Genetics Exam 1 Study Guide PDF

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A dense study guide of all of the material covered for the first exam. Dr. Bin Shuai's course....

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Genetics Exam 1 Study Guide

CHAPTER 1 1.1 The Birth of Genetics Purple pea + white pea —> purple pea* + purple pea* —> 3:1 purple:white Individual plant cells carry two copies of the gene controlling flower color, but when gametes are formed, only one copy of the gene enters into these reproductive cells. Then, when egg and sperm unite, there will once again be two copies. Chromosome theory: Inheritance of traits is controlled by genes on chromosomes. Multifactorial hypothesis: Explains quantitative variation by proposing the traits are controlled by a large number of genes, each with a small effect on the trait. One-gene-one-enzyme hypothesis: Originally proposed that each gene (nucleotide sequence) encodes a polypeptide sequence; generally true, with the exception of untranslated functional RNA; proposed that genes encode enzymes that carry out biochemical fx within cells. AT - double H bond GC - triple H bond Genes have regulatory elements (specific DNA sequences to which a regulatory protein binds and acts as either an activator or repressor of the expression of the gene) that regulate gene expression. Central Dogma: DNA —Transcription—> RNA —Translation—> Protein Codon: a set of three consecutive nucleotides in the mRNA that specifies an amino acid in a protein. 1.2 After Cracking the Code Model organism: small, inexpensive, short generation time, small genome, many offspring, easy to mate. Deletion stocks: each have just one gene deleted from the genome to allow geneticists to study the function of each gene by examining how it is affected when the gene is removed.

DNA polymerases: Make a copy of a single DNA strand by synthesizing a matching strand with the complementary sequence of A, G, T, C Nucleases: Cut DNA molecules in specific locations or degrade an entire DNA molecule into single nucleotides. Ligases: Join 2 DNA molecules together end-to-end. Transformation: Insertion of foreign DNA molecules into the genomes of many species 1.3 Genetics Today Blockage of CD73 gene – this gene is involved in cell signaling Single nucleotide polymorphisms (SNPs): Differences in the nucleotide sequences between the copy we inherited from our mother and the one we inherited from our father; simple and most common form of genetic variation The risk of an inherited disorder for a child is greater as the parents age and also that fathers are more likely than mothers to contribute new mutations to their children. Point mutations: A change of one letter in the DNA code to another that can occur during DNA replication. Ex. A change of A to G from parents to child. New mutations that arise in somatic cells as they divide during the growth and development of our bodies are not passed on to our offspring. However, a new mutation that occurs in the germline (lineage that divides to produce eggs and sperm) can be transmitted to the offspring. Genome sequences of parents and their children clarify the factors that contribute to new point mutations. Fathers contribute four times as many new mutations to their offspring as do mothers. The number of new mutations passed on from a father to his children rises with the age of the father. Quantitative trait locus (QTL) mapping: QTL is a genetic locus that contributes incrementally or quantitatively to variation for a trait. Mendel’s gene for flower color had two categorical alleles: one for purple flowers and the other for white flowers. QTL have alleles that usually engender only partial changes such as the difference between a pale purple and a medium purple. EPAS1: Why does EPAS1 direct our bodies to produce more RBCs when the oxygen levels in our tissues are low? The EPAS1 response to low oxygen may be how our bodies normally respond to anemia (too few red blood cells). People with low RBC counts get too little oxygen in their

tissues, and so EPAS1 could signal the body to make more RBCs to correct anemia. This mechanism could explain why people who live at low elevation need the EPAS1 gene. Now, let’s think about how a person from low elevation would respond if they move to high elevation. Because of the thin air at high elevation, their tissues would get less oxygen. If their bodies interpreted low oxygen due to thin air as a sign of anemia, then EPAS1 would try to correct the problem by signaling their body to make more RBCs. However, since they are not anemic and already have enough RBCs, their blood would become overloaded with RBCs. Too many RBCs can cause pulmonary hypertension and the formation of blot clots, the conditions underlying CMS. POWERPOINT NOTES: How genes function inside cells to control a trait: one-gene-one-enzyme hypothesis Transcription: RNA synthesis (produces mRNA) Translation: protein synthesis Genes have: regulatory and coding regions • Reg proteins bind to regulatory region on gene • RNA polymerase complex binds also • Transcription occurs SNPs: could change aa sequence to stop codon (TCG to TAG) VOCAB: adenine (A): A purine base that pairs with thyme in the DNA double helix. allele: One of the different forms of a gene that can exist at a single locus. chromosome theory: Inheritance of traits is controlled by genes on chromosomes. codon: A section of RNA (three nucleotides in length) that encodes a single amino acid. complementary: Refers to specific pairing between adenine and thymine and between guanine and cytosine. cytosine (C): A pyrimidine base that pairs with guanine. DNA polymerase: In E. Coli, the large multisubunit complex at the replication fork consisting of two catalytic cores and many accessory proteins.

