mendel\ s law
TRANSCRIPT
MENDEL’S LAWMENDEL’S LAW
Gregor Mendel Gregor Mendel 1822-18841822-1884 An An Austrian scientistAustrian scientist
=research in a =research in a Czechoslovakian Czechoslovakian monastery.monastery.
Established the Established the basis basis of modern genetic of modern genetic science. science.
Objective = Objective = understand how understand how physical traits are physical traits are passed from a parent passed from a parent to its offspring. to its offspring.
Important conceptsImportant concepts
Dominance vs RecessivenessDominance vs RecessivenessPrinciple of Segregation. Principle of Segregation. Principle Independent Assortment Principle Independent Assortment
Monohybrid and Dihybrid crossMonohybrid and Dihybrid cross
Important TermsAlleles – Genetic factors that controls a trait, Dominant = ability to mask the expression of a recessive allele (Capital)
Recessive = masked by a dominant allele
Homozygous- 2 identical alleles (TT, tt)
Heterozygous- 2 different alleles (Tt)
Genotype- genes of an organism = alleles received during fertilization.
Phenotype = the physical appearance of a trait in an organism . Eg blue eyes, yellow flower
EgsEgs
Genotype = genes present in an organism (usually abbreviated as two letters
TT- Homozygous Dominant (PURE) tt-Homozygous Recessive (PURE) Tt- Heterozygous
AllelesAlleles
Alternative forms of the same gene. Eg….Eg…. Gene for hair texture (curly? Straight?)Gene for hair texture (curly? Straight?) One form of the hair texture gene codes One form of the hair texture gene codes
for curly hair. A different code for of for curly hair. A different code for of the the same genesame gene makes hair straight. makes hair straight.
= So the gene for hair texture exists as = So the gene for hair texture exists as two alleles --- one curly code, and one two alleles --- one curly code, and one straight code. straight code.
tall stem x short stem = (F1) ALL tall stem x short stem = (F1) ALL TALLTALL
yellow seeds x green seeds = (F1) yellow seeds x green seeds = (F1) ALL YELLOWALL YELLOW
round seeds x wrinkled seeds = round seeds x wrinkled seeds = (F1)ALL ROUND(F1)ALL ROUND
Monohybrid crossMonohybrid cross
Punnet squarePunnet square
Conclusion of Exp 1Conclusion of Exp 1
phenotypes of the offspring resembled only one phenotypes of the offspring resembled only one of the parent plants. of the parent plants.
alleles compete randomly for expression in the alleles compete randomly for expression in the offspring depending on Dom/Rec statusoffspring depending on Dom/Rec status
F1 = T x tt = All Tt . the tall factor seems to F1 = T x tt = All Tt . the tall factor seems to DOMINATE the short factor". DOMINATE the short factor".
F2 = The trait not shown in the F1 reappeared in F2 = The trait not shown in the F1 reappeared in the F2 in about 25% of the offspringthe F2 in about 25% of the offspring
Different offspringDifferent offspring of the same parents have of the same parents have different sets of hereditary informationdifferent sets of hereditary information
Mendels LawMendels LawThe Law of Segregation The Law of Segregation
pair of alleles of each pair of alleles of each parent separate and parent separate and only one allele passes only one allele passes from each parent on from each parent on to an offspring. to an offspring.
Which allele in a Which allele in a parent's pair of alleles parent's pair of alleles is inherited is a matter is inherited is a matter of chance. of chance.
segregation of alleles segregation of alleles occurs during the occurs during the process of sex cell process of sex cell formation = MEIOSISformation = MEIOSIS
Mendel's Law of Independent AssortmentMendel's Law of Independent Assortment
Alleles for Alleles for differentdifferent traits are distributed to sex traits are distributed to sex cells (& offspring) independently of one another. cells (& offspring) independently of one another.
Conseq ; new combinations of genes present in Conseq ; new combinations of genes present in neither parent are possible. neither parent are possible.
Eg:Eg:
two two differentdifferent traits: traits: (1) seed texture (round or wrinkled) & (1) seed texture (round or wrinkled) & (2) pod color (green or yellow). (2) pod color (green or yellow).
The The differentdifferent traits do not influence the inheritance of each other. They traits do not influence the inheritance of each other. They are inherited INDEPENDENTLYare inherited INDEPENDENTLY
Yellow round, green wrinkled vs Yellow wrinkled, green roundYellow round, green wrinkled vs Yellow wrinkled, green round
where where "G" = dominant allele for yellow pods "G" = dominant allele for yellow pods "g" = recessive allele for green pods "g" = recessive allele for green pods
““W" = dominant allele for round seeds W" = dominant allele for round seeds “w" = recessive allele for wrinkled seeds “w" = recessive allele for wrinkled seeds ..
GGWW x ggww vs GGww x ggWWGGWW x ggww vs GGww x ggWW
Dihybrid crossDihybrid cross
9:3:3:19:3:3:1
Eg. 2Eg. 2
Purple round, White wrinkled Purple round, White wrinkled vs vs
Purple wrinkled, white roundPurple wrinkled, white round
Purple dominant (P),Purple dominant (P),
Round dominant (W), Round dominant (W),
Eg. 3Eg. 3
Red Tall x White short vs Red Tall x White short vs
Red short, White TallRed short, White Tall
Red dominant (R), Red dominant (R),
Tall dominant (T) Tall dominant (T)
PPWW x ppww vs PPww x ppWWPPWW x ppww vs PPww x ppWW
RRTT x rrtt vs RRtt x rrTTRRTT x rrtt vs RRtt x rrTT
SummarySummary
11stst Law = Dominance Law = DominanceParent TT x tt (tall x short)Parent TT x tt (tall x short)Offspring = All tallOffspring = All tall
22ndnd Law = Segregation Law = Segregation
Parent = Tt x Tt (tall x tall)Parent = Tt x Tt (tall x tall)
Offspring = 75% tall 25% short Offspring = 75% tall 25% short
33rdrd Law = Independent assortment. Law = Independent assortment.2 traits2 traitsParent = GgWw x GgWwParent = GgWw x GgWwOffspring Offspring 9/16 yellow pods & round seeds 9/16 yellow pods & round seeds
3/16 green pods & round seeds 3/16 green pods & round seeds 3/16 yellow pods & wrinkled seeds 3/16 yellow pods & wrinkled seeds 1/16 green pods & wrinkled seeds &1/16 green pods & wrinkled seeds &