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Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
Genetics
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Genetics

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  • 1. <ul><li>Genetics is the science of heredity </li></ul><ul><li>These black Labrador puppies are purebred—their parents and grandparents were black Labs with very similar genetic makeups </li></ul><ul><ul><li>Purebreds often suffer from serious genetic defects </li></ul></ul>Purebreds and Mutts — A Difference of Heredity
  • 2. <ul><li>The parents of these puppies were a mixture of different breeds </li></ul><ul><ul><li>Their behavior and appearance is more varied as a result of their diverse genetic inheritance </li></ul></ul>
  • 3. <ul><li>Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants </li></ul>9.2 Experimental genetics began in an abbey garden Figure 9.2A, B Stamen Carpel
  • 4. <ul><li>Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation </li></ul>Figure 9.2C <ul><li>This illustration shows his technique for cross-fertilization </li></ul>1 Removed stamens from purple flower White Stamens Carpel Purple PARENTS (P) OFF-SPRING (F 1 ) 2 Transferred pollen from stamens of white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod
  • 5. <ul><li>Mendel studied seven pea characteristics </li></ul>Figure 9.2D <ul><li>He hypothesized that there are alternative forms of genes (although he did not use that term), the units that determine heredity </li></ul>FLOWER COLOR FLOWER POSITION SEED COLOR SEED SHAPE POD SHAPE POD COLOR STEM LENGTH Purple White Axial Terminal Yellow Green Round Wrinkled Inflated Constricted Green Yellow Tall Dwarf
  • 6. <ul><li>From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic </li></ul><ul><ul><li>One characteristic comes from each parent </li></ul></ul>9.3 Mendel’s principle of segregation describes the inheritance of a single characteristic P GENERATION (true-breeding parents) F 1 generation F 2 generation Purple flowers White flowers All plants have purple flowers Fertilization among F1 plants (F 1 x F 1 ) 3 / 4 of plants have purple flowers 1 / 4 of plants have white flowers Figure 9.3A
  • 7. <ul><li>A sperm or egg carries only one allele of each pair </li></ul><ul><ul><li>The pairs of alleles separate when gametes form </li></ul></ul><ul><ul><li>This process describes Mendel’s law of segregation </li></ul></ul><ul><ul><li>Alleles can be dominant or recessive </li></ul></ul>GENETIC MAKEUP (ALLELES) P PLANTS F 1 PLANTS (hybrids) F 2 PLANTS PP pp All P All p All Pp 1 / 2 P 1 / 2 p Eggs P p P PP p Sperm Pp Pp pp Gametes Gametes Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp Figure 9.3B
  • 8. <ul><li>Alternative forms of a gene (alleles) reside at the same locus on homologous chromosomes </li></ul>9.4 Homologous chromosomes bear the two alleles for each characteristic GENE LOCI Figure 9.4 P a B DOMINANT allele RECESSIVE allele P a b GENOTYPE: PP aa Bb HOMOZYGOUS for the dominant allele HOMOZYGOUS for the recessive allele HETEROZYGOUS
  • 9. <ul><li>The offspring of a testcross often reveal the genotype of an individual when it is unknown </li></ul>9.6 Geneticists use the testcross to determine unknown genotypes TESTCROSS: B_ GENOTYPES bb BB Bb or Two possibilities for the black dog: GAMETES OFFSPRING All black 1 black : 1 chocolate B b B b b Bb Bb bb Figure 9.6
  • 10. <ul><li>The inheritance of many human traits follows Mendel’s principles and the rules of probability </li></ul>9.8 Connection: Genetic traits in humans can be tracked through family pedigrees Figure 9.8A
  • 11. <ul><li>Most such disorders are caused by autosomal recessive alleles </li></ul><ul><ul><li>Examples: cystic fibrosis, sickle-cell disease </li></ul></ul>9.9 Connection: Many inherited disorders in humans are controlled by a single gene Figure 9.9A D D d d Normal Dd Normal Dd DD Normal Dd Normal (carrier) Dd Normal (carrier) dd Deaf Eggs Sperm PARENTS OFFSPRING
