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Chapter 9

0. Chapter 9. Patterns of Inheritance. In your own words, in 3 lines, describe what genetics is, and how traits are expressed. Do Now. Purebreds and Mutts–A Difference of Heredity Purebred dogs Are very similar on a genetic level due to selective breeding.

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Chapter 9

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  1. 0 Chapter 9 Patterns of Inheritance

  2. In your own words, in 3 lines, describe what genetics is, and how traits are expressed. Do Now

  3. Purebreds and Mutts–A Difference of Heredity Purebred dogs Are very similar on a genetic level due to selective breeding

  4. Mutts, or mixed breed dogs on the other hand Show considerably more genetic variation

  5. MENDEL’S LAWS 9.1 The science of genetics has ancient roots The historical roots of genetics, the science of heredity date back to ancient attempts at selective breeding Pangenesis-particles travel from each part of an organism’s body to the eggs or sperm and are then passed to the next generation. Changes that occur in various parts of the body during an organism’s life are passed on in this way.

  6. 9.2 Experimental genetics began in an abbey garden Modern genetics Began with Gregor Mendel’s quantitative experiments with pea plants Petal Stamen Carpel Figure 9.2 A Figure 9.2 B

  7. 1Removed stamens from purple flower White Stamens Mendel crossed pea plants that differed in certain characteristics And traced traits from generation to generation Carpel 2 Transferred pollen from stamens of white flower to carpel of purple flower Parents(P) Purple 3 Pollinated carpel matured into pod 4 Planted seedsfrom pod Offspring(F1) Figure 9.2 C

  8. Purple Flower color White Terminal Axial Flower position Mendel hypothesized that there are alternative forms of genes The units that determine heritable traits Green Yellow Seed color Seed shape Round Wrinkled Pod shape Inflated Constricted Green Yellow Pod color Tall Stem length Dwarf Figure 9.2 D

  9. Self-fertilization-sperm-carrying pollen grains released from the stamens land on the egg-containing carpel of the same flower. Cross-fertilization-fertilization of one plant by pollen from a different plant. True-breeding-Varieties of plants in which self-fertilization produces offspring that are identical to the parents Hybrid-the offspring of two different varieties

  10. Cross-(hybridization)-the cross-fertilization itself P Generation-the true-breeding parents F1 Generation-the hybrid offspring of the P generation F2 Generation-the offspring of the F1 plants self-fertilization, or fertilization with each other.

  11. 9.3 Mendel’s law of segregation describes the inheritance of a single characteristic Monohybrid cross-a breeding experiment in which the parental varieties differ in only one trait. From his experimental data, Mendel deduced that an organism has two genes (alleles) for each inherited characteristic Allele-alternative versions of a gene. Figure 9.3 A

  12. For each characteristic, an organism inherits two alleles, one from each parent Homozygous-an organism has two identical alleles for a gene Heterozygous-an organism has two different alleles for a gene

  13. If the two alleles of an inherited pair differ Then one determines the organism’s appearance and is called the dominantallele The other allele Has no noticeable effect on the organism’s appearance and is called the recessiveallele

  14. Mendel’s law of segregation Predicts that allele pairs separate from each other during the production of gametes Applies to all sexually reproducing organisms. Figure 9.3 B

  15. P plants Genetic makeup (alleles) pp PP Gametes All p All P F1 plants (hybrids) All Pp 1 2 1 2 P p Gametes Phenotype-an organism’s expressed, physical traits Genotype-an organism’s genetic makeup Sperm p P F2 plants Phenotypic ratio 3 purple : 1 white Pp P PP Eggs Genotypic ratio 1 PP: 2 Pp: 1 pp Pp p pp

  16. Dominantallele Gene loci a B P 9.4 Homologous chromosomes bear the two alleles for each characteristic Alleles (alternative forms) of a gene Reside at the same locus on homologous chromosomes a b P Recessiveallele Genotype: PP aa Bb Heterozygous Homozygousfor thedominant allele Homozygousfor therecessive allele Figure 9.4

  17. 9.5 The law of independent assortment is revealed by tracking two characteristics at once By looking at two characteristics at once Mendel tried to determine how two characteristics were inherited

  18. Hypothesis: Independent assortment Hypothesis: Dependent assortment RRYY P generation rryy RRYY rryy ry ry Gametes Gametes RY  RY RrYy RrYy F1 generation Sperm Sperm Mendel’s law of independent assortment States that alleles of a pair segregate independently of other allele pairs during gamete formation 1 4 1 4 1 4 1 4 ry ry RY RY 1 2 1 2 ry RY 1 4 RY 1 2 RY RrYY RRYY RRYy RrYy F2 generation Eggs 1 4 ry 1 2 ry rrYY rrYy RrYy RrYY Eggs Yellowround 9 16 1 4 Ry RrYy RRyy RRYy Rryy Greenround 3 16 1 4 ry Yellowwrinkled Actual resultscontradict hypothesis 3 16 rryy RrYy rrYy Rryy Greenwrinkled 1 16 Actual resultssupport hypothesis Figure 9.5 A

