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GREGOR JOHANN MENDEL
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PRESENTED BY :SANJEEV KUMARU.A.S.G.K.V.K.BENGALURU.
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ABOUT MENDEL
Johann born on july 22,1822,in the village hyncice in the province of silesia,part of Hapsburg Empire.
Father Anton mendel ,soldire during nepolian war serwing austrian army and had a farm .
Mother Rosiny.
Sisters : Veronica(born 2 year brfore him ) Theresa (born seven year after him )
4Mendel birth certificate.
Veronica Theresa
L.Schindler
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He attended village school in hyncis.mendel was unusual talent boy in 1883 arranged to attend advanced school in lipnik.
Johann well at new school and next year transferred to more advanced Gymnasium(equivalent to American high school)
Mendel graduated from Gymnacium 1840(when he was 18 )
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Mendel attended the secondary school at opova from 1834 – 1840.
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Mendel joined agustanian monastery at brunn in september 7 ,1843,as custom he adopted new name gregor.
In 1846 attended courses in phelosophical acadamy in brunn.
1847 he became priest. He became a high school suplimentory and he
was sent to study natural science at the university vienna from 1851-1853.
Mendel returned to brunn and resumed his teaching in1854.
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Mendel attended the university of vienna from 1851- 1854 .
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In spring of 1856, he began experimental crossing pea verities.
1863 completed his experiments , he taken 2 year in summarizing and analysis of data.
In1865 he presented his findings before the “Natural history society of brunn” at meeting february 8 and march 8.
This paper entitled “experiments in plant hybrediaztion” was published in germen language in annals proceedings of the society(volume 4 ) in 1866.
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Mendel also studied on
Honey bee .(failed due to haplo-diploid condition)
Hawk weed.(failed due to apomixis)
Mendel died in january6 ,1884 (at the age of 62)
due to chronic inflammation to kidney and abnormal over growth of heart . Gregor mendel is burried in
monastry vault at the central cemetery in brno.
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The first page of manuscript of mendel`s “Experiments in plant hybridization”(1865).
Greoger mendel is buried in the monastery vault at the central cemetary in brno.
This page from mendel`s notebook.
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Mendel proposed some basic genetic principles. But unfortunately his remarkable piece of work remained unattended and unappreciated up to 1900.
In 1900 Hugo de Vries in Holland, Carl Correns in Germany, Eric von Tshermack in Austria, rediscovered the
paper by Mendel during their search of literature for supporting their own findings.
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Mendel’s experimental design
• Statistical analyses:– Worked with large numbers of
plants– counted all offspring– made predictions and tested
them• Excellent experimentalist
– controlled growth conditions– focused on traits that were easy
to score– chose to track only those
characters that varied in an “either-or” manner
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Crossing Pea Plants
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Removed stamensfrom purple flower
Transferred sperm-bearing pollen fromstamens of white flower to egg-bearing carpel of purple flower
Parentalgeneration(P)
Pollinated carpelmatured into pod
Carpel(female)
Stamens(male)
Planted seedsfrom pod
Examinedoffspring:all purpleflowers
Firstgenerationoffspring(F1)
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Mendel’s Studied Discrete Traits
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Genetic Vocabulary
• Character: a heritable feature, such as flower color
• Trait: a variant of a character, such as purple or white flowers
• Each trait carries two copies of a unit of inheritance, one inherited from the mother and the other from the father
• Alternative forms of traits are called alleles
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Dominant
Recessive
Antagonistic traits
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Characters and chromosome no on which they present
Chromosome no. Character present.
chromosome no 1 1.seed coat
2.seed cotyledon colour.
chromosome no 4 3.plant hight.
4.position of flower.
5.pod shape.
chromosome no 5 6.pod colour.
chromosome no 7 7.seed shape.
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Mendel’s experimental design
• Mendel also made sure that he started his experiments with varieties that were “true-breeding”
X
X
X X
X
X
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Genetic Vocabulary
• Phenotype – observable characteristic of an organism
• Genotype – pair of alleles present in and individual• Homozygous – two alleles of trait are the same
(YY or yy)• Heterozygous – two alleles of trait are different
(Yy)• Capitalized traits = dominant phenotypes• Lowercase traits= recessive phenotypes
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Genetic Vocabulary
• Generations:– P = parental generation– F1 = 1st filial generation, progeny of the P generation– F2 = 2nd filial generation, progeny of the F1 generation
(F3 and so on)• Crosses:
– Monohybrid cross = cross of two different true-breeding strains (homozygotes) that differ in a single trait.
– Dihybrid cross = cross of two different true-breeding strains (homozygotes) that differ in two traits.
