1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Lectures by Erin Barley Kathleen Fitzpatrick Mendel and the Gene Idea Chapter 14

2. Overview: Drawing from the Deck of Genes What genetic principles account for the passing of traits from parents to offspring? The “blending” hypothesis is the idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) © 2011 Pearson Education, Inc. BUT THIS IS WRONG

3. The “particulate” hypothesis is the idea that parents pass on discrete heritable units (genes) – This hypothesis can explain the reappearance of traits after several generations – Mendel documented this through his experiments with garden peas © 2011 Pearson Education, Inc. Thanks, Mendel! You’re the best.

4. Concept 14.1: Mendel being a boss and discovering stuff Advantages of pea plants for genetic study – There are many varieties with distinct features called traits – Mating can be controlled – Each flower has sperm- producing organs (stamens) and an egg-producing organ (carpel) © 2011 Pearson Education, Inc. Parental generation (P) Stamens Carpel First filial generation offspring (F 1 ) TECHNIQUE RESULTS 3 2 1 4 5

5. Pea plants were particularly well suited for use in Mendel's breeding experiments for all of the following reasons except that a)peas show easily observed variations in a number of characters, such as pea shape and flower color. b)it is possible to control matings between different pea plants. c)it is possible to obtain large numbers of progeny from any given cross. d)peas have an unusually long generation time. e)many of the observable characters that vary in pea plants are controlled by single genes.

6. First, Mendel mated two contrasting, true-breeding varieties, a process called hybridization – The true-breeding parents are the P generation – The hybrid offspring of the P generation are called the F 1 generation – When F 1 individuals self-pollinate or cross- pollinate with other F 1 hybrids, the F 2 generation is produced © 2011 Pearson Education, Inc. P Generation EXPERIMENT ( true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers Self- or cross-pollination 705 purple- flowered plants 224 white flowered plants Mendel discovered a ratio of about three to one, purple to white flowers, in the F 2 generation

7. Mendel called the purple flower color a dominant trait and the white flower color a recessive trait What Mendel called a “heritable factor” is what we now call a gene © 2011 Pearson Education, Inc.

8. Mendel’s Model 1.Alternative versions of genes are called alleles 2.An organism inherits two alleles, one from each parent 3.Typically one allele will be dominant and determine the appearance and the recessive will not 4.Law of segregation: the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes © 2011 Pearson Education, Inc. Allele for purple flowers Locus for flower-color gene Allele for white flowers Pair of homologous chromosomes

9. A cross between homozygous purple-flowered and homozygous white-flowered pea plants results in offspring with purple flowers. This demonstrates a)the blending model of genetics. b)true-breeding. c)dominance. d)a dihybrid cross. e)the mistakes made by Mendel.

10. The possible combinations of sperm and egg can be shown using a Punnett square – A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele – This helps us predict genetic combinations of offspring! © 2011 Pearson Education, Inc.

11. Figure 14.5-1 P Generation Appearance: Genetic makeup: Gametes: Purple flowers White flowers PP pp P p

12. Figure 14.5-2 P Generation F 1 Generation Appearance: Genetic makeup: Gametes: Appearance: Genetic makeup: Gametes: Purple flowers White flowers Purple flowers Pp PP pp P P p p 1/21/2 1/21/2

13. Figure 14.5-3 P Generation F 1 Generation F 2 Generation Appearance: Genetic makeup: Gametes: Appearance: Genetic makeup: Gametes: Purple flowers White flowers Purple flowers Sperm from F 1 ( Pp ) plant Pp PP pp P P P P p p p p Eggs from F 1 ( Pp ) plant PP pp Pp 1/21/2 1/21/2 3 : 1

14. Useful Genetic Vocabulary Homozygous Heterozygous Genotype Phenotype © 2011 Pearson Education, Inc. Phenotype Purple White 3 1 1 1 2 Ratio 3:1 Ratio 1:2:1 Genotype PP (homozygous) Pp (heterozygous) pp (homozygous)

15. The Testcross How can we tell the genotype of an individual with the dominant phenotype? – Testcross: breeding the mystery individual with a homozygous recessive individual – If any offspring display the recessive phenotype, the mystery parent must be heterozygous © 2011 Pearson Education, Inc.

16. Figure 14.7 Dominant phenotype, unknown genotype: PP or Pp ? Recessive phenotype, known genotype: pp Predictions If purple-flowered parent is PP If purple-flowered parent is Pp or Sperm Eggs or All offspring purple 1 / 2 offspring purple and 1 / 2 offspring white Pp pp p ppp P P P p TECHNIQUE RESULTS

17. Law of independent assortment The law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation – That’s why in punnett squares we separate out the alleles. Monohybrid is easy, but dihybrid requires more work. © 2011 Pearson Education, Inc.

