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Core Concepts

Core Concepts. Mendel’s Law of Segregation states that there are two alleles for every gene determining a specific characteristic, and these alleles are segregated into separate gametes during reproduction.

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Core Concepts

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  1. Core Concepts • Mendel’s Law of Segregationstates that there are two alleles for every gene determining a specific characteristic, and these alleles are segregated into separate gametes during reproduction. • When the 2 different alleles occur together in one individual (heterozygote), the dominant allele will be the one that is expressed in the phenotype of the individual. • Mendel’s Law of Independent Assortmentsays that 2 or more different genes, if found on separate chromosomes, are determined independently of each other. • The Addition Ruleis used to combine probabilities, when there are 2 or more ways to arrive at a given outcome. • The Multiplication Ruleis used to combine probabilities of 2 or more different events that need to occur in combination. • Many characteristics have been found to follow patterns of inheritance that are modifications of Mendel’s rules.

  2. Keywords • gene • allele • dominant • recessive • character • trait • phenotype • genotype • pure breeding • hybrid • homozygous • heterozygous • P (parental generation) • F1 (first filial generation) • F2 (second filial generation) • Punnett Square • forked line

  3. TRAITS CHARACTERS Mendel’s Discoveries • Pre-Mendel beliefs in genetics: blending theory • Augustinian monk and science teacher • Why Pisum sativum? • Pea plants available in many varieties • character (heritable feature) • trait (character variant) • Perfect flowers • cross-pollination and self-pollination • Short generation time • Many offspring

  4. MONOHYBRID CROSS inheritance of a single trait P Generation (true-breeding parents) x Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation Cross-fertilization self-pollination 224 plants 705 plants

  5. Results for other hybrid (F1) characters

  6.  Blending inheritance  Complete dominance

  7. Allele for purple flowers ( P) Mendelian InheritanceComplete dominance Homologous pair of chromosomes Locus for flower-color gene • Alternative versions of genes exist (alleles) • Dominant • Recessive • Organism inherits 2 alleles • Dominant is fully expressed • Recessive has no visible effect Allele for white flowers ( p )

  8. Alternative versions of genes exist (alleles) • Dominant • Recessive • Organism inherits 2 alleles (genotype) • Dominant is fully expressed • Recessive has no visible effect PP pp Pp PP or Pp pp

  9. Other terms in genetics • Homozygous – identical alleles, true-breeding • Heterozygous – different alleles • Phenotype – physical appearance • Genotype – genetic make-up

  10. Mendelian InheritanceLaw of Segregation 2 alleles for one character separate and go to different gametes

  11. Parental generation • Pure-breeding parents are homozygous for different traits for flower color • Each parent produces only one type of gamete: purple parent (P), white parent (p) • F1 generation • Hybrids are heterozygous for flower color • Can produce two kinds of gametes: P or p • F2 generation • Due to the law of segregation, eggs and sperm with different kinds of gametes combine to form a specific ratio • Genotypic ratio 1 PP : 2 Pp : 1 pp • Phenotypic ratio  3 purple : 1 white

  12. Problem-solving An organism displays the dominant phenotype. It may be either homozygous or heterozygous for the trait. How can its genotype be determined? Perform a test-cross: Dominant phenotype x recessive phenotype

  13. Dihybrid crossInheritance of two characters • Produces four phenotypes in the F2 generation

  14. Dihybrid crossInheritance of two characters • Characters are NOT transmitted as a package (YR and yr only) • Genes are packaged into gametes in all possible combinations of alleles (YR, Yr, yR, yr)

  15. Law of independent assortmentAllele pairs separate independently during the formation of gametes

  16. Genetics and Probability Monohybrid cross Round seed shape is dominant over wrinkled seeds in pea plants. What percentage of the F2 generation can be expected to: • Be homozygous dominant for seed shape? • Be heterozygous for seed shape? • Have round seeds?

  17. Genetics and Probability Dihybrid cross Round seed shape is dominant over wrinkled seeds in pea plants. Green pod color is dominant over yellow pods. What percentage of the F2 generation can be expected to: • Be heterozygous for both characters? • Have round seeds in green pods? • Have wrinkled seeds in green pods?

  18. Genetics and Probability Trihybrid cross Round seed shape is dominant over wrinkled seeds in pea plants. Green pod color is dominant over yellow pods. Tall plants are dominant over short ones. What percentage of the F2 generation can be expected to: • Be heterozygous for all characters? • Be tall plants with round seeds in yellow pods? • Be short plants with round seeds in green pods?

  19. Find the genotypic and phenotypic ratios of the offspring from the following crosses using the forked line method: AaBb x aaBb AaBbCC x Aabbcc www.youtube.com

  20. Non-mendelian inheritanceAlleles with different degrees of dominance and recessiveness

  21. www.flickr.com

  22. www.bio.georgiasouthern.edu

  23. www.buzzle.com

  24. http://nevinerk.weebly.com/uploads/5/2/9/9/5299320/236178.png?402http://nevinerk.weebly.com/uploads/5/2/9/9/5299320/236178.png?402

  25. Sample problems 1. A cross between a blue blahblah bird & a white blahblah bird produces silver blahblah birds. a) What are the genotypes of the parent blahblah birds in the original cross? b) What is the genotype of the silver offspring? c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds? 2. The color of fruit for plant "X" is determined by two alleles. When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit. What are the genotypes of the parent orange-fruited plants? 3. Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a red roan bull. 4. What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?

  26. Sample problems 5. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). a) What pattern of inheritance does this illustrate? b) What percent of kittens would have tan fur if a tabby cat is crossed with a black cat? 6. A woman with Type O blood and a man who is Type AB are expecting a child. What are the possible blood types of the kid? 7. What are the possible blood types of a child whose parents are both heterozygous for "B" blood type? 8. What are the chances of a woman with Type AB and a man with Type A having a child with Type O? 9. Determine the possible genotypes & phenotypes with respect to blood type of the offspring of a couple whose blood types are A and B. Both sets of grandparents have the AB blood type.

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