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Ch 9

Ch 9. Patterns in Inheritance. Gregor Mendel. 1860’s Crossed pea plants Character vs trait. Purple. Flower color. White. Terminal. Axial. Flower position. Green. Yellow. Seed color. Seed shape. Round. Wrinkled. Pod shape. Inflated. Constricted. Green. Yellow. Pod color.

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Ch 9

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  1. Ch 9 Patterns in Inheritance

  2. Gregor Mendel 1860’s Crossed pea plants Character vs trait

  3. Purple Flower color White Terminal Axial Flower position Green Yellow Seed color Seed shape Round Wrinkled Pod shape Inflated Constricted Green Yellow Pod color Tall Stem length Dwarf Genes • Mendel hypothesized that there are alternative forms of genes the units that determine heritable traits • Self-fertilization • Cross fertilization

  4. Terms • True-breeding • Hybrid • Mono-hybrid • Dihybrid • Cross • P generation • F1 Generation • F2 Generation • Phenotype • Genotype

  5. Mendel’s Observations of Inheritance Patterns • Mendel’s law of segregation • 2 alleles inherited • If the 2 alleles of an inherited pair differ • Heterozygous • Dominant allele • Recessive allele • If the 2 alleles are the same, no conflict • Homozygous

  6. Homologous chromosomes • Two alleles for each characteristic. • Alternative forms of a gene at the same locus

  7. Dominance • Dominant • Gene that determines phenotype • Recessive • Gene that has no noticeable effect

  8. Disorders • Present in genotype • Recessive • Carriers • Dominant • Some cases, homozygous dominant is lethal

  9. Table 9.9

  10. Fetal Testing • Amniocentesis and chorionic villus sampling (CVS) • Allow doctors to remove fetal cells that can be tested for genetic abnormalities Amniocentesis Chorionic villus sampling (CVS) Needle inserted through abdomen to extract amniotic fluid Ultrasound monitor Ultrasound monitor Suction tube inserted through cervix to extract tissue from chorionic villi Fetus Fetus Placenta Placenta Chorionic villi Uterus Cervix Cervix Uterus Amniotic fluid Centrifugation Fetal cells Fetal cells Biochemical tests Several weeks Several hours Karyotyping Figure 9.10 A

  11. Fetal Imaging • Ultrasound imaging • Uses sound waves to produce a picture of the fetus Figure 9.10 B

  12. Incomplete Dominance Intermediate phenotypes

  13. Hypercholestorolemia Figure 9.12 B

  14. Multiple Alleles/Codominance • ABO blood type in humans • Alleles for A and B blood types are codominant

  15. Pleiotropy • A single gene which affects many phenotypic characteristics

  16. Polygenic A single characteristic that is influenced by many genes

  17. (male) (female) Parents’ diploid cells 44 + XX 44 + XY 22 + X 22 + Y 22 + X Egg Sperm Offspring (diploid) 44 + XX 44 + XY Sex Determination

  18. 22 + X 22 + XX 76 + ZW 76 + ZZ 32 16 Other systems of sex determination exist in other animals and plants Figure 9.22 B Figure 9.22 C Figure 9.22 D

  19. Independent Assortment • Mendels Law of Independent Assortment • Each pair of alleles segregates independently of other pairs during gamete formation ****Not entirely true

  20. Linked Genes Experiment Purple flower PpLI PpLI Long pollen • Observed Prediction • Phenotypes offspring (9:3:3:1) Purple long Purple round Red long Red round 215 71 71 24 284 21 21 55 Explanation: linked genes P L Parental diploid cell PpLI P I Meiosis Most gametes P L P I Fertilization Sperm P I P L P L P L P L Most offspring P L P I Eggs P I P I P I P I P L 3 purple long : 1 red round Not accounted for: purple round and red long Linked genes are close to each other on the same chromosome and tend to be inherited together

  21. Sex Linked Genes • Genes carried on sex chromosomes • XrX, XrY • Fruit Fly eye color- carried on X • R=dominant red eye (R) • R=recessive white eye (r) What proportion of offspring will have white eyes is mom is heterozygous red eyed and dad is homozygous red eyed?

  22. Sex Linked Affect mostly males

  23. Punnett Squares • A diagram that is used to predict an outcome of a particular cross or breeding experiment • Determine the probability of an offspring having a particular genotype

  24. Genetic makeup (alleles) P plants pp PP Gametes All All p P Fig. 9-3b F1 plants (hybrids) All Pp p P 1 – 2 1 – 2 Gametes Sperm p P P PP Pp F2 plants Phenotypic ratio 3 purple : 1 white Eggs Genotypic ratio 1 PP : 2 Pp : 1 pp Pp pp p

  25. Practice problems • Monohybrid cross • Blue eyes b, Brown eyes B • B is dominant • Both parents heterozygous brown eyed (Bb) • Homozygous for trait P • Mom is PP, dad is pp

  26. Female Male Fig. 9-21c XR Xr XR Y Sperm Y XR XR XR XR XR Y Eggs Xr Y Xr XR Xr

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