Chapter 5 Beyond Mendelian Law PDF

CYTOGENETICS MIDTERMS CHAPTER 5 BEYOND MENDEL'S LAW MULTIPLE ALLELE Refer to the presence of more than two EXCEPTION TO MENDEL'S LAW alternative forms (alleles) o...

CYTOGENETICS MIDTERMS CHAPTER 5 BEYOND MENDEL'S LAW MULTIPLE ALLELE Refer to the presence of more than two EXCEPTION TO MENDEL'S LAW alternative forms (alleles) of a gene that All genes are not determined by only two can exist within a population. alleles- one dominant and one recessive. There Different allele combinations can are some exceptions to Mendel's Laws. produce variations in the phenotype. Multiple alleles expand the genetic LETHAL ALLELE diversity of a population and result in a A homozygous genotype (allele combination) broader range of phenotypes. that causes death before birth or shorten lifespan. Lethal allele can alter mendelian ratios by eliminating a certain genotypes from the population. DIFFERENT DOMINANCE LETHAL ALLELE RELATIONSHIPS Achondroplasia is caused by a dominant COMPLETE DOMINANCE mutation in the FGFR3 gene. This means that occurs when one allele completely masks the only one copy of the mutated gene is needed for effect of the other allele in a heterozygous an individual to develop the condition. individual. The dominant allele's trait is fully Thanatophoric dysplasia is a severe form of expressed, while the recessive allele's trait is not dwarfism caused by a different mutation in the visible at all. FGFR3 gene. This mutation is considered a INCOMPLETE DOMINANCE lethal allele, meaning it is incompatible with life. occurs when the heterozygote expresses a phenotype that is intermediate between the phenotypes of the two homozygous individuals. Neither allele completely masks the other. CODOMINANCE occurs when both alleles are expressed equally in the heterozygote. Neither allele masks the other. Kimberly Shane Villa 1  CYTOGENETICS MIDTERMS PENETRANCE & EXPRESSIVITY These two terms describe the degrees of expression of a single gene PENETRANCE Refers to the percentage of individuals who have a particular genotype who have the associated phenotype. It's the likelihood that a gene will manifest its expected trait. Complete Penetrance: If a gene has complete penetrance, every individual with the specific genotype will express the trait. Incomplete Penetrance: If a gene has incomplete penetrance, only a portion of individuals with the genotype will express the trait. EPISTASIS Phenomenon in genetics where the EXPRESSIVITY expression of one gene is influenced by Refers to the variability in severity of a the presence or absence of one or more phenotype. The extent to which the gene other genes. is expressed. Epistatic Gene: The gene that masks or PLEIOTROPY modifies the expression of another gene. MARFAN SYNDROME Hypostatic Gene: The gene whose expression is This genetic disorder is caused by a mutation in masked or modified. the FBN1 gene, which produces fibrillin-1, a protein essential for connective tissue. The mutation leads to a variety of symptoms, including: Tall stature: Individuals with Marfan syndrome are often tall and thin. Long limbs: Their limbs are disproportionately long. Heart problems: The aorta, a major blood vessel, can be weakened and prone to rupture. Kimberly Shane Villa 2  CYTOGENETICS MIDTERMS Eye problems: The lens of the eye can Cornelia de Lange Syndrome (CdLS) is a rare become dislocated. genetic disorder that affects many parts of the PHENOCOPY body, leading to a wide range of physical, Phocomelia and thalidomide incident cognitive, and behavioral differences. An environmentally caused condition has symptoms and a recurrence pattern similar to those of a known inherited traits Key points: - Environmental Influence - Mimicry - Non-Hereditary GENETIC HETEROGENEITY Refers to the phenomenon where different genetic mechanisms can lead to the same or similar phenotypes Two types: Allelic Heterogeneity: This occurs MITOCHONDRIAL GENE when different mutations within the same gene lead to the same or similar phenotypes. Locus Heterogeneity: This occurs when mutations in different genes can cause the same or similar phenotypes. Allelic Heterogeneity: In cystic fibrosis, over 2,000 different mutations in the CFTR gene have been identified, each causing varying degrees of disease severity. Locus Heterogeneity: Cornelia de Lange syndrome is the best example of a disease MITOCHONDRIA caused by locus heterogeneity. This disease can The cellular organelles that house the be acquired through a single mutation in any of reactions that derive energy from five different genes: nutrients NIPBL, SMC1A, HDAC8, RAD21, and Each of the hundreds of mitochondria in SMC3. each human cell contains several copies Kimberly Shane Villa 3  CYTOGENETICS MIDTERMS of a " mini-chromosome" that carries proteins essential for mitochondrial just 37 gene function. 