Transcript Chapter 4-1
Chapter 4-1 Mendel’s Work 1 Some Important Terms 2 Heredity – the passing of physical characteristics from parents to offspring Trait – a characteristic that an organism can pass on to its offspring through its genes Genetics – the scientific study of heredity Gregor Mendel 3 Priest and gardener at a monastery in Europe Mid-1800s Worked with pea plants Mendel’s Experiments Crossing Pea Plants Began by crossing plants with contrasting traits 4 Example: tall and short plants Used purebred plants 5 F1 Offspring F1 = first filial (son/daughter) generation The offspring of a cross of purebred tall and purebred short plants 6 Parent plants are called P generation All offspring in F1 were tall, despite 1 parent being short F2 Offspring F2 = second filial Plants from F1 were bred Offspring were a mixture of tall and short plants ¾ were tall; 7 ¼ were short 8 9 Experiments with other traits Mendel also did experiments with other contrasting traits In all crosses, only 1 form of the trait appeared in the F1 However, in F2, the “lost” trait always reappeared in ¼ of the plants 10 11 Dominant and Recessive Mendel reasoned that individual factors, or sets of genetic “information” must control the inheritance of traits in the peas These factors exist in pairs 12 Female gives 1 part of pair Male gives 1 part of pair A factor can “mask” or “cover” another factor Genes and Alleles Gene – factors that control a trait Alleles – different forms of the gene • Example: in the gene that controls height, there is an allele for tall and short • Each plant inherits 2 alleles; one from the mother and one from the father 13 An organism’s traits are controlled by the alleles it inherits Some are dominant; others recessive Dominant – trait always shows up Recessive – hidden whenever dominant is present 14 This trait will only show up if the organism doesn’t have the dominant Alleles in Mendel’s work P generation – tall had 2 dominant, short had 2 recessive F1 generation – all plants had 1 of each F1 all hybrids 15 Hybrid – organism that has 2 different alleles for a trait F2 generation – ¾ dominant and ¼ recessive Symbols for Alleles 16 Geneticists use letters to represent alleles Dominant alleles are capital letters (ex: T) Recessive alleles are lowercase (ex: t)