bio chp 16 notes - Chp16:Mendel,Genes&Inheritance 03:39...

This preview shows page 1 - 5 out of 12 pages.

Chp 16: Mendel, Genes, & Inheritance 03:39 Blending Theory of Inheritance - Popular belief until about 1900 Hereditary traits blend evenly in offspring through mixing of parents’ blood - Does not explain some observations: Extremes do not gradually disappear Offspring sometimes have different traits than either parent Are any human traits determined by a single gene? - Heredity The passing of characteristics from parent to offspring through their genes Traits that are determined by the instructions a person carries at one gene are called single-gene traits . Pea Experiments - Garden pea ( Pisum sativum ) - Easy to grow - Clearly defined characteristics or traits (shape and color) - True-breeding varieties Self-fertilized plants (same trait each generation) - Easy to cross Cross-pollination between parents
Flower Color Cross - P generation Purple flowers crossed with white flowers - F 1 generation All F 1 seeds formed purple flowers Purple flower offspring crossed - F 2 generation Purple flowers (75%) White flowers reappeared (25%) Mendel’s First Hypothesis - Genes for genetic characters occur in pairs One gene inherited from each parent Alleles are different versions of a gene - Diploid : two copies of each gene Mendel’s Second Hypothesis - If two alleles of a gene are different, one allele is dominant over the other Dominant allele is expressed Recessive allele is masked
- Recessive alleles only expressed when two copies of the allele are present * Mendel is considered the founder of genetics. Phenotypes and Genotypes - The outward appearance of an individual is called their phenotype . - The genetic constitution of an organism is called their genotype . Test-Cross - A test-cross enables us to figure out which alleles an individual carries. - Determines if an individual with a dominant phenotype is a heterozygote or homozygote. - In a test-cross, an individual with a dominant phenotype and an unknown genotype is mated with a homozygous recessive individual. - The phenotypes of the offspring reveal the unknown genotype. Punnett Square - Used to determine relative proportions of genotypes and phenotypes Mendel’s Third Hypothesis - Two alleles of a gene segregate (separate) and enter gametes singly Half of the gametes carry one allele, half carry the other allele ( haploid ) Principle of Segregation
-

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture