Chapter 10 Patterns of Inheritance

Nature vs. Nurture Some genetic traits are very obviously controlled by simple dominant/recessive patterns Others have a genetic influence, but you can’t necessarily tell what’s going to happen just by knowing the person’s genes ◦ Obesity ◦ Cancer risks ◦ Height

Mendel’s Laws Gregor Mendel ◦ Austrian monk ◦ 1860’s ◦ Crosses between pea plants ◦ Wasn’t the first or last person to keep track of inherited traits ◦ Was the first one to figure out some important concepts  Careful, methodical, good record keeping  Also—lucky

Setting up Mendel’s experiments Preliminary experiments ◦ He didn’t just choose peas randomly, or the traits within the peas Why peas? ◦ Easy to cultivate (grow) ◦ Short generation time ◦ Normally self-pollinate, can be pollinated by hand ◦ Many varieties (22) ◦ True-breeding lines available

What did he figure out? The “particulate theory of inheritance” ◦ He didn’t have the word “gene” in his vocabulary ◦ Said there were miniscule particles that conserved the trait and passed it from one generation to the next

Mendel’s Results Can be shown in a Punnett square ◦ But Mendel didn’t use these squares ◦ They were developed later by Reginald Punnett Crossing two pure-breeding parents  all offspring being like one parent Let those offspring self-pollinate  3:1 ratio of original parent phenotypes

Testcross Crossing a dominant individual with a questionable pure-bred status with a recessive individual ◦ If dominant individual is pure-bred, all offspring should show dominant phenotype ◦ If dominant individual is heterozygous/hybrid, offspring should be ½ dominant and ½ recessive

Two Laws Law of Segregation ◦ Inherited “particles” come in pairs ◦ Gametes only have ½ of each pair Law of Independent Assortment ◦ Each set of “particles” is inherited independently of one another ◦ Ex: flower color had nothing to do/no bearing on seed color

Modern View “Particles” = genes Dominant & recessive Genotype & phenotype ◦ Homozygous & heterozygous Segregation ◦ Due to homologous chromosomes separating in meiosis Independent Assortment ◦ Due to genes being on separate chromosomes or far apart on same chromosome

Rule of Multiplication The chance of 2 or more independent events occurring together = the product of their individual chances Can use this idea for as many traits together as you need to Easier than enormous Punnett squares

Beyond Mendel’s Observations Incomplete Dominance Multiple alleles Polygenic inheritance Effect of environment Pleiotropy Sex-linked Linked genes