Presentation is loading. Please wait.

Presentation is loading. Please wait.

9.2 Experimental genetics began in an abbey garden Gregor Mendel Augustinian monk who taught natural science to high school students Mendel's brilliant.

Similar presentations


Presentation on theme: "9.2 Experimental genetics began in an abbey garden Gregor Mendel Augustinian monk who taught natural science to high school students Mendel's brilliant."— Presentation transcript:

1 9.2 Experimental genetics began in an abbey garden Gregor Mendel Augustinian monk who taught natural science to high school students Mendel's brilliant performance at school as a youngster encouraged his family to support his pursuit of a higher education, but their resources were limited, so Mendel entered an Augustinian monastery Copyright © 2009 Pearson Education, Inc. Gregor Mendel discovered principles of genetics in experiments with the garden pea Mendel showed that parents pass heritable factors to offspring (heritable factors are now called genes)

2 9.2 Experimental genetics began in an abbey garden Crosses meticulously documented Crosses numerically/statistically analyzed Scientists of 1860s did not understand and appreciate Work lost in journals for 50 years Rediscovered in 1900s independently by 3 scientists

3 Terms to know and understand The phenotype is the appearance or expression of a trait Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene If the alleles differ, the dominant allele determines the organisms appearance, and the recessive allele has no noticeable effect Homozygous individuals have the same allele on both homologues Heterozygous individuals have a different allele on each homologue

4 Mating of plants can be controlled Each pea plant has sperm- producing organs (stamens) and egg-producing organs (carpels) Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another

5 In a typical experiment, Mendel mated two contrasting, true-breeding varieties 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, the F 2 generation is produced Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

6 Transferred pollen from stamens of white flower to carpel of purple flower Stamens Carpel Parents (P) Purple 2 White Removed stamens from purple flower 1 Pollinated carpel matured into pod 3 Offspring (F 1 ) Planted seeds from pod 4

7 Mendels crosses led to questions When Mendel crossed contrasting, true- breeding white and purple flowered pea plants, all of the F 1 hybrids were purple Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

8 Fig EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers

9 Fig EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers F 1 Generation (hybrids) All plants had purple flowers

10 Mendels crosses led to questions When Mendel crossed contrasting, true- breeding white and purple flowered pea plants, all of the F 1 hybrids were purple When Mendel crossed the F 1 hybrids, many of the F 2 plants had purple flowers, but some had white Mendel discovered a ratio of about three to one, purple to white flowers, in the F 2 generation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

11 Fig EXPERIMENT P Generation (true-breeding parents) Purple flowers White flowers F 1 Generation (hybrids) All plants had purple flowers F 2 Generation 705 purple-flowered plants 224 white-flowered plants

12 Questions are... Questions that arise –Why does one trait seemed to disappear in the F 1 generation? –Why does that trait reappear in one quarter of the F 2 offspring? Answers?

13 Mendel reasoned that only the purple flower factor was affecting flower color in the F 1 hybrids Mendel called the purple flower color a dominant trait and the white flower color a recessive trait These inherited factors are what we now call a genes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

14 Table 14-1

15 Mendels Model Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F 2 offspring Four related concepts make up this model These concepts can be related to what we now know about genes and chromosomes Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

16 1.The first concept is that alternative versions of genes account for variations in inherited characters For example, the gene for flower color in pea plants exists in two versions, one for purple flowers and the other for white flowers Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

17 2. The second concept is that for each character an organism inherits two alleles, one from each parent Mendel made this deduction without knowing about the role of chromosomes The two alleles at a locus on a chromosome may be identical, as in the true-breeding plants of Mendels P generation - homozygous Alternatively, the two alleles at a locus may differ, as in the F 1 hybrids - heterozygous Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

18 3. The third concept is that if the two alleles at a locus differ, then one (the dominant allele) determines the organisms appearance, and the other (the recessive allele) has no noticeable effect on appearance In the flower-color example, the F 1 plants had purple flowers because the allele for that trait is dominant Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

19 4. The fourth concept, now known as the law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

20 Lets look at this example again Before we were only looking at phenotype just like Gregor Mendel Lets apply his hypotheses and look at genotype as well Draw a Punnett square that would represent true breeding purple flowers crossed with true breeding white flowers