DNA replication: The process of synthesizing two identical copies of a DNA molecule from one original copy. DNA sequencing: The process used to decipher the sequence of A’s, C’s, G’s, and T’s in a DNA molecule. dominant: The phenotype shown by a heterozygote. gametes: Sex cells in multicellular organisms, such as egg and sperm cells. gene: The fundamental physical and functional unit of heredity, which carries information from one generation to the next; a segment of DNA composed of a transcribed region and a regulatory sequence that makes transcription possible. gene expression: The process by which a gene’s DNA sequence is transcribed into RNA and, for protein-coding genes, into a polypeptide. genetically modified organism (GMO): A popular term for a transgenic organism, especially applied to transgenic agricultural organisms. genetics: The study of genes and the study of inheritance. genomics: The cloning and molecular characterization of entire genomes. guanine: A purine base that pairs with cytosine. ligase: An important enzyme in DNA replication and repair that seals the DNA backbone by catalyzing the formation of phosphodiester bonds. messenger RNA (mRNA): An RNA molecule transcribed from the DNA of a gene; a protein is translated from this RNA molecule by the action of ribosomes. model organism: A species used in experimental biology with the presumption that what is learned from the analysis of that species will hold true for other species, especially other closely related species. multifactorial hypothesis: A hypothesis that explains quantitative variation by proposing that traits are controlled by a large number of genes, each with a small effect on the trait.

nuclease: An enzyme that can cut DNA molecules in specific locations or degrade an entire DNA molecule into single nucleotides. one-gene-one-enzyme hypothesis: A mid-twentieth-century hypothesis that originally proposed that each gene (nucleotide sequence) encodes a polypeptide sequence; generally true, with the exception of untranslated functional RNA. point mutation: A mutation that alters a single base position in a DNA molecule by converting it to a different base or by the insert/deletion of a single base in a DNA molecule. quantitative trait locus (QTL): A gene contributing to the phenotypic variation in a trait that shows complex inheritance, such as height and weight. regulatory element: DNA sequence motif that influences the timing, cell or tissue specificity, or level of expression of a gene. single nucleotide polymorphism (SNP/snip): A nucleotide-pair difference at a given location in the genomes two or more naturally occurring individuals. somatic cells: Non-sex cells in multicellular organisms. thymine (T): A pyrimidine base that pairs with adenine. transcription: The synthesis of RNA from a DNA template. transformation: The directed modification of a genome by the external application of DNA from a cell of different genotype. translation: The ribosome- and tRNA-mediated production of a polypeptide whose amino acid sequence is derived from the codon sequence of an mRNA molecule.

QUESTIONS: 1) A researcher has determined that five genes contribute to hair color in a new species of monkey. Depending on the alleles for each of these genes, monkey hair color can range anywhere from light gray to black. These five genes probably are:

2) Researchers are studying a gene in bacteria. They notice that in a mutant bacterial strain the gene they are studying is activated much earlier than expected. In this bacterial strain, a mutation likely occurred that affected the _____ of the gene being studied.

3) Why is genetic variation important for natural selection?

4) DNA is a molecule that stores information. Which component of DNA is the source of this information?

5) Is the following statements regarding amino acids TRUE or FALSE? An mRNA contains adjacent codons composed of three nucleotides, each of which encodes a distinct amino acid. 6) Would the constancy of form between parents and offspring remain if DNA replication was a highly error-prone event?

