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Heredity (Inheritance) and Genetics Heredity 1. Is it possible for two parents with blue eyes to have a brown eyed child? Heredity 2. Is it possible for two parents with brown eyes to have a blue-eyed child? Heredity 3. Rebecca and Leah look so much alike that everyone says they must be sisters. What kind of test should we do to determine if they are sisters? Review What do you know about each of the following: • DNA • Genes • Chromosomes Chromosomes have genetic information and are passed to offspring Dividing onion cells chromosomes chromosomes cell wall nucelus Chromosomes have genetic information and are passed to offspring Human chromosomes stained with a special chemical and viewed under a high-powered microscope What exactly are chromosomes? How do chromosomes contain genetic information? Chromosome structure- DNA • Chromosomes = long pieces of DNA Chromosome structure- genes • Parts of chromosomes are called genes • Genes help determine your characteristics – what are some example characteristics? Human chromosome # 7 • Contains about 1,800 genes • Contains over 150 million nucleotides Link to view genes and DNA sequence Trait – a characteristic of an organism – Example: “flower color” Gene – part of a chromosome that helps determine a specific trait – Example: “flower color gene” Allele – a form of a gene – Example: • One allele is the “blue” form of the gene • One allele is the “red” form of the gene Review How do the terms trait, chromosome, gene, and allele relate to each other? Chromosomes come in pairs Cut out from picture and match each in pairs. This is called a KARYOTYPE Homologous chromosomes? • Humans = 23 chromosome pairs, or 46 total. We think we have about 20,000 genes. • Pea flower = 7 chromosome pairs (14 total) • Fruit fly = 4 chromosome pairs (8 total) 13,601 genes identified so far! – What part of a chromosome do you think is homologous or identical? – What effect do these differences have on characteristics? Chromosomes come in pairs • You get one copy of a chromosome from one parent and one copy of a chromosome from the other parent. • This pair of chromosomes is called a “homologous pair” because they have the same genes on them flower color gene Flower chromosome 3 From Dad From Mom Chromosomes come in pairs IMPORTANT: homologous pairs have the same genes, but they are NOT IDENTICAL – Alleles can be different flower color gene “Blue” allele of flower color gene “Red” allele of flower color gene From Dad From Mom Chromosomes are shuffled When homologous chromosomes are reunited following meiosis and sex, the combination of Alleles can be different flower color gene “Blue” allele of flower color gene “Red” allele of flower color gene From Dad From Mom The combination of alleles determines the observed characteristics RED Chromosome combination Allele combination RED allele allele red, red RED BLUE allele allele red, blue (or blue, red) BLUE allele BLUE allele blue, blue Observed characteristic RED ? BLUE Dominant and recessive alleles Only one red allele is needed for the flower to look red. • Scientists call this a DOMINANT allele Two blue alleles are needed for the flower to look blue. • Scientists call this a RECESSIVE allele Symbols used for alleles • The traditional symbols used for alleles are big and small letters • The letter chosen usually refers to the dominant allele Example: R = Red allele r = Blue allele The combination of alleles determines the observed characteristics RED Chromosome combination Allele combination RED allele allele red, red RED BLUE allele allele red, blue (or blue, red) BLUE allele BLUE allele blue, blue Observed characteristic RED RED BLUE The combination of alleles determines the observed characteristics Chromosome combination Allele combination R R R r RR Rr RED RED r r rr Observed characteristic BLUE Phenotype – the observed (or measurable) trait of an organism that relates to one gene Genotype – the two alleles that an organism has for a trait Example: Trait = Phenotype = Genotype = “flower color” “RED” or “BLUE” “RR” or “Rr” or “rr” The combination of alleles determines the observed characteristics Chromosome combination Allele combination R R R r RR Rr RED RED r r rr Observed characteristic BLUE The combination of alleles determines the observed characteristics Chromosome combination GENOTYPE R R R r RR Rr RED RED r r rr PHENOTYPE BLUE Homozygous – the two alleles are the same • RR and rr are homozygous genotypes Heterozygous – the two alleles are different • Rr is a heterozygous genotype Review • What are homologous chromosomes? • What part of a chromosome do you think is homologous or identical. • What is a dominant allele? • What is a recessive allele? • What is homozygous? • What is heterozygous? • What is phenotype? • What is genotype? Modeling Genetic crosses • Documents and Models how genetic information is passed along. • Accounts for patterns seen in a pedigree • Makes predictions about the phenotypes and genotypes seen in the next generation Possible combinations of inherited chromosomes/genes Dad Parents Rr Mom Rr X RR Possible Offspring Order doesn’t matter, these two are the same (Rr) Rr r R r r What are all possible genotypes