Patterns of inheritance

1. Patternsofinheritance Chapter 9

3. The first genetics research “lab” was a monk’s abbey garden The same genetic defect that causes sickle-cell disease can also protect you against malaria

4. In certain isolated communities, one out of 100 boys is born with the genetic defect that causes Duchenne muscular dystrophy Intermarriage caused the disease hemophilia to spread through the royal families of Europe

5. TESTING YOUR BABY • Allows expectant parents to test for possibilities in their unborn child • Includes amniocentesis and CVS • Has risks associated with it • Genetic testing

6. HERITABLE VARIATION AND PATTERNS OF INHERITANCE • Wild type traits are traits most commonly found in nature

7. Various traits exist in organisms • These traits are usually inherited in particular patterns

8. Parents: Parents: Wild-type Sky-blue Wild-type Wild-type First- generation offspring: Wild-type wild-type Offspring: All All Matings Second- generation offspring: (a) Offspring from the mating of two wild-type birds and 1/4 3/4 Sky-blue Wild-type (b) Two generations of offspring from the mating of a wild-type with a sky-blue bird

9. Was the first person to analyze patterns of inheritance • Deduced the fundamental principles of genetics • Gregor Mendel

10. In an Abbey Garden • Mendel studied garden peas • These plant are easily manipulated • These plants can self-fertilize Stamen Carpel

11. White 1 Removed stamens from purple flower • Mendel carried out some cross-fertilization Stamens 2 Transferred pollen from stamens of white flower to carpel of purple flower Carpel Purple Parents (P) 3 Pollinated carpel matured into pod 4 Planted seeds from pod Offspring (F1)

12. Mendel then crossed two different true-breeding varieties, creating hybrids • He also created true-breeding varieties of plants

13. Mendel’s Principles of Segregation • Mendel performed many experiments • He tracked several characteristics in pea plants from which he formulated several hypotheses

14. Dominant Recessive Recessive Dominant Pod shape Constricted Inflated Flower color Purple White Pod Color Yellow Green Flower position Axial Terminal Seed color Yellow Green Stem length Dwarf Tall Seed shape Round Wrinkled

15. MonohybridCrosses P Generation (true-breeding parents) Purple flowers Whiteflowers • A monohybrid cross is a cross between parent plants that differ in only one characteristic All plants have purple flowers F1 Generation Fertilization among F1 plants (F1  F1) F2 Generation 1/4 of plants have white flowers 3/4 of plants have purpleflowers (a) Mendel’s crosses tracking one characteristic (flower color)

16. There are alternative forms of genes, now called alleles • For each characteristic, each organism has two genes • Gametes carry only one allele for each inherited characteristic • Alleles can be dominant or recessive • Mendel developed four hypotheses from the monohybrid cross

17. Genetic makeup (alleles) pp PP P plants All P p Gametes All • An explanation of Mendel’s results, including a Punnett square F1 plants: (hybrids) All Pp P Gametes 1/2 1/2 p P P Sperm Eggs F2 plants: PP p p Phenotypic ratio 3 purple : 1 white Pp Pp pp Genotypic ratio 1 PP : 2 Pp : 1 pp (b) Explanation of the results in part (a)

18. Phenotype • An organism’s physical traits • Genotype • An organism’s genetic makeup

19. Purple and white sweet pea flowers Principle of segregation: Pairs of alleles segregate (separate) during gamete formation; the fusion of gametes during fertilization pairs alleles once again

20. P:Tall (TT) x Dwarf (tt) F1: F2: Round x Wrinkled seeds (RR) seeds (rr) F1: F2: Using a Punnett square derive the phenotypes and genotypes in the F1 and F2 generations (from self-fertilization of F1) of the following crosses between true-bred plants

21. Genetic Alleles and Homologous Chromosomes • Homologous chromosomes • Have genes at specific loci • Have alleles of a gene at the same locus

22. Homologous chromosomes: Gene loci Dominant allele a P B a b P Recessive allele aa Bb PP Genotype: Homozygous for the dominant allele Heterozygous Homozygous for the recessive allele

23. Homozygous • When an organism has identical alleles for a gene • Heterozygous • When an organism has different alleles for a gene

24. Mendel’s Principle of Independent Assortment • Two hypotheses for gene assortment in a dihybrid cross • Dependent assortment • Independent assortment

25. Hypothesis: (a) Dependent assortment (b) Independent assortment RRYY rryy P Generation rryy RRYY ry Gametes RY ry Gametes RY F1 Generation RrYy RrYy 1/4 RY RY 1/4 Sperm Eggs Eggs Sperm 1/4 rY rY 1/2 1/4 RY 1/2 RY RRYY 1/4 1/2 ry 1/2 Ry Ry ry RrYY RrYY 1/4 F2 Generation ry ry 1/4 RRYy rrYY RRYy 1/4 RrYy RrYy RrYy RrYy Yellow round 9/16 Green round RRyy rrYy rrYy 3/16 Yellow wrinkled Rryy Rryy Actual results contradict hypothesis 3/16 rryy Green wrinkled 1/16 Actual results support hypothesis

26. Mendel’s principle of independent assortment • Each pair of alleles segregates independently of the other pairs during gamete formation

27. Blind Blind Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn Phenotypes Black coat, blind(PRA) B_nn Black coat, normal vision B_N_ Genotypes (a) Mating of heterozygotes (black, normal vision) BbNn BbNn Phenotypic ratio of offspring 1 chocolate coat, blind (PRA) 3 chocolate coat, normal vision 9 black coat, normal vision 3 black coat, blind (PRA) (b)

