MENDELIAN
GENETICS
MENDELIAN GENETICS
 ASEXUAL REPRODUCTION PRODUCES WHAT KIND
OF OFFSPRING?
 IDENTICAL
 SEXUAL REPRODUCTION PRODUCES WHAT KIND
OF OFFSPRING?
 SIMILAR, BUT DIFFERENT
 HOW COME THE OFFSPRING ARE SIMILAR?
 MEIOTIC CELL DIVISION AND THE FUSION OF
GAMETES
MENDELIAN GENETICS
 IF EACH PARENT IS DONATING GENETIC INFO
WHEN THE GAMETES FUSE, WHICH GENETIC INFO
IS THE ONE THAT DETERMINES THE TRAITS?
 THE STUDY OF THIS QUESTION, HOW TRAITS ARE
INHERITED AND EXPRESSED IS REFERRED TO AS:
GENETICS!!!!
MENDELIAN GENETICS
GENETICS…
I AM YOUR
FATHER!!!
 MENDEL IS
CONSIDERED THE
FATHER OF
GENETICS FOR HIS
INITIAL WORK IN THE
FIELD
MENDELIAN GENETICS
MENDEL’S
WORK
FOCUSED ON
PEA PLANTS,
AND
THE DIFFERENT
TRAITS THEY
DISPLAYED
MENDELIAN GENETICS
 MENDEL WAS VERY LUCKY
THAT HE CHOSE PEA PLANTS,
BECAUSE THEY HAPPEN TO
HAVE EXTREMELY SIMPLE
PATTERN OF INHERITANCE
 THIS WOULD THEN TRANSLATE TO A MORE
COMPLEX UNDERSTANDING, THAT MAY NOT
HAVE BEEN POSSIBLE IF HE USED A MORE
COMPLICATED ORGANISM
MENDELIAN GENETICS
 WHAT DID MENDEL FIND OUT?
 THE LAW OF DOMINANCE
 WHEN TWO PURE-BRED
PLANTS OF DIFFERENT TRAITS
WERE MIXED, ONLY ONE OF
THOSE TRAITS IS DISPLAYED
IN THE OFFSPRING
 THE DISPLAYED TRAIT IS
CALLED DOMINANT, THE
NON-DISPLAYED IS CALL
RECESSIVE
MENDELIAN GENETICS
 WHAT DID MENDEL FIND OUT?
 THE LAW OF SEGREGATION
 WHEN THE RECESSIVE TRAIT
“DISAPPEARS”, IT DOESN’T
ACTUALLY “DISAPPEAR”;
INSTEAD IT IS HIDDEN BUT STILL
HAS THE ABILITY TO END UP IN
FUTURE OFFSPRING
 TRAITS ARE CONTROLLED BY
FACTORS THAT EXIST IN PAIRS,
THOSE PAIRS CAN SEPARATE
(SEGREGATE) DURING GAMETE
FORMATION AND RECOMBINE
DURING FERTILIZATION
MENDELIAN GENETICS
 WHAT MENDEL DIDN’T KNOW
 CHROMOSOMES!! THEY WEREN’T DISCOVERED
YET…SO IT WASN’T UNTIL MANY YEARS LATER THAT
SCIENTISTS FIGURED OUT THE:
GENE-CHROMOSOME THEORY
 THINK ABOUT THE LAW OF SEGREGATION…WHERE
HAVE WE SEEN/DISCUSSED SOMETHING TO DO WITH
THE SEPARATION OF PAIRS?
 MEIOSIS
 CHROMOSOMES ARE WHERE THESE “FACTORS” THAT
MENDEL LABELED EXIST…WE NOW CALL THEM
GENES!!!
MENDELIAN GENETICS
 GENE-CHROMOSOME THEORY
MENDELIAN GENETICS
 SO WHAT IS A GENE EXACTLY?
 A SPECIFIC SEGMENT OF A CHROMOSOME, OR
PIECE OF DNA, THAT CONTROLS A PARTICULAR
TRAIT
MENDELIAN GENETICS
 HOW DO WE DISTINGUISH GENES THAT ARE FOR
THE SAME TRAIT, BUT HAVE DIFFERENT
INFORMATION…LIKE TALL VS SHORT IN THE PEA
PLANT?
