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TECHNIQUE

TECHNIQUE. 1. 2. Parental generation (P). Stamens. Carpel. 3. 4. RESULTS. First filial gener- ation offspring (F 1 ). 5. EXPERIMENT. P Generation (true-breeding parents). ï‚´. Purple flowers. White flowers. F 1 Generation (hybrids). All plants had purple flowers.

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TECHNIQUE

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  1. TECHNIQUE 1 2 Parental generation (P) Stamens Carpel 3 4 RESULTS First filial gener- ation offspring (F1) 5

  2. EXPERIMENT P Generation (true-breeding parents)  Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation 224 white-flowered plants 705 purple-flowered plants

  3. Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers

  4. P Generation Purple flowers Appearance: White flowers Genetic makeup: PP pp p Gametes: P F1 Generation Appearance: Purple flowers Genetic makeup: Pp p Gametes: 1/2 1/2 P Sperm F2 Generation p P P PP Pp Eggs p pp Pp 3 1

  5. Phenotype Genotype PP Purple 1 (homozygous) Pp 3 Purple (heterozygous) 2 Pp Purple (heterozygous) pp White 1 1 (homozygous) Ratio 3:1 Ratio 1:2:1

  6. TECHNIQUE  Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp Predictions If PP If Pp or Sperm Sperm p p p p P P Pp Pp Pp Pp Eggs Eggs P p pp Pp pp Pp RESULTS or All offspring purple 1/2 offspring purple and 1/2 offspring white

  7. EXPERIMENT YYRR yyrr P Generation Gametes yr YR  F1 Generation YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predictions Sperm or Predicted offspring of F2 generation 1/4 1/4 1/4 yr 1/4 YR yR Yr Sperm YR yr 1/2 1/2 1/4 YR YYRr YYRR YyRR YyRr 1/2 YR YyRr YYRR 1/4 Yr Eggs YYRr YYrr Yyrr YyRr Eggs 1/2 yr YyRr yyrr 1/4 yR YyRR YyRr yyRR yyRr 3/4 1/4 1/4 yr Phenotypic ratio 3:1 Yyrr yyRr YyRr yyrr 3/16 1/16 9/16 3/16 Phenotypic ratio 9:3:3:1 RESULTS Phenotypic ratio approximately 9:3:3:1 315 108 101 32

  8. Rr Rr  Segregation of alleles into sperm Segregation of alleles into eggs Sperm 1/2 1/2 R r R R R 1/2 r R 1/4 1/4 Eggs r r r R 1/2 r 1/4 1/4

  9. P Generation Red White CRCR CWCW CR CW Gametes Pink F1 Generation CRCW 1/2 1/2 CR CW Gametes Sperm 1/2 1/2 CR CW F2 Generation 1/2 CR CRCW CRCR Eggs 1/2 CW CRCW CWCW

  10. Carbohydrate Allele Phenotype (blood group) Red blood cell appearance Genotype IA A B IB i none (a) The three alleles for the ABO blood groups and their associated carbohydrates IAIA or IA i A B IBIB or IB i AB IAIB ii O (b) Blood group genotypes and phenotypes

  11. BbCc BbCc Sperm 1/4 1/4 1/4 1/4 BC bC Bc bc Eggs 1/4 BC BBCc BBCC BbCC BbCc 1/4 bC bbCC bbCc BbCC BbCc 1/4 Bc BBcc Bbcc BBCc BbCc 1/4 bc BbCc bbCc Bbcc bbcc : 4 9 : 3

  12. AaBbCc AaBbCc Sperm 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 Eggs 1/8 1/8 1/8 1/8 Phenotypes: 1/64 6/64 15/64 20/64 15/64 1/64 6/64 Number of dark-skin alleles: 2 6 0 3 4 5 1

  13. Key Affected male Male Mating Offspring, in birth order (first-born on left) Affected female Female 1st generation (grandparents) Ww Ww ww ww 2nd generation (parents, aunts, and uncles) Ww Ww Ww ww ww ww 3rd generation (two sisters) WW ww or Ww No widow’s peak Widow’s peak (a) Is a widow’s peak a dominant or recessive trait? 1st generation (grandparents) Ff Ff Ff ff 2nd generation (parents, aunts, and uncles) ff ff FF Ff Ff or Ff ff 3rd generation (two sisters) FF ff or Ff Attached earlobe Free earlobe (b) Is an attached earlobe a dominant or recessive trait?

  14. Amniotic fluid withdrawn Centrifugation Fetus Fetus Suction tube inserted through cervix Placenta Placenta Chorionic villi Cervix Uterus Fluid Bio- chemical tests Fetal cells Several hours Fetal cells Several hours Several weeks Several hours Several weeks Karyotyping (b) Chorionic villus sampling (CVS) (a) Amniocentesis

  15. Degree of dominance Example Description Heterozygous phenotype same as that of homo- zygous dominant Complete dominance of one allele PP Pp Heterozygous phenotype intermediate between the two homozygous phenotypes Incomplete dominance of either allele CRCW CRCR CWCW Codominance Heterozygotes: Both phenotypes expressed IAIB Multiple alleles In the whole population, some genes have more than two alleles ABO blood group alleles IA , IB , i One gene is able to affect multiple phenotypic characters Sickle-cell disease Pleiotropy

  16. Relationship among genes Example Description Epistasis One gene affects the expression of another BbCc BbCc BC bC Bc bc BC bC Bc bc : 3 : 4 9 A single phenotypic character is affected by two or more genes Polygenic inheritance AaBbCc AaBbCc

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