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Phenotype vs Genotype
Figure 14.6
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1 1
2
1
Phenotype
Purple
Purple
Purple
White
Genotype
PP(homozygous)
Pp(heterozygous)
Pp(heterozygous)
pp(homozygous)
Ratio 3:1 Ratio 1:2:1
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Dominant & recessive alleles (Fig. 10.7):
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Mendel’s Experimental Design
• In a typical breeding experiment Mendel mated two contrasting, true-breeding varieties, a process called hybridization
• The true-breeding parents are called the P generation
• The hybrid offspring of the P generation are called the F1 generation
• When F1 individuals self-pollinate the F2 generation is produced
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Mendel’s Observations• When Mendel crossed contrasting, true-breeding white and purple flowered pea
plants all of the offspring were purple• When Mendel crossed the F1 plants, many of the plants had purple flowers, but
some had white flowers• A ratio of about three to one, purple to white flowers, in the F2 generation
P Generation
(true-breeding parents) Purple
flowersWhiteflowers
×
F1 Generation (hybrids)
All plants hadpurple flowers
F2 Generation
EXPERIMENT True-breeding purple-flowered pea plants andwhite-flowered pea plants were crossed (symbolized by ×). Theresulting F1 hybrids were allowed to self-pollinate or were cross-pollinated with other F1 hybrids. Flower color was then observedin the F2 generation.
RESULTS Both purple-flowered plants and white-flowered plants appeared in the F2 generation. In Mendel’sexperiment, 705 plants had purple flowers, and 224 had whiteflowers, a ratio of about 3 purple : 1 white.
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Mendel’s Ratios
• In the F1 plants, only the purple trait was affecting flower color in these hybrids
• Purple flower color was dominant, and white flower color was recessive
• Mendel developed a hypothesis to explain the 3:1 inheritance pattern that he observed among the F2 offspring
• There are four related concepts that are integral to this hypothesis
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Heredity Concepts1. Alternative versions of genes account for variations in inherited
characters, which are now called alleles
2. For each character an organism inherits two alleles, one from each parent, A genetic locus is actually represented twice
3. If the two alleles at a locus differ, the dominant allele determines the organism’s appearance
4. The law of segregation - the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes
Allele for purple flowers
Locus for flower-color geneHomologouspair ofchromosomes
Allele for white flowers
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Law of Segregation
• Mechanism of gene transmission
Fertilization:alleles unite
Gametogenesis:alleles segregate
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Parental P0 cross
F1 cross
P Ppp
P pPp
Determine the genotype and phenotype
Mendelian Genetics• Classical Punett's Square is a way to determine ways traits
can segregate
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Parental P0 cross
F1 cross
P Pp Pp Ppp Pp Pp
P pPp
Determine the genotype and phenotype
Mendelian Genetics• Classical Punett's Square is a way to determine ways traits
can segregate
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Parental P0 cross
F1 cross
Determine the genotype and phenotype
Mendelian Genetics• Classical Punett's Square is a way to determine ways traits can
segregate
P Pp Pp Ppp Pp Pp
P pP PP Ppp Pp pp
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Mendel’s Law Of Segregation, Probability And The Punnett Square
P Generation
F1 Generation
F2 Generation
P p
P p
P p
P
p
PpPP
ppPp
Appearance:Genetic makeup:
Purple flowersPP
White flowerspp
Purple flowersPp
Appearance:Genetic makeup:
Gametes:
Gametes:
F1 sperm
F1 eggs
1/21/2
×Each true-breeding plant of the parental generation has identicalalleles, PP or pp.
Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele.
Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple-flower allele is dominant, allthese hybrids have purple flowers.
When the hybrid plants producegametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele.
3 : 1
Random combination of the gametesresults in the 3:1 ratio that Mendelobserved in the F2 generation.
This box, a Punnett square, shows all possible combinations of alleles in offspring that result from an F1 × F1 (Pp × Pp) cross. Each square represents an equally probable product of fertilization. For example, the bottomleft box shows the genetic combinationresulting from a p egg fertilized bya P sperm.
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Purple(Pp)
Purple(PP)
Pp p p
P
P
P
p
F1 generationAll purple
White(pp)
Purple(Pp)
Pp PpPPGametes
F2 generation¾ purple, ¼ white
GametesGametes
GametesPp
Pp PpPp
pp
Mendel’s Monohybrid Cross
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Smooth and wrinkled parental seed strains crossed.
