Chp. 15 Notes - Exam 3 PDF

Chapter 15 – Transmission of Genetic Information from Parents to Offspring I: Patterns That Follow Mendel’s Laws Chapter Outline 1. Mendel’s laws of inheritance 2....

Chapter 15 – Transmission of Genetic Information from Parents to Offspring I: Patterns That Follow Mendel’s Laws Chapter Outline 1. Mendel’s laws of inheritance 2. Chromosome theory of inheritance 3. Pedigree analysis of human traits 4. Variations in inheritance patterns and their molecular basis 5. Sex chromosomes and X- linked inheritance patterns 15.1 Mendel’s Laws of Inheritance Section 15.1 Learning Outcomes 1. List the advantages of using the garden pea to study inheritance 2. Describe the difference between dominant and recessive traits 3. Distinguish between genotype and phenotype 4. Predict the outcome of genetic crosses using a Punnett square 5. State Mendel’s law of segregation and law of independent assortment 15.1 Mendel’s Laws of Inheritance Parents and offspring often show a striking resemblance to each other; inheritance is the acquisition of traits by their transmission from parent to offspring Observations of chromosome transmission during mitosis and meiosis provided evidence for particulate inheritance Particulate inheritance is the idea that determinants of Loading… hereditary traits (now called genes) are transmitted in discrete units from one generation to the next A gene can be broadly defined as a unit of heredity 15.1 Mendel’s Laws of Inheritance Many different patterns of inheritance exist 15.1 Mendel’s Laws of Inheritance In 1856 Gregor Mendel, an Austrian monk, began his studies on pea plants; Mendel analyzed thousands of pea plants over 8 years A trait is an identifiable characteristic of an organism; Loading… the term trait usually refers to a variant for a character Fig 12.1, Principles of Life, 2014 Sinauer Associates, Inc. 15.1 Mendel’s Laws of Inheritance Mendel Chose the Garden Pea to Study Inheritance Advantageous properties of pea plants: Pea plants are normally self-fertilizing; a female gamete is fertilized by a male gamete from the same plant The stamens form male gametes and the ovules form female gametes  15.1 Mendel’s Laws of Inheritance By Following the Inheritance Pattern of Single Traits, Mendel’s Work Revealed the Law of Segregation Mendel began his work by studying the inheritance patterns of plants that differed in a single character; he conducted single-factor crosses (monohybrid crosses) Mate “true-breeding” plants: All offspring are ‘MONOHYBRIDS’ (heterozygous) that all show Dominant trait: Mate the Monohybrids and the “recessive trait” comes out of hiding: 15.1 Mendel’s Laws of Inheritance By Following the Inheritance Pattern of Single Traits, Mendel’s Work Revealed the Law of Segregation Mendel named the trait that was displayed by the F1 generation the dominant trait; the trait that was masked in the F1 generation and reappeared in the F2 generation was called the recessive trait Mendel found that two “particles” generated each trait. We call these particles alleles As long as one dominant particle is inherited, the dominant trait will be expressed. Alleles are inherited in pairs. Two alleles (one maternal and one paternal) at every gene locus. 15.1 Mendel’s Laws of Inheritance By Following the Inheritance Pattern of Single Traits, Mendel’s Work Revealed the Law of Segregation Mendel concluded that each plant carried 2 versions (alleles) of a gene. But the gametes the plant made only carried 1 allele each. The offspring then inherited one maternal allele and on paternal allele. These ideas are formally stated in Mendel’s law of segregation The two alleles of a gene separate (segregate) from each other during the process that gives rise to gametes so that every gamete receives only one allele 15.1 Mendel’s Laws of Inheritance By Following the Inheritance Pattern of Single Traits, Mendel’s Work Revealed the Law of Segregation After gametes are made, they unite in Fertilization. Depending on the gamete genotypes, there will be different possible genotypes of the offspring. A Punnett square is a visual way to see these possible offspring genotypes.  15.1 Mendel’s Laws of Inheritance Loading… The genotype is the genetic composition of an individual; it is often represented with letters (numbers and symbols may also be used) TT is homozygous dominant Tt is heterozygous tt is homozygous recessive The phenotype is the physical or behavioral characteristics that are the result of gene expression TT and Tt have a tall phenotype tt has a dwarf phenotype 15.1 Mendel’s Laws of Inheritance Analyzing the Inheritance Pattern of Two Characters Demonstrated the Law of Independent Assortment Mendel asked: Does the separation of alleles at one gene locus have any influence on the separation of allele at a second locus? 15.1 Mendel’s Laws of Inheritance Analyzing the Inheritance Pattern of Two Characters Demonstrated the Law of Independent Assortment Mendel asked: Does the separation of alleles at one gene locus have any influence on the separation of allele at a second locus? The Punnett square with 4 gametes from each parent has 16 offspring possible genotypes 15.1 Mendel’s Laws of Inheritance Analyzing the Inheritance Pattern of Two Characters Demonstrated the Law of Independent Assortment Mendel asked: Does the separation of alleles at one gene locus have any influence on the separation of allele at a second locus? The Punnett square with 4 gametes from each parent has 16 offspring possible genotypes 9/16 show both dominant traits 3/16 show one dominant and one recessive trait 3/16 show the opposite dominant and recessive trait 1/16 show both recessive traits Only need to learn the 9:3:3:1 ratio of offspring phenotypes 15.2 Chromosome Theory of Inheritance Section 15.2 Learning Outcomes 1. Outline the principles of the chromosome theory of inheritance 2. Relate the behavior of chromosomes during meiosis to Mendel’s two laws of inheritance  15.2 Chromosome Theory of Inheritance At the time of Mendel’s work, the nature and location of “genes” was unknown As time progressed, other scientists used microscopes to observe dividing cells and suggested that chromosomes are