LIFESCI 4 Lecture Notes - Lecture 2: Phenotype, Allele, Heredity
Mendel s conclusions
From the experiments:
• Gene - determinant of heredity that affects certain characteristics (e.g. flower color)
• Allele - separate forms of a gene (purple vs red)
• Each individual has 2 copies of each gene
• Each sex cell has 1 copy of each gene
• Either of the two alleles goes with equal frequency into sex cell (and progeny)
• Sex cell union is random
Mendel s model explains data
• One parent is round, one parent is wrinkled
• Both have same gene (R gene) -> controls shape of pea
• Both plants have 2 copies of the gene (RR or rr)
• Sex cells only have 1 copy of gene (R or r)
• F1: Rr -> all round peas
• Genotype = genetic makeup
• Phenotype = appearance
• F2:
- Genotype ratio = RR:Rr:rr = 1:2:1
- Phenotype ratio = round : wrinkled = 3 : 1
Mendel’s 1st law
• MENDEL'S 1ST LAW: LAW OF SEGREGATION
1. Characters are determined by particulate factors
2. Factors exist in pairs in each organism. (e.g. Rr)
- One parent transmits one member of a pair toan offspring; therefore they
"segregate" (e.g. either R or r transmitted to offspring)
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Document Summary
Mendel"s 1st law: mendel"s 1st law: law of segregation, characters are determined by particulate factors, factors exist in pairs in each organism. (e. g. rr) One parent transmits one member of a pair to an offspring; therefore they. segregate (e. g. either r or r transmitted to offspring) A progeny gets one factor from its mother and one factor from its father and thus has a pair of factors: test cross (backcross): always to homozygous recessive. Mendel"s 2nd law: mendel"s 2nd law: law of independent assortment. Allele pairs separate independently during the formation of the gametes: dihybrid cross: Inheritance of r gene independent of inheritance of y gene. P (rr and yy occurring at the same time) + p(rr and yy at the same time) P(rryy) = 1/4 x 1/4 = 1/16, p(rryy) = 1/2 x 1/4 =1/8. P (rryy or rryy) = 1/16+1/8=3/16: clicker question.