  19. Heterozygous x Heterozygous 9:3:3:1

  20. Blind Blind The phenotypic ratio resulting from a dihybrid cross showing independent assortment is expected to be 9:3:3:1. Phenotypes Genotypes Black coat, normal vision B_N_ Black coat, blind (PRA) B_nn Chocolate coat, normal vision bbN_ Chocolate coat, blind (PRA) bbnn Mating of heterozygotes (black, normal vision) BbNn  BbNn 9 black coat, normal vision 3 black coat, blind (PRA) 1 chocolate coat, blind (PRA) 3 chocolate coat, normal vision Phenotypic ratio of offspring Figure 9.5 B

  21. Testcross: Genotypes bb B_ 9.6 Geneticists use the testcross to determine unknown genotypes The offspring of a testcross, a mating between an individual of unknown genotype and a homozygous recessive individual can reveal the unknown’s genotype Two possibilities for the black dog: BB or Bb Gametes B b B b Bb b bb Bb 1 black : 1 chocolate All black Offspring Figure 9.6

  22. Number of times an event is expected to happen • Probability= Number of times an event could happen 9.7 Mendel’s laws reflect the rules of probability Inheritance follows the rules of probability

  23. F1 genotypes Bbmale Formation of sperm Bbfemale Formation of eggs The rule of multiplication Calculates the probability of two independent events The rule of addition Calculates the probability of an event that can occur in alternate ways 1 2 1 2 b B b B B B 1 2 B 1 4 1 4 F2 genotypes 1 2 B b b b b 1 4 1 4 Figure 9.7

  24. Do Now Using a six-sided die, what is the probability of rolling either a 5 or a 6? 1/6 + 1/6 = 1/3

  25. CONNECTION Dominant Traits Recessive Traits Freckles No freckles 9.8 Genetic traits in humans can be tracked through family pedigrees The inheritance of many human traits follows Mendel’s laws Widow’s peak Straight hairline Free earlobe Attached earlobe Figure 9.8 A

  26. D ? John Eddy Dd Abigail Linnell D ? Hepzibah Daggett Dd Joshua Lambert dd Jonathan Lambert Dd Elizabeth Eddy D ? Abigail Lambert Family pedigrees Can be used to determine individual genotypes Dd Dd dd Dd Dd Dd dd Female Male Deaf Hearing Figure 9.8 B

  27. CONNECTION 9.9 Many inherited disorders in humans are controlled by a single gene Some autosomal disorders in humans Table 9.9

  28. Parents Normal Dd Normal Dd X Sperm Dd Dd Normal (carrier) Recessive Disorders Most human genetic disorders are recessive A carrier of a genetic disorder who does not show symptoms is most likely to be heterozygous for the trait and able to transmit it to offspring. DD Normal D Offspring Eggs Dd Normal (carrier) dd Deaf d Figure 9.9 A

  29. Dominant Disorders Some human genetic disorders are dominant Figure 9.9 B

  30. CONNECTION 9.10 New technologies can provide insight into one’s genetic legacy New technologies Can provide insight for reproductive decisions

  31. Identifying Carriers • For an increasing number of genetic disorders • Tests are available that can distinguish carriers of genetic disorders

  32. Fetal Testing • Amniocentesis and chorionic villus sampling (CVS) • Allow doctors to remove fetal cells that can be tested for genetic abnormalities Chorionic villus sampling (CVS) Amniocentesis Needle inserted through abdomen to extract amniotic fluid Ultrasound monitor Ultrasound monitor Suction tube inserted through cervix to extract tissue from chorionic villi Fetus Fetus Placenta Placenta Chorionic villi Uterus Cervix Cervix Uterus Amniotic fluid Centrifugation Fetal cells Fetal cells Biochemical tests Several weeks Several hours Karyotyping Figure 9.10 A

  33. Fetal Imaging • Ultrasound imaging • Uses sound waves to produce a picture of the fetus Figure 9.10 B

  34. Newborn Screening • Some genetic disorders can be detected at birth • By simple tests that are now routinely performed in most hospitals in the United States

  35. Ethical Considerations • New technologies such as fetal imaging and testing • Raise new ethical questions

  36. VARIATIONS ON MENDEL’S LAWS 9.11 The relationship of genotype to phenotype is rarely simple Mendel’s principles are valid for all sexually reproducing species But genotype often does not dictate phenotype in the simple way his laws describe

  37. Find the phenotype of an individual the offspring of an individual from a RR mother and rr father using incomplete dominance where RR-red and rr-white. Do Now

