Patterns of Inheritance Ch

Objectives 1.Mendel’s methods 2.Explain the principal of segregation 3.Genotype vs. Phenotype 4.Principal of independent assortment

Who is this guy? Any guesses?

Mendel struggled with many questions, such as: How do offspring receive the traits that they have? Why do some offspring look more like parents than others? Why may later generations look more like grandparents than parents? This all has to do with traits. What’s a trait? Trait: –Variation of a character i.e., plant color; red vs. white Gregor Mendel

Blending Hypothesis Early 1800’s Used to explain how offspring inherit characteristics from parents Red plant with yellow plant --> orange plant This wasn’t always so Mendel decided to experiment... his work gave rise to... genetics: –The study of heredity.

Plant Breeding Experiments Bred pea plants for seven years Developed a particulate hypothesis of inheritance: –Parents pass on genes that are responsible for inherited traits –Genes retain their identity generation after generation –Genes are like marbles of different colors, not like paints; meaning that genes retain their own identities Mendel’s Garden

Plant Breeding Experiments Identified true-breeding pea plants –All offspring identical every time Crossed true-breeding plants with different traits Purple pea plant fertilized with pollen from white pea plant: What color would the offspring be?

Mendel’s Principle of Segregation Hybrids: –offspring of two true- breeding varieties Monohybrid cross: –testing ONE trait in a cross (i.e., flower color) What did Mendel find? ?

Monohybrid Cross ALL plants in F 1 generation purple. Not a blend! Was the gene for white flowers now lost? Let F 1 (filial, greek for son) generation fertilize themselves Gene for white flowers was present. 1/4 of plants had white flowers!

Investigated 6 other traits and found the same thing: for each character, 1 of the 2 traits disappeared in F 1, and reappeared in F 2

Mendel’s 4 Hypotheses 1.Alternative forms of genes (alleles) 2.Each gene has 2 alleles  One from each parent  Homozygous: same (PP)  Heterozygous: different (Pp) 3.Dominant vs. Recessive alleles  Allele affects trait --> dominant (P);  Alleles with no affect in a heterozygous individual are recessive (p). 4.The 2 alleles for a trait separate during meiosis (Principal of Segregation) and reunite during fertilization.

Genotype vs. Phenotype Genotype: –The genetic makeup –i.e., Pp Phenotype: –Observable trait –i.e, purple flowers

What’s your genotype/phenotyp e worksheet

Check your neighbor See if you can remember what Mendel’s 4 hypotheses are? Use your own words if possible. 1.Alternative forms of genes (alleles) 2.Each gene has 2 alleles 3.Dominant vs. Recessive alleles  Allele affects trait --> dominant (P);  Alleles with no affect in a heterozygous individual are recessive (p). 4.The 2 alleles for a trait separate during meiosis (Principal of Segregation) and reunite during fertilization.

Probability Through Punnett Squares Punnett Square: –Shows possible genetic outcomes Each individual square is an individual offspring Each individual receives ONE allele from each parent What’s the probability that offspring will be purple for match #1? #2?

Testcross What is the genotype of an organism that displays a dominant phenotype? Cross of a plant with an unknown genotype (PP or Pp) with a homozygous recessive individual, will yield one of two possible results: –pp x PP = 100% (Pp) –pp x Pp = 50% (pp) : 50% (Pp) Do you see how this works?

Independent Assortment Dihybrid cross: –crossing organisms differing in two characteristics Principle of Independent Assortment: A particular allele in one character can be paired with either allele of another –R can end up with y or Y and r can end up with Y or y –Just because the seed is yellow, does NOT mean it will be wrinkled.

Punnett Square Worksheet Let’s try a worksheet and see if you understand...