1. BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 9 Patterns of Inheritance Modules 9.11 – 9.23

2. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mendel’s principles are valid for all sexually reproducing species –However, often the genotype does not dictate the phenotype in the simple way his principles describe VARIATIONS ON MENDEL’S PRINCIPLES The relationship of genotype to phenotype is rarely simple

3. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings When an offspring’s phenotype—such as flower color— is in between the phenotypes of its parents, it exhibits incomplete dominance 1. Incomplete dominance results in intermediate phenotypes P GENERATION F 1 GENERATION F 2 GENERATION Red RR GametesRr White rr Pink Rr Rr RR rr 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 1/21/2 SpermEggs Pink Rr Pink rR White rr Red RR Figure 9.12A

4. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Incomplete dominance in human hypercholesterolemia Figure 9.12B GENOTYPES: HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors PHENOTYPES: LDL LDL receptor Cell NormalMild diseaseSevere disease

5. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In a population, multiple alleles often exist for a characteristic –The three alleles for ABO blood type in humans is an example 2. Many genes have more than two alleles in the population

6. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.13 –3. Codominance--The alleles for A and B blood types are codominant, and both are expressed in the phenotype Blood Group (Phenotype) O Genotypes Antibodies Present in Blood Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left OABAB A B ii I A or I A i I B or I B i I A I B Anti-A Anti-B Anti-A

7. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings There are at least 29 different blood groups including the ABO blood group.

8. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Calico Cat-codominance 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] phaeomelanineumelanin good luck[1] The spotting gene causes white patches to cover the colored furspotting gene

9. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Co-Dominance ---Both Alleles express themselves

10. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 4. A single gene may affect many phenotypic characteristics A single gene may affect phenotype in many ways –This is called pleiotropy –The allele for sickle-cell disease is an example

11. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Individual homozygous for sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped Sickle cells Breakdown of red blood cells Clumping of cells and clogging of small blood vessels Accumulation of sickled cells in spleen Physical weakness Anemia Heart failure Pain and fever Brain damage Damage to other organs Spleen damage Kidney failure Rheumatism Pneumonia and other infections Paralysis Impaired mental function Figure 9.14

12. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings This situation creates a continuum of phenotypes –Example: skin color 5. A single characteristic may be influenced by many genes

13. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.16 P GENERATION F 1 GENERATION F 2 GENERATION aabbcc (very light) AABBCC (very dark) AaBbCc EggsSperm Fraction of population Skin pigmentation

14. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetic testing can be of value to those at risk of developing a genetic disorder or of passing it on to offspring 9.15 Connection: Genetic testing can detect disease-causing alleles Figure 9.15B Figure 9.15A Dr. David Satcher, former U.S. surgeon general, pioneered screening for sickle-cell disease Thallasemia, Cystic Fibrosis, Tay Sachs,

15. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Canavan Disease -- This condition is most common in people of Ashkenazi Jewish ancestry, with a carrier incidence of 1 in 40. Canavan disease is a central nervous system disease that is usually fatal in childhood, with a few people surviving to adulthood. This disease is the result of a substance that destroys the central nervous system over time. There is presently no effective treatment for Canavan disease. Fragile X Syndrome -- The Fragile X syndrome is not specific to a certain ethnic background. It is an inherited condition that can cause a range of intellectual and behavioral problems, from learning disabilities to mental retardation to autism. While Fragile X syndrome tends to be more severe in boys, it occurs in both males or females. It can be passed on to family members by individuals who have no signs of the syndrome. Review of your family history with a genetic counselor may help determine if Fragile X carrier testing is indicated. Sickle Cell Disease -- This condition is most common in persons of African-American, African, Mediterranean, Hispanic and South American ancestry, with the carrier risk ranging from 1/10 to 1/40, depending on your ethnic background. Sickle cell disease is caused by a variant hemoglobin that changes the shape of the red blood cells. This causes anemia, severe pain, a tendency toward infection, and other serious health problems. Frequent blood transfusions and infection preventing antibiotics are available treatment. Tay Sachs Disease -- People of both Ashkenazi Jewish and French Canadian ancestry have the greatest chance of being carriers of Tay Sachs disease, about 1/30 versus 1/250 in the general population. The disease results from a build up of certain substances in the brain, and is fatal in early childhood. There is presently no effective treatment for Tay Sachs disease. Thalassemia -- Individuals of Mediterranean, Southeast Asian and African ancestry have the greatest chance - 1 in 3 and 1 in 30, respectively -- of being carriers for thalassemia. In general, this group of blood disorders affects a person's ability to produce hemoglobins, the protein in our blood that carries oxygen and nutrients to all parts of the body. In severe cases, children with thalassemia may not survive. Others have anemia, bone growth problems and liver and spleen involvement. Blood transfusions may be needed for treatment.

16. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ethnic disorders continued Cystic fibrosis (CF) is a progressive disorder that causes the body to produce an abnormally thick, sticky mucus which is present in the lungs and digestive system. There are a variety of symptoms including frequent respiratory infections, poor weight gain, and progressive lung damage. Treatment of CF depends upon the stage of the disease and the organs involved. The condition is life shortening. The average age of death is in the early 30's. Although CF is no more common among Ashkenazi Jews than it is among other caucasians, it is one of the most common genetic disorders among Jews and non-Jews alike. Disease frequency: One in every 3,200 live Caucasian births. Carrier frequency:Approximately 1 in 25 in Caucasians and similar frequency in those of Jewish ancestry. Diagnosis:By measuring amount of salt in sweat ("sweat test") or by testing the CF gene. Inheritance:Autosomal Recessive Carrier testing:Available by testing the CF gene. Prenatal diagnosis:Available by testing the CF gene

17. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Prenatal diagnosis for couples testing positive after genetic testing Chorionic villus sampling at 8 weeks of gestation. Amniocentesis at 12-18 weeks of gestation. Pre-implantation genetic testing and In vitro fertilization

18. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genes are located on chromosomes –Their behavior during meiosis accounts for inheritance patterns THE CHROMOSOMAL BASIS OF INHERITANCE 9.17 Chromosome behavior accounts for Mendel’s principles

19. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The chromosomal basis of Mendel’s principles Figure 9.17

20. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Question? What is the phenotypic ratio between a dihybrid cross involving two heterozygotes? 9:3:3:1

21. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Certain genes are linked –They tend to be inherited together because they reside close together on the same chromosome 9.18 Genes on the same chromosome tend to be inherited together When would they not be inherited together?

22. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.18 If you cross PpLl x PpLl, what Phenotypic ratio do you expect? When the organism was selved or self pollinated, most of the progeny looked like the parent but the 9:3:3:1 ratio was not realized!! Linked genes were then suspected.

23. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings This produces gametes with recombinant chromosomes The fruit fly Drosophila melanogaster was used in the first experiments to demonstrate the effects of crossing over 9.19 Crossing over produces new combinations of alleles

24. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A B a b TetradCrossing over AB a ba BAb Gametes Figure 9.19A, B When does crossing over take place?

25. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Question? What is the phenotypic ratio between a dihybrid cross involving two heterozygotes? 9:3:3:1

26. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.19C When you cross a di-hybrid heterozygote with a homozygous recessive, you expect a ¼ distribution of each potential phenotype. GgLl X ggll When this particular cross was performed, this was not the case. Most of the organisms resembled the parents. A few had the independently assorted phenotypes. What had occurred is that genes for body color and wing type were on the same chromosome (linked) and in some gametes, crossing over did occur, but in most gamestes, G and L were linked as were g and l.

27. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Crossing Over and Linkage Is crossing over more likely to occur between genes that are close together or farther apart? Does crossing over comply with Mendel’s Law of Independent Assortment? Law of Segregation?

28. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Crossing over is more likely to occur between genes that are farther apart –Recombination frequencies can be used to map the relative positions of genes on chromosomes. –Determine the location of g and c and l on the chromosome. Recombination frequency between g and c is 9%, between c and l is 9.5%, and between g and l is 17%. 9.20 Geneticists use crossover data to map genes g Figure 9.20B Chromosome cl 17% 9%9.5%

29. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings answer Answer: 3.6% recombination 3.6 map units 3.6 centiMorgans

30. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In corn C (colored) is dominant to c (colorless) and for the endosperm (part of seed where food is stored for embryo) Full (F) is dominant to shrunken (f). When an CcFf was test crossed, the results were as follows: Colored, full 4032 colored, shrunken 149 Colorless, full 152 Colorless, shrunken 4035 What do you expect if the genes are not linked? CcFf x ccff? 1:1:1:1 We got 27:1:1:27

31. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Chinese primrose-slate color (s) is recessive to blue (S), red stigma(r) is recessive to green stigma (R), and long style (l) is recessive to short style (L). All three genes are on the same chromosome. The F1 of a cross of true breeding strains, was test crossed and gave the following: Slate, green, short27 Slate, red, short 85 Blue, red short 402 Slate, red, long 977 Slate, green, long 427 Blue, green, long 95 Blue, green, short 960 Blue, red,long 27 Total 3000

32. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Answer the following questions: What were the genotypes of the parents in the cross of the two true-breeding strains? Make a map of the genes, showing gene order and distance between them. Answer: hum??????????????????

33. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings slate (s) red (r) long (l) Blue (S) Green (R) short (L) SsRrLl x ssrrll Expect 1:1:1:1 If not expect crossing over. To determine placement of genes on chromosomes: –Inspect for highest frequencies for parental phenotypes. (NO crossing over) –Inspect for other phenotypes to show single and double crossing over. (Lowest # is double crossing over) –Determine position of genes on chromosome. The gene that has changed position relative to the other two is the central (observe double cross overs only). –Designate regions I and II and calculate crossing over in those regions. Add all combinations in each region (both single cross over and double) to determine cross over frequency in that region.

34. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Blue, Green, Short and slate, red, long are parental phenotypes Blue, red, long and slate, Green, Sort are the double crossovers. Flower color (Blue vs slate)has changed position relative to stigma and style. “S: is in the middle. Rsl and RSL Region I ---Rsl and rSL + RsL and rSl = 427 + 402 + 27 + 27 = 883/3000 = 29.43% Region II ---RSl and rsL + RsL and rSl = 95 + 85 + 27 + 27 = 234/3000 = 7.8% Thus, R----------------S-----L

35. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings answer Between r and s the distance is 29.4 map units Between s and l is 7.8 map units.

36. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Alfred H. Sturtevant, seen here at a party with T. H. Morgan and his students, used recombination data from Morgan’s fruit fly crosses to map genes Figure 9.20A

37. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A partial genetic map of a fruit fly chromosome Figure 9.20C Short aristae Black body (g) Cinnabar eyes (c) Vestigial wings (l) Brown eyes Long aristae (appendages on head) Gray body (G) Red eyes (C) Normal wings (L) Red eyes Mutant phenotypes Wild-type phenotypes

38. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A human male has one X chromosome and one Y chromosome A human female has two X chromosomes Whether a sperm cell has an X or Y chromosome determines the sex of the offspring SEX CHROMOSOMES AND SEX-LINKED GENES 9.21 Chromosomes determine sex in many species

39. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.21A XY Male (male) Parents’ diploid cells (female) Sperm Offspring (diploid) Egg

40. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Other systems of sex determination exist in other animals and plants Figure 9.21B-D –The X-O system –The Z-W system –Chromosome number

41. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings All genes on the sex chromosomes are said to be sex-linked –In many organisms, the X chromosome carries many genes unrelated to sex –Fruit fly eye color is a sex-linked characteristic 9.22 Sex-linked genes exhibit a unique pattern of inheritance Figure 9.22A

42. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Their inheritance pattern reflects the fact that males have one X chromosome and females have two Figure 9.22B-D –These figures illustrate inheritance patterns for white eye color (r) in the fruit fly, an X-linked recessive trait FemaleMaleFemaleMaleFemaleMale XrYXrYXRXRXRXR XRXrXRXr XRYXRY XRXR XrXr Y XRXrXRXr XRXR XrXr XRXRXRXR XRXR Y XRYXRY XrXRXrXR XRYXRY XrYXrY XRXrXRXr XRXR XrXr XrXr Y XRXrXRXr XrXrXrXr XRYXRY XrYXrY XrYXrY R = red-eye allele r = white-eye allele

43. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Most sex-linked human disorders are due to recessive alleles –Examples: hemophilia, red-green color blindness –These are mostly seen in males –A male receives a single X-linked allele from his mother, and will have the disorder, while a female has to receive the allele from both parents to be affected 9.23 Connection: Sex-linked disorders affect mostly males Figure 9.23A

44. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A high incidence of hemophilia has plagued the royal families of Europe Figure 9.23B Queen Victoria Albert AliceLouis AlexandraCzar Nicholas II of Russia Alexis