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Understanding Mendelian Patterns of Inheritance and Genetic Principles

This comprehensive overview explores the fundamental concepts of Mendelian patterns of inheritance as pioneered by Gregor Mendel, the father of genetics. It discusses key principles including the law of segregation, law of independent assortment, and the significance of alleles and phenotype in genetics. Mendel's experiments with garden peas illustrate inheritance patterns, showcasing how traits are passed from one generation to the next. This guide serves as an essential resource for anyone seeking to grasp basic genetic principles and the foundational laws of heredity.

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Understanding Mendelian Patterns of Inheritance and Genetic Principles

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  1. CH-11 • MENDELIAN PATTERNS OF INHERITANCE CH-11(8) Mendelian Patterns of Inheritance

  2. 11.1 Gregor MENDEL – FATHER of Genetics – 1860s • Laws of Heredity • 1 - Each trait controlled by 2 alleles – Particulate Theory • 2 - Alleles on homologous chromosomes at a specific site – gene locus. CH-11(8) Mendelian Patterns of Inheritance

  3. Gregor Mendel • Austrian monk Breeding experiments with the garden pea. Gathered and documented mathematical data from his experiments • Formulated fundamental laws of heredity in early 1860s. CH-11(8) Mendelian Patterns of Inheritance

  4. Blending Concept – Before Mendel • Both sexes contribute equally • But parents of contrasting appearance produce offspring of intermediate appearance CH-11(8) Mendelian Patterns of Inheritance

  5. TERMS • Alleles – alternative forms of a gene – occur at the same locus on homologous • Dominant allele – masks the expression of recessive alleles • Recessive allele – expressed only in the homo-rec form • Homozygous – • Both alleles are either dominant or recessive • Heterozygous – • Alleles are different – one dominant. one recessive CH-11(8) Mendelian Patterns of Inheritance

  6. A A A A y y Y Y Alleles CH-11(8) Mendelian Patterns of Inheritance

  7. Genotype– • refers to the alleles an organism receives at fertilization. • HOMOZYGOUS DOMINANT • RECESSIVE. • HETEROZYGOUS CH-11(8) Mendelian Patterns of Inheritance

  8. PHENOTYPE • PHYSICAL APPEARANCE OF THE ORGANISM. • THE EXPRESSION OF THE ALLELE. CH-11(8) Mendelian Patterns of Inheritance

  9. Mendel’s Experiments Garden Pea – – True breeders offspring like parents and each other • True breeders – yield homozygous offspring. • Trait is always expressed. CH-11(8) Mendelian Patterns of Inheritance

  10. Garden Pea TraitsStudied by Mendel CH-11(8) Mendelian Patterns of Inheritance

  11. 11.2 ONE TRAIT INHERITANCE • Cross Pollination between two strains • P-Generation original parents • F1 – first generation of Offspring • Tall Plants x Short Plants • Short plants pollinated Tall Plants • F1 generation – ALL TALL • F1 PLANTS SELF-POLLINATED • ¾ Tall ¼ short • 3:1 ratio CH-11(8) Mendelian Patterns of Inheritance

  12. One-Trait Test CrossUnknown is Homozygous Dominant CH-11(8) Mendelian Patterns of Inheritance

  13. LAW 1 – LAW OF SEGREGATION • EACH ORGANISM W/ 2 FACTORS FOR EACH TRAIT • FACTORS SEPARATE DURING MEIOSIS SO EACH GAMETE CONTAINS ONLY ONE FACTOR CH-11(8) Mendelian Patterns of Inheritance

  14. 11.2c MONOHYBRID GENETICS PROBLEMS: • To solve these: • Which characteristic is dominant • Must determine Genotype of both parents • Crossing a dominant phenotype with a recessive phenotype indicates the genotype of the dominant phenotype CH-11(8) Mendelian Patterns of Inheritance

  15. Used to figure out probable results of a genetic cross. Tall vs short PUNNETT SQUARE FOIL method CH-11(8) Mendelian Patterns of Inheritance

  16. LAWS OF PROBABILITY • Chance has no memory • Flipping a coin… • Chance of H = 0.5 Chance of T = 0.5 CH-11(8) Mendelian Patterns of Inheritance

  17. Multiplicative Law – The chance of 2 or more independent events occurring together is the PRODUCT of their chance of occurring Separately. Genotype = Aa crossed with Aa Chance of A = 0.5. chance of a = 0.5 CH-11(8) Mendelian Patterns of Inheritance

  18. ADDITIVE Law- to determine Phenotypes • – chance that event can occur in 2 or more different ways is SUM of individual chances. chance of getting specific PHENOTYPE is sum of chances of getting all the right genotypes CH-11(8) Mendelian Patterns of Inheritance

  19. Dihybrid cross: Dihybrids are the PRODUCT of two different strains that differ in regard to two traits CH-11(8) Mendelian Patterns of Inheritance

  20. 11.3TWO-TRAIT Inheritance • 2nd series of Crosses • Crossed True breeders differing in two traits • Tall green X short yellow • If so then only 2 Phenotypes. Tall Green and Short/Yellow would occur. CH-11(8) Mendelian Patterns of Inheritance

