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. canine hip dysplasia

4. 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

5. 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

6. The inheritance of acquired characters (or characteristics) is the hereditary mechanism by which changes in physiology acquired over the life of an organism (such as muscle enlarged through use) are purportedly transmitted to offspring. It is also commonly referred to as the theory of adaptation equated with the evolutionary theory of FrenchnaturalistJean-Baptiste Lamarck (1744-1829).

7. Genetic Disproof • There are many formulations of the genetic disproof, but all have roughly the same structure as the following: • Acquired traits do not affect an organism's genome. • Only the genome is passed to the offspring. • Therefore, acquired traits cannot be passed to the offspring.

8. 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

10. 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

11. 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

12. Punnett Squares • Professor Reginald Crundall Punnett, FRS (June 20, 1875 – January 3, 1967) was a Britishgeneticist who co-founded, with William Bateson, the Journal of Genetics in 1910. Punnett is probably best remembered today as the creator of the Punnett square, a tool still used by biologists to predict the probability of possible genotypes of offspring. His Mendelism (1905) is sometimes said to have been the first textbook on genetics; it was probably the first popular science book to introduce genetics to the public.

14. 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

15. 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 1.Law of segregation • 2. 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

16. 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- One allele is dominant over the other with regard to Mendelian Traits. 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

17. 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: 3.Principle of independent assortment

18. 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

19. 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

20. http://www.athro.com/evo/gen/punexam.html

21. A dihybrid cross

22. The Female Calico Cat-X-Linked Calico coloring is a mix of phaeomelanin based colors (red) and eumelanin based color (black, chocolate and cinnamon). Cats of this coloration are believed to bring good luck in the folklore of many cultures.[1] The spotting gene causes white patches to cover the colored fur

24. 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

25. 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

26. 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

27. 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 OMIM- http://www.ncbi.nlm.nih.gov/sites/entrez?db=omim Figure 9.8A

28. 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

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