24 genes encode for RNA molecules MERRF (Myoclonic Epilepsy with - 22 tRNAs Ragged Red Fibers): This disorder is - 2 rRNAs frequently linked to a mutation in the 13 genes encode protein that function in tRNA Lys gene on mDNA. This cellular respiration mutation affects the production of proteins involved in mitochondrial energy production. Kearns-Sayre Syndrome (KSS): This rare disease is typically caused by large deletions in mDNA, affecting multiple genes. These deletions can disrupt the production of proteins involved in various mitochondrial functions. Mitochondrial Neurogastrointestinal MITOCHONDRIA DISEASES Encephalomyopathy (MNGIE): This A class of diseases results from disorder is caused by mutations in the mutations in mitochondrial genes are thymidine phosphorylase (TP) gene. TP called mitochondrial myopathies is involved in the breakdown of Symptoms arises from tissues whose thymidine, a building block of DNA. cells normally have many mitochondria, Mutations in TP can lead to the such as skeletal muscles accumulation of thymidine, which can Diseases considered to be mitochondrial interfere with mtDNA replication and may also result from mutations in genes function. in the nucleus that encode proteins that Alpers Disease: This rare, severe are essential for mitochondria to neurological disorder is often caused by function mutations in the POLG gene. These Maternal inheritance and Autosomal mutations can lead to mtDNA depletion Dominant or Recessive and dysfunction, affecting the brain and liver. LINKAGE Linked traits are genes that are located close to each other on the same chromosomes More likely to be Inherited together. MELAS (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes): This disease is often caused by a mutation in the tRNA Leu gene located on mDNA. This mutation disrupts the synthesis of GENETIC MAP Kimberly Shane Villa 4  CYTOGENETICS MIDTERMS Are diagrams that show the relative pinpoint specific genes involved in positions of genes on chromosomes disease susceptibility. Linkage is used to derive genetic maps 2. Biotechnology and Genetic Engineering: because the frequency of recombination Gene Editing and Manipulation: between two genes is proportional to the Knowing the order and distance of distance between them on the genes is essential for targeted gene chromosomes editing using technologies like This will help geneticist in determining CRISPR-Cas9. This allows for precise the order of genes on a chromosomes modifications of specific genes, and the relative distance between them enabling the development of new therapies and the improvement of crops and livestock. Gene Therapy: Gene mapping helps identify genes that are potential targets for gene therapy. Knowing the location and function of genes allows for the development of therapies that replace or modify defective genes, potentially curing genetic diseases. 3. Forensic Science: DNA Fingerprinting: Gene mapping IMPORTANCE OF GENE MAPPING helps understand the variability of DNA 1. Genetic Mapping and Disease Research: sequences, which is crucial for DNA Identifying Disease-Associated Genes: fingerprinting used in forensic By mapping genes, researchers can investigations. Knowing the order and pinpoint regions of the chromosome distance of genes allows for the linked to specific diseases or traits. This identification of individuals based on information helps identify candidate their unique DNA profiles. genes for further investigation and 4. Breeding and Agriculture: potential therapeutic targets. Improving Crop Yield and Quality: Understanding Disease Inheritance Gene mapping allows breeders to Patterns: Knowing the order and identify desirable traits and select for distance between genes helps predict them in breeding programs. Knowing inheritance patterns of diseases, the order and distance of genes helps allowing for better genetic counseling predict the inheritance of traits and and informed family planning. improve the efficiency of breeding Genome-Wide Association Studies efforts. (GWAS): GWAS rely on linkage Developing Disease-Resistant Crops: disequilibrium (non-random association Gene mapping helps identify genes of alleles) to identify regions of the responsible for disease resistance. This genome associated with diseases. information allows breeders to develop Understanding gene order and distance crops with enhanced resistance to helps interpret GWAS results and specific pathogens, reducing crop losses and improving food security. Kimberly Shane Villa 5