Transcript History
History of Genetics Biology Genetics • How characteristics are transmitted from parents to offspring Gregor Mendel Gregor Mendel (1822-1884) • worked with Pisum satium (pea plant) Mendel studied 7 characteristics • Flower color • Flower position along stem • Seed color • Seed shape • Pod shape • Pod color • Stem length Mendel’s Experiments Mendel’s First Cross • Crossed “purebred” purple with “purebred” white + P (parent) generation - F1 – purple • Crossed F1 hybrids + produced F2 generation - 3 purple : 1 white Mendel’s Ideas of Inheritance • Alternative versions of genes (alleles) account for variations in inherited characters. + each gene resides at a particular location of a chromosome and can exist in variable forms (two different forms for flower color) P Pp p Mendel’s Ideas of Inheritance • For each characteristic, an organism inherits two alleles, one from each parent. + an organism is either homozygous (two of the same alleles) or heterozygous (two different alleles) Homozygous Heterozygous Mendel’s Ideas of Inheritance • If the two alleles differ, the dominant allele is fully expressed and the recessive allele has no noticeable affect on appearance. + heterozygotes express the dominant trait RR rr Rr Mendel’s Law of Segregation • The two alleles for each character segregate during gamete production. + ovum/sperm get only one of the two alleles (haploid) P generation Phenotype: Purple/White Genotype: PP/pp F1 generation Phenotype: Purple Genotype: Pp F2 generation? Genotype/Phenotype can be predicted using a Punnet Square Mendel’s Law of Independent Assortment Each pair of alleles segregates into gametes independently. WH wh Wh wH Mendel’s Law of Independent Assortment Parental Genotypes Parental Gametes? GGWW ggww GW gw GgWw F1 Genotypes? F1 Gametes? GW Gw gW gw Beyond Mendel... Different Types of Inheritance: Complete Dominance Mendel’s Traits Incomplete Dominance Snapdragon Color Incomplete Dominance One allele does not dominant the other in the heterozygous condition. Both alleles are expressed but a new phenotype appears that is intermediate. RR Rr rr Codominance Both alleles in the Heterozygous condition are dominant. CC Cc cc Codominance & Multiple Alleles