Chapter 11 – Observable Patterns of Inheritance

11.1 Mendel’s Insight into Inheritance Patterns Monk in Austria -experimented with pea plants to see how genes are passed on to generation. -found that sperm and egg cells contain genetic information that play a part in the genes of the offspring. Gregor Mendel “Father of Genetics”

Terms to Know: Gene locus – location of a specific gene Allele – variations of a gene

Genes Units of information about specific traits. When identical alleles are passed on generation after generation this is called a true-breeding lineage. When offspring inherit a pair of non-identical alleles for a trait this is called a hybrid offspring.

Homozygous -when both alleles are identical (TT) Heterozygous -when alleles are not identical (Tt)

Genotype and Phenotype Genotype – genetic makeup of an individual. Phenotype – physical appearance of an individual. Observable traits.

Tracking Inheritance P = parental generation F1 = first-generation offspring F2 = second-generation offspring

11.2 Mendel’s Theory of Segregation Mendel tested the idea that a plant inherits two units (genes) of information about a trait. He performed a Monohybrid Cross -cross of two parents that are homozygous for different versions of a single trait. F1 offspring will be hybrid, heterozygous.

Monohybrid Cross P F1 F2 Tall x Dwarf Phenotype DD dd Genotype Homozygous Dominant Homozygous Recessive All Tall Clearly Tall is Inherited… What happened to Dwarf? F1 Dd Tall is dominant to tall. Heterozygous F1 x F1 = F2 possible gametes Punnett Square: D d 3/4 Tall 3:1 ratio 1/4 Dwarf F2 D Tall DD Tall Dd possible gametes d Tall Dd Dwarf dd Dwarf is not missing…just masked as “recessive” in a diploid state…

Probability The chance that an event will occur.

Punnett-square Method If half of a plant’s sperm or eggs were a and half were A, then four outcomes would be possible each time a sperm fertilized an egg. Not precise Possible event Probable outcome Sperm A meets egg A ¼ AA offspring Sperm A meets egg a ¼ Aa Sperm a meets egg A Sperm a meets egg a ¼ aa

Testcrosses Fertilizing different genotype plants to see results. Test results may reveal whether the organism is homozygous dominant or heterozygous.

Segregation Diploid cells have pairs of genes, on pairs of homologous chromosomes. The two genes of each pair are separated from each other during meiosis, so they end up in different gametes. They do not effect eachother.

11.3 Independent Assortment Dihybrid Crosses – crossing two traits. Mendel crosses pea plants with two pairs of genes that were homozygous. 9:3:3:1 ratio