offspring is a combination of the phenotype of the parents. When two alleles for a trait are equally expressed with neither being recessive or dominant, it creates codominance. Occurs when both alleles express their effects along with each other in the offspring, and no allele expresses dominant on another allele. Codominance is very easy to spot in plants and animals that have more than one pigment colour. Spotted cows and flowers with petals of two different colours are examples of codominance. Remember! "With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together. " 3.) MULTIPLE ALLELES Alleles or allelomorphs are the alternative forms of a gene present at the same locus on the homologous chromosomes. Some genes have more than two allelic forms, which is referred to as multiple alleles. Multiple alleles are the many different versions of a trait that exist within a population. When there are more than two different variants of a gene at a certain locus, multiple alleles, a type of genetic diversity, appear. The presence of multiple alleles within a population enhances genetic diversity by providing an array of combinations, increasing the chances for a population to adapt and survive in different environments. The ABO blood type system used by people is one of the most well-known examples of multiple alleles. Blood type A, B and O are the three alleles that can come together in different ways to make different blood types: AB, AA, BB, OO, AO and BO. 4.) SEX-LINKED TRAITS A sex-linked trait is an observable characteristic of an organism that is influenced by the genes on the chromosomes that determine the organism’s sex. There are two sex chromosomes in each person, one of which is inherited from each parent. Refers to characteristics (or traits) that are influenced by genes carried on the sex chromosomes. In humans, the term often refers to traits or disorders influenced by genes on the X chromosome, as it contains many more genes than the smaller Y chromosome. Traits carried on the X-chromosome are called sex-linked traits. Recessive sex-linked traits are more common that dominant. Key Terms: Carrier Example: Himophilia 5.) SEX-INFLUENCED TRAITS Sex-influenced traits are autosomal traits that are influenced by sex. If a male has one recessive allele, he will show that trait, but it will take two recessive for the female to show that same trait. Those that are dominant in one sex but recessive in the other. This is due to the different cellular environments in males and females provided by sex hormones. Different hormonal environments affect expression of heterozygote of a trait but homozygotes are unaffected and express the trait unrelated of the hormones produced. Example of Sex-Influenced Traits Pattern Baldness Pattern Baldness can occur in both males and females, however it is much more common in males. Why is this? Because the pattern baldness trait is influenced by the hormone testosterone. Sample problem: Rita and Robert are expecting to have a baby this year. Robert is carrier of a heterozygous bald trait (XBYb) while Rita is a carrier of Heterozygous Non-bald trait (XBXb). Will there be a chance that their child be a male non-bald carrier? Rita & Robert XB Xb XB XBXB XBXb Yb XBYb XbYb Identify the traits of the parents Robert: Heterozygous bald (XBYB) Rita: Heterozygous Non-Bald (XBXb) Genotypic ratio 1 XBXB : 1 XBXb 1 XBYb : 1 XbYb Phenotypic ratio: 1 Female bald 1 Female Non-bald 1 Male bald 1 Male Non-bald Probaility: Female bald 25% Female Non-bald 25% Male bald 25% Male Non-bald 25% 6.) PLEIOTROPY In genetics, Pleiotropy is defined as the expression of multiple traits by a single gene. Pleiotropy is derived from a Greek word meaning more ways. The term ”pleiotropy’’ was coined in 1910 by Festschrift.  This differs from polygenic inheritance, in which many genes influence one trait. A mutation (change) in the DNA of a pleiotropic gene will have an impact on many phenotypes, or expressed traits, in an organism. Pleiotropism When a single pair of gene control the production of many chracteristics. The gene is called pleiotropic gene. Gene Pleiotropy refers to a gene that focuses on the number of functions of a specific gene. It is also known as molecular-gene pleiotropy. A simple example of a Pleiotropy is phenylketonuria is a disease. It is a genetic disorder caused by the low metabolism of the amino acid phenylalanine in the body cells. 7.) EPISTASIS Epistasis is the genetic phenomenon in which the presence of one gene inhibits the expression of a phenotype encoded in another separate gene. The gene which does the inhibiting is the epistatic gene.  “Epistasis” is a word derived from Greek roots that mean “standing upon”. The “masked or silenced” alleles are said to be hypostatic, whereas the alleles that are doing the masking are called epistatic. An example of epistasis is the interaction between hair colour and baldness. A gene for total baldness would be epistatic to one for blond hair or red hair. The hair-colour genes are hypostatic to the baldness gene. The baldness phenotype supersedes genes for hair colour, and so the effects are non-additive. Types of epistasis: There are many ways in which epistasis can occur, which are as follows: 1.) Recessive Epistasis Takes place when recessive alleles at one locus hide the expression of both (dominant and recessive) alleles at another locus. 2.) Dominant Epistasis Occurs when the expression of both alleles (dominant and recessive) at another locus is masked by a dominant allele at one location. 3.) Dominant (Inhibitory) Epistasis A dominant allele at one location blocks the expression of both dominant and recessive alleles at the second locus. 4.) Duplicate Recessive Epistasis Occurs when a dominant allele at one of two loci can hide the expression of recessive alleles at both loci. 5.) Duplicate Dominant Epistasis When a dominant allele at either of the two locations masks the expression of the other alleles. 6.) Polymeric Gene Interaction Two dominant alleles working together to intensify the phenotype or produce a median variance 8.) GENETIC BACKGROUND AND ENVIRONMENT It generally implies that an individual's traits or characteristics are influenced by more complex genetic mechanisms than those outlined in Mendelian inheritance, and that the environment plays a significant role in the expression of these traits. Environment refers to all external factors—such as nutrition, temperature, lifestyle, stress, and exposure to toxins—that influence how genes are expressed. The expression of a gene can be influenced by the genetic background of the individual (the presence of other genes) and environmental factors. Example The height of a plant is influenced by its genes, but it can also be affected by environmental factors such as sunlight, water availability, and nutrient levels. Similarly, the expression of certain genes involved in disease susceptibility can be influenced by environmental factors like diet, stress, and exposure to toxins.  References: BYJU'S. (n.d.). Test your Knowledge on Non-Mendelian Inheritance! BYJU'S. https://byjus.com/biology/non-mendelian-inheritance/ BYJU'S. (n.d.). Test your knowledge on Incomplete Dominance. BYJU'S. https://byjus.com/biology/incomplete-dominance/ Gonzaga, M. V., & Mujtaba, G. (2023, August 13). Incomplete dominance. Biology Online. https://www.biologyonline.com/dictionary/incomplete-dominance (n.d.). Codominance examples in humans. Study.com. https://study.com/learn/lesson/codominance-examples-inhumans.html (n.d.). Codominance. Biology Online. https://www.biologyonline.com/dictionary/codominance BYJU'S. (n.d.). Alleles or allelomorphs are the alternative forms of a gene present at the same locus on the homologous chromosomes. Some genes have more than two allelic forms, which is referred to as multiple alleles. A diploid cell contains any of the two alleles, one each on the homologous chromosomes and a haploid cell contains only one allele. BYJU'S. https://byjus.com/neet/multiple-alleles-notes/ (2023, May 14). Multiple Alleles. Anthroholic. https://anthroholic.com/multiple-alleles Sex-linked gene. Biology Online. https://www.biologyonline.com/dictionary/sex-linked-gene (n.d.). Sex-Influenced Traits. SlidePlayer. https://slideplayer.com/slide/6967194/ Patel, A. (n.d.). Sex linked inheritance, Sex Influence inheritance and sex limited characters. SlideShare. https://www.slideshare.net/AashishPatel14/sex-linked-inheritance-sex-influence- inheritance-and-sex-limited-characters (2021, November 19). Pleiotropy: Overview & Examples. Study.com. https://study.com/learn/lesson/pleiotropy-example-gene-traits.html (2023, April 23). Pleiotropy – An Overview and Related Disorders. GeeksforGeeks. https://www.geeksforgeeks.org/pleiotropy/ (n.d.). Pleiotropy. ScienceDirect. https://www.sciencedirect.com/topics/medicine-and-dentistry/pleiotropy (2022, January 27). What is Epistasis? Study.com. https://study.com/learn/lesson/epistasis-overview-examples.html BYJU'S. (n.d.). What is Epistasis? BYJU'S. https://byjus.com/neet/what-is-epistasis/