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The Work ofThe Work ofGregor MendelGregor Mendel
1822-18841822-1884
Gregor MendelGregor Mendel
1st person to trace successive generations1st person to trace successive generationsof living thingsof living things
Augustinian Monk – BrAugustinian Monk – Bruunn, Austriann, Austriataught natural science in high schooltaught natural science in high school
““How did plants obtain atypical characteristics?”How did plants obtain atypical characteristics?”
Vocabulary Used in Genetics
phenotype: physical expression of a gene
genotype: a make of genes in a chromosome
homozygous: alleles for a trait are the same
heterozygous: alleles for a trait are opposite TallTall ShortShort
Tall = TTall = T short = tshort = t
T TT T t tt t
T TT T
T tT t
More Vocabulary Used in GeneticsMore Vocabulary Used in Genetics
traitstraits:: inherited characteristicsinherited characteristics
geneticsgenetics:: study of hereditystudy of heredity
heredity:heredity: passing characteristics from passing characteristics from parents to offspringparents to offspring
allele:allele: factor that controls expression factor that controls expression of a of a trait trait
filial =filial = son or daughter: son or daughter: FF
parent generation:parent generation: PP
pollinization:pollinization: plant fertilization plant fertilization
zygote:zygote: cell produced by fertilization cell produced by fertilization
fertilization:fertilization: uniting of male and uniting of male and female female gametesgametes
gametes:gametes: sex cells (sperm and egg)sex cells (sperm and egg)
More Vocabulary Used in GeneticsMore Vocabulary Used in Genetics
Mendel’s FindingsMendel’s Findings:
Hereditary factors do not combine, but are passed Hereditary factors do not combine, but are passed intact to offspring.intact to offspring.
Each member of the parental generation transmitsEach member of the parental generation transmitsonly half of its hereditary factors to each offspring.only half of its hereditary factors to each offspring.
Certain factors are "dominant" over others.Certain factors are "dominant" over others.
Different offspring of the same parents receiveDifferent offspring of the same parents receivedifferent sets of hereditary factors.different sets of hereditary factors.
Mendel's work became, and still is, the foundation Mendel's work became, and still is, the foundation for modern genetics.for modern genetics.
Mendel's work became, and still is,Mendel's work became, and still is,the foundation for modern genetics.the foundation for modern genetics.
However-------However-------
Mendel's work became, and still is,Mendel's work became, and still is,the foundation for modern genetics.the foundation for modern genetics.
Gregor Mendel and the Laws of GeneticsGregor Mendel and the Laws of Genetics
I.I. Why Mendel succeeded:Why Mendel succeeded:
A.A. used controlled experimentsused controlled experiments
B.B. studied only one trait at a timestudied only one trait at a time
C.C. did mathematical analysis of did mathematical analysis of datadata
II.II. Mendel’s Monohybrid CrossesMendel’s Monohybrid Crosses
A.A. First Generation CrossFirst Generation Cross
1. tall pea plants = P1. tall pea plants = P11
2. short pea plants = P2. short pea plants = P11
3. all offspring were tall = F3. all offspring were tall = F11
B. Second Generation Cross
1. 2 tall offspring from first generation cross = F1
2. ¾ of these offspring = Tall = F2
3. ¼ of these offspring = Short = F2
C. Mendel’s conclusions: Rules
1. Rule of Unit Factors
Each organism has 2 factors for each of its traits(alleles: gene alternatives)
2. Rule of Dominance
For each trait there exists 2 possible factorsthat are expressed in physical characters,one that may be dominant, and the other recessive.
3. Law of Segregation
The two alleles for each trait must separatewhen gametes form.
D.D. Expression of TraitsExpression of Traits
1. phenotype: physical expression of a gene
2. genotype: a make of genes on a chromosome
3. homozygous: alleles for a trait are the same
4. heterozygous: alleles for a trait are opposite
III. Reginald Punnett and the Punnett Squares
A. English Biologist
B. 1905: devised a shorthand way of finding the expected proportions of possible genotypes in the offspring of a cross
C. Method called: Punnett Square
1. Takes into account that fertilizationoccurs randomly
2. Agrees with Mendel’s law of segregation
3. If you know the genotype of the parents,you can use a Punnett square to predictthe possible genotypes of their offspring.
