Bellwork: Design an experiment to determine whether pink flowers on petunia plants result from incomplete dominance

Other patterns of inheritance Section 11.3

Mendel’s work is not infallible Life is not always so simple Many genes have more than two alleles Many traits are controlled by more than one gene Incomplete dominance – some alleles are neither dominant or recessive Phenotype lies between two end members Example – flower color in some plants Codominance – Phenotypes from both alleles are expressed Possible to get black and white feathered chickens Seen in humans with proteins that control cholesterol

Multiple alleles Many genes exist in several forms and have multiple alleles A gene with more than 2 has multiple alleles Individuals still only have 2 copies of the genes Human blood type – great example (page 320)

Polygenic traits Many traits are produced by the interaction of several genes Polygenic = many genes Wide range of phenotypes Example – human skin colour

Genes and the environment Environmental conditions can effect gene expressions and influence genetically determined traits Phenotype is not just determined by genes Can you think of any examples in nature of how the environment can affect phenotype?

Meiosis Section 11.4

How many sets of genes are found in most adult organisms? Homologous – chromosomes from the male parent have a corresponding chromosome from the female parent Diploid (2n) – contains two complete sets of inherited chromosomes and two complete sets of genes Haploid (n)– only a single set of chromosomes, and a single set of genes Gametes are haploid How many chromosomes do humans have?

Phases of meiosis

Comparing mitosis to meiosis Mitosis – a form of asexual reproduction Daughter cells receive complete genetic copy Meiosis – early stage of sexual reproduction Alleles are segregated Chromosome number halved

Gene linkage Each chromosome is a group of linked genes Independent assortment holds true BUT chromosomes assort independently, not individual genes Mendel missed it, because by luck or design, several of the studied genes were on different chromosomes, or were far apart

Gene mapping The further apart genes are on a chromosome, the more likely crossing over will occur The closer together the less likely they are to cross over Possible to work out where exactly on the chromosome a gene is