CHAPTER 10 MENDELIAN GENETICS GENETIC STUDIES BASED ON WORK BY GREGOR MENDEL [ ]

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

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

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]

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]

ALLELES [FORMS OF GENE] 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

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

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]

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]

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]

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

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