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BIOL 1500
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Biology Chapter 7 Notes: Mendelian Inheritance Gene Inheritance: Each human offspring inherits one maternal and paternal set of 23 chromosomes Heredity: the passing of characteristics from parents to offspring through their genes; some traits are controlled by a single gene (single trait genes); observing heredity is easy, understanding was difficult; breeding Mendel: what do parents give their offspring that confers similarity? • no obvious answer at that time (1800s) • applied and tried and true methodical experimentation and scientific thinking 1. Chose a good organism to study; garden pea; easy to take care of in large numbers; short time to breed; relatively easy to fertilize manually by pollen dusting; easy to collect hundreds of offspring from a single cross; conduct experiments that lasted for multiple generations 2. Focused on categorized traits; wrinkled or round shape of seed; yellow or green in colour 3. Began by repeatedly breeding together similar plants until he had many distinct populations (true-breeding); after his true-breeding plants, Mendel began a straightforward process of experimentation • purple-flower trait dominant; white-flower trait recessive 1. Parents put into every sperm or egg it makes a single set of instructions for building the trait (gene) 2. Offspring receive two copies of the instructions from any trait 3. Trait observed in an individual depends on the two copies of the gene it inherits from its parents Homozygous: individual inherits the same two alleles for this gene Heterozygous: individual inherits different allele from each parent Mendel's Law of Segregation: two copies of each individual's gene is contributed from the two sets of alleles from the mother and father Phenotype: visible or physical features / Genotype: genetic composition of the organism Unable to deduce an individual's genotype from observing the phenotypes Punnett Square: a tool to analyze and predict the outcome of a cross between two individuals • genes on same chromosomes are sometimes inherited together; red hair and freckles; sometimes alleles for two genes are inherited together and expressed almost as a package deal; some genes are close together on a chromosome called linked genes; during the production of gametes, the crossing of the parental/maternal genes end up interacting Probability and Chance Aa X aa = 0.5 x 1.0 = 0.5 of the recessive gene to be passed (albinism); Tt X Tt = 0.5 X 0.5 = 0.25 of recessive gene passed (Tay Sachs) Test Cross: test out the uncertainty between the genotypes of the organism; genes are invisible but their identity can be revealed by a test-cross; Albino X Non-albino will be test crossed to determine if the non-albino is a homozygous dominant or a heterozygous Pedigrees Square: Male Circle: Female Shaded: Trait of interest Blank: No trait of interest • used to decipher and pre
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