  • 12. <ul><li>A few are caused by dominant alleles </li></ul>Figure 9.9B <ul><ul><li>Examples: achondroplasia, Huntington’s disease </li></ul></ul>
  • 13. <ul><li>Karyotyping and biochemical tests of fetal cells and molecules can help people make reproductive decisions </li></ul><ul><ul><li>Fetal cells can be obtained through amniocentesis </li></ul></ul>9.10 Connection: Fetal testing can spot many inherited disorders early in pregnancy Figure 9.10A Amniotic fluid Fetus (14-20 weeks) Placenta Amniotic fluid withdrawn Centrifugation Fetal cells Fluid Uterus Cervix Cell culture Several weeks later Karyotyping Biochemical tests
  • 14. <ul><li>In a population, multiple alleles often exist for a characteristic </li></ul><ul><ul><li>The three alleles for ABO blood type in humans is an example </li></ul></ul>9.13 Many genes have more than two alleles in the population
  • 15. <ul><li>When an offspring’s phenotype—such as flower color— is in between the phenotypes of its parents, it exhibits incomplete dominance </li></ul>9.12 Incomplete dominance results in intermediate phenotypes P GENERATION F 1 GENERATION F 2 GENERATION Red RR Gametes R r White rr Pink Rr R r R R r r 1 / 2 1 / 2 1 / 2 1 / 2 1 / 2 1 / 2 Sperm Eggs Pink Rr Pink rR White rr Red RR Figure 9.12A
  • 16. <ul><ul><li>The alleles for A and B blood types are codominant, and both are expressed in the phenotype </li></ul></ul>Figure 9.13 Blood Group (Phenotype) O Genotypes Antibodies Present in Blood Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left O A B AB A B AB ii I A I A or I A i I B I B or I B i I A I B Anti-A Anti-B Anti-B Anti-A
  • 17. 9.14 A single gene may affect many phenotypic characteristics <ul><li>A single gene may affect phenotype in many ways, a phenomenon called pleiotropy </li></ul><ul><ul><li>The allele for sickle-cell disease is an example </li></ul></ul>Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickle cells Breakdown of red blood cells Clumping of cells and clogging of small blood vessels Accumulation of sickled cells in spleen Physical weakness Anemia Heart failure Pain and fever Brain damage Damage to other organs Spleen damage Kidney failure Rheumatism Pneumonia and other infections Paralysis Impaired mental function Figure 9.14
  • 18. Figure 9.16 P GENERATION F 1 GENERATION F 2 GENERATION aabbcc (very light) AABBCC (very dark) AaBbCc AaBbCc Eggs Sperm Fraction of population Skin pigmentation
  • 19. <ul><li>The chromosomal basis of Mendel’s principles </li></ul>Figure 9.17
  • 20. Figure 9.21A X Y Male (male) Parents’ diploid cells (female) Sperm Offspring (diploid) Egg
  • 21. <ul><li>Other systems of sex determination exist in other animals and plants </li></ul>Figure 9.21B-D <ul><ul><li>The X-O system </li></ul></ul><ul><ul><li>The Z-W system </li></ul></ul><ul><ul><li>Chromosome number </li></ul></ul>
  • 22. <ul><ul><li>Their inheritance pattern reflects the fact that males have one X chromosome and females have two </li></ul></ul>Figure 9.22B-D <ul><ul><li>These figures illustrate inheritance patterns for white eye color ( r ) in the fruit fly, an X-linked recessive trait </li></ul></ul>Female Male Female Male Female Male X r Y X R X R X R X r X R Y X R X r Y X R X r X R X r X R X R X R Y X R Y X r X R X R Y X r Y X R X r X R X r X r Y X R X r X r X r X R Y X r Y X r Y R = red-eye allele r = white-eye allele
  • 23. <ul><li>Most sex-linked human disorders are due to recessive alleles </li></ul><ul><ul><li>Examples: hemophilia, red-green color blindness </li></ul></ul><ul><ul><li>These are mostly seen in males </li></ul></ul><ul><ul><li>A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the allele from both parents to be affected </li></ul></ul>9.23 Connection: Sex-linked disorders affect mostly males Figure 9.23A

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