Transcript Biology 105
Biology 105 Chapter 11: Principles of Heredity Pgs 237-261 Student Outcomes Describe Mendel’s principles of segregation and independent assortment Solve genetic problems involving monohybrid, dihybrid, and test crosses Use probability to predict outcomes of genetic crosses. Student Outcomes Define linkage and how it occurs in meiosis Describe the genetic determination of sex and the inheritance of X-linked genes in mammals Use methods other than dominance/recessive to explain genetic problems. Key Terms Heredity-the passing of genetic information from parent to offspring Genetics – the study of heredity Genetic variation – differences between parents and offspring or among individuals of a population. History of Genetics Mid 1800’s Gregor Mendel worked with pea plants and proposed the basic principles of genetics. This was unaccepted by many for several decades. However, in the early 1900’s, after science advancements, Mendel’s ideas gained momentum History of Genetics Burbank - in late 1800’s created over 800 new breeds of plants Thomas Morgan - fruit fly studies in 1908 Watson, Wilkins and Crick - DNA structure in 1953 History continued Genetics proceeded through the 1900’s with developments in crops (large yield, resistance to disease) In the 1990’s an exponential growth occurred with the location of several genetic diseases (cystic fibrosis) Has continued with the Human Genome Project (HGP) through the 21st century. More key terms Dominant-factor being expressed Recessive-factor being hidden (masked) Phenotype – physical appearance of an organism Genotype–genetic makeup of an organism Gene-factors determining a trait (30,000 for human) Allele-alternative forms of a gene Homozygous–having similar allele makeup (purebred) Heterozygous–having dissimilar allele makeup (hybrid) Locus-the location of a gene on a chromosome. Punnett square-chart used to predict outcomes Mendel’s principles • Principle of segregation • Before sexual reproduction occurs, the two alleles carried by an individual parent must separate. Each sex cell carries only one allele for each trait. Mendel’s principles Principle of independent assortment Gene pairs separate independent of each other Monohybrid Cross A single trait is studied (from one locus) Tall vs short TT, Tt, tt Test Cross will determine the parent genotype – test cross must be homozygous recessive. (tt) Dihybrid Cross Two traits located at two loci *TTEE, TtEe Linked Genes If different genes are located very close to each other on a chromosome, they may be ‘linked’ and inherited together. Sex Linked traits Found on Sex chromosomes (X, Y) Hemizygous - have only 1 chromosome so only 1 allele Sex Chromosomes X and Y XX - female XY- male X0?? XXY?? More than 1/2 of conceived babys are male - Why?? Dosage compensation When a single X chromosome has as much influence as two (XX) as in the female. Exceptions to the rule Incomplete dominance - blending of alleles (white and red flower color) Codominance- both are expressed Multiple Alleles - Three of more alleles code for a trait. Pleiotropy Ability of a single gene to have multiple effects. (CF) Polygenic inheritance Multiple gene pairs at different locations affect a trait Example skin color