Hereditary patterns
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The document discusses heritable variation and patterns of inheritance. It describes how traits are usually inherited in particular patterns from parents to offspring. Gregor Mendel performed experiments with pea plants to analyze inheritance patterns and deduce fundamental genetic principles. Through his work, he developed hypotheses about alternative gene forms (alleles), genetic makeup, gamete formation, and dominant and recessive alleles.
Hereditary patterns
- 1. HERITABLE VARIATION & PATTERNS OF INHERITANCE •“Wild type” traits are traits most commonly found in nature Figure 9.2 03/12/12 1
- 2. • Various traits exist in organisms x These traits are usually inherited in particular patterns 03/12/12 2
- 3. Parents: X X Parents: Wild-type Wild-type Wild-type Sky-blue First- wild-type Offspring: All All Wild-type generation offspring: Matings Second- generation (a) Offspring from the mating offspring: 3/4 and /4 1 of two wild-type birds Wild-type Sky-blue (b) Two generations of offspring from the mating of a wild-type with a sky-blue bird Figure 9.3 03/12/12 3
- 4. Mendelian Genetics • Gregor Mendel G Was the first to analyze patterns of inheritance – Deduced the fundamental principles of genetics Figure 9.4 03/12/12 4
- 5. In an Abbey Garden • Mendel studied garden peas e These plants are easily manipulated – These plants can self-fertilize stamen Stamen Carpel carpel Figure 9.5 03/12/12 5
- 6. Mendelian White 1 Removed Genetics stamens from purple flower • Mendel carried out Stamens some cross- Carpel 2 Transferred pollen from stamens of fertilization Parents (P) Purple white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod Offspring (F1) Figure 9.6 03/12/12 6
- 7. Mendelian Genetics • He also created true-breeding varieties of plants Mendel then crossed two different true-breeding varieties, creating hybrids 03/12/12 7
- 8. Mendel’s Principles of Segregation • Mendel performed many experiments He tracked several characteristics in pea plants from which he formulated several hypotheses 03/12/12 8
- 9. Traits in Pea Plants Dominant Recessive Dominant Recessive Pod shape Inflated Constricted Flower color Purple White Pod Color Green Yellow Flower position Axial Terminal Seed color Yellow Green Stem length Tall Dwarf Seed shape Round Wrinkled Figure 9.7 03/12/12 9
- 10. Monohybrid Crosses P Generation • A monohybrid (true-breeding parents) Purple White cross is a cross flowers flowers between parent F1 Generation All plants have plants that differ purple flowers in only one among F1 plants characteristic (F1 × F1) Fertilization F2 Generation 1 /4 of plantsHave 3 /4 of plants have whiteflower purple flowers s (a) Mendel’s crosses tracking one characteristic (flower color) Figure 9.8a 03/12/12 10
- 11. • Mendel developed four hypotheses from the monohybrid cross: – 1) There are alternative forms of genes, now called alleles – 2) For each characteristic, each organism has two genes – 3) Gametes carry only one allele for each inherited characteristic – 4) Alleles can be dominant or recessive 03/12/12 11
- 12. Mendel’s Results Genetic makeup (alleles) P plants PP PP • Including a Gametes All P All p Punnett square F1 plants: (hybrids) All Pp Gametes 1 /2 P 1 /2 p Eggs P P Sperm F2 plants: p PP p Phenotypic ratio Pp Pp 3 purple : 1 white pp Genotypic ratio 1 PP : 2 Pp : 1 pp (b) Explanation of the results in part (a) Figure 9.8b 03/12/12 12
- 13. Describing Traits: • Phenotype s An organism’s physical traits • Genotype • An organism’s genetic makeup 03/12/12 13
- 14. Mendel’s Principle of Segregation Pairs of alleles segregate (separate) during gamete formation; the fusion of gametes at fertilization creates allele pairs again 03/12/12 14
- 15. Genetic Alleles & Homologous Chromosomes • Homologous chromosomes: & Have genes at specific loci (locations on the chromosome) – Have alleles of a gene at the same locus 03/12/12 NCBI Human Ch 21 15
- 16. Genetic Alleles & Homologous Chromosomes Homologous chromosomes: Gene loci Dominant allele P a B P a b Recessive allele Genotype: PP aa Bb Homozygous Homozygous Heterozygous for the for the dominant allele recessive allele Figure 9.9 03/12/12 16
- 17. Genetic Alleles & Homologous Chromosomes • Homozygous s When an organism has identical alleles for a gene • Heterozygous - When an organism has different alleles for a gene 03/12/12 17