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Genetics DNA Review Mutations: Sex vs Body Important Science Guy • Gregor Mendel – father of genetics, he worked with peas in a monastary Who was this Mendel and what the heck is he doing in a monastery? • born in 1822 • trained himself to be a naturalist early in life • worked as a substitute science teacher • failed the qualifying exams to be a regular high school teacher! • joined a monastery in Brunn, Austria • sent to Vienna U. to study science and math MendelWeb Mendel’s first published work: "Versuche über Pflanzen-Hybriden“ or Experiments in Plant Hybridization was a landmark in clarity and insight! Trained as a mathematician and a biologist, he figured out the laws of inheritance… mathematically!! The work of Gregor Mendel • worked with pea plants… …he called them his children! Why pea plants??? There was a long-standing tradition of breeding pea plants at the monastery where Mendel lived and worked So…they were readily available and they come in lots of varieties! …there were plants with different flower colors, seed color, flower position etc.. ‘Brother Greg... We grow tired of peas again!!!’ And best of all… Pea plants flowers can reproduce by themselves This allowed Mendel to see if strains were true breeding and to produce hybrids What the heck does that mean? • True-breeding: when plants self pollinate, all their offspring will be identical to themselves • Hybrid: when parents with different traits are crossed, this is what we call the offspring • SO – he could see if the plants would produce offspring identical to themselves and how parents with different traits would affect the offspring How Mendel made hybrids… He’d then tie little bags around the flowers to prevent contact with stray pollen. Mendel’s hybridization experiments… Monohybrid crosses: Parental Generation F1 generation True-breeding purple flower x True-breeding white flower All purple flowers (the hybrids) Allowed F1 offspring to self-fertilize F2 generation 705 purple 224 white The results of Mendel’s monohybrid crosses led him to propose… 1. All organisms contain two “units of heredity” for each trait (alleles). 2. Dominant and recessive alleles… …and organisms can have any combination of the two alleles (2 dominants, 2 recessives or a mixture 1 dominant and 1 recessive). •Alternative versions of genes (called alleles) account for the variations in inherited characteristics •For each character an organism inherits two alleles, one from each parent •If the two alleles differ, then one, the dominant allele, is fully expressed in the organism’s phenotype– the other (recessive) allele has no noticeable effect on the organism’s phenotype • The Law of Segregation – during gamete formation, these two alleles separate randomly into separate gametes, but each gamete gets one copy of each gene A bit of genetic jargon… phenotype vs. genotype What the organism looks like What alleles the organism has - its genetic makeup More jargon… • Genes are usually controlled by two alleles – expressed by two letters • These alleles may be dominant or recessive: – Dominant: allele that is expressed in the phenotype • Expressed as a capital letter (A) – Recessive: alleles that is completely masked in the phenotype • Expressed as a lower case letter (a) More jargon… homozygous vs. heterozygous P 2 of the same alleles: PP or pp 2 different alleles: p Pp Sometimes refer to heterozygous individuals as carriers because they carry both the recessive and dominant allele and can give either to their offspring, but only express the dominant allele A Punnett square… Gametes from one parent p P Gametes from other parent P PP purple p Pp purple Pp purple pp white Ratio: 3:1 or ¾ purple, ¼ white A Punnett square Let’s relate Mendel’s findings to what we now know about gamete formation True-breeding purple flower P all purple P P P P P True-breeding white flower x P p p p p p p p F1 generation purple hybrid P F2 p P purple hybrid p P P P x p P p P p p p P PP (purple) Pp (purple) Pp - purple pp - white p Law of Independent Assortment • States that each allele pair segregates independently during gamete formation • AKA: Alleles for different genes separate independently (alone) during meiosis when egg and sperm cells are being made – so alleles for seed color wouldn’t affect alleles for seed coat Activity: • Cross the following alleles and determine the phenotypic and genotypic ratios. Phenotypic ratio Aa x Aa AA x Aa aa x Aa AA x aa Genotypic ratio Activity Answers Aa x Aa Phenotypic ratio 3:1 (dom:rec) Genotypic ratio 1:2:1 (hd:h:hr) AA x Aa 1:0 (dom:rec) 1:1:0 (hd:h:hr) or all dominant aa x Aa 1:1 (dom:rec) 0:1:1 (hd:h:hr) AA x aa 1:0 (dom:rec) 0:1:0 (hd:h:hr) or all dominant Pedigrees • Geneticists tool • These are family trees that describe the occurrence of heritable characters in parents and offspring across many generations Pedigree