  21. Instead ALL Four phenotypes occurred • tall green short green • tall yellow short yellow CH-11(8) Mendelian Patterns of Inheritance

  22. MENDEL’s 2nd LAW of Inheritance • LAW of INDEPENDENT ASSORTMENT. • Members of one pair of factors separate independently of members of another pair of factors. All possible combinations of factors can occur. CH-11(8) Mendelian Patterns of Inheritance

  23. Dihybrid Cross • (parents differ in TWO traits) • Cross a HOMOZYGOUS DOMINANT with a HOMOZYGOUS RECCESSIVE • Tall green TTGG v short yellow ttgg • TG and tg = TtGg CH-11(8) Mendelian Patterns of Inheritance

  24. Dihybrid cross • F1 Generation is TtGg = heterozygous for two traits. (4 possible gametes) • Then cross that and f2 generation yields an CH-11(8) Mendelian Patterns of Inheritance

  25. 2-Trait Test cross • Is individual w/ dominant traits homozygous or heterozygous for either of the 2 traits. • cross a dom pheno with a rec. pheno • Is a test cross necessary for determining the genotype of a homozygous recessive individual? CH-11(8) Mendelian Patterns of Inheritance

  26. 11.4 human genetic disorders • inherited alleles • autosomal chromosomes – somatic cells – non-sex cells. • Pedigree chart – to determine if condition is dom. or rec. CH-11(8) Mendelian Patterns of Inheritance

  27. Pedigree Charts autosomal recessive char. autosomal dominant char. patterns of inheritance CH-11(8) Mendelian Patterns of Inheritance

  28. Autosomes: • non-sex chromosomes same between sexes. CH-11(8) Mendelian Patterns of Inheritance

  29. Autosomal Recessive Pedigree Chart CH-11(8) Mendelian Patterns of Inheritance

  30. AUTOSOMAL RECESSIVE DISORDERS • TAY-SACHS DISEASE • CYSTIC FIBROSIS • PHENYLKETONURIA CH-11(8) Mendelian Patterns of Inheritance

  31. AUTOSOMAL DOMINANT DISORDERS • Children can get it if only one parent is affected • Heterozygotes are affected • Affected parents can have normal offspring • unaffected parents will have unaffected children • males and females w/ equal chances. CH-11(8) Mendelian Patterns of Inheritance

  32. Autosomal Dominant Pedigree Chart CH-11(8) Mendelian Patterns of Inheritance

  33. ASDs • NEUROFIBROMATOSIS • HUNTINGTON DISEASE CH-11(8) Mendelian Patterns of Inheritance

  34. INCOMPLETE DOMINANCE • red v white flower = pink • protein missing or inactive • wavy hair - curly & straight parents • sickle cell disease CH-11(8) Mendelian Patterns of Inheritance

  35. PLEIOTROPY: • SOME GENES MAY AFFECT MORE THAN ONE CHARACTERISTIC • ALLELE LINKED TO TWO OR MORE CHARACTERS • MARFAN SYNDROME –TALL. THIN PERSON W/ LONG THIN FINGERS AND OTHER PROBLEMS. CH-11(8) Mendelian Patterns of Inheritance

  36. MULTIPLE ALLELES • Several forms of a gene control a trait • ABO blood types (codominance) • More than one allele is fully expressed. • Ia = A antigen on rbc • Ib = B • ii = no antigens CH-11(8) Mendelian Patterns of Inheritance

  37. CO-DOMINANCE: • BOTH ALLELES ARE FULLY EXPRESSED • BLOOD TYPE • AB – BLOOD ALLELES PRODUCE SPECIFIC SET OF GLYCOPROTEINS • A – ALLELES produce different glycoproteins • B – ALLELES produce another set of glycoproteins.. CH-11(8) Mendelian Patterns of Inheritance

  38. Inheritance of Blood Type CH-11(8) Mendelian Patterns of Inheritance

  39. MULTIPLE ALLELES: • More than one pair of alleles may be REQUIRED. • PEPPERED MOTH. • 3 sets of color-coding genes. • m M’ and M • MM. MM’. Mm  dark moth • M’M’ and M’m  lighter moth • mm  lightest moth CH-11(8) Mendelian Patterns of Inheritance

  40. POLYGENIC INHERITANCE • one trait governed by several genes • For example: • Seed color in wheat • Height in humans • Skin color in humans CH-11(8) Mendelian Patterns of Inheritance

  41. Height in Human Beings CH-11(8) Mendelian Patterns of Inheritance

  42. ENVIRONMENT PLAYS ROLE • Affects phenotype. • Some genes modify the effects of others. • Two more genes can control one trait • Dominance can occur in degrees CH-11(8) Mendelian Patterns of Inheritance

  43. ENVIRONMENTAL EFFECTS: • Temperature: • HIMALAYAN RABBITS CH-11(8) Mendelian Patterns of Inheritance

  44. EPISTASIS • Gene at one place on chromosome INTERFERS with the EXPRESSION (Phenotypic) of gene at another locus. Example: Sweet Peas • 2 gene pairs affect color. and HOMO REC of either pair results in lack of color. • Genes at two different loci interact to control a single trait. CH-11(8) Mendelian Patterns of Inheritance

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