18. Monohybrid Example: In unicorns purple hair is dominant to pink hair. Cross two heterozygous individuals.

19. Dihybrid Example #1: In unicorns glitter horns are dominant to glossy horns and purple hair is dominant to pink hair. Cross two heterozygous individuals for each trait.

20. DO NOW In unicorns glitter horns are dominant to glossy horns and purple hair is dominant to pink hair. Cross one heterozygous individual and one homozyous for glitter horns and homozygous for pink hair.

22. Concept 14.2: The laws of probability govern Mendelian inheritance Genetics=probability! – Tossing a coin- outcome of one toss has no impact on the next toss – In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles © 2011 Pearson Education, Inc.

23. The Multiplication and Addition Rules Applied to Monohybrid Crosses The multiplication rule -probability that two or more independent events will occur together is the product of their individual probabilities Segregation is like flipping a coin: – Each gamete has a 50% chance of carrying the dominant 50% chance of carrying the recessive © 2011 Pearson Education, Inc.

24. Figure 14.9 Segregation of alleles into eggs Segregation of alleles into sperm Sperm Eggs 1/21/2 1/21/2 1/21/2 1/21/2 1/41/4 1/41/4 1/41/4 1/41/4 Rr R R R R R R r r r r r  r

25. The addition rule -the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities – used to figure out the probability that an F 2 plant will be heterozygous or homozygous © 2011 Pearson Education, Inc.

26. Figure 14.UN01 Probability of YYRR Probability of YyRR 1 / 4 (probability of YY) 1 / 2 (Yy) 1 / 4 (RR) 1 / 16 1/81/8       Chance of at least two recessive traits ppyyRr ppYyrr Ppyyrr PPyyrr ppyyrr 1 / 4 (probability of pp)  1 / 2 (yy)  1 / 2 (Rr) 1/4  1/2  1/21/4  1/2  1/2 1/2  1/2  1/21/2  1/2  1/2 1/4  1/2  1/21/4  1/2  1/2 1/4  1/2  1/21/4  1/2  1/2  1 / 16  2 / 16  1 / 16  6 / 16 or 3 / 8

27. Concept 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics © 2011 Pearson Education, Inc. Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical In incomplete dominance, the phenotype of F 1 hybrids is somewhere between the phenotypes of the two parental varieties In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways

28. Multiple Alleles Most genes exist in populations in more than two allelic forms – EX: the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells. I A adds the A carbohydrate I B adds the B carbohydrate i allele adds neither © 2011 Pearson Education, Inc.

29. Figure 14.11 Carbohydrate Allele (a) The three alleles for the ABO blood groups and their carbohydrates (b) Blood group genotypes and phenotypes Genotype Red blood cell appearance Phenotype (blood group) A A B B AB none O IAIA IBIB i ii IAIBIAIB I A I A or I A i I B I B or I B i

30. Pleiotropy Most genes have multiple phenotypic effects, a property called pleiotropy – Ex: pleiotropic alleles cause multiple symptoms of certain diseases (cystic fibrosis and sickle-cell) © 2011 Pearson Education, Inc. Some traits may be determined by two or more genes

31. Epistasis In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus – EX: bin Labrador retrievers coat color depends on two genes One gene determines the pigment color (with alleles B for black and b for brown) The other gene (with alleles E for color and e for no color) determines whether the pigment will be deposited in the hair © 2011 Pearson Education, Inc. Sperm Eggs 9 : 3 : 4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 1/41/4 BbEe BE bE Be be BBEE BbEE BBEeBbEe BbEE bbEEBbEe bbEe BBEe BbEe BBeeBbee BbEebbEe Bbee bbee

32. Polygenic Inheritance Quantitative characters are those that vary in the population along a continuum – Usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype Ex: Skin color © 2011 Pearson Education, Inc. Eggs Sperm Phenotypes: Number of dark-skin alleles: 0 12345 6 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1/81/8 1 / 64 6 / 64 15 / 64 20 / 64 15 / 64 6 / 64 1 / 64 AaBbCc

33. Nature and Nurture: The Environmental Impact on Phenotype Phenotype depends on environment as well as genotype – The norm of reaction is the phenotypic range of a genotype influenced by the environment EX: hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity © 2011 Pearson Education, Inc.

34. Pedigree Analysis A pedigree is a family tree that describes the interrelationships of parents and children across generations Inheritance patterns of particular traits can be traced and described using pedigrees © 2011 Pearson Education, Inc.

