13Terms to Know before moving on: Genes: Genetic information that codes for specific traits. Genes have specific loci on a chromosome.Diploid (2n)/haploid (n)True-breeding: Inherit identical alleles generation after generationHybrid: Offspring of a cross that has inherited a pair of nonidentical alleles for a trait.Homozygous: Identical pair of Alleles (TT or tt)Heterozygous: Pair of different alleles for a gene (one allele to be tall (T) and one to be short (t)
14Terms to Know before moving on: Dominant alleles are allele that will mask any recessive allele for the same trait.Dominant alleles are represented with a capital letter (tall = D)Recessive alleles are represented with a lowercase letter (short = d)Genotype refers to an individual’s particular genes.Phenotype refers to the individual’s observable or physical traits.
15Gene loci Dominant allele P a B P a b Recessive allele Genotype: PP aa Gene lociDominantallelePaBPabRecessivealleleFigure 9.4 Matching gene loci on homologous chromosomes.Genotype:PPaaBbHomozygousfor thedominant alleleHomozygousfor therecessive alleleHeterozygous
16A pea plant has the genotype Tt. Do NowT=tall t=shortA pea plant has the genotype Tt.Which trait is dominant? Which is recessive?What is the individual’s phenotype?Explain the individual’s genotype.Could this plant be a true bred plant?Explain what big ‘T’ and little ‘t’ are actually representing. What are they made of? Where would you find them? How are they related to one another? How did the plant get them?
17What causes the plant to be tall gibberellin 3-beta-hydroxylase, a biosynthetic enzyme crucial to the division and elongation of the cells in the plant's stem3β-hydroxylase which converts GA20 to GA1Tallness in pea plants is regulated by a gibberellin (active), GA1, which promotes stem growth.Gibberellins had been discovered in the 1950s, but it was not until the early 1980s that the group connected it to stem height.CU and Australian scientists clone Mendel's historic pea-plant gene By Blaine P. Friedlander Jr.
18gibberellin 3-beta-hydroxylase - 358 AA What is “T”?gibberellin 3-beta-hydroxylase AAATGCCTGCTATGTTAACAGATGTGTTTAGAGGCCATCCCATTCACCTCCCACACTCTCAC ATACCTGACTTCACATCTCTCCGGGAGCTCCCGGATTCTTACAAGTGGACCCCTAAAGAC GATCTCCTCTTCTCCGCTGCTCCTTCTCCTCCGGCCACCGGTGAAAACATCCCTCTCATC GACCTCGACCACCCGGACGCGACTAACCAAATCGGTCATGCATGTAGAACTTGGGGTGCC TTCCAAATCTCAAACCACGGCGTGCCTTTGGGACTTCTCCAAGACATTGAGTTTCTCACC GGTAGTCTCTTCGGGCTACCTGTCCAACGCAAGCTTAAGTCTGCTCGGTCGGAGACAGGT GTGTCCGGCTACGGCGTCGCTCGTATCGCATCTTTCTTCAATAAGCAAATGTGGTCCGAA GGTTTCACCATCACTGGCTCGCCTCTCAACGATTTCCGTAAACTTTGGCCCCAACATCAC CTCAACTACTGCGATATCGTTGAAGAGTACGAGGAACATATGAAAAAGTTGGCATCGAAA TTGATGTGGTTAGCACTAAATTCACTTGGGGTCAGCGAAGAAGACATTGAATGGGCCAGT CTCAGTTCAGATTTAAACTGGGCCCAAGCTGCTCTCCAGCTAAATCACTACCCGGTTTGT CCTGAACCGGACCGAGCCATGGGTCTAGCAGCTCATACCGACTCCACCCTCCTAACCATT CTGTACCAGAACAATACCGCCGGTCTACAAGTATTTCGCGATGATCTTGGTTGGGTCACC GTGCCACCGTTTCCTGGCTCGCTCGTGGTTAACGTTGGTGACCTCTTCCACATCCTATCC AATGGATTGTTTAAAAGCGTGTTGCACCGCGCTCGGGTTAACCAAACCAGAGCCCGGTTA TCTGTAGCATTCCTTTGGGGTCCGCAATCTGATATCAAGATATCACCTGTACCGAAGCTG GTTAGTCCCGTTGAATCGCCTCTATACCAATCGGTGACATGGAAAGAGTATCTTCGAACA AAAGCAACTCACTTCAACAAAGCTCTTTCAATGATTAGAAATCACAGAGAAGAATGA
21T vs. t, what does this really mean? Researchers have demonstrated that in the tall pea plants used by Mendel, the tallness gene codes for an enzyme (gibberellin 3-beta-hydroxylase) that adds a hydroxyl (OH) group at a very particular location onto GA20, which is the is the immediate precursor of GA1.In the dwarf plants there is a change of one base in the DNA sequence, which leads to a change of one amino acid in the resulting protein. In turn, this results in an enzyme that is still active in converting GA20 into GA1, but at 1/20th the rate.Therefore, dwarf peas are less efficient at synthesizing the gibberellin responsible for promoting stem growth. The plant becomes growth deficient.
22What is “T”?Dwarf peas have a defective 3β-hydroxylase which converts GA20 to GA1. This conversion makes an inactive GA into an active GA. This explains why the dwarf plants are dwarf...they lack appreciable active GA.Spraying such dwarf peas with gibberellic acid (GA3 an active GA) can result in pea plants of normal height.
