10.1 Curiosity about Inheritance The “Blending” Hypothesis –E–Early 1800s thought… If you mix red + yellow = orange Same idea for hereditary information? BUT?! –H–How do you explain getting “reds” and “yellows” –S–Second generation offspring not all orange *Did not explain how traits that disappear in one generation can reappear in later ones!
Gregor Mendel First to apply an experimental approach to inheritance questions Gregor’s experiment –7–7 years bred pea plants and recorded inheritance patterns of offspring Formed the Particulate Hypothesis –P–Parents pass on to their offspring separate and distinct factors (?) that are responsible for inherited traits
Mendel ’ s Experiment 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 –W–W–W–What colors were in the next generation?
10.2 Inheritance ’ s Rules of Chance Terminology: –P–Parents = P PP P generation –H–Hybrid offspring = F FF F1 generation Offspring of 2 different true-breeding varieties are “hybrids” –F–F1 plants self-fertilize or fertilize each other their offspring = F FF F2 generation
Inheritance ’ s Rules of Chance Monohybrid Cross ( (( (he did this w/o calling it this) –1–1 trait (color) Each produced same pattern Mendel Saw 1 of the 2 traits disappears in F1 and then reappeared in ¼ of F2 Caused Mendel to form 4 hypotheses…
Mendel ’ s Hypotheses 1. Alternating forms of genes called alleles1. Alternating forms of genes called alleles Genotype = letters (AA, Aa, aa) Phenotype = observe (purple, white)
Mendel ’ s Hypotheses 2. For each trait organism has 2 alleles –Same 2 alleles = homozygous (AA, aa) –Different alleles = heterozygous (Aa)
Mendel ’ s Hypotheses 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 Hypotheses
Monohybrid crosses P = Purple (dominant) p = white (recessive)
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 R RR RR RR R RRRRRRRR RrRrRrRr RrRrRrRr R R R r If R= Hairy r = smooth What will the offspring look like? (phenotype) What are the genotypes?
Cross H. Recessive X Heterozygous If R= Hairy r = smooth What will the offspring look like? (phenotype) What are the genotypes?
Cross Heterozygous X Heterozygous If R= Hairy r = smooth What will the offspring look like? (phenotype) What are the genotypes?
Cross H. Dominant X H. Recessive If R= Hairy r = 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
If BB, then: Bb B B bbbb X Bbbb Bbbb B b bbbb If Bb, then All black eyes 50%
Test Cross If the unknown individual is Homozygous dominant all the offspring will show the dominant characteristic Bb B B bbbb 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. Bbbb Bbbb B b bbbb X Bb X bb 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?
Cross a Hetero for tall with Hetero for Tall T = tall t = short Tt X Tt
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???
Dihybrid Crosses Crossing individuals differing in 2 characteristics
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
tt R r T t r r Janet’s Genotype Alic’s Genoty pe
Key to Punnett Squares LABEL EVERYTHING –CHECK YOUR RATIOS
Homozygous Dominant = AA Heterozygous = Aa Homozygous Recessive = aa Letters = genotype (AA, Aa, aa) What you see = phenotype ( color, height)