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Introduction to Genetics Chapter 11 Slide 2 What is genetics? Genetics is the scientific study of heredity Slide 3 Mendels Work In the mid-1800s, an Austrian monk named Gregor Mendel studied how traits were passed from one generation to the next using pea plants His ideas form the foundation of the principles of heredity, known as Mendelian genetics Slide 4 Mendels Work Pea plants can produce purebreds (genetically identical offspring to the parent plant through self- pollination) Mendel did cross- pollination to interbreed the pea plants Slide 5 Mendels Work Mendel studied 7 traits (specific characteristics), such as seed color or plant height The parent generation is called the P generation The offspring from those parents are called the F 1 generation (first filial) Slide 6 Mendels F 1 crosses Slide 7 Mendels Conclusions 1.Biological inheritance is determined by factors (genes) that are passed from one generation to the next Each trait is controlled by one gene occurring in two contrasting forms the different forms of each gene are called alleles for example, the gene for plant height has alleles for both tall and short plants Slide 8 Mendels Conclusions 2. Some alleles are dominant and others are recessive if the dominant allele is present, that form of the trait will always be present the recessive trait will only show if there is no dominant allele Slide 9 Mendels F 2 Cross Mendel allowed the F 1 generation to self- pollinate Slide 10 Mendels F 2 Cross Alleles are segregated from each other so that each gamete (egg, sperm) carries only a single copy of each gene Slide 11 Probability The likelihood that an event will occur is called probability For example, coin flipping: - the probability of flipping heads is (50%) - the probability of flipping three heads in a row is x x = 1/8 (1 in 8 chance) Past outcomes do not affect future ones! Slide 12 Punnett Squares A Punnett square is a diagram to identify possible combinations of alleles in offspring when two parents are crossed Slide 13 Two types of alleles DOMINANT alleles are represented by CAPITAL letters ex: T is for tall recessive alleles are represented by lowercase letters ex: t is for short Slide 14 Which of the following alleles are DOMINANT? AtqRsAtqRs Which of the following alleles are recessive ? AtqRsAtqRs Which of the following alleles are DOMINANT? A tq R s Dominant or recessive? Which of the following alleles are recessive ? A tq R s Slide 15 Two types of alleles Each person has 2 alleles one from mom, one from dad homozygous means you have 2 of the same allele (either both dominant, TT, or both recessive, tt) also known as purebred heterozygous means you have 2 different alleles (one dominant, one recessive: Tt) also known as hybrid Slide 16 Homozygous or heterozygous? Label the following as homozygous (homoz) or heterozygous (heteroz): Hh BB rr Ss Tt qq HH Label the following as homozygous (homoz) or heterozygous (heteroz): Hh heteroz BB homoz rr homoz Ss heteroz Tt heteroz qq homoz HH homoz Slide 17 Genotype and phenotype A phenotype is the physical characteristic (what it looks like) ex: tall plants A genotype is the genetic make-up (the actual alleles) ex: TT or Tt Slide 18 Monohybrid Crosses single gene cross (each parent has one gene, each with two alleles) Slide 19 Monohybrid Crosses parents go along the top and side offspring shown in the middle 4 squares Slide 20 Monohybrid Crosses cross a homozygous tall plant with a homozygous short plant