Lesson 7 Modification of Mendelian Ratios PDF

MODIFICATION OF MENDELIAN RATIOS Focus of this topic Mendelian principles dictate the transmission of alleles from parent to offspring, but they may not always exhibit the dominant-recessive relationship observed by Mendel. Unlike Mendelian genetics, which focuses on a single characteristi...

MODIFICATION OF MENDELIAN RATIOS Focus of this topic Mendelian principles dictate the transmission of alleles from parent to offspring, but they may not always exhibit the dominant-recessive relationship observed by Mendel. Unlike Mendelian genetics, which focuses on a single characteristic, many cases show that multiple genes can influence its phenotype. Mendelian inheritance exceptions include genes on sex chromosomes, where males receive only one copy of those genes. Focus of this topic Phenotypes are the result of a combination of genetics and the environment in which genes are expressed. Mendelian principles are violated by various exceptions, leading to phenotypes that differ from those produced by mono-, di-, and tri-hybrid crosses.. Extranuclear inheritance, influenced by DNA expression in mitochondria and chloroplasts, can alter Mendelian inheritance patterns, which are transmitted through the female gamete. Mendel’s Postulates #1: Unit factors come in pairs. #1: Chromosomes come in pairs. #2:Unit factors have either a #2: GENES have either a dominant or recessive form. dominant or recessive form. #3: Unit factors segregate/ #3: Chromosomes segregate/ separate during gamete separate during gamete formation. formation. #4: Unit factors assort #4: Chromosomes assort independently from one another. independently from one another. Mendel’s Postulates Mendel’s postulates for OTHER inheritance patterns do NOT hold true in all respects These both hold TRUE for other types of inheritance ￭ #3: Unit factors segregate/ separate during gamete formation. ￭ #4: Multiple unit factors assort independently from one another. These postulates DO NOT. ￭ #1: Unit factors come in pairs. ￭ #2: Unit factors have either a dominant or recessive form. Alleles Alter Phenotypes in Different Ways Function of Alleles Alleles are alternative forms of the same gene. Wild-Type Allele ￭ Appears most frequently in a population ￭ Also as the normal allele ￭ Often the DOMINANT ￭ Used as the standard which all mutations are compares. Mutant Allele ￭ Contains modified genetic information and specifies an altered gene product. Null Allele ￭ Mutation that results in loss of function mutation in functional proteins Partial dominance In partial dominance, one allele is not completely dominant. The phenotype of the heterozygous individual is intermediate or a blend of the phenotypes associated with each homozygous genotype. Codominance In codominance, both alleles are fully expressed in the phenotype of a heterozygous individual, contributing independently and being visibly expressed. CO-DOMINANCE AND MULTIPLE ALLELES Occurs when both genes/alleles in the genotype are equally dominant. Multiple Alleles occurs when more than 2 genes/alleles determine a characteristic ￭ KARL LANDSTEINER identified the ABO blood group system, which categorizes human blood into four main groups: A, B, AB, and O. Rhesus Factor also known as the Rh factor, is a protein that can be present on the surface of red blood cells  Forward Blood Typing Forward typing is the initial step in blood typing, where the laboratory determines the recipient’s blood type (patient). It involves testing the recipient's blood for the presence or absence of specific antigens, primarily those of the ABO blood group system.  Steps in Forward Blood Typing Patient Sample Collection: Obtain a blood sample from the patient. Labeling and Identification: Properly label the blood sample with the patient's identification information to prevent any mix-ups. Centrifugation: Centrifuge the blood sample to separate the cellular components.  Steps in Forward Blood Typing Tube Testing: Prepare test tubes for the blood typing reaction. Each test area should contain reagents specific to the A, B, and Rh antigens. Add reagents: Add anti-A serum to one area, anti-B serum to another, and anti-Rh serum (anti-D) to a third area. Mix and Incubation: Mix a small amount of the patient's red blood cells with each type of anti-serum on the slide or in the tubes. Steps in Forward Blood Typing Observation: Observe the reactions for the presence or absence of agglutination under appropriate lighting conditions. For Rh typing, check for agglutination in the presence of anti-Rh serum. ￭ If agglutination occurs, the blood type is Rh-positive; ￭ if there is no agglutination, the blood type is Rh-negative. Record the result Forward Blood typing Forward typing (patient RBC mixed with commercially available antibody) will be mixed field or non- agglutinated due to the transfused type O red cells Reverse Blood typing reverse typing (patient plasma mixed with commercially available reagent RBCs) will detect the patient’s native anti-A or anti-B antibodies, leading to discordant or indeterminate reports