CHAPTER 9Patterns of Inheritance: CHAPTER 9 Patterns of Inheritance Modules 9.1 – 9.10


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 Purebreds and Mutts — A Difference of Heredity


Slide3: The parents of these puppies were a mixture of different breeds Their behavior and appearance is more varied as a result of their diverse genetic inheritance


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 MENDEL’S PRINCIPLES 9.1 The science of genetics has ancient roots


Slide5: Gregor Mendel Figure 9.2Ax


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


Slide7: Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation Figure 9.2C This illustration shows his technique for cross-fertilization 1 Removed stamens from purple flower White Stamens Carpel Purple PARENTS (P) OFF-SPRING (F1) 2 Transferred pollen from stamens of white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod


Slide8: Mendel studied seven pea characteristics Figure 9.2D He hypothesized that there are alternative forms of genes (although he did not use that term), the units that determine heredity 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


Slide9: Purple and white sweet pea flowers Figure 9.3x


9.3 Mendel’s principle of segregation describes the inheritance of a single characteristic: From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic One characteristic comes from each parent 9.3 Mendel’s principle of segregation describes the inheritance of a single characteristic P GENERATION (true-breeding parents) F1 generation F2 generation Purple flowers White flowers All plants have purple flowers Fertilization among F1 plants (F1 x F1) 3/4 of plants have purple flowers 1/4 of plants have white flowers Figure 9.3A


Slide11: A sperm or egg carries only one allele of each pair The pairs of alleles separate when gametes form This process describes Mendel’s law of segregation Alleles can be dominant or recessive GENETIC MAKEUP (ALLELES) P PLANTS F1 PLANTS (hybrids) F2 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


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 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


9.5 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 9.5 The principle of independent assortment is revealed by tracking two characteristics at once


Slide14: Figure 9.5A HYPOTHESIS: DEPENDENT ASSORTMENT HYPOTHESIS: INDEPENDENT ASSORTMENT P GENERATION F1 GENERATION F2 GENERATION RRYY rryy Gametes RY Yellow round ry RrYy Eggs Sperm RY ry RY ry 1/2 1/2 1/2 1/2 Actual results contradict hypothesis RRYY rryy RY ry Gametes RrYy Eggs RY rY 1/4 1/4 Ry ry 1/4 1/4 RY rY Ry ry 1/4 1/4 1/4 1/4 RRYY RrYY RrYY RRYy rrYY RrYy RrYy RrYy RrYy RrYy rrYy RRyy rrYy Rryy Rryy rryy 9/16 3/16 3/16 1/16 Green round Yellow wrinkled Yellow wrinkled ACTUAL RESULTS SUPPORT HYPOTHESIS


Slide15: Independent assortment of two genes in the Labrador retriever Figure 9.5B PHENOTYPES Black coat, normal vision B_N_ Blind GENOTYPES MATING OF HETEROZYOTES (black, normal vision) PHENOTYPIC RATIO OF OFFSPRING Black coat, blind (PRA) B_nn Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn 9 black coat, normal vision 3 black coat, blind (PRA) 3 chocolate coat, normal vision 1 chocolate coat, blind (PRA) Blind BbNn BbNn


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 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


9.7 Mendel’s principles reflect the rules of probability: 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 9.7 Mendel’s principles reflect the rules of probability F1 GENOTYPES Bb female F2 GENOTYPES Formation of eggs Bb male Formation of sperm 1/2 1/2 1/2 1/2 1/4 1/4 1/4 1/4 B B B B B B b b b b b b Figure 9.7


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 9.8 Connection: Genetic traits in humans can be tracked through family pedigrees Figure 9.8A


Slide19: Family pedigrees are used to determine patterns of inheritance and individual genotypes Figure 9.8B Dd Joshua Lambert Dd Abigail Linnell D_ Abigail Lambert Female Dd Elizabeth Eddy D_ John Eddy ? D_ Hepzibah Daggett ? ? dd Dd Dd Dd dd Dd Dd Male Deaf Hearing dd Jonathan Lambert


9.9 Connection: Many inherited disorders in humans are controlled by a single gene: Most such disorders are caused by autosomal recessive alleles Examples: cystic fibrosis, sickle-cell disease 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


Slide21: A few are caused by dominant alleles Figure 9.9B Examples: achondroplasia, Huntington’s disease


Slide22: Table 9.9


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 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


Slide24: Chorionic villus sampling is another procedure that obtains fetal cells for karyotyping Figure 9.10B Fetus (10-12 weeks) Placenta Chorionic villi Suction Several hours later Fetal cells (from chorionic villi) Karyotyping Some biochemical tests


Slide25: Examination of the fetus with ultrasound is another helpful technique Figure 9.10C, D