Mendel garden pea plants –Gregor Mendel discovered principles of genetics in experiments with garden pea plants Mendel showed that parents pass heritable factors to offspring –What do we call heritable factors today? GenesGenes
Terms 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 generation Hybrid: 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)
Terms 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.
Gene loci Homozygous for the dominant allele Dominant allele Homozygous for the recessive allele Heterozygous Recessive allele Genotype: P B a P PP a aa b Bb
Do Now T=tall t=short A 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?
What 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 stem 3β-hydroxylase which converts GA 20 to GA 1 Tallness 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.
What is “T”? gibberellin 3-beta-hydroxylase - 358 AA ATGCCTGCTATGTTAACAGATGTGTTTAGAGGCCATCCCATTCACCTCCCACACTCTCAC ATACCTGACTTCACATCTCTCCGGGAGCTCCCGGATTCTTACAAGTGGACCCCTAAAGAC GATCTCCTCTTCTCCGCTGCTCCTTCTCCTCCGGCCACCGGTGAAAACATCCCTCTCATC GACCTCGACCACCCGGACGCGACTAACCAAATCGGTCATGCATGTAGAACTTGGGGTGCC TTCCAAATCTCAAACCACGGCGTGCCTTTGGGACTTCTCCAAGACATTGAGTTTCTCACC GGTAGTCTCTTCGGGCTACCTGTCCAACGCAAGCTTAAGTCTGCTCGGTCGGAGACAGGT GTGTCCGGCTACGGCGTCGCTCGTATCGCATCTTTCTTCAATAAGCAAATGTGGTCCGAA GGTTTCACCATCACTGGCTCGCCTCTCAACGATTTCCGTAAACTTTGGCCCCAACATCAC CTCAACTACTGCGATATCGTTGAAGAGTACGAGGAACATATGAAAAAGTTGGCATCGAAA TTGATGTGGTTAGCACTAAATTCACTTGGGGTCAGCGAAGAAGACATTGAATGGGCCAGT CTCAGTTCAGATTTAAACTGGGCCCAAGCTGCTCTCCAGCTAAATCACTACCCGGTTTGT CCTGAACCGGACCGAGCCATGGGTCTAGCAGCTCATACCGACTCCACCCTCCTAACCATT CTGTACCAGAACAATACCGCCGGTCTACAAGTATTTCGCGATGATCTTGGTTGGGTCACC GTGCCACCGTTTCCTGGCTCGCTCGTGGTTAACGTTGGTGACCTCTTCCACATCCTATCC AATGGATTGTTTAAAAGCGTGTTGCACCGCGCTCGGGTTAACCAAACCAGAGCCCGGTTA TCTGTAGCATTCCTTTGGGGTCCGCAATCTGATATCAAGATATCACCTGTACCGAAGCTG GTTAGTCCCGTTGAATCGCCTCTATACCAATCGGTGACATGGAAAGAGTATCTTCGAACA AAAGCAACTCACTTCAACAAAGCTCTTTCAATGATTAGAAATCACAGAGAAGAATGA
T 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.
What is “T”? Dwarf peas have a defective 3β- hydroxylase which converts GA 20 to GA 1. 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 (GA 3 an active GA) can result in pea plants of normal height.
Genes & Alleles In genetic crosses: Each original pair of plants is the P (parental) generation. The offspring are called the F 1, or “first filial,” generation.
Genes & Alleles F 1 only The F 1 hybrid plants all had the character of only one of the parents. In each cross the other parent’s trait seemed to have disappeared
Genes & Alleles Mendel’s F 1 Crosses on Pea Plants
Genes & Alleles Mendel’s F 1 Crosses on Pea Plants
Genes & Alleles Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next. genes Today, scientists call the factors that determine traits genes.
Genes and Alleles Genes are sections of a chromosome that code for a trait. Most organisms have two copies of every gene and chromosome, one from each parent.
Genes and Alleles Each 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.
Geneticists use the testcross to determine unknown genotypes –Testcross Mating between an unknown genotype and a homozygous recessive individual –Will show whether the unknown genotype includes a recessive allele –Used by Mendel to confirm true- breeding genotypes
B_ or Two possibilities for the black dog: Testcross: Genotypes Gametes Offspring1 black : 1 chocolate All black Bb bb BB Bbbb B b Bb b b B
1.If purple is dominant to white, show a cross between a homozygous Dominant purple flower with a white flower. 2.Show a cross of the F1 generation. 3.What is the genotypic ratio of the F2? 4.What is the phenotypic ratio of the F2? 5.What percentage of the total offspring would one expect to be purple? 6.What percentage of the purple flowers would one expect to be heterozygous.
P plants 1–21–2 1–21–2 Genotypic ratio 1 PP : 2 Pp : 1 pp Phenotypic ratio 3 purple : 1 white F 1 plants (hybrids) Gametes Genetic makeup (alleles) All All P p Sperm Eggs PP p ppPp P p P p P P p PP pp All Gametes F 2 plants
–Gametes are also known as genes. sex cells. alleles. hybrids. Review
–The offspring of crosses between parents with different traits are called alleles. hybrids. gametes. dominant. Review
–In Mendel’s pea experiments, the male gametes are the eggs. seeds. pollen. sperm. Review
–In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F 1 generation consists of all short plants. all tall plants. half tall plants and half short plants. all plants of intermediate height. Review
–If a particular form of a trait is always present when the allele controlling it is present, then the allele must be dominant. Review
A form of a gene that is not expressed when paired with a dominant allele is called a ______________________ recessive allele
Review Sections of chromosomes that code for a trait are called ______________________ genes
Review Organisms usually get one copy of each gene from each parent. The different forms of the same gene are called ______________________ alleles
Flip a coin What 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.
Flip a coin –Each 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
Section 3.9 Pedigree conventions Parents are connected by a single horizontal line, and vertical lines lead to their offspring If the parents are related (consanguineous), such as first cousins, they are connected by a double line Offspring are called sibs (siblings) and are connected by a horizontal sibship line