• Punnett square
– F1 genotypes: 4/4 Ss
– F1 phenotypes: 4/4 smooth
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Mendel Observed The Same Pattern In Characters
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The Testcross
• In pea plants with purple flowers the genotype is not immediately obvious
• A testcross– Allows us to determine the genotype of an
organism with the dominant phenotype, but unknown genotype
– Crosses an individual with the dominant phenotype with an individual that is homozygous recessive for a trait
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Test Cross
• To determine whether an individual with a dominant phenotype is homozygous for the dominant allele or heterozygous, Mendel crossed the individual in question with an individual that had the recessive phenotype:
PP
P P
pp p
p
Recessivephenotype
DominantPhenotype
Gametes
Gametes
Alternative 1 – Plant with dominant phenotype is
homozygous
?Pp
P p
p
ppp
Recessivephenotype
?Alternative 2 – Plant with dominant phenotype is
heterozygousDominantPhenotype
Gametes
Gametes
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Test Cross
• To determine whether an individual with a dominant phenotype is homozygous for the dominant allele or heterozygous, Mendel crossed the individual in question with an individual that had the recessive phenotype:
PP
If all offspring are purple;unknown plant ishomozygous.
P P
pp p
p
Pp
PpPp
Pp
Recessivephenotype
DominantPhenotype
Gametes
Gametes
Alternative 1 – Plant with dominant phenotype is
homozygous
?Pp
If half of offspring arewhite; unknown plantis heterozygous.
P p
p
ppp
pp
ppPp
PpRecessivephenotype
?Alternative 2 – Plant with dominant phenotype is
heterozygousDominantPhenotype
Gametes
Gametes
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The Testcross
×
Dominant phenotype,unknown genotype:
PP or Pp?
Recessive phenotype,known genotype:
pp
If PP,then all offspring
purple:
If Pp,then 1⁄2 offspring purpleand 1⁄2 offspring white:
p p
P
P
Pp Pp
PpPp
pp pp
PpPpP
p
p p
APPLICATION An organism that exhibits a dominant trait,such as purple flowers in pea plants, can be either homozygous forthe dominant allele or heterozygous. To determine the organism’sgenotype, geneticists can perform a testcross.
TECHNIQUE In a testcross, the individual with theunknown genotype is crossed with a homozygous individualexpressing the recessive trait (white flowers in this example). By observing the phenotypes of the offspring resulting from this cross, we can deduce the genotype of the purple-flowered parent.
RESULTS
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The Law of Independent Assortment• Mendel derived the law of segregation by following a single trait
– 2 alleles at a single gene locus segregate when the gametes are formed
– The F1 offspring produced in this cross were monohybrids, heterozygous for one character
• Mendel identified his second law of inheritance by following two characters at the same time
– Mendel was interested in determining whether alleles at 2 different gene loci segregate dependently or independently
– Crossing two, true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters
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Dihybrid Cross
• With his monohybrid crosses, Mendel determined that the 2 alleles at a single gene locus segregate when the gametes are formed.
• With his dihybrid crosses, Mendel was interested in determining whether alleles at 2 different gene loci segregate dependently or independently.
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• For example, in pea plants seed shape is controlled by one gene locus where round (R) is dominant to wrinkled (r) while seed color is controlled by a different gene locus where yellow (Y) is dominant to green (y).
• Mendel crossed 2 pure-breeding plants: one with round yellow seeds and the other with green wrinkled seeds.
Dihybrid Cross
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Dependent Segregation• If dependent segregation (assortment) occurs:
– Alleles at the 2 gene loci segregate together, and are transmitted as a unit.
– Therefore, each plant would only produce gametes with the same combinations of alleles present in the gametes inherited from its parents:
Parents
Parental Gametes
F1 Offspring
RY
F1 Offspring’s Gametes
R RY Y
r ry y
ry
R rY y
RY
ry
What is the expected phenotypic ratio for the F2?
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R RY Y
R rY y
R rY y
r ry y
RY
RY
F2 With Dependent Assortment:
ry
ry
Ratio is 3 round, yellow : 1 wrinkled, green
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Independent Segregation• Alleles at the 2 gene loci segregate (separate) independently, and are
NOT transmitted as a unit. Therefore, each plant would produce gametes with allele combinations that were not present in the gametes inherited from its parents:
Parents
Parental Gametes
F1 Offspring
RY
F1 Offspring’s Gametes
R RY Y
r ry y
ry
R rY y
Ry
ry
What is the expected phenotypic ratio for the F2?
