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Transcript
Mendelian Genetics Mendel & His Pea Plants Genetics – the study of heredity Heredity – how traits are passed from parent to offspring A man by the name of Gregor Mendel was curious as to how traits were passed from parent to child. – He did his own mathematical experiments with pea plants. – For all of his work, he is known as the “Father of Genetics.” Mendel & His Pea Plants Mendel decided to use pea plants for the following reasons: – The plants were small – They were easy to grow – They were inexpensive – They produced a lot of offspring in a short time Mendel & His Pea Plants He also liked to use pea plants because they were easy to pollinate. A single plant had both male and female parts on the same flower. – The stamen is the male part (holds sperm) – The pistil is the female part (holds eggs) Mendel studied 7 traits Mendel’s Experiments First, Mendel created a Parental (P) Generation of tall & short purebred plants. – Purebreds will only produce offspring like themselves. – Tall purebred plants only produce tall offspring. – Short purebred plants only produce short offspring. Mendel’s Experiments Step 1: Mendel crossed a purebred tall plant with a purebred short plant by cross pollination. This meant dusting the pollen of one flower onto the pistil of a different flower. – All the offspring came out TALL! – He called this generation the F1 generation. – Mendel was thoroughly confused. – Shortness had somehow disappeared! Mendel’s Experiments Step 2: Mendel crossed two of the tall plants from the F1 generation by self pollination. This meant dusting the pollen of one flower onto the pistil of the same flower. – ¾ of the plants were Tall and ¼ were Short! – He called this generation the F2 generation. – Mendel was now thoroughly frustrated. – Shortness had reappeared! Let’s Recap P F1 Step 1 ? = All Tall! F2 Step 2 ? = ¾ Tall & ¼ Short! Mendel’s Conclusion Mendel concluded that parents pass traits to their offspring via things called “factors”. – We now know that the factors Mendel was talking about are called genes. – Genes are pieces of your DNA. – Genes control all your traits. Mendel’s Conclusion Mendel also concluded that there are different forms of the same gene. – Different forms of a gene are called alleles – Everyone has 2 alleles for a single gene – One allele comes from mom, one from dad Learning Terminology Dominant allele – The allele that always shows when present – Represented by a Capital letter – THINK! – What allele can we use to represent Tallness? T Recessive allele – The allele that is masked by the dominant one – Only shows up if the dominant allele is NOT present – Represented by a Lower-case letter of the dominant trait – THINK! – What allele can we use to represent shortness? t Homozygous for a trait – 2 of the same alleles for a gene Heterozygous for a trait – 2 different alleles for a gene Learning Terminology Phenotype – What an organism looks like; physical appearance – THINK! – What do the following organisms look like? • TT = Tall • Tt = Tall • tt = Short Genotype – The 2 alleles an organism possesses – Think of it as the combination of letters – THINK! – What are the genotypes for the following: • Tall = TT or Tt • Short = tt Let’s Recap: Write the Genotypes P F1 TT tt Tt Tt Tt Tt F2 Tt Tt TT Tt Tt tt