7) A researcher is studying the same segment of DNA in three individuals, two parents and their son. She notices that the son demonstrates a point mutation that is not observed in either his mother or father. This point mutation in the son is likely the result of a mutation occurring in the:

8) Gene variants are the raw material for evolution, and these variants are generated by:

CHAPTER 2 2.1 Single-Gene Inheritance Patterns Mendel’s Law of Equal Segregation: 1. A hereditary factor called a gene is necessary for producing pea color. 2. Each plant has a pair of this type of gene. 3. The gene comes in two forms called alleles. If the gene is phonetically called a “wye” gene, then the two alleles can be represented by Y (standing for the yellow phenotype) and y (standing for the green phenotype). 4. A plant can be either Y/Y, y/y, or Y/y. The slash shows that the alleles are a pair. 5. In the Y/y plant, the Y allele dominates, and so the phenotype will be yellow. Hence, the phenotype of the Y/y plant defines the Y allele as dominant and the y allele as recessive. 6. In meiosis, the members of a gene pair separate equally into the cells that become eggs and sperm, the gametes. This equal separation has become known as Mendel's first law or as the law of equal segregation. Hence, a single gamete contains only one member of the gene pair. 7. At fertilization, gametes fuse randomly, regardless of which of the alleles they bear. All 1:1, 3:1, and 1:2:1 genetic ratios are diagnostic of single-gene inheritance and are based on equal segregation in a heterozygote. 2.2 The Chromosomal Basis of Single-Gene Inheritance Patterns Mitosis – somatic cell division Meiosis – gametic cell divison • Two divisions; 2n  n + n + n + n

2.3 The Molecular Basis of Mendelian Inheritance Patterns Mutant sites in the PKU gene (phenylalanine hydroxylase) • PKU (phenylketouria) is autosomal recessive disorder • Defective liver enzyme PAH(converts phenylalanine in food to aa tyrosine) • Can’t convert phenylalanine to tyrosine • Mental retardation if not treated Most mutations that alter phenotype alter the amino acid sequence of the gene’s protein product, resulting in reduced or absent function. 2.4 Some Genes Discovered by Observing Segregation Ratios Testcross: The cross of an individual of unknown heterozygosity (for one gene or more) with a fully recessive parent; tests whether genotype is homozygous or heterozygous. The principles of inheritance (such as the law of equal segregation) can be applied in two directions: (1) inferring genotypes from phenotypic ratios and (2) predicting phenotypic ratios from parents of known genotypes. 2.5 Sex-Linked Single-Gene Inheritance Patterns Human body cells have 46 chromosomes: 22 homologous pairs of autosomes plus 2 sex chromosomes. Males : • Heterogametic • Y is shorter than X • genes in differential regions are hemizygous Females : • homogametic X vs Y linkage (see vocab)

POWERPOINT NOTES: How is a single gene inherited from one generation to the next? Chromosomal basis of Mendel’s first law (equal segregation): Equal segregation of homologous chromosomes during meiosis.

Mitosis: • Replication (Interphase, Prophase) • Segregation (Metaphase, Anaphase, Telophase) • Daughter cells (x2 2n cells) Meiosis: • Replication (Interphase, Prophase I) • Pairing (Prophase I, Metaphase I) • Segregation (Metaphase I, Anaphase I, Telophase I) • Prophase II • Segregation (Metaphase II, Anaphase II, Telophase II) • Products (x4 n cells, 2 from each split after Telophase I) The Y chromosome is smaller and carries less alleles than the X chromosome. Men give their daughters their X chromosome, so male-carried mutations are passed on more to their daughters.

Vocab: allele: One of the different forms of a gene that can exist at a single locus. ascus: In a fungus, a sac that encloses a tetrad or an octad of ascospores. bivalents: Two homologous chromosomes paired at meiosis. character: An attribute of individual members of a species for which various heritable differences can be defined. chromatid: One of the two side-by-side replicas produced by chromosome division. cross: The deliberate mating of two parental types of organisms in genetic analysis dimorphism: A polymorphism with only two forms. dioecious species: A plant species in which male and female organs are on separate plants. dominant: The phenotype shown by a heterozygote.