35. Figure 14.15 Key Male Female Affected male Affected female Mating Offspring 1st generation 2nd generation 3rd generation 1st generation 2nd generation 3rd generation Is a widow’s peak a dominant or recessive trait? (a)Is an attached earlobe a dominant or recessive trait? b) Widow’s peak No widow’s peak Attached earlobe Free earlobe FF or Ff WW or Ww Ww ww Ww ww Ff ff FF or Ff ff

36. Recessively Inherited Disorders Many genetic disorders are inherited in a recessive manner These range from relatively mild to life- threatening © 2011 Pearson Education, Inc.

37. The Behavior of Recessive Alleles Recessively inherited disorders show up only in individuals homozygous for the allele Carriers are heterozygous individuals who carry the recessive allele but are phenotypically normal; most individuals with recessive disorders are born to carrier parents Albinism is a recessive condition characterized by a lack of pigmentation in skin and hair © 2011 Pearson Education, Inc.

38. Figure 14.16 Parents Normal Aa Sperm Eggs Normal Aa AA Normal Aa Normal (carrier) Aa Normal (carrier) aa Albino A A a a

39. If a recessive allele that causes a disease is rare, then the chance of two carriers meeting and mating is low Consanguineous matings (i.e., matings between close relatives) increase the chance of mating between two carriers of the same rare allele Most societies and cultures have laws or taboos against marriages between close relatives © 2011 Pearson Education, Inc.

40. Cystic Fibrosis Cystic fibrosis is the most common lethal genetic disease in the United States, striking one out of every 2,500 people of European descent Symptoms include mucus buildup in some internal organs and abnormal absorption of nutrients in the small intestine © 2011 Pearson Education, Inc.

41. Sickle-Cell Disease Sickle-cell disease affects one out of 400 African-Americans – Substitution of a single amino acid in the hemoglobin protein – Symptoms: physical weakness, pain, organ damage, and even paralysis – Homozygous all hemoglobin is abnormal (sickle-cell) – Heterozygotes (have sickle-cell trait) are usually healthy but may suffer some symptoms ( less susceptible to the malaria parasite) © 2011 Pearson Education, Inc. https://www.youtube.co m/watch?v=1fN7rOwD yMQ

42. Dominantly Inherited Disorders Some human disorders are caused by dominant alleles – Dominant alleles that cause a lethal disease are rare and arise by mutation Achondroplasia is a form of dwarfism caused by a rare dominant allele © 2011 Pearson Education, Inc. Parents Dwarf Dd Sperm Eggs Dd Dwarf dd Normal Dd Dwarf dd Normal D d d d Normal dd

43. Huntington’s Disease: A Late-Onset Lethal Disease The timing of onset of a disease significantly affects its inheritance Huntington’s disease is a degenerative disease of the nervous system – The disease has no obvious phenotypic effects until the individual is about 35 to 40 years of age – Once the deterioration of the nervous system begins the condition is irreversible and fatal © 2011 Pearson Education, Inc. https://www.youtub e.com/watch?v=P LCvg7Vp3qc

44. Multifactorial Disorders Heart disease, diabetes, alcoholism, mental illnesses, and cancer have both genetic and environmental components – Little is understood about the genetic contribution to most multifactorial diseases © 2011 Pearson Education, Inc.

45. Counseling Based on Mendelian Genetics and Probability Rules Using family histories, genetic counselors help determine the odds that their children will have genetic disorders Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available Couples could also be genetically tested for certain diseases © 2011 Pearson Education, Inc. https://www.youtube.com/watc h?v=hbZiL1LErZA https://www.youtube.com/ watch?v=U5aBfCbQeY0

46. Fetal Testing In amniocentesis, the liquid that bathes the fetus is removed and tested (amniotic fluid) In chorionic villus sampling (CVS), a sample of the placenta is removed and tested Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero © 2011 Pearson Education, Inc. Video: Ultrasound of Human Fetus I

47. Figure 14.19 (a) Amniocentesis (b) Chorionic villus sampling (CVS) Ultrasound monitor Amniotic fluid withdrawn Fetus Placenta UterusCervix Centrifugation Fluid Fetal cells Several hours Several weeks Biochemical and genetic tests Karyotyping Ultrasound monitor Fetus Placenta Chorionic villi Uterus Cervix Suction tube inserted through cervix Several hours Fetal cells Several hours 11223 https://www.youtube.com/watc h?v=uOXjK_IHgzY

48. 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 © 2011 Pearson Education, Inc.