  38. P generation Red RR White rr  r R Gametes F1 generation Pink Rr 9.12 Incomplete dominance results in intermediate phenotypes When an offspring’s phenotype is in between the phenotypes of its parents It exhibits incomplete dominance Genotypes: HH Homozygous for ability to make LDL receptors Hh Heterozygous 1 2 hh Homozygous for inability to make LDL receptors 1 2 r R Gametes Sperm Phenotypes: 1 2 1 2 r R LDL LDL receptor Pink rR 1 2 Red RR R Eggs F2 generation Pink Rr White rr 1 2 Cell r Mild disease Severe disease Normal Figure 9.12 A Figure 9.12 B

  39. 9.13 Many genes have more than two alleles in the population The expression of both alleles for a trait in a heterozygous individual illustrates codominance. RR rr Rr

  40. Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left Blood Group (Phenotype) Antibodies Present in Blood Genotypes O A B AB Anti-A Anti-B ii O The ABO blood type in humans Involves three alleles of a single gene The alleles for A and B blood types are codominant And both are expressed in the phenotype IAIA or IAi Anti-B A IBIB or IBi Anti-A B — AB IAIB Figure 9.13

  41. Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin 9.14 A single gene may affect many phenotypic characteristics In pleiotropy, a single gene may affect phenotype in many ways Sickle-cell disease represents codominance and pleiotropy. Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickle cells 5,555 Clumping of cells and clogging of small blood vessels Breakdown of red blood cells Accumulation of sickled cells in spleen Brain damage Pain and fever Damage to other organs Spleen damage Physical weakness Heart failure Anemia Impaired mental function Pneumonia and other infections Kidney failure Paralysis Rheumatism Figure 9.14

  42. P generation aabbcc (very light) AABBCC (very dark) 9.15 A single characteristic may be influenced by many genes Polygenic inheritance creates a continuum of phenotypes where a single phenotypic characteristic is determined by the additive effects of two or more genes Essentially the converse of pleiotropy  F1 generation AaBbCc AaBbCc 15 64 20 64 15 64 1 64 1 64 6 64 6 64 Sperm 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 20 64 1 8 F2 generation 1 8 15 64 1 8 1 8 Eggs 1 8 Fraction of population 6 64 1 8 1 8 1 64 1 8 Skin color Figure 9.15

  43. 9.16 The environmental affects many characteristics Many traits are affected, in varying degrees By both genetic and environmental factors Figure 9.16

  44. CONNECTION 9.17 Genetic testing can detect disease-causing alleles Predictive genetic testing May inform people of their risk for developing genetic diseases

  45. THE CHROMOSOMAL BASIS OF INHERITANCE 9.18 Chromosome behavior accounts for Mendel’s laws Genes are located on chromosomes Whose behavior during meiosis and fertilization accounts for inheritance patterns Chromosome Theory of Inheritance The behavior of chromosomes during meiosis and fertilization accounts for patterns of inheritance.

  46. All round yellow seeds(RrYy) F1 generation R y r Y r R r R Metaphase Iof meiosis(alternative arrangements) y Y y Y r R r R Anaphase Iof meiosis Y y y Y r r R R The chromosomal basis of Mendel’s laws Metaphase IIof meiosis y y Y Y y Y Y Y y y Y y Gametes R r r R r R r R 14 14 14 14 RY ry rY Ry Fertilization among the F1 plants : 3 F2 generation 9 : 3 : 1 (See Figure 9.5A) Figure 9.18

  47. Experiment Purple flower PpLI  PpLI Long pollen • Observed Prediction • Phenotypes offspring (9:3:3:1) Purple long Purple round Red long Red round 215 71 71 24 284 21 21 55 Explanation: linked genes P L Parental diploid cell PpLI P I Meiosis 9.19 Genes on the same chromosome tend to be inherited together Linked Genes Tend to be inheritedtogether because they reside close together onthe same chromosome Do not follow the laws of independent assortment Most gametes P L P I Fertilization Sperm P I P L P L P L P L Most offspring P L P I Eggs P I P I P I P I P L 3 purple long : 1 red round Not accounted for: purple round and red long Figure 9.19

  48. A B a b 9.20 Crossing over produces new combinations of alleles The mechanism that "breaks" the linkage between linked genes is crossing-over. A B a b A b a B Crossing over Tetrad Gametes Figure 9.20 A

  49. Thomas Hunt Morgan Performed some of the early studies of crossing over using the fruit fly Drosophila melanogaster Figure 9.20 B

  50. Experiment Black body, vestigial wings Gray body, long wings (wild type)  GgLI ggll Male Female Offspring Gray long Black long Black vestigial Gray vestigial 965 944 206 185 Parental phenotypes Recombinant phenotypes Morgan’s experiments Demonstrated the roleof crossing over in inheritance 391 recombinants Recombination frequency = = 0.17 or 17% 2,300 total offspring Explanation g l G L ggll (male) GgLI (female) g g l l g g g G L l G l L l Eggs Sperm g g L G L G l l g g g g l l l l Offspring Figure 9.20 C

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