produced from the parents? RR, Rr, rr Punnett squares organize all possible offspring combinations Dad Rr Mom X Rr Your turn: R r R RR Rr r Rr rr What are all possible genotypes produced by crossing Rr with rr? Punnett squares predict ratios of all genotypes and phenotypes produced R r R RR Rr r Rr rr Genotypic ratio = 1RR: 2Rr:1rr or 25%RR:50%Rr:25%rr Phenotypic ratio = 3 Red:1 blue or 75% Red:25% Blue Predicted ratios determine the probability of each genotype/phenotype R r R RR Rr r Rr rr Genotypic ratio = 1RR: 2Rr:1rr Phenotypic ratio = 3 Red:1 blue 1 out of 4 possibilities is rr = 25% chance of rr • What is probability of Rr? • How many out of 4 are red? • What is the probability of red? • What is the probability of blue? Punnett square practice Calculate the predicted genotypic and phenotypic ratios Calculate the probability of each genotype and phenotype 1) Hh X HH – H(hairy) is dominant over h(not hairy) 2) Gg X gg – G(green sepals) is dominant over g(yellow sepals) Review • What is the relationship between genotype and phenotype? • What is the relationship between Homozygous and Heterozygous • Give an example of a heterozygous genotype for height (T = tall; t = short): • Give an example of a homozygous genotype for height (T = tall; t = short): • What is the phenotype of a plant heterozygous for the height gene? Dihybrid cross • Used to predict the combinations of 2 traits contained on two separate chromosomes. • For example for the traits of stripes and tails on a cat: – Two double-heterozygous striped, with tail cats are crossed. – How many offspring will be striped and have a tail, how many will be striped with no tail, how many will be plain with a tail… Practice • • • Construct a Punnett Square for each of the following crosses. Remember: the two traits are on two different chromosomes. Write the Genotypic and Phenotypic Ratio below the Punnett Squares. 1. SsTt X SsTt 2. SSTt X SsTt 3. SSTT X SsTt S = striped s = plain T = tail t = no tail SsTt X SsTt ST S = striped s = plain T = tail t = no tail SsTt X SsTt ST St S = striped s = plain T = tail t = no tail SsTt X SsTt ST St sT S = striped s = plain T = tail t = no tail SsTt X SsTt ST St sT st S = striped s = plain T = tail t = no tail SsTt X SsTt ST ST St sT st St sT st S = striped s = plain T = tail t = no tail SsTt X SsTt ST St sT st ST SSTT SSTt SsTT SsTt St SSTt SStt SsTt sT SsTT SsTt ssTT ssTt st SsTt ssTt Sstt S = striped s = plain T = tail t = no tail Sstt sstt Genotypes: 1 SSTT: 2 SSTt: 1 SStt: 2 SsTT: 4 SsTt: 2 Sstt: 1 ssTT: 2 ssTt: 1 sstt Phenotypes: 9 striped, tail : 3 striped, no tail : 3 plain, tail : 1 plain, no tail SSTt X SsTt ST St sT st ST SSTT SSTt SsTT SsTt St SSTt SStt SsTt Sstt ST Same as above Same as above Same as above Same as above St Same as above Same as above Same as above Same as above S = striped s = plain T = tail t = no tail If they are the same as above you do NOT have to rewrite the genotype Genotypes: 1 SSTT: 1SSTt: 1SsTT: 1SsTt: 1SSTt: 1SStt: 1SsTt: 1Sstt Phenotypes: 6 Striped with Tail: 2 Striped with no tail (3:1 reduced) SSTT X SsTt ST Same ST St sT st SSTT SSTt SsTT SsTt ST ST ST Genotypes: 1 SSTT: 1 SSTt: 1 SsTT: 1 SsTt Phenotypes: 4 Striped Tail (100%) S = striped s = plain T = tail t = no tail Inheritance quiz #1 #2 #3 #1 #2 #3 Width/thickness/petals 1. What is the trait for the flowers? __________________ Type of Hair 2. What is the trait for the animals? __________________ f (or narrow) 3. What is the recessive allele for the flower trait? _______ H (or straight) 4. What is the dominant allele for the animal trait? _______ #1 5. Which flower is heterozygous? ___________ #2 6. Which animal is homozygous dominant? __________ Ff 7. What is the genotype of flower #1? ________________ HH 8. What is the genotype of animal #2? ________________ Wide 9. What is the phenotype of flower #2? ________________ Straight Hair 10.What is the phenotype of animal #3? ________________ Punnett Square F f Genotypic ratio: f Ff ff 1 Ff : 1 ff (2 Ff : 2 ff is OK) Phenotypic ratio: f Ff ff 1 fat : 1 skinny (2 fat : 2 skinny is OK) Review In flowers, red color (R) is dominant to blue color (r). 1. What possible genotypes produce a blue flower? What possible genotypes produce a red flower? 2. Explain how you could determine the actual genotype of a red flower by performing a genetic cross many times and looking at the offspring phenotypes. Review • • • How many sets of your 23 chromosomes do you have (1, 2, 3, or 4?) How many of each type of chromosome is inherited from your mom? How many of each type of chromosome is inherited from your dad? If parents have two copies of each chromosome, how do they pass on only one to their offspring? • MEIOSIS is the process of cell division that decreases the number of chromosomes to make sperm or egg cells Sperm or egg cells Original cell The purposes of Meiosis: 1. Split the total number of chromosomes in half so that only ONE chromosome from each pair is inherited from each parent. 2. Produce variation in offspring by randomly sorting the chromosomes. Meiosis Original cell •Diploid (pairs of chromosomes) Sperm or egg cells •Haploid (single chromosomes) Fertilization Sperm Egg Gametes: (haploid sex cells) Zygote: (diploid embryo) Fertilized egg