CHAPTER 9 Patterns of Inheritance

1. CHAPTER 9Patterns of Inheritance Modules 9.1 – 9.10

2. Purebreds and Mutts — A Difference of Heredity • Genetics is the science of heredity • These black Labrador puppies are purebred—their parents and grandparents were black Labs with very similar genetic makeups • Purebreds often suffer from serious genetic defects

3. Their behavior and appearance is more varied as a result of their diverse genetic inheritance • The parents of these puppies were a mixture of different breeds

4. MENDEL’S PRINCIPLES 9.1 The science of genetics has ancient roots • The science of heredity dates back to ancient attempts at selective breeding • Until the 20th century, however, many biologists erroneously believed that • characteristics acquired during lifetime could be passed on • characteristics of both parents blended irreversibly in their offspring

5. 9.2 Experimental genetics began in an abbey garden • Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants Stamen Carpel Figure 9.2A, B

6. White 1 Removed stamensfrom purple flower • Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation Stamens Carpel 2 Transferred pollen from stamens of white flower to carpel of purple flower PARENTS(P) Purple 3 Pollinated carpel matured into pod • This illustration shows his technique for cross-fertilization 4 Planted seeds from pod OFF-SPRING(F1) Figure 9.2C

7. FLOWER COLOR Purple White FLOWER POSITION • Mendel studied seven pea characteristics Axial Terminal • He hypothesized that there are alternative forms of genes (although he did not use that term), the units that determine heredity SEED COLOR Yellow Green SEED SHAPE Round Wrinkled POD SHAPE Inflated Constricted POD COLOR Green Yellow STEM LENGTH Figure 9.2D Tall Dwarf

8. 9.3 Mendel’s principle of segregation describes the inheritance of a single characteristic P GENERATION(true-breedingparents) • From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic • One characteristic comes from each parent Purple flowers White flowers All plants have purple flowers F1generation Fertilization among F1 plants(F1 x F1) F2generation 3/4 of plantshave purple flowers 1/4 of plantshave white flowers Figure 9.3A

9. GENETIC MAKEUP (ALLELES) P PLANTS PP pp Gametes All P All p • The pairs of alleles separate when gametes form • This process describes Mendel’s law of segregation • Alleles can be dominant or recessive • A sperm or egg carries only one allele of each pair F1 PLANTS(hybrids) All Pp Gametes 1/2P 1/2p P P Eggs Sperm PP F2 PLANTS p p Pp Pp Phenotypic ratio3 purple : 1 white pp Genotypic ratio1 PP : 2 Pp : 1 pp Figure 9.3B

10. 9.4 Homologous chromosomes bear the two alleles for each characteristic • Alternative forms of a gene (alleles) reside at the same locus on homologous chromosomes GENE LOCI DOMINANT allele P a B P a b RECESSIVE allele GENOTYPE: PP aa Bb HOMOZYGOUSfor thedominant allele HOMOZYGOUSfor therecessive allele HETEROZYGOUS Figure 9.4

11. 9.5 The principle of independent assortment is revealed by tracking two characteristics at once • By looking at two characteristics at once, Mendel found that the alleles of a pair segregate independently of other allele pairs during gamete formation • This is known as the principle of independent assortment

12. HYPOTHESIS: DEPENDENT ASSORTMENT HYPOTHESIS: INDEPENDENT ASSORTMENT RRYY rryy PGENERATION RRYY rryy ry ry Gametes RY Gametes RY F1GENERATION RrYy RrYy Eggs 1/2 RY 1/2 RY Sperm Eggs 1/4 RY 1/4 RY 1/2 ry 1/2 ry 1/4 rY 1/4 rY RRYY 1/4 Ry 1/4 Ry RrYY RrYY F2GENERATION 1/4 ry 1/4 ry RRYy rrYY RrYy Yellow round RrYy RrYy RrYy RrYy 9/16 Actual resultscontradict hypothesis Green round rrYy RRyy rrYy 3/16 ACTUAL RESULTSSUPPORT HYPOTHESIS Yellow wrinkled Rryy Rryy 3/16 Yellow wrinkled rryy 1/16 Figure 9.5A

13. Independent assortment of two genes in the Labrador retriever Blind Blind Black coat, normal visionB_N_ Black coat, blind (PRA)B_nn Chocolate coat, normal visionbbN_ Chocolate coat, blind (PRA)bbnn PHENOTYPES GENOTYPES MATING OF HETEROZYOTES(black, normal vision) BbNn BbNn 9 black coat,normal vision 3 black coat,blind (PRA) 3 chocolate coat,normal vision 1 chocolate coat,blind (PRA) PHENOTYPIC RATIO OF OFFSPRING Figure 9.5B

