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Genetics and Heredity • Genetics is the study of heredity • Heredity is how different genes are passed down from parents to children Genes • Your GENES, not your JEANS. • A gene is a segment of DNA that codes for a certain trait Genetics Terminology: Genome, Chromosomes & Genes • ________ -Complete complement of an organism’s DNA. • Cellular DNA is organized in ___________. • ______ have specific places on chromosomes. From the Virtual Cell Biology Classroom on ScienceProfOnline.com Gregor Mendel (lived in 1800s) - Austrian monk who taught natural science Interested in how traits are passed on Crossbred snow pea plants to figure it out Is known as “The father of Genetics” Genetics- the study of heredity The work of Gregor Mendel Earlier Notions of Inheritance – Blending – Spermists – Ovists Mendel was first to show both parents contribute equally “Father of Genetics” • Mendel performed breeding experiments with garden peas • Found mathematical patterns of inheritance • His work was not appreciated until 1900, 16 years after his death Mendel’s work • Why breed peas? • They were available in many varieties, inexpensive, short life cycle, simple procedures, easy to grow. • The use of plants also allowed strict control over the mating. • He chose to study only characters that varied in an ‘either-or’ rather than a ‘more-or-less’ manner. Why peas? -not too many traits to keep track of -Pea traits-pea color, pea shape, plant height, pod shape, pod color, flower color, flower position Mendel crossed purple flowers with white flowers. (Purebreds) - all of the resulting flowers were purple Then he let the F1s self-fertilize. Result in F2 generation: - 75% of the flowers purple - 25% of the flowers white Explain! F1 Interpreting Mendel’s Data Parent Cross F1 generation F2 Actual Probability generation Ratio Ratio Round x 100% round 5,474 round 2.96:1 wrinkled 1,850 wrink. 3:1 Yellow x green pea 100% yellow 6,022 yell 2,001 green 3.01:1 3:1 Long x short stem 100% long stem 787 long 277 short 2.84:1 3:1 Mendel’s Observations • “dominant” vs “recessive” • Before “genes” and “meiosis” were known, Mendel theorized “inheritance factors”… – are in the pollen and ova of peas as alternate forms for different traits. – occur in pairs, (equal contribution from both parents) – separate during gamete formation and pair up again at fertilization Mendel's Laws 1. Law of Dominance 2. Law of Segregation 3. Law of Independent Assortment Image: Gregor Mendel, Mendel's Principles of Heredity: A Defense by Bateson, William. From the Virtual Cell Biology Classroom on ScienceProfOnline.com 1. Mendel’s Law of _________ • In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. • Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. Mendel’s Law of Segregation • Each hereditary characteristic is controlled by two factors (alleles) that separate and pass into reproductive cells (gametes). 2. Mendel’s Law of ________ • Alternative versions of genes (alleles) result in variations in inherited characteristics. • For each character, an organism inherits 2 alleles (one from each parent). • The alleles for each character segregate (separate) during gamete production (_______). • Alleles for a trait are recombined at fertilization, becoming genotype for the traits of the offspring. Table showing how the genes exchange according to segregation or independent assortment during meiosis and how this translates into Mendel's laws. Mendel’s Law of Independent Assortment • Pairs of inheritance factors (alleles) segregate independently of each other when sex cells (gametes) are formed. 3. Mendel’s Law of _____ ______ Alleles for different traits are distributed to sex cells (& Diagram of how the genes exchange according to segregation or independent assortment during meiosis and how this translates into Mendel's laws. offspring) independently of one another. Show me a video! Remember…Mendel came up with this stuff BEFORE we know about the existence of DNA, genes, chromosomes! Image: Independent assortment and segregation diagram, Mariana Ruiz. From the Virtual Cell Biology Classroom on ScienceProfOnline.com Mendel’s Laws: 1. Law of Dominance: - In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. - Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. 2. Law of Segregations: - During the formation of gametes (eggs or sperm), the two alleles (hereditary units) responsible for a trait separate from each other. - Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. 3. Law of Independent Assortment: - Alleles for different traits are distributed to sex cells (& offspring) independently of one another. From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Gregor Mendel, Mendel's Principles of Heredity: A Defense by Bateson, William Mendelian Inheritance in Humans dominant recessive • • • • Tongue Roller (T) Free Earlobes (F) Dimples (D) Widow’s Peak (P) • • • • Can’t roll tongue (t) Attached lobes (f) No dimples (d) Straight hairline (w) Genetics and Probability Discuss… Coin flipping Card picking Punnett Square probability vs actuality Some Vital Vocab. • • • • Genetics Gene vs Chromosome Alleles Dominant vs Recessive Some Vital Vocab. • • • • • Genotype vs Phenotype Homozygous vs Heterozygous Diploid vs Haploid Mitosis vs Meiosis Zygote Problem Solving from Mendelian Genetics • Consider inheritance patterns for – – – – – Cystic Fibrosis Sickle Cell Anemia Huntington’s disease Hemophelia Colorblindness pedigree Exceptions to Complete Dominance • Polygenic Traits • Intermediate Expression (aka incomplete dominance) • Multiple Alleles • Several described at this link!