RY
rY
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Mendelian Genetics
Dihybrid cross - parental generation differs in two traitsexample-- cross round/yellow peas with wrinkled/green ones
Round/yellow is dominant
RY Ry rY ryRYRyrYry
What are the expected phenotype ratios in the F2 generation?round, yellow = round, green =wrinkled, yellow = wrinkled, green =
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RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
RY
RY
ry
ry
Phenotypic ratio is 9 : 3 : 3 : 1
F2 with independent assortment:
Ry
rY
rYRy
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YYRRP Generation
Gametes YR yr×
yyrr
YyRrHypothesis ofdependentassortment
Hypothesis ofindependentassortment
F2 Generation(predictedoffspring)
1⁄2 YR
YR
yr
1 ⁄2
1 ⁄2
1⁄2 yr
YYRR YyRr
yyrrYyRr
3 ⁄4 1 ⁄4
Sperm
Eggs
Phenotypic ratio 3:1
YR1 ⁄4
Yr1 ⁄4
yR1 ⁄4
yr1 ⁄4
9 ⁄163 ⁄16
3 ⁄161 ⁄16
YYRR YYRr YyRR YyRr
YyrrYyRrYYrrYYrr
YyRR YyRr yyRR yyRr
yyrryyRrYyrrYyRr
Phenotypic ratio 9:3:3:1
315 108 101 32 Phenotypic ratio approximately 9:3:3:1
F1 Generation
Eggs
YR Yr yR yr1 ⁄4 1 ⁄4 1 ⁄4 1 ⁄4
Sperm
CONCLUSION The results support the hypothesis ofindependent assortment. The alleles for seed color and seed shape sort into gametes independently of each other.
EXPERIMENT Two true-breeding pea plants—one with yellow-round seeds and the other with green-wrinkled seeds—were crossed, producing dihybrid F1 plants. Self-pollination of the F1 dihybrids, which are heterozygous for both characters, produced the F2 generation. The two hypotheses predict different phenotypic ratios. Note that yellow color (Y) and round shape (R) are dominant.
A Dihybrid Cross• How are two characters transmitted from parents to offspring?
– As a package?– Independently?
• A dihybrid cross– Illustrates the inheritance of two characters– Produces four phenotypes in the F2 generation
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Dihybrid cross
• F2 generation ratio:
9:3:3:1
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Law of Independent Assortment
• Mendel’s dihybrid crosses showed a 9:3:3:1 phenotypic ratio for the F2 generation.
• Based on these data, he proposed the Law of Independent Assortment, which states that when gametes form, each pair of hereditary factors (alleles) segregates independently of the other pairs.
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Laws Of Probability Govern Mendelian Inheritance
• Mendel’s laws of segregation and independent assortment reflect the rules of probability
– The multiplication rule States that the probability that two or more
independent events will occur together is the product of their individual probabilities
– The rule of addition States that the probability that any one of two or more
exclusive events will occur is calculated by adding together their individual probabilities
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Laws Of Probability - Multiplication Rule
• The probability of two or more independent events occurring together is the product of the probabilities that each event will occur by itself
• Following the self-hybridization of a heterozygous purple pea plants (Pp), what is the probability that a given offspring will be homozygous for the production of white flowers (pp)?
• Probability that a pollen seed will carry p: ½ • Probability that an egg will carry p: ½
• Probability that the offspring will be pp:• 1/2 X 1/2 = 1/4
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Laws Of Probability - Addition Rule
• The probability of either of two mutually exclusive events occurring is the sum of their individual probabilities
• Following the self-hybridization of a heterozygous purple pea plant (Pp), what is the probability that a given offspring will be purple?
• Probability of maternal P uniting with paternal P: 1/4• Probability of maternal p uniting with paternal P: 1/4• Probability of maternal P uniting with paternal p: 1/4
• Probability that the offspring will be purple:• 1/4 + 1/4 + 1/4 = 3/4
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Probability In A Monohybrid Cross
• Can be determined using these rules
×RrSegregation of
alleles into eggs
RrSegregation of
alleles into sperm
R r
rR
RR
R1⁄2
1⁄2 1⁄2
1⁄41⁄4
1⁄4 1⁄4
1⁄2 rr
R rr
Sperm
×
Eggs
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Mendel’s conclusions
• Genes are distinct entities that remain unchanged during crosses
• Each plant has two alleles of a gene• Alleles segregated into gametes in equal
proportions, each gamete got only one allele• During gamete fusion, the number of alleles
was restored to two
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Summary of Mendel’s Principles
• Mendel’s Principle of Uniformity in F1:
– F1 offspring of a monohybrid cross of true-breeding strains resemble only one of the parents.
– Why? Smooth seeds (allele S) are completely dominant to wrinkled seeds (alleles).
• Mendel’s Law of Segregation:
– Recessive characters masked in the F1 progeny of two true-breeding strains, reappear in a specific proportion of the F2 progeny.
– Two members of a gene pair segregate (separate) from each other during the formation of gametes.
• Mendel’s Law of Independent Assortment:
– Alleles for different traits assort independently of one another.– Genes on different chromosomes behave independently in gamete
production.
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