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Chapter 10

Chapter 10 notes (Mendelian and inheritance).docx

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Biology 1201A
Richard Gardiner

Biology: Exploring the Diversity of Life Chapter 10: Mendelian Genetics (PAGES 181-182, 191-203) Concepts of Heredity - During 1700’s Anton van Leeuwenhoek saw “animalcules” in sperm of humans and animals - Some scientists speculated they saw little man in each sperm - Pangenesis – males and females formed “pangenes” in every organ  These pangenes then moved through their blood to the genitals and then to children  The terms “blood relative”, “full-blooded” and “royal blood” - Until 1900, scientists believed in the blending theory of inheritance  Suggests that hereditary traits blend evenly though the mixing of the parents’ blood  Assuming that traits of children appear halfway between those of their parents  Gregory Mendel  An Augustinian monk who lived in a monastery in the Czech republic  Experimented with garden peas preformed in the 1860s o Why peas?  Peas worked better  Peas had 7 traits that gave results Mendel could understand (Rule of good science: work with what you know)  Normally pee plants self-fertilize  Male gametes are sperm nuclei contained in the pollen and produced in the anther  Female gametes are eggs cells produced in the carpel  Mendel prevented self-fertilization by cutting off anthers, so they had to receive pollen from another plant (called cross-pollination)  He studied a variety of heritable characteristics called characters such as flower color or seed shape o A variation in character, such as a purple of white flower is called a trait  Mendel’s Methods  In a typical breeding experiment, Mendel would cross-pollinate (hybridize – mating or crossing two varieties) two contrasting, true-breeding pea varieties.  The true-breeding parents are the P generation and their hybrid offspring are the F1 generation.  Mendel would then allow the F1 hybrids to self-pollinate to produce an F2 Generation. o It was mainly Mendel’s quantitative analysis of F2 plants that revealed the two fundamental principles of heredity: the law of segregation and the law of independent assortment.  Law of segregation  The pairs of alleles that control a character segregate (separate) as gametes are formed  Half the gametes carry one allele and the other half carry the other allele  Law of independent Assortment  Stating that for every pair of unit factors (alleles), each of them would assort independently into the newly formed gametes. o Monohybrid cross – cross that tracks the inheritance of a single character (parents differ by one pair of alleles) o Alleles – alternate versions of a gene o Dominant allele – fully expressed allele (Upper case) o Recessive allele – allele showing no noticeable effect (Lower case) o Phenotype – an organisms expressed visible traits o Genotype – an organisms genetic makeup  Summary of Mendel`s Efforts o Adult ( 2N ) traits involve 2 alleles o Alleles segregate in gametes (1N) {no blending of traits} o Each gamete contains only one allele  LAW OF SEGREGATION o Dominant alleles mask the expression of recessive alleles in heterozygotes (two different alleles) o True-breeding adults have identical alleles – homozygous (Two identical alleles)  Mendels Cross  It is not possible to predict the genotype of an organism with a dominant phenotype.  The organism must have one dominant allele, but it could be homozygous dominant or heterozygous. Tests cross, breeding a homozygous recessive with dominant phenotype, but unknown genotype, can determine the identity of the unknown allele. In one dihybrid cross experiment, Mendel studied the inheritance of seed color and seed shape. - The allele for yellow seeds (Y) is dominant to the allele for green seeds (y). - The allele for round seeds (R) is dominant to the allele for wrinkled s
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