Biology Concepts and Applications 9e Starr Evers Starr Chapter 13 Observing Patterns in Inherited Traits Cengage Learning 2015 Cengage Learning 2015
After completing today s activities, students should be able to: 1. Describe Mendel s experiments that led to our understanding of genetics. 2. Define and distinguish between self-fertilization, cross-fertilization, true-breeding organisms, hybrids, the P generation, the F 1 generation, and the F 2 generation. 3. Define and distinguish between the following pairs of terms: heterozygous versus homozygous, dominant allele versus recessive allele, genotype versus phenotype. 4. Define the law of segregation and explain how it applies to reproduction. 5. Define locus.
Do Your Ears Hang Low?
Biology and Society: Our Longest-Running Genetic Experiment: Dogs People have selected and mated dogs with preferred traits for more than 15,000 years. Over thousands of years, such genetic tinkering has led to the incredible variety of body types and behaviors in dogs today. The biological principles underlying genetics have only recently been understood. 2013 Pearson Education, Inc.
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HERITABLE VARIATION AND PATTERNS OF INHERITANCE Heredity is the transmission of traits from one generation to the next. Genetics is the scientific study of heredity. Gregor Mendel worked in the 1860s, was the first person to analyze patterns of inheritance, and deduced the fundamental principles of genetics. 2013 Pearson Education, Inc.
Mendel studied garden peas because they -were easy to grow -came in many readily distinguishable varieties -are easily manipulated -can self-fertilize
Traits of Mendel s Pea Plants Dominant Recessive Dominant Recessive Flower color Purple White Pod shape Inflated Constricted Pod Color Green Yellow Flower position Axial Terminal Seed color Yellow Green Stem length Tall Dwarf Seed shape Round Wrinkled Figure 9.4
Self-Fertilization Mendel studied garden peas These plant are easily manipulated These plants can self-fertilize Stamen Carpel Figure 9.2
Cross-Fertilization 1 Removed stamens from purple flower White Parents (P) Carpel Purple 2 Stamens Transferred pollen from stamens of white flower to carpel of purple flower 3 Pollinated carpel matured into pod 4 Planted seeds from pod Offspring (F 1 ) Figure 9.3
True Breeding When offspring inherit a pair of identical alleles for a trait in many generations Mendel had True-breeding pea plants for white flowers and purple flowers Purple flowers Purple flowers All plants have purple flowers Mendel s Observation: Some of my pea plants always produce purple flowers while some always produce white flowers.
Hybrid More Terminology The offspring of two different true-breeding organisms The offspring of a genetic cross P Generation The parents in the genetic cross F 1 generation The hybrid offspring of the genetic cross F 2 generation Offspring of two F 1 organisms
Mendel frames a question around his observation: What will happen if I cross a true-breeding purple-flower plant with a true-breeding whiteflower plant? Mendel Hypothesizes: Let s make some hypotheses to answer the question
Mendel makes predictions based on his hypotheses: Mendel carries out experiment
Monohybrid Crosses A cross between plants that differ in only one trait P Generation (true-breeding parents) F 1 Generation Purple flowers White flowers All plants have purple flowers So, which hypothesis was correct? Figure 9.5
Mendel s Next Question Was the gene for white flowers lost? Hypothesis: Prediction: Mendel crosses the F 1 plants to each other to find out.
What type of cross is this? P Generation (true-breeding parents) F 1 Generation Purple flowers White flowers All plants have purple flowers Fertilization among F 1 plants (F 1 F 1 ) F 2 Generation 3 / 4 of plants have purple flowers 1 / 4 of plants have white flowers Figure 9.5
Hypothesis 1 There are alternative forms of genes called alleles. Flower color gene has 2 alleles: purple and white
Hypothesis 2 For each trait, an organism has two alleles - One from the egg; one from the sperm Homozygous An organism that has two identical alleles for a gene Heterozygous An organism that has two different alleles for a gene
Hypothesis 3 If the two alleles of a pair differ, then one allele determines the organism s appearance and the other has no effect on the organism Dominant Alleles An allele is dominant when its effect on a trait masks the effect of a recessive allele that is paired with it. Indicated by a capital letter (e.g. P for purple) Recessive Alleles An allele is recessive when its effect on a trait is masked by the presence of a dominant allele that is paired with it Indicated by a lower case letter (e.g. p for white)
Hypothesis 4 Now known as The Law of Segregation A sperm or egg carries only one allele for each trait. Fertilization creates allele pairs again.
Phenotype: An individual s physical traits. Ex: Purple or white flowers Genotype: The genetic alleles that an individual carries Ex: PP, Pp, or pp Punnett Square: A tool used to predict the outcome of a genetic cross Figure 9.6
Genotype vs. Phenotype Genotype = genetic makeup Phenotype = appearance or observable traits Figure 13-3 p207
Figure 9.7 Genetic Alleles and Homologous Chromosomes Homologous chromosomes Gene loci Dominant allele P a B P a b Genotype: PP aa Bb Homozygous for the dominant allele Homozygous for the recessive allele Recessive allele Heterozygous with one dominant and one recessive allele 2016 Pearson Education, Inc.