21 To make a Punnett Square... The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

22 Lets look at this example again Before we were only looking at phenotype just like Gregor Mendel Lets apply his hypotheses and look at genotype as well PP pp PpPp PP p p PpPpPpPp PpPpPpPp Flowers will all be purple because of dominance

23 Lets look at this example again Before we were only looking at phenotype just like Gregor Mendel Lets apply his hypotheses and look at genotype as well Draw the Punnett square that would represent two of the F1 generation breedingt PP pp PpPp PP p p PpPpPpPp PpPpPpPp This cross gives us the F 1 generation

24 Lets look at this example again Allow F1 generation to self-pollinate and fill out the next Punnett square PP pp PpPp PPPpPpPpPppp Pp p P

25 Lets look at this example again Allow F1 generation to self-pollinate and fill out the next Punnett square PP pp PpPp PPPpPpPpPppp Pp p PPPpPp PpPppp ¾ of flowers will all be purple because of dominance. ¼ will be white. P

26 Lets look at this example again PP pp PpPp PPPpPpPpPppp Pp p PPPpPp PpPppp P Genotypic ratio 1 PP : 2 Pp : 1 pp Phenotypic ratio 3 purple : 1 white Single trait cross

27 9.3 Mendels law of segregation describes the inheritance of a single character Four Hypotheses 1.Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene 2.For each characteristic, an organism inherits two alleles, one from each parent; the alleles can be the same or different –A homozygous genotype has identical alleles –A heterozygous genotype has two different alleles Copyright © 2009 Pearson Education, Inc.

28 9.3 Mendels law of segregation describes the inheritance of a single character Four Hypotheses 3.If the alleles differ, the dominant allele determines the organisms appearance, and the recessive allele has no noticeable effect –The phenotype is the appearance or expression of a trait –The same phenotype may be determined by more than one genotype 4.Law of segregation: Allele pairs separate (segregate) from each other during the production of gametes so that a sperm or egg carries only one allele for each gene Copyright © 2009 Pearson Education, Inc.

29 Freckles Widows peak Free earlobe No freckles Straight hairline Attached earlobe Dominant TraitsRecessive Traits Three traits that are determined by single genes with alternate alleles The dominant allele determines the phenotype when at least one copy is present Humans show dominant and recessive traits PTC taste strips

30 Some Genetic Disorders/Anomalies Polydactyly - dominant Tay Sachs - recessive Cystic Fibrosis - recessive Huntingtons Disease - dominant Sickle Cell Anemia - recessive –Cause? –Single substitution of an amino acid in hemoglobin

31 Polydactyly Alfredo Alfonseca "The Six Shooter", former Chicago Cubs relief pitcher Six fingers and toes on each hand, all functional

32 9.8 Genetic traits in humans can be tracked through family pedigrees A pedigree –Shows the inheritance of a trait in a family through multiple generations –Demonstrates dominant or recessive inheritance –Can also be used to deduce genotypes of family members Copyright © 2009 Pearson Education, Inc.

33 Ff FemaleMale Marriage Unaffected First generation (grandparents) Second generation (parents, aunts, and uncles) Third generation (two sisters) Ff ff FF or Siblings Affected Pedigree for a family inheritance of a recessive trait such as deafness

34 Recessive disease Rr ? rr

35 Dominant disease

36 dd Dd

37 Huntingtons Disease - handouthandout

38 Huntingtons Disease Questions What are the chances of a parent with HD passing with HD passing the gene on to any one of his or her children? Thinking of all the ways in which the number of repeats may be passed on to children, discuss the possibility that John may get an HD gene –from his mother –from his father From which parent did Dink get the gene for HD? Explain how you can tell. Do you expect John's mother to show symptoms of HD? Why or why not.

39 Huntingtons Disease Questions John's Aunt Barbara refused to have the test for HD. Discuss some reasons that she may have had for coming to that decision. When she applied for a job as an airline pilot, the company, knowing of the occurrence of HD in the family, insisted that she be tested. Does the company have the right to require the test? Explain why or why not. When John reaches the age of 18, he may make the decision of whether or not to be tested for the HD gene. Consider this question from the perspective of John, John's future children, John's future wife, John's employer, John's medical insurer. –Explain to John why he should have the test done. –Explain to John why he should not have the test done.