28. Using a Testcross to Determine an Unknown Genotype Testcross: • A testcross is a mating between Genotypes • An individual of unknown genotype and • A homozygous recessive individual P_ pp Two possibilities for the purple flower: PP Pp Gametes P p P P p pp Pp Pp Offspring 1 purple : 1 white All purple

29. The Rules of Probability F1 Genotypes B b male B b female Formation of eggs Formation of sperm • The probability of a compound event is the product of the separate probabilities of the independent events • The rule of multiplication 1/2 B B 1/2 1/2 B B b b 1/4 1/2 (1/2  1/2) b B B b 1/4 1/4 b b F2 Genotypes 1/4

30. What is the probability of a ‘bb’ offspring from aBb x Bb cross? P: Bb x Bb Gametes: B (½) b (½) B (½) b (½) F1: bb ½ * ½ = ¼

31. What are the chances of getting a ‘Bb’ outcome from a Bb x Bb cross? P: Bb x Bb Gametes: B (½) b (½) B (½) b (½) F1: Bb Bb ½*½ = ¼ and ½*½ = ¼ ¼ + ¼ = ½

32. Two organisms have the genotype AaBbCc. What is the probability that an offspring with genotype aabbcc will be produced from their cross? AaBbCc x AaBbCc  aabbcc *** A trihybrid cross is equivalent to three monohybrid crosses**** Aa x Aa: probability of ‘aa’ offspring = ½ * ½ = ¼ Bb x Bb: probability of ‘bb’ offspring = ½ * ½ = ¼ Cc x Cc: probability of ‘cc’ offspring = ½ * ½ = ¼ Thus, probability of an ‘aabbcc’ offspring = ¼*¼*¼ = 1/64

33. Family Pedigrees Recessive Traits Dominant Traits • Mendel’s principles apply to the inheritance of many human traits Freckles No freckles Straight hairline Widow’s peak Free earlobe Attached earlobe

34. Shows the history of a trait in a family • Allows researchers to analyze human traits • A family pedigree Female Male Deaf Joshua Lambert Abigail Linnell John Eddy Hepzibah Daggett Hearing Abigail Lambert Jonathan Lambert Elizabeth Eddy

35. Female Male Deaf Dd Joshua Lambert Dd Abigail Linnell D_ John Eddy D_ Hepzibah Daggett Hearing D_ Abigail Lambert dd Jonathan Lambert Dd Elizabeth Eddy Dd Dd dd Dd Dd Dd dd

36. Human Disorders Controlled by a Single Gene • Many human traits • Show simple inheritance patterns • Are controlled by genes on autosomes

38. Recessive Disorders • Individuals can be carriers of these diseases • Most human genetic disorders are recessive Normal Dd Normal Dd Parents: D D Eggs Sperm DD Normal d d Dd Normal (carrier) Dd Normal (carrier) Offspring: dd Deaf

39. Dominant Disorders • Some human genetic disorders are dominant • Achondroplasia is a form of dwarfism

40. Fetal testing can spot many inherited disorders early in pregnancy • Karyotyping and biochemical tests of fetal cells and molecules can help people make reproductive decisions • Fetal cells can be obtained through amniocentesis Amnioticfluidwithdrawn Centrifugation Amnioticfluid Fluid Fetalcells Fetus(14-20weeks) Biochemicaltests Placenta Severalweeks later Uterus Cervix Karyotyping Cell culture

41. Chorionic villus sampling is another procedure that obtains fetal cells for karyotyping Fetus(10-12weeks) Several hourslater Placenta Suction Karyotyping Fetal cells(from chorionic villi) Some biochemical tests Chorionic villi

42. Examination of the fetus with ultrasound is another helpful technique

43. Genetic testing can detect disease-causing alleles • Genetic testing can be of value to those at risk of developing a genetic disorder or of passing it on to offspring Dr. David Satcher, former U.S. surgeon general, pioneered screening for sickle-cell disease

44. BEYOND MENDEL • Some patterns of genetic inheritance are not explained by Mendel’s principles

45. Incomplete Dominance in Plants and People P Generation Red RR White rr • In incomplete dominance F1 hybrids have an appearance in between the phenotypes of the two parents r Gametes R F1 Generation Pink Rr 1/2 1/2 r R Gametes 1/2 Sperm R R 1/2 Eggs Red RR 1/2 r r 1/2 Pink rR Pink Rr F2 Generation White rr

46. Incomplete dominance in carnations: red, pink, white

47. Is a human trait that is incompletely dominant • Hypercholesterolemia LDL (carries cholesterol) LDL receptor (mops up LDL) Cell Normal HH Mild disease Hh Severe disease hh Genotypes: Homozygous for ability to make LDL receptors Heterozygous Homozygous for inability to make LDL receptors

48. Multiple Alleles and Blood Type • The ABO blood groups in humans are examples of multiple alleles • Two of the human blood type alleles exhibit codominance • Discovered by Karl Landsteiner (1930 – Nobel Prize in Physiology and Medicine) • Both alleles are expressed in the phenotype

49. Blood Antibody Antigen TypeGenotype(serum)(RBC) AB IAIB - AgA, AgB A IAIA, IAi B AgA - B IBIB, IBi A - AgB O ii AB - -

50. Blood group identification Antibody  Blood grouping 