Genetics Unit Outline

HIGH SCHOOL BIOLOGY ENDURING KNOWLEDGE FOR GENETICS

Statement of Enduring Knowledge

Overarching questions  How are traits transmitted from parent to offspring?  How are traits controlled by DNA?  How can changes in genes help or harm an individual, society, or the environment?

Background Information

DNA provides for both the continuity of traits from one generation to the next and the variations that can lead to differences within and between species. Understanding DNA makes possible an explanation of such phenomena as the similarities and differences between parents and offspring, hereditary diseases, and the evolution of new species. This understanding also makes it possible for scientists to manipulate genes, thereby creating new combinations of traits and new varieties of organisms.

At the conclusion of the Genetics Unit, students will demonstrate their understanding of the content and concepts of genetics by making a model that shows how information contained in DNA is passed from parent to offspring over many generations. The patterns of the transmission of traits can be used to make statistical predictions about the genetic makeup of future generations.

Students will be able to present their findings of individual research on specific genetic and environmentally induced disorders. Through independent research, students will be able to explain the effects of these genetic and environmentally induced disorders on the growth, development, and differentiation of various living systems.

Cells use the information in their DNA to make copies of themselves. There are several types of cell division. Simple cell division in prokaryotes may occur by a process known as fission. One type of cell division (mitosis) in eukaryotes maintains the chromosome number and produces somatic or body cells. Another type of division (meiosis) reduces the number of chromosomes of the species by one-half and produces gametes or sex cells. The many body cells in an individual can be structurally and functionally very diverse even though they are all descended from a single cell and thus have essentially identical genetic instructions. Different parts of the DNA instructions are used in different types of cells and are influenced by the cell’s environment and past history.

The information passed from parents to offspring is encoded in DNA molecules. Genes are segments of DNA molecules that code for making specific proteins needed by an organism. Inserting, deleting, and substituting DNA segments or nucleotide sequences can alter genes. An altered gene may be passed on to every cell that develops from it. Depending on the genes involves, the resulting features may help, harm, or have little to no effect on the success of the offspring in its environment. The sorting and recombination of genes in sexual reproduction

BCPS Summer 2003 1 Genetics Unit Outline result in a great variety of possible gene combinations in the offspring of any two parents. Gene mutations can be caused by such things as radiation and chemicals. When they occur in sex cells, mutations can be passed to offspring; if they occur in other cells, they are passed on to descendent cells, only. The experiences an organism has during its lifetime can affect is offspring only if the genes in its own sex cells are changed by the experience. Gene mutation may result in uncontrolled cell division called cancer.

The work of the cell is done largely by the many different types of protein molecules it assembles. The genetic information in DNA contains instructions for assembling proteins using the intermediary molecule, messenger-RNA (m-RNA). Messenger-RNA translates the DNA code and carries the information to ribosomes where protein synthesis takes place. The code used is virtually the same for all life forms. Every three bases in the sequence of DNA or m- RNA codes for a specific amino acid. Amino acids are the “building blocks” of proteins. Protein molecules are long, usually folded or looped chains made from 20 different kinds of amino acids. The function of each protein molecule depends on the proper sequence of amino acids. The shape the chain of amino acids takes is also a direct consequence of the sequence of amino acids and resulting attractions between different parts of the chain. Similar proteins in different species (encoded by the DNA present in the nuclei of the cells of that species) may have slightly different sequences in amino acids resulting in species differences.

REVIEW OUTLINE FOR GENETICS UNIT ASSESSMENT

I. Meiosis and Sexual Reproduction A. Meiosis 1. forms gametes needed for sexual reproduction 2. reduces the number of chromosomes, as compared to the parent cell, by half 3. segregation, independent assortment, and crossing-over result in a variety of gene combinations within gametes 4. nondisjunction is an error during meiosis that results in gametes having an incorrect number of chromosomes and can lead to disorders such as Down Syndrome and Klinefelter’s Syndrome B. Sexual Reproduction 1. gametes combine during the process of fertilization 2. fertilization restores the diploid number of chromosomes within the zygote

Essential vocabulary: crossing-over meiosis diploid mitosis fertilization nondisjunction gamete segregation haploid somatic cell independent assortment zygote

BCPS Summer 2003 2 Genetics Unit Outline

II. Mendel and the Principles of Genetics A. Origin of genetics 1. Mendel’s experiments using pea plants 2. contrasting phenotypic ratios of F1 and F2 generations B. Mendel’s laws 1. “particles of heredity,” each organism inherits two for every trait 2. certain factors prevent the expression of others 3. pure breeding versus hybrid organisms 4. law of segregation 5. law of independent assortment 6. relationship between meiotic events and genetic diversity C. Predicting genotypes and phenotypes 1. using Punnett squares to predict the genotypes and phenotypes of offspring 2. using pedigrees to show the inheritance of a trait over several generations D. Patterns of inheritance 1. complete dominance 2. incomplete dominance 3. codominance 4. sex-linked traits

Essential vocabulary: allele genotype P generation codominance Gregor Mendel pedigree chart dominant heredity phenotype F1 generation heterozygous probability F2 generation homozygous Punnett square gene incomplete dominance recessive genetics monohybrid cross sex-linked

III. How DNA is a code for traits A. Structure of DNA 1. DNA is made of two strands of nucleotides twisted into a double helix 2. each nucleotide contains a molecule of the sugar deoxyribose, a phosphate group, and one of four nