Transcript CHAPTER 10 MENDELIAN GENETICS

CHAPTER 10
MENDELIAN GENETICS
GENETIC STUDIES BASED ON
WORK BY GREGOR MENDEL
[1822-1884]
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
USE CAPITAL LETTER—EFREE 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