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Understanding Mendelian Genetics: Keys to Inheritance Patterns

Explore Mendelian genetics with an emphasis on allele forms, dominant/recessive traits, and genetic studies based on Gregor Mendel's work. Understand single-gene inheritance, Punnett squares, and dihybrid crosses. Key concepts include homozygous, heterozygous, phenotype, and genotype.

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Understanding Mendelian Genetics: Keys to Inheritance Patterns

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  1. CHAPTER 10MENDELIAN GENETICS GENETIC STUDIES BASED ON WORK BY GREGOR MENDEL [1822-1884]

  2. OFFSPRING LOCUS GAMETES DIPLOID HAPLOID GENOME GENOTYPE THE TYPE GENES AN ORGANISM HAS USUALLY SHOWN BY LETTERS PHENOTYPE THE APPEARANCE OF THE ORGANISM TERMS TO KNOW

  3. SINGLE GENE INHERITANCE • ALLELES • An alternative or different form of a gene for example two different shapes of earlobes [p. 171] • DOMINANT CHARACTERISTIC USE CAPITAL LETTER—E-FREE EARLOBES RECESSIVE CHARACTERISTIC • USE A SMALL LETTER—e-attached earlobes

  4. HOMOZYGOUS STATE • IF BOTH ALLELES ARE JUST ALIKE IN THE ORGANISM IT IS SAID TO BE HOMOZYGOUS OR PURE FOR THAT CHARACTERISTIC • AN EXAMPLE IS ATTACHED EARLOBES [ee]

  5. HETEROZYGOUS STATE • IF THERE ARE TWO DIFFERENT GENES [ALLELES] FOR THE SAME CHARACTERISTIC THE ORGANISM IS SAID TO BE HETEROZYGOUS OR HYBRID FOR THAT CHARACTERISTIC • FOR EXAMPLE Ee • The dominant characteristic will appear in the organism in earlobes—free earlobes [p.171]

  6. DOMINANT ALLELE SHOWS IN THE PHENOTYPE OR APPEARANCE IN BOTH THE HOMOZYGOUS OR HETEROZYGOUS STATE RECESSIVE ALLELE SHOWS IN THE PHENOTYPE ONLY IN THE HOMOZYGOUS STATE ALLELES [FORMS OF GENE]

  7. CODOMINANCE • THIS IS ALSO CALLED INCOMPLETE DOMINANCE • THERE IS A “BLENDING” OF CHARACTERISTICS • EXAMPLES ARE SEEN IN • BLOOD TYPES—TYPES A AND B ARE INCOMPLETELY DOMINANT TO EACH OTHER- TYPE AB BLOOD • IN CERTAIN FLOWERS –RED AND WHITE WILL PRODUCE PINK • See page 174

  8. SAMPLE PROBLEM [PART A] • PARENTAL CROSS—P1 CROSS • ONE PARENT IS PURE FOR TALL TT • ONE PARENT IS PURE FOR SHORT tt • THE OFFSPRING CALLED THE F1 GENERATION has Tt genotype but will all be tall [phenotype] because tall is dominant [see board]

  9. SAMPLE PROBLEM [PART B] • WHEN TWO OF THE F1 GENERATION ARE CROSSED Tt xTt THE RESULTS WILL BE A 3:1 ratio OF TALL PLANTS TO SHORT PLANTS PHENOTYPIC RATIO GENOTYPIC RATIO IS 1 PURE TALL:2 HYBRID TALL: 1 PURE SHORT [USE PUNNETT SQUARE]

  10. MONOHYBRID CROSS CONTINUED • F1 PHENOTYPE ALL TALL—BECAUSE TALL IS THE DOMINANT CHARACTERISTIC • F1 GENOTYPE ALL HYBRID—Tt HYBRID OR HETEROZYGOUS BECAUSE THERE ARE 2 DIFFERENT GENES FOR HEIGHT REPRESENTED BY THE LETTERS T and t [this would be on a section of the chromosome]

  11. DIHYBRID CROSSES [part 1] • P1 CROSS TTWW x ttww • T=tall t=short W=white flowers w=yellow • GAMETES OF TTWW=TW • GAMETES OF ttww=tw • GENOTYPE OF F1=TtWw • F1 all hybrid all tall with white flowers

  12. DIHYBRID CROSSES [part 2] • TWO ORGANISM OF F1 ARE CROSSED TO GET THE F2 GENERATION • TtWw x TtWw • COMPLETE A PUNNETT SQUARE TO GET THE FINAL RESULTS [SEE BOARD] • MALE —> TW Tw tW tw {all possible gametes} • FEMALE—>TW Tw tW tw {all possible gametes} • UPON COMPLETING THE PUNNETT SQUARE THE RESULTS WILL BE A 9:3:3:1 RATIO [9 TALL WHITE:3TALL YELLOW:3 SHORT WHITE:1SHORT YELLOW

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