dyad: A pair of sister chromatids joined at the centromere, as in the first division of meiosis. first filial generation (F ): The progeny individuals arising from a cross of two homozygous diploid lines. 1

forward genetics: The classical approach to genetic analysis, in which genes are first identified by mutant alleles and mutant phenotypes and later cloned and subjected to molecular analysis. gene: The fundamental physical and functional unit of heredity, which carries information from one generation to the next; a segment of DNA composed of a transcribed region and a regulatory sequence that makes transcription possible. gene discovery: The process whereby geneticists find a set of genes affecting some biological process of interest by the single-gene inheritance patterns of their mutant alleles or by genomic analysis. genetic dissection: The use of recombination and mutation to piece together the various components of a given biological function. genotype: The allelic composition of an individual or of a cell—either of the entire genome or, more commonly, of a certain gene or a set of genes. haploinsufficient: Describes a gene that, in a diploid cell, is insufficient to promote wild-type function in only one copy (dose). haplosufficient: Describes a gene that, in a diploid cell, can promote wild-type function in only one copy (dose). hemizygous: A gene present in only one copy in a diploid organism—for example, an X-linked gene in a male mammal. heterogametic sex: The sex that has heteromorphic sex chromosomes (for example, XY) and hence produces two different kinds of gametes with respect to the sex chromosomes. heterozygote: An individual organism having a heterozygous gene pair. heterozygous see heterozygous gene pair: In diploids, a gene pair consisting of two different alleles of that specific gene—for example, A/a or A /A . 1

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heterozygous gene pair: In diploids, a gene pair consisting of two different alleles of that specific gene—for example, A/a or A /A . 1

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homogametic sex: The sex with homologous sex chromosomes (for example, XX). homozygote: An individual organism that is homozygous. homozygous dominant: Refers to a genotype such as A/A. homozygous recessive: Refers to a genotype such as a/a. law of equal segregation (Mendel’s first law): The production of equal numbers (50 percent) of each allele in the meiotic products (for example, gametes) of a heterozygous meiocyte. leaky mutation: A mutation that confers a mutant phenotype but still retains a low but detectable level of wild-type function. meiocyte: A cell in which meiosis takes place. meiosis: Two successive nuclear divisions (with corresponding cell divisions) that produce gametes (in animals) or sexual spores (in plants and fungi) that have one-half of the genetic material of the original cell. mitosis: A type of nuclear division (occurring at cell division) that produces two daughter nuclei identical with the parent nucleus. monohybrid: A single-locus heterozygote of the type A/a. monohybrid cross: A cross between two individuals identically heterozygous at one gene pair— for example, A/a × A/a. morph: One form of a genetic polymorphism; the morph can be either a phenotype or a molecular sequence. mutant: An organism or cell carrying a mutation. mutation: (1) The process that produces a gene or a chromosome set differing from that of the wild type. (2) The gene or chromosome set that results from such a process. null allele: An allele whose effect is the absence either of normal gene product at the molecular level or of normal function at the phenotypic level.

parental generation (P): The two strains or individual organisms that constitute the start of a genetic breeding experiment; their progeny constitute the F generation. 1

pedigree analysis: Deducing single-gene inheritance of human phenotypes by a study of the progeny of matings within a family, often stretching back several generations. phenotype: (1) The form taken by some character (or group of characters) in a specific individual. (2) The detectable outward manifestations of a specific genotype. polymorphism: The occurrence in a population of multiple forms of a trait or multiple alleles at a genetic locus. product of meiosis: One of the (usually four) cells formed by the two meiotic divisions. product rule: The probability of two independent events occurring simultaneously is the product of the individual probabilities. property: A characteristic feature of an organism, such as size, color, shape, or enzyme activity. propositus: In a human pedigree, the person who first came to the attention of the geneticist. pseudoautosomal regions 1 and 2: Small regions at the ends of the X and Y sex chromosomes; they are homologous and undergo pairing and crossing over at meiosis. pure line: A population of individuals all bearing the identical fully homozygous genotype. recessive see recessive allele: An allele whose phenotypic effect is not expressed in a heterozygote. reverse genetics: An experimental procedure that begins with a cloned segment of DNA or a protein sequence and uses it (through directed mutagenesis) to introduce programmed mutations back into the genome to investigate function. second filial generation (F ): The progeny of a cross between two individuals from the F generation. 2

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self: To fertilize eggs with sperms from the same individual. sex chromosome: A chromosome whose presence or absence is correlated with the sex of the bearer; a chromosome that plays a role in sex determination.

sex linkage: The location of a gene on a sex chromosome. SRY gene: The maleness gene, residing on the Y chromosome. testcross: A cross of an individual organism of unknown genotype or a heterozygote (or a multiple heterozygote) with a tester. tester: An individual organism homozygous for one or more recessive alleles; used in a testcross. tetrad: (1) Four homologous chromatids in a bundle in the first meiotic prophase and metaphase. (2) The four haploid product cells fro...