Lecture 11 Genetics F2024 PDF

Heredity- the transmission of traits from parent to offspring through their genes Genetics- the scientific study of heredity Gregor Mendel Homunculus Blending Inheritance Mendel stressed that genes retain their individual identities generation after generation, no ma...

Heredity- the transmission of traits from parent to offspring through their genes Genetics- the scientific study of heredity Gregor Mendel Homunculus Blending Inheritance Mendel stressed that genes retain their individual identities generation after generation, no matter how they are mixed up or temporarily masked Character- a heritable feature that varies among individuals within a population, such as flower color in pea plants or eye color in humans Character State- a variant of a character found within a population, such as purple flowers in pea plants or blue eyes in people  Mendel chose Binary characters which made his experiments easier to interpret P generation F1 generation F2 generation Monohybrid cross: Result of a cross between two true- breeding parents that express different traits for only one character  The Results of Mendel’s Garden Pea Hybridizations Characteristic Contrasting P0 Traits F1 Offspring Traits F2 Offspring Traits F2 Trait Ratios Flower color Violet vs. white 100 percent violet 705 violet 3.15:1 224 white Flower position Axial vs. terminal 100 percent axial 651 axial 3.14:1 207 terminal Plant height Tall vs. dwarf 100 percent tall 787 tall 2.84:1 277 dwarf Seed texture Round vs. wrinkled 100 percent round 5,474 round 2.96:1 1,850 wrinkled Seed color Yellow vs. green 100 percent yellow 6,022 yellow 3.01:1 2,001 green Pea pod texture Inflated vs. constricted 100 percent inflated 882 inflated 2.95:1 299 constricted Pea pod color Green vs. yellow 100 percent green 428 green 2.82:1 152 yellow 3 big ideas from Mendel’s mating experiments: 1. Each parent puts into every sperm or egg it makes a single set of instructions for building the trait (these instructions are now known as a gene). 2. For each inherited trait (character), offspring receive two copies of the instructions (alleles) 3. The trait observed in an individual (phenotype) depends on the two copies of the gene it inherits from the parents. When they receive the same 2 alleles for the gene, their genotype is homozygous. When the offspring receives 2 different alleles for the gene, their genotype is heterozygous. The dominant allele will be expressed as phenotype if the genotype is heterozygous.  The Product Rule and Sum Rule Product Rule Sum Rule For independent events A and For mutually exclusive events B, the probability (P) of them A and B, the probability (P) both occurring (A and B) is that at least one occurs (PA × PB) (A or B) is (PA + PB)  Punnett Square: visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid. How does the idea of Alleles relate to Homologous Chromosomes? Locus (Loci): the particular site where a gene is found on a chromosome Mendel’s Law of Segregation: Paired unit factors (i.e. genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors If two animals have the same genotype, must they have the same phenotype? If they have the same phenotype, must they have the same genotype? Snowflake “Copito de nieve” Dihybrid: Result of a cross between two true- breeding parents that express different traits for two characteristics Mendel’s Law of Independent Assortment: genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur TtQq ttQq In alligators, dark color is the dominant trait and white color (albinism) is the recessive trait. If you have a dark gator, how can you determine what its genotype is? If you have or had attached earlobes, what are the possible genotypes of your parents?  Most human genetic disorders controlled by a single gene are recessive. Why do you think this is the case? John (27) had a father who recently passed away from Huntington’s disease (a dominant genetic disease), but his mother shows no signs of the disease. Using a Punnett square, calculate the chances that John also has the dominant allele that causes the disease. Also, do you think he should get tested to see if he has the Huntington’s disease allele?  We have talked about one gene (with two alleles) causing two different phenotypes. What other possibilities of inheritance are there? Incomplete Dominance: a type of inheritance in which the phenotype of a heterozygote is intermediate between the phenotypes of the two types of homozygotes Multiple alleles  Multiple alleles can lead to codominance A AB B O Codominance: in a heterozygote, complete and simultaneous expression of both alleles for the same character Suppose a female with Type A blood mated with a male with Type B blood. What genotypes and phenotypes are possible for their offspring and what is the probability of each type? Use a Punnett Square to determine the answer. What is the difference between codominance and incomplete dominance? Pleiotropy- when one gene influences multiple, different traits Sickle-cell anemia Polygenic Inheritance: the additive effect of two or more genes on a single phenotypic character Epistasis: Antagonistic interaction between genes such that one gene masks or interferes with the expression of another “Twins have a special claim upon our attention. It is, that their history, affords means of distinguishing between the effects of tendencies received at birth, and those that were imposed by the special circumstances of their after lives.” -Sir Francis Galton  What are some examples of characters that result from a combination of heredity and environment?  Epigenetics- heritable changes in gene expression (active versus inactive genes) that does not involve changes to the underlying DNA sequence; a change in phenotype without a change in genotype Linked genes- genes located close enough together on a chromosome that they are usually inherited together (they travel with each other during meiosis). Is it possible for a brother and sister to be identical twins? Punnett Square with Sex- linked genes A mother who is a carrier for colorblindness and a father who is not colorblind. What percentage of their children would be colorblind? Walter Sutton Theodor Boveri Eleanor Carothers Chromosomal Theory of Inheritance -During meiosis, homologous chromosomes pairs migrate as discrete structures that are independent of other chromosome pairs -Chromosome sorting from each homologous pair into pre-gametes appears to be random -Each parent synthesizes gametes that contain only half their chromosomal complement -Even though male and female gametes (sperm and egg) differ in size and morphology, they have the same number of chromosomes, suggesting equal genetic contributions from each parent. -The gametic chromosomes combine during fertilization to produce offspring with the same chromosome number as their parents Alfred Sturtevant Karyotype: an individual’s chromosome number and appearance; includes the size, banding patterns, and centromere position Nondisjunction: Failure of synapsed homologs or sister chromatids to completely separate and migrate to separate poles during meiosis X inactivation Chromosome inversion: detachment, 180° rotation, and reinsertion of part of a chromosome Translocation: Process by which one chromosome segment dissociates and reattaches to a different, nonhomologous chromosome