24Genes & AllelesIn genetic crosses:Each original pair of plants is the P (parental) generation.The offspring are called the F1, or “first filial,” generation.
25The F1 hybrid plants all had the character of only one of the parents. Genes & AllelesThe F1 hybrid plants all had the character of only one of the parents.In each cross the other parent’s trait seemed to have disappeared
26Mendel’s F1 Crosses on Pea Plants Genes & AllelesMendel’s F1 Crosses on Pea PlantsWhen Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.
27Mendel’s F1 Crosses on Pea Plants Genes & AllelesMendel’s F1 Crosses on Pea PlantsWhen Mendel crossed plants with contrasting characters for the same trait, the resulting offspring had only one of the characters. From these experiments, Mendel concluded that some alleles are dominant and others are recessive.
28Genes & AllelesMendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next.Today, scientists call the factors that determine traits genes.
29Genes are sections of a chromosome that code for a trait. Genes and AllelesGenes are sections of a chromosome that code for a trait.Most organisms have two copies of every gene and chromosome, one from each parent.
30The different forms of a gene are called alleles. Genes and AllelesEach of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.The different forms of a gene are called alleles.Certain alleles can hide or dominate over other alleles.
40Geneticists use the testcross to determine unknown genotypes TestcrossMating between an unknown genotype and a homozygous recessive individualWill show whether the unknown genotype includes a recessive alleleUsed by Mendel to confirm true-breeding genotypesStudent Misconceptions and Concerns1. Students using Punnett squares need to be reminded that the calculations are expected statistical probabilities and not absolutes. Just as we would expect that any six playing cards dealt might be half black and half red, we frequently find that this is not true. This might be a good time to show how larger sample sizes increase the likelihood that sampling will reflect expected ratios.Teaching Tips1. Consider challenging your students to explain why a testcross of two black Labs of unknown genotypes might not reveal the genotype of each dog. (If both dogs are heterozygous, or homozygous, the results would reveal the genotypes because the offspring would either be three dark and one brown or all dark. But if one black Lab was homozygous and the other heterozygous, we could not determine which Lab has which genotype.)
41Two possibilities for the black dog: Testcross:GenotypesB_bbTwo possibilities for the black dog:BBorBbFigure 9.6 Using a testcross to determine genotype.If the black Labrador retriever has the Bb genotype, chocolate offspring are expected.To test whether a round-seeded pea plant is true breeding, what plant would you use for the testcross? A wrinkled-seeded plant.What result would show that the round-seeded plant was NOT true breeding? Having wrinkled-seeded plants among the offspring of the testcross.GametesBBbbBbbBbbbOffspringAll black1 black : 1 chocolate
43DO NOW P=purple, p=white P is dominant to p If purple is dominant to white, show a cross between a homozygous Dominant purple flower with a white flower.Show a cross of the F1 generation.What is the genotypic ratio of the F2?What is the phenotypic ratio of the F2?What percentage of the total offspring would one expect to be purple?What percentage of the purple flowers would one expect to be heterozygous.
44PP P P P P pp All All p p Genetic makeup (alleles) P plants Gametes PPppGametesAllPAllpF1 plants(hybrids)All PpPGametes1–21–2pSpermFigure 9.3B Explanation of the crosses in Figure 9.3A.A Punnett square is used to show all possible fertilization events for parental gametes. In three quarters of the F2 genotypes, there will be at least one dominant allele.PpF2 plantsPhenotypic ratio3 purple : 1 whitePPPPpEggsGenotypic ratio1 PP : 2 Pp : 1 pppPppp
45Gametes are also known as ReviewGametes are also known asgenes.sex cells.alleles.hybrids.
46ReviewThe offspring of crosses between parents with different traits are calledalleles.hybrids.gametes.dominant.
47In Mendel’s pea experiments, the male gametes are the ReviewIn Mendel’s pea experiments, the male gametes are theeggs.seeds.pollen.sperm.
48ReviewIn a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F1 generation consists ofall short plants.all tall plants.half tall plants and half short plants.all plants of intermediate height.
49ReviewIf a particular form of a trait is always present when the allele controlling it is present, then the allele must bedominant.
50ReviewA form of a gene that is not expressed when paired with a dominant allele is called a ______________________recessive allele
51ReviewSections of chromosomes that code for a trait are called ______________________genes
52ReviewOrganisms usually get one copy of each gene from each parent. The different forms of the same gene are called ______________________alleles
74What are the chance of a coin landing on heads? On tails? Flip a coinWhat are the chance of a coin landing on heads? On tails?The chance, or probability, of either outcome is equal. Therefore, the probability that a single coin flip will land heads up is 1 chance in 2. This amounts to 1/2, or 50 percent.
75Flip a coinEach coin flip is an independent event, with a one chance in two probability of landing heads up.With that in mind, if you flip a coin three times in a row, what is the probability that it will land heads up every time?1/2 × 1/2 × 1/2 = 1/8
95Section 3.9 Pedigree conventions Parents are connected by a single horizontal line, and vertical lines lead to their offspringIf the parents are related (consanguineous), such as first cousins, they are connected by a double lineOffspring are called sibs (siblings) and are connected by a horizontal sibship line