40 VARIATIONS ON MENDELS LAWS Copyright © 2009 Pearson Education, Inc.

41 9.11 Incomplete dominance results in intermediate phenotypes Incomplete dominance –Neither allele is dominant over the other –Expression of both alleles is observed as an intermediate phenotype in the heterozygous individual Copyright © 2009 Pearson Education, Inc.

42 P generation 1–21–2 1–21–2 1–21–2 1–21–2 1–21–2 1–21–2 F 1 generation F 2 generation Red RR Gametes Eggs Sperm RR rR Rrrr R r R r R r Pink Rr R r White rr

43 HH Homozygous for ability to make LDL receptors hh Homozygous for inability to make LDL receptors Hh Heterozygous LDL receptor LDL Cell Normal Mild disease Severe disease Genotypes: Phenotypes:

44 9.12 Many genes have more than two alleles in the population Multiple alleles –More than two alleles are found in the population –A diploid individual can carry any two of these alleles –The ABO blood group has three alleles, leading to four phenotypes: type A, type B, type AB, and type O blood Copyright © 2009 Pearson Education, Inc.

45 9.12 Many genes have more than two alleles in the population Codominance –Neither allele is dominant over the other –Expression of both alleles is observed as a distinct phenotype in the heterozygous individual –Observed for type AB blood Copyright © 2009 Pearson Education, Inc.

46 Blood Group (Phenotype) Genotypes O A ii I A or I A i Red Blood Cells Carbohydrate A B I B or I B i Carbohydrate B AB IAIBIAIB

47 Blood Type PhenotypeGenotype AI A I A, I A i BI B I B, I B i ABI A I B Oi

48 Blood Genetics I A I B I B i I A i i i I A i I B i

49 Given a mom with blood type AB and child with blood type A, what are the possible blood types of the father? I A I A I A i I A I B ? ____ Blood Typing Questions IAIA i IAIA IAIAIAIA

50 Dominance Worksheet Copyright © 2009 Pearson Education, Inc.

51 9.13 A single gene may affect many phenotypic characters Pleiotropy –One gene influencing many characteristics –The gene for sickle cell disease –Affects the type of hemoglobin produced –Affects the shape of red blood cells –Causes anemia –Causes organ damage –Is related to susceptibility to malaria Copyright © 2009 Pearson Education, Inc.

52 Clumping of cells and clogging of small blood vessels Pneumonia and other infections Accumulation of sickled cells in spleen Pain and fever Rheumatism Heart failure Damage to other organs Brain damage Spleen damage Kidney failure Anemia Paralysis Impaired mental function Physical weakness Breakdown of red blood cells Individual homozygous for sickle-cell allele Sickle cells Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped

53 9.14 A single character may be influenced by many genes Polygenic inheritance –Many genes influence one trait –Skin color is affected by at least three genes Copyright © 2009 Pearson Education, Inc.

54 P generation 1–81–8 F 1 generation F 2 generation Fraction of population Skin color Eggs Sperm 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 aabbcc (very light) AABBCC (very dark) AaBbCc 1 –– –– 64 6 –– 64 1 –– –– 64 6 –– –– 64 1 –– –– 64 6 –– –– 64

55 9.15 The environment affects many characters Phenotypic variations are influenced by the environment –Skin color is affected by exposure to sunlight –Susceptibility to diseases, such as cancer, has hereditary and environmental components Copyright © 2009 Pearson Education, Inc.

56 EnvironmentIt can fool you

57 EnvironmentIt can fool you ! The hydrangea flower color is controlled first by flower color genes similar to those in the pea. Purple vs. white has complete dominance. But, pink vs. blue is controlled by the acidity of the soil

58 EnvironmentIt can fool you ! The hydrangea flower color is controlled first by flower color genes similar to those in the pea. Purple vs. white has complete dominance. But, pink vs. blue is controlled by the acidity of the soil


Download ppt "9.2 Experimental genetics began in an abbey garden Gregor Mendel Augustinian monk who taught natural science to high school students Mendel's brilliant."

Similar presentations


Ads by Google