the carriers of hereditary information Fig 12.1, Principles of Life, 2014 Sinauer Associates, Inc.  15.2 Chromosome Theory of Inheritance A modern view of the chromosome theory of inheritance: Chromosomes contain DNA, which is the genetic material. Genes are found within the chromosomes. Chromosomes are replicated and passed from parent to offspring. The nucleus of a diploid cell contains 2 sets of chromosomes, which are found in homologous pairs. Maternal and paternal sets of homologous chromosomes are functionally equivalent; each set carries a full complement of genes. At meiosis, one member of each homologous pair segregates into one daughter nucleus, and its homolog segregates into the other daughter nucleus. Members of different homologous pairs segregate independently of one another. Gametes are haploid cells that combine to form a diploid cell during fertilization, with each gamete transmitting one set of chromosomes to the offspring.  15.2 Chromosome Theory of Inheritance Law of Segregation Is Explained by the Segregation of Homologous Chromosomes During Meiosis A gene’s locus is its physical location on a chromosome Each member of a homologous pair carries an allele of the same gene at the same locus The pairing and segregation of homologous chromosomes during meiosis explains the patterns that led to Mendel’s law of segregation  15.2 Chromosome Theory of Inheritance Law of Segregation Is Explained by the Segregation of Homologous Chromosomes During Meiosis The chromosomal basis of allele segregation is depicted in the figure Mendel’s law of segregation states that the two alleles of a gene separate (segregate) from each other during the process that gives rise to gametes so that every gamete receives only one allele 15.3 Pedigree Analysis of Human Traits Section 15.3 Learning Outcomes 1. Apply pedigree analysis to deduce inheritance patterns in humans 2. Distinguish between recessive disorders and dominant disorders 15.3 Pedigree Analysis of Human Traits Human geneticists rely on information contained in pedigrees, or family trees, to determine patterns of inheritance Pedigree analysis allows us to determine whether a mutant allele is dominant or recessive and to predict the likelihood of an individual being affected A wild-type allele is common and a mutant allele is rare Most genes display autosomal inheritance patterns Genes located on the sex chromosomes display distinct inheritance patterns 15.3 Pedigree Analysis of Human Traits The adjacent pedigree traces a disease (cystic fibrosis) that displays an autosomal recessive pattern Individuals who are homozygous recessive for the mutant allele experience the disease Important feature two unaffected individuals can produce an affected offspring Presumed heterozygotes However those same two parents can also produce an unaffected offspring 15.3 Pedigree Analysis of Human Traits The pedigree below traces a disease (Huntington disease) that displays an autosomal dominant pattern Individuals who are heterozygous (or homozygous dominant) for the mutant allele experience the disease Important feature every affected individual has an affected parent However an affected parent can also produce an unaffected offspring 15.4 Variations in Inheritance Patterns & Molecular Basis Section 15.4 Learning Outcomes 1. Relate dominant and recessive alleles and genotypes to protein function 2. Describe pleiotropy, and explain why it occurs 3. Predict the outcome of crosses that exhibit incomplete dominance 4. Discuss how the environment plays a critical role in determining the outcome of traits 15.4 Variations in Inheritance Patterns & Molecular Basis The phrase Mendelian inheritance describes the inheritance patterns of genes that segregate and assort independently In simple Mendelian inheritance the alleles are dominant or recessive There are many other types of inheritance patterns Understanding protein function at the molecular level explains differences in inheritance patterns 15.4 Variations in Inheritance Patterns & Molecular Basis Protein Function Explains the Phenomenon of Dominance A wild-type allele usually encodes a protein that is made in the proper amount and functions normally Mutations that produce recessive alleles are often loss-of- function alleles Sometimes a single copy of the dominant allele is sufficient; there is enough functional protein to provide a normal phenotype heterozygote displays dominant phenotype Heterozygotes may also use gene regulation to increase the expression of the functional allele 15.4 Variations in Inheritance Patterns & Molecular Basis #1: Incomplete Dominance Incomplete dominance occurs when the heterozygote shows an intermediate phenotype In this case, the heterozygote (CRCW) does not produce enough pigment to appear red; instead it appears pink Genotype and phenotype ratios for the F2 are both 1:2:1 15.4 Variations in Inheritance Patterns & Molecular Basis #2: The Environment Role in Phenotype An organism’s genotype provides the plan to create the phenotype; the environment provides nutrients and energy so the plan can be executed The norm of reaction is the phenotype range that individuals with a particular genotype exhibit under differing environmental conditions Genetically identical plants grow to different heights in different temperatures 15.5 Sex Chromosomes and X-Linked Inheritance Patterns Section 15.5 Learning Outcomes 1. Describe the different systems of sex determination in animals and plants Loading… 2. Predict the outcome of crosses when genes are located on sex chromosomes 3. Explain why X-linked recessive traits are more likely to occur in males 15.5 Sex Chromosomes and X-Linked Inheritance Patterns In Many Species, Sex Differences Are Due to the Presence of Sex Chromosomes Sex chromosomes are different between males and females and determine the sex of individuals Sex chromosomes are found in many (but not all) species with 2 sexes 15.5 Sex Chromosomes and X-Linked Inheritance Patterns In Humans, X-Linked Recessive Traits Are More Likely to Occur in Males Sex-linked genes are the gene on X and Y Male mammals are hemizygous for X-linked genes; they have only one copy of genes on the X chromosome