 ALLELES
 DIFFERENT COPIES OR FORMS OF A GENE
CONTROLLING A CERTAIN TRAIT
 EVERY PERSON HAS 2 ALLELES FOR EACH TRAIT,
ANYONE KNOW WHY?
 BECAUSE EVERY PERSON HAS 2 CHROMOSOMES THAT
EXIST IN PAIRS
MENDELIAN GENETICS
 BECAUSE EVERYONE HAS TWO ALLELES WE CAN
DESCRIBE PEOPLE HAS EITHER
HOMOZYGOUS OR HETEROZYGOUS
MENDELIAN GENETICS
 WHEN WE REFER TO SOMEONE AS HOMOZYGOUS
OR HETEROZYGOUS, WE ARE SIMPLY REFERRING
TO THEIR GENETIC (ALLELIC) MAKEUP…HOWEVER,
WE USUALLY JUST LOOK AT WHAT PEOPLE LOOK
LIKE AND DON’T CONSIDER THEIR GENES…SO WE
DESCRIBE PEOPLE BOTH GENETICALLY AND
PHYSICALLY, OR
GENOTYPE VS PHENOTYPE
MENDELIAN GENETICS
MENDELIAN GENETICS
 KNOWING ABOUT GENOTYPES AND PHENOTYPES,
AND KNOWING ABOUT MENDEL’S LAWS ALLOWS
US TO MAKE PREDICTIONS ABOUT WHAT
OFFSPRING WILL LOOK LIKE
 PUNNETT SQUARES
 ORGANIZED/HELPFUL WAY
TO SHOW THE RESULTS OF
ANY CROSS BETWEEN TWO
PARENTS AND THE POSSIBLE
GENETIC COMBINATIONS
OF THEIR OFFSPRING
MENDELIAN GENETICS
 PUNNETT SQUARE PRACTICE
 QUESTION:
 A BROWN-EYED COUPLE,
BOTH HETEROZYGOUS FOR
EYE COLOR (Bb), HAVE
THREE BROWN-EYED
CHILDREN AND ARE
EXPECTING A FOURTH
CHILD. THE MOTHER INSISTS
THAT THE CHILD SHE IS
CARRYING WILL HAVE BLUE
EYES…IS SHE RIGHT?
MENDELIAN GENETICS
 PUNNETT SQUARES HAVE
USEFULNESS IN
GENETICS…SPECIFICALLY,
THE
TEST CROSS
MENDELIAN GENETICS
 OTHER CONCEPTS IN GENETICS (I.E. STUFF
MENDEL HAD NO CLUE ABOUT)
 THE LAW OF INDEPENDENT ASSORTMENT
 INCOMPLETE DOMINANCE
 CODOMINANCE
 MULTIPLE ALLELES
MENDELIAN GENETICS
 THE LAW OF
INDEPENDENT
ASSORTMENT
 EXPLAINS
HOW MORE
THAN ONE
TRAIT AT A
TIME IS
PASSED ON
(DIHYBRID
CROSSES)
MENDELIAN GENETICS
 THE LAW OF INDEPENDENT ASSORTMENT
 DIHYBRID CROSSES PRODUCE SPECIFIC
PHENOTYPIC RATIOS
MENDELIAN GENETICS
 INCOMPLETE DOMINANCE (A.K.A. BLENDED
INHERITANCE)
MENDELIAN GENETICS
 CODOMINANCE
MENDELIAN GENETICS
 MULTIPLE ALLELES
 WHAT IS AN ALLELE?
 THE DIFFERENT FORMS THAT A TRAIT CAN EXIST AS
(EXAMPLE, TALL ALLELE VS. SHORT ALLELE)
 THERE IS NO RULE THAT THERE CAN ONLY BE TWO
ALLELES, WHEN THEY ARE MORE THAN TWO ALLELES
THIS IS FOLLOWS THE INHERITANCE PATTERN REFERRED
TO AS
MULTIPLE ALLELES
MENDELIAN GENETICS
 MULTIPLE ALLELES
MENDELIAN GENETICS
 MENDELS WORK, AND
INHERITANCE,
FOCUSED ON SEEING
TRAITS ON THE
OUTSIDE…BUT WHAT
IS GOING ON INSIDE
THE BODY/CELLS THAT
IS CONTROLLING ALL
THIS STUFF TO BEGIN
WITH?
 MODERN GENETICS
NEXT!!!!