what made mendel successful? 3 key points to any successful biological experiment:
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What made Mendel successful? 3 key points to any successful biological experiment: Choosing the appropriate organism to study Designing and performing the experiment correctly Analyzing the data properly. What organism did he study??? Pisum sativum – The common pea plant Why the pea plant? - PowerPoint PPT PresentationTRANSCRIPT
Recall: several hypotheses about inheritanceWhat made Mendel successful?3 key points to any successful biological
experiment:1. Choosing the appropriate organism to study2. Designing and performing the experiment correctly3. Analyzing the data properly
What organism did he study???
Pisum sativum – The common pea plant
Why the pea plant?1. Commercially available across Europe2. Easy to grow and matured quickly3. Sexual organs entirely enclosed in flower
(self-pollinate) Control which plants reproduced
4. Different traits could be observed easily
To setup his experiment, Mendel obtained purebreed plants Purebreed – decended from ancestors of a distinct type
or breed Ie. All tall vs. All short plants
Thus, Mendel produced plants that were true breeding – only producing offspring that grew either tall or short
Mendel repeated this several times for 7 different traits:
- Stem length, flower position, seed shape, seed colour, pod shape, pod colour, flower colour
Mendel’s First Experiment: Monohybrid Crosses
P generation (parent generation) Crossed a true-breeding TALL pea plant with a true-
breeding SHORT pea plant
The offspring were the 1st filial generation (F1 generation) This generation consisted of hybrid plants since they
were the result of a cross between 2 purebred plants Monohybrid cross when only 1 trait is involved
Discussion: What trait did the F1 generation
demonstrate?Tall or short or medium?...or
something we’ve never even heard about?
Mendel concluded that the “TALL” trait is dominant and the “SHORT” trait is recessive
Dominant trait – characteristic that is always expressed in an individual
Recessive trait – characteristic that is latent and therefore not usually expressed in an individual
***May be expressed if it is the only trait present
He did this several times using true breeding plants for 7 traits that he chose to study
Stem length Flower position Seed shape Seed colour Pod shape Pod colour Flower colour
Every time: one trait was always dominant over the other
Therefore...Mendel formulatedthe Principle of Dominance:When individuals with contrastingtraits are crossed, the offspring will express only the dominant trait.
Law of Segregation
Next step:Breeding the F1 generationOffspring was the 2nd filial generation (F2
generation)
Discussion:What trait did the offspring of the F2
generation express?
Answer:3 out of 4 plants in the F2 generation were tall and 1 was short
The same result occurred with all 7 traits
75% of the time – expressed dominant 25% of the time – expressed recessive
3:1 ratio = Mendelian ratio
Mendel’s Law of Segregation
Thus, Mendel drew the following conclusions:In the F1 generation, each parent starts with
2 heredity “factors” – one dominant, one recessive
The factors segregate and only one factor from each parent is given to the F2 generation offspring; therefore, the offspring has 1 factor from each parent
If the dominant factor is present it will be expressed (even if the recessive factor is also present)
The recessive factor will only be expressed if only recessive factors are present
Modern day’s terminology:“factors” = genesGenes have:
Dominant alleles Recessive alleles
*Note: When a dominant and recessive allele are together, the dominant allele will be expressed but the recessive allele is still there and still can be passed onto the next generation
Homozygous vs. Heterozygous
HOMOZYGOUS: the alleles are the sameHETEROZYGOUS: alleles are different
Ex. Trait: Tall and shortT = tall t = shortTT = homozygous dominant talltt = homozygous recessive short Tt / tT = heterozygous dominant tall
(Demonstrate generations on board)
Punnett Squares
Used to calculate probability of inheriting a particular trait.
Allows you to determine the: Genotype: the genetic make-up behind a trait Phenotype: The actual physical appearance of the
trait
T
t
t
T
Example:Applying Mendel’s first law: a monohybrid cross
Problem: A plant grown purebred homozygous tall seed crossed with a homozygous short seed
a) Show the possible gametes from each parent (possible offspring)
b) Show the possible gamete combinations at fertilization
c) What are the possible genotypes of F1d) What are the possible phenotypes of F1
Example 2:
Problem: A plant grown from heterozygous round seeds is crossed with a plant grown from wrinkled seeds (Let R = dominant round, r = recessive wrinkled)
a) Show the possible gametes produced from each parent
b) Show the possible gamete combinationsc) What are the possible genotypes?d) What are the possible phenotypes?
Example 3:
In sheep, the allele for white wool (W) is dominant over the allele for black wool (w). If two white sheep mated,
a) What are the possible genotypes of the two parent?
b) What is the probability that an offspring of the two white sheep will be black? (Create Punnet squares for each possible parent combinations)
Pedigrees
How can we apply this to us?Pedigrees are diagrams that illustrate the
genetic relationships among a group of related individuals
It organizes medical, historical, and family records extending across several generations
Pedigrees been able to show simple dominant traits (only 2 possibilities – dominant, recessive) Ie. Widow’s peak, tongue-rolling, freckles, long
eyelashes, unattached ear lobes, etc