Punnett SquarePunnett Square
Reginald Punnett 1905Reginald Punnett 1905
T
T T
t
t
t T t
tTtT
V. Monohybrid Crosses
♂♂
♀♀
IV.IV. Mendel’s Dihybrid Crosses(cross involving two different traits)
A.A. experimenting with plants that had two different traits that differed from each other
1.1. used true-breeding pea plants that had
round yellow seeds (RRYY) 2.2. crossed with true-breeding pea plants that
had wrinkled green seeds (rryy)
3.3. smooth was dominant and wrinkled was recessive
4.4. yellow was dominant and green was recessive
yellow seedsRR YY
round seeds
true-breeding pea plants that hadround yellow seeds
RRYY
green seedsrr yy
wrinkled seeds
rryy
true-breeding pea plants that hadwrinkled green seeds (rryy)
true-breeding pea plants that had
round yellow seeds
true-breeding pea plants that had
wrinkled green seeds
RRYY (rryy)
++
++
RRYYrryy
RRrrYYrr
or
r
r
R
RY
y
Y
y
Y Y
y
y
r
r
RR
R
R
R
R
R
R
R
R Y
Y
Y
Y
Y
Y
Y
Y R
R
R
R
R
R
R
R
Y
Y
Y
Y Y
Y
Y
Yr r r r
r r r r
r r r r
r r r r
y y y y
y y yy
y y y y
y y y y
P1P1
true-breeding pea plants that had
round yellow seeds
true-breeding pea plants that had
wrinkled green seeds
RRYY (rryy)
++
++
Result was 100Result was 100% round yellow seeded plants% round yellow seeded plants
Offspring of P1 cross pea plants that had
round yellow seeds
Offspring of P1 cross pea plants that had
wrinkled green seeds
RrYy (RrYy)
++
++
Result was different.Result was different.
??
R
R
R
RY
Y
Y
Y
y y
y
y
r
r
rr
R
R
R
R
R
R
R
R Y
Y
Y
Y
Y
Y
Y
Y r
r
r
r
r
r
r
r
y
y
y
y y
y
y
yR R R R
R R R R
r r r r
r r r r
Y Y Y Y
y y yy
Y Y Y Y
y y y y
F1F1
9 round yellow
RRYYRrYyRRYyRrYY
3 round green3 round green
RRyy
Rryy
1 wrinkled green1 wrinkled green
rryy
1/164/162/162/16
1/16
2/16
1/16
3 wrinkled yellow3 wrinkled yellow
rrYY
rrYy
1/16
2/16
9/16
3/16
3/16
1/16
16/16
Ratio
= 9:
3:3:
1
Ratio
= 9:
3:3:
1
B. F1 generation produced all round yellow seeds
C. F2 generation produced
9 round yellow
D. The Law of Independent Assortment
Genes for different traits are inheritedGenes for different traits are inheritedindependently of each other.independently of each other.
3 round green
3 wrinkled yellow
1 wrinkled green
Haploidn
Diploid
2n
S-phase of cell cycleS-phase of cell cycle
2n x 22n x 2
Meiosis IMeiosis I2n x 22n x 2
2n2n2n2n
AA BB
Meiosis IIMeiosis II
2n2n
nn
nn
AA
2n2n
nnnn
BB
Dominant ExamplesDominant ExamplesBrown Eyes over Blue EyesBrown Eyes over Blue Eyes
Color Vision over Color BlindnessColor Vision over Color Blindness
Hairy Heads over Bald HeadsHairy Heads over Bald Heads
Curly Tongue over Flat TongueCurly Tongue over Flat Tongue
Extra Fingers over Five FingersExtra Fingers over Five Fingers
Double Recessive Examples ExamplesDouble Recessive Examples ExamplesHemophiliaHemophilia
Sickle-Cell DiseaseSickle-Cell DiseaseTay-Sachs DiseaseTay-Sachs Disease
DwarfismDwarfism
V.V. ProbabilityProbability
VI. Genetic VariationVI. Genetic Variation
VII. Crossing OverVII. Crossing Over
VIII. NONDISJUNCTION
46
23 23
Normal distribution of chromosomes during meiosis.
NONDISJUNCTION
46
24 22
Trisomy(21)Trisomy(21) Down SyndromeDown Syndrome
Monosomy:Monosomy: Turner SyndromeTurner Syndrome
Hexapoid:Hexapoid:WheatWheat
Trisomy(13)Trisomy(13) Patau’s SyndromePatau’s Syndrome
Triploid:Triploid: ApplesApples
Polyploid:Polyploid: chrysanthamumschrysanthamums