Heredity Heredity
Dec 31, 2015
10.1 Curiosity about 10.1 Curiosity about InheritanceInheritance
• The “Blending” Hypothesis– Early 1800s thought…
• If you mix red + yellow = orange • Same idea for hereditary information?Same idea for hereditary information?
•BUT?!– How do you explain getting “reds” and
“yellows”– Second generation offspring not all orange
*Did not explain how traits that *Did not explain how traits that disappear in one generation can disappear in one generation can reappear in later ones!reappear in later ones!
Gregor MendelGregor Mendel• First to apply an experimental
approach to inheritance questions• Gregor’s experimentGregor’s experiment
– 7 years bred pea plants and recorded inheritance patterns of offspring
• Formed the Particulate Hypothesis – Parents pass on to their offspring separate and distinct
factors (?) that are responsible for inherited traits
Mendel’s Mendel’s ExperimentExperiment
• 1- Identify true-breeding plants• White plants ONLY Purple plants ONLY
• 2-Cross 2 different true-breeding plants• 3- Those offspring become parents for
next generation breeding (cross fertilization)
• 4- Observed the patterns of inheritance– What colors were in the next generation?What colors were in the next generation?
10.2 Inheritance’s Rules of Chance
Terminology:Terminology:
– Parents = PP generation
– Hybrid offspring = F1F1 generation•Offspring of 2 different true-breeding
varieties are “hybrids”
– F1 plants self-fertilize or fertilize each
other their offspring = F2F2 generation
Inheritance’s Rules of Inheritance’s Rules of ChanceChance
• Monohybrid Cross (he did this w/o calling it this)(he did this w/o calling it this)
– 1 trait (color)• Each produced same pattern
• Mendel SawMendel Saw 1 of the 2 traits disappears in F1 and then 1 of the 2 traits disappears in F1 and then
reappeared in ¼ of F2reappeared in ¼ of F2
Caused Mendel to form 4 hypotheses…Caused Mendel to form 4 hypotheses…
Mendel’s Mendel’s HypothesesHypotheses
• 1. Alternating forms of genes called alleles1. Alternating forms of genes called alleles
Genotype = letters (AA, Aa, aa)
Phenotype = observe (purple, white)
Mendel’s Mendel’s HypothesesHypotheses
2. For each trait organism has 2 alleles– Same 2 alleles = homozygous (AA, aa)– Different alleles = heterozygous (Aa)
Mendel’s Mendel’s HypothesesHypotheses
3. When only 1 of the 2 traits in a heterozygous organisms is visible the allele is dominant (R) the non visible is recessive (r)
4. The 2 alleles for a character separate during meiosis (gametes) Principle of segregation!!
Mendel’s HypothesesMendel’s Hypotheses
Punnett Squares
• Calculate probabilities/outcomes of a genetic cross– Genotype genetic makeup– Phenotype observable trait
• Manipulate genotypes that then show the phenotypes– Phenotypic ration 3:1– Genotypic ratio 1PP: 2Pp: 1pp
Cross H. Dominant X Heterozygous
RR X Rr
RR RR RRRR
RRrr RRrr
R
R
R
r
If If
R= Hairy R= Hairy
r = smoothr = smooth
What will the offspring look like? (phenotype)
What are the genotypes?
Cross H. Recessive X Heterozygous
If If
R= Hairy R= Hairy
r = smoothr = smooth
What will the offspring look like? (phenotype)
What are the genotypes?
Cross Heterozygous X Heterozygous
If If
R= Hairy R= Hairy
r = smoothr = smooth
What will the offspring look like? (phenotype)
What are the genotypes?
Cross H. Dominant X H. Recessive
If If
R= Hairy R= Hairy
r = smoothr = smooth
What will the offspring look like? (phenotype)
What are the genotypes?
Question
If Delani has brown eyes and Mihir has brown eyes what
are their genotypes?
A = brown and a = blue
Test Cross• Possible genotype for
– Purple PP Pp
– White pp
How do you know if you have PP or Pp?
– Test Cross!!!!
– Cross your unknown with homozygous recessive
Testcross
When an individual with a dominant phenotype whose genotype is
unknown breeds with a homozygous recessive individual.
BB or Bb? bb
X
Test Cross
• If the unknown individual is Homozygous dominant all the offspring will show the dominant characteristic
Bb Bb
Bb Bb
B B
b
b
X
All black eyes
BB X bb
Test Cross
• If the unknown individual is heterozygous dominant half the offspring will show the dominant characteristic and half will show the recessive characteristic.
Bb bb
Bb bb
B b
b
b
X
Bb X bb
50% 50%
Questions
• Otis Oompah has an orange face and is married to Ona Oompah who has a blue face. They have 60 children, 31 of them have orange faces. What are the genotypes of the parents.
• Oompahs generally have a blue face which is caused by a dominant gene. The recessive condition results in an orange face.
• A blue faced Oompah (homozygous) is married to an orange faced Oompah. How many children will have blue faces?
In fat orange cats being striped is dominant to being solid orange.
What could you do to determine if Garfield is heterozygous or homozygous for his strips if you did not know???
Sample DiHybrid
Janet has a homozygous recessive short, heterozygous seeded plant. Alice has a heterozygous for height, homozygous recessive wrinkled-seeded plant. If
they were to breed their plants together what would be the outcome of the offspring? What are the offspring genotypes, phenotypes and ratios?
(T=tall, t=short
R=rounded seed, r = wrinkled seed)
Janet : ttRr
Alice: Ttrr starting genotypes