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Albia Dugger Miami Dade College Chapter 13 Observing Patterns in Inherited Traits.

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Presentation on theme: "Albia Dugger Miami Dade College Chapter 13 Observing Patterns in Inherited Traits."— Presentation transcript:

1 Albia Dugger Miami Dade College Chapter 13 Observing Patterns in Inherited Traits

2 13.1 Menacing Mucus Cystic fibrosis (CF) is the most common fatal genetic disorder in the United States

3 Figure 13-1a p203 ATP ΔF508

4 13.2 Mendel, Pea Plants, and Inheritance Patterns Recurring inheritance patterns are observable evidence of how heredity works Before the discovery of genes, it was thought that inherited traits resulted from a blend of parental characters

5 Gregor Mendel

6 Garden Pea Plant: Self Fertilization and Cross-Fertilization carpel A anther B C D E

7

8 Flower cross1

9 Terms Used in Modern Genetics Genes are heritable units of information about traits Each gene has a specific locus on a chromosome Alleles are different molecular forms of a gene

10 Loci of Some Human Genes

11 Figure 13-3a p205 ribosomal RNA skin pigmentation 15 (Tay–Sachs disease) fibrillin 1 (Marfan syndrome)

12 Figure 13-3b p BRCA1 (breast, ovarian cancer) NF1 (neurofibromatosis) (Canavan disease) serotonin transporter Growth hormone p53 tumor antigen

13 Figure 13-3c p205 19LH, β chain HCG, β chain (Warfarin resistance) green/blue eye color brown hair color insulin receptor LDL receptor (coronary artery disease)

14 Figure 13-3d p GHRH (acromegaly) prion protein (Creutzfeldt– Jakob disease) oxytocin

15 Figure 13-3e p205 (green-deficient color blind) X (red-deficient color blind) (hemophilia A) (hemophilia B) XIST X chromosome inactivation control IL2RG (SCID-X1) dystrophin (muscular dystrophy) (anhidrotic ectodermal dysplasia)

16 Terms Used in Modern Genetics Genotype Homozygous (AA or aa) Heterozygous (Aa)

17 Terms Used in Modern Genetics Phenotype: observable traits Any mutated gene is a new allele, whether or not it affects phenotype

18 Terms Used in Modern Genetics An allele is dominant if its effect masks the effect of a recessive allele paired with it Capital letters (P) signify dominant alleles; lowercase letters (p) signify recessive alleles Homozygous dominant (PP) Homozygous recessive (pp) Heterozygous (Pp)

19 Genotypes Give Rise to Phenotypes Pp (heterozygous at the P gene locus) genotype: phenotype: PP (homozygous for dominant allele P) pp (homozygous for recessive allele p)

20 13.3 Mendel’s Law of Segregation Pairs of genes on homologous chromosomes separate during meiosis, so they end up in different gametes Mendel showed that garden pea plants inherit two “units” of information for a trait, one from each parent

21 Gene Segregation Homologous chromosomes (and all the alleles they carry) segregate into separate gametes during meiosis

22 Calculating Probabilities Probability A measure of the chance that a particular outcome will occur Punnett square A grid used to calculate the probability of genotypes and phenotypes in offspring

23 Stepped Art gametes (p) meiosis II gametes (P) DNA replication meiosis I 1 2 zygote (Pp) 3 female gametes male gametes 4 Figure 13-5 p206

24 Figure 13-5b p206 male gametes female gametes

25 Monohybrid Crosses A monohybrid cross is a testcross that checks for a dominance relationship between two alleles at a single locus May be a cross between true breeding (homozygous) individuals (PP x pp), or between identical heterozygotes (Pp x Pp)

26 Generations in a Monohybrid Cross P stands for parents, F for filial (offspring) F 1 : First generation offspring of parents F 2 : Second generation offspring of parents

27 Mendel’s Monohybrid Crosses Mendel used monohybrid crosses to find dominance relationships among pea plant traits When he crossed plants that bred true for white flowers with plants that bred true for purple flowers, all F 1 plants had purple flowers When he crossed two F 1 plants, ¾ of the F 2 plants had purple flowers, ¼ had white flowers

28 Table 13-1 p207

29 Testcrosses A testcross is a method of determining if an individual is heterozygous or homozygous dominant An individual with unknown genotype is crossed with one that is homozygous recessive (PP x pp) or (Pp x pp)

30 Mendel’s Dihybrid Cross parent plant homozygous for purple flowers and long stems PPTT pptt dihybrid PpTt four types of gametes parent plant homozygous for white flowers and short stems PPTTPPTtPpTTPpTt PPTtPPttPpTtPptt PpTTPpTtppTTppTt PpTtPpttppTtpptt PTPtpTpt PT pt PTPtpTpt PP Pt pT pt Stepped Art