14. 9.6 Geneticists use the testcross to determine unknown genotypes • The offspring of a testcross often reveal the genotype of an individual when it is unknown TESTCROSS: GENOTYPES B_ bb Two possibilities for the black dog: BB or Bb B B b GAMETES b Bb b Bb bb OFFSPRING Figure 9.6 All black 1 black : 1 chocolate

15. 9.7 Mendel’s principles reflect the rules of probability F1 GENOTYPES • Inheritance follows the rules of probability • The rule of multiplication and the rule of addition can be used to determine the probability of certain events occurring Bb female Bb male Formation of eggs Formation of sperm 1/2 B B 1/2 B B 1/2 b b 1/2 1/4 B b b B 1/4 1/4 b b F2 GENOTYPES 1/4 Figure 9.7

16. 9.8 Connection: Genetic traits in humans can be tracked through family pedigrees • The inheritance of many human traits follows Mendel’s principles and the rules of probability Figure 9.8A

17. Family pedigrees are used to determine patterns of inheritance and individual genotypes Dd Joshua Lambert Dd Abigail Linnell D_ JohnEddy ? D_ HepzibahDaggett ? D_ Abigail Lambert ? dd JonathanLambert Dd Elizabeth Eddy Dd Dd dd Dd Dd Dd dd Female Male Deaf Hearing Figure 9.8B

18. 9.9 Connection: Many inherited disorders in humans are controlled by a single gene Normal Dd Normal Dd PARENTS • Most such disorders are caused by autosomal recessive alleles • Examples: cystic fibrosis, sickle-cell disease D D Eggs Sperm DD Normal d d Dd Normal (carrier) Dd Normal (carrier) OFFSPRING dd Deaf Figure 9.9A

19. Examples: achondroplasia, Huntington’s disease • A few are caused by dominant alleles Figure 9.9B

20. Table 9.9

21. 9.10 Connection: 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 Figure 9.10A Uterus Cervix Karyotyping Cell culture

22. 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 Figure 9.10B

23. Examination of the fetus with ultrasound is another helpful technique Figure 9.10C, D

24. Section 9-1VOCABULARY REVIEW • The F1 generation consists of the offspring of a • cross between two parents; the F2 generation consists • of the offspring of a cross between two individuals • in the same F1 generation.

25. 2. A dominant factor is one that masks the effect of • another factor for the same characteristic; a recessive • factor is one whose effect is masked by another • factor for the same characteristic.

26. 3. Self-pollination occurs between flowers on the same • plant. Cross-pollination occurs between flowers on • different plants.

27. 1. c • 2. a • 3. d • 4. b

28. 1. An allele is each of two alternative forms of a • gene.

29. 2. In meiosis, the two alleles of each gene are segregated • when the two chromosomes in each pair of • homologues are separated into different gametes. • Alleles of genes located on different chromosomes • or far apart on the same chromosome assort independently • when homologues are randomly separated • during meiosis.

30. 3. Orange flower color is dominant. All of the F1 • plants will have orange flowers.

31. 4. Mendel would have observed that the traits • controlled by dominant factors for these characteristics • almost always appeared together. Thus, he • might not have concluded that the factors for different • characteristics are assorted independently.

32. Possible combinations are RB, Rb, rB, and rb.

33. Section 9-2VOCABULARY REVIEW • 1. In complete dominance, heterozygous and dominant • homozygous individuals have the same phenotype. • For example, in pea plants, the P allele is • completely dominant over the p allele, so both PP • and Pp plants have purple flowers.

34. 2. In incomplete dominance, neither allele is completely • dominant over the other and both influence • the phenotype. For example, in four o’clocks, • neither the R nor r allele is completely dominant, • so Rr plants have pink flowers.

35. 3. In codominance, neither allele is dominant or • recessive; both are expressed in heterozygotes. • For example, in MN blood blood types, both M and • N molecules are produced by an LMLN individual.

36. MULTIPLE CHOICE • 1. b • 2. a • 3. c • 4. d • 5. c

37. SHORT ANSWER • 1. In a homozygous individual, both alleles of a pair • are the same; in a heterozygous individual, the • two alleles of a pair are different.

38. 2. 0.25 × 80 individuals = 20 individuals

39. 3. AA and Aa will result. 100% will have the dominant • phenotype.

40. 4. In a testcross, the dominant phenotype would • appear in all of the offspring if the cow were • homozygous dominant but in only about 50% of • the offspring if the cow were heterozygous. With • only one individual per F1 generation, distinguishing • between these two possibilities would • take a long time, until a calf with the recessive • phenotype was born.

41. STRUCTURES AND FUNCTIONS • Arrangements of the offspring alleles will vary • according to the order of the parental alleles in the • Punnett square. 1. 9/16 2. 1/4 3. 1/16 4. 1/16