31 Offspring of Mendel’s Monohybrid Cross

32 Mendel’s Law of Segregation Mendel observed a phenotype ratio of 3:1 in the F 2 offspring of his monohybrid crosses Consistent with the probability of the pp genotype in the offspring of a heterozygous cross (Pp x Pp) This is the basis of Mendel’s law of segregation Diploid cells have pairs of genes on pairs of homologous chromosomes The two genes of each pair separate during meiosis, and end up in different gametes

33 13.4 Mendel’s Law of Independent Assortment Mendel’s law of independent assortment During meiosis, members of a pair of genes on homologous chromosomes get distributed into gametes independently of other gene pairs

34 Dihybrid Crosses Dihybrid crosses test for dominance relationships between alleles at two loci Individuals that breed true for two different traits are crossed (PPTT x pptt) F 2 phenotype ratio is 9:3:3:1 (four phenotypes) Individually, each dominant trait has an F 2 ratio of 3:1 – inheritance of one trait does not affect inheritance of the other

35 The Contribution of Crossovers Independent assortment also occurs when the genes are on the same chromosome, but far enough apart that crossing over occurs between them very frequently Genes that have loci very close to one another on a chromosome tend to stay together during meiosis and not assort independently

36 Linkage Groups All genes on one chromosome are called a linkage group The farther apart two genes are on a chromosome, the more often crossing over occurs between them Linked genes are very close together; crossing over rarely occurs between them The probability that a crossover will separate alleles of two genes is proportional to the distance between those genes

37 13.5 Beyond Simple Dominance Mendel focused on traits based on clearly dominant and recessive alleles; however, the expression patterns of genes for some traits are not as straightforward

38 Codominance Two nonidentical alleles of a gene are both fully expressed in heterozygotes, so neither is dominant or recessive May occur in multiple allele systems Multiple allele systems Genes with three or more alleles in a population Example: ABO blood types

39 Codominance in ABO Blood Types Phenotypes (blood type): Genotypes: O OO BABA AA or AO AB BB or BO

40 Incomplete Dominance Incomplete dominance One allele is not fully dominant over its partner The heterozygote’s phenotype is somewhere between the two homozygotes, resulting in a 1:2:1 phenotype ratio in F 2 offspring Example: Snapdragon color RR is red Rr is pink rr is white

41 Figure p210 homozygous (RR)homozygous (rr) heterozygous (Rr)

42 Figure 13-10b p210

43 Epistasis Two or more gene products influence a trait Typically, one gene product suppresses the effect of another Example: Coat color in dogs Alleles B and b designate colors (black or brown) Two recessive alleles ee suppress color

44 Coat Colors in Labrador Retrievers

45 Figure 13-11b p211

46 Pleiotropy A pleiotropic gene influences multiple traits Example: Some tall, thin athletes have Marfan syndrome, a potentially fatal genetic disorder

47 13.6 Nature and Nurture Variations in traits aren’t always the result of differences in alleles – many traits are influenced by environmental factors

48 Environment and Gene Expression The environment affects the expression of many genes We can summarize this relationship as: genotype + environment → phenotype

49 Environment and Epigenetics Environmentally driven changes in gene expression patterns can be permanent and heritable Example: Many environmental factors affect DNA methylation patterns, enhancing or suppressing gene expression

50 Effects of Temperature on Gene Expression

51 Figure 13-14a p212 c Mature cutting at low elevation (30 meters above sea level) a Mature cutting at high elevation (3,060 meters above sea level) b Mature cutting at mid-elevation (1,400 meters above sea level)

52 Figure 13-15a p213 A Light micrograph of a living water flea.

53 Figure 13-15b p213 B Electron micrographs comparing Daphnia body form that develops in the presence of few predators (left) with the form that develops in the presence of many predators (right). Note the difference in the length of the tail spine and the pointiness of the head. Chemicals emitted by the water flea’s insect predators provoke the change.

54 Mood Disorders in Humans Environment is a factor in schizophrenia, bipolar disorder, depression, and other mood disorders Example: Stress-induced depression causes methylation- based silencing of a particular nerve growth factor – some antidepressants work by reversing this methylation Future treatments for many disorders may involve deliberate modification of epigenetic marks in one’s DNA

55 13.7 Complex Variations in Traits Individuals of most species vary in some of their shared traits Many traits (such as eye color) show a continuous range of variation

56 Continuous Variation Continuous variation Traits with a range of small differences The more factors that influence a trait, the more continuous the distribution of phenotype Bell curve When continuous phenotypes are divided into measurable categories and plotted as a bar chart, they form a bell- shaped curve

57 Continuous Variation in Height (Females)

58 Continuous Variation in Height (Males)

59 The Bell Curve

60 Regarding the Unexpected Phenotype Phenotype results from complex interactions among gene products and the environment Enzymes and other gene products control steps of most metabolic pathways Mutations, interactions among genes, and environmental conditions may result in unpredictable traits Example: Camptodactyly can affect any fingers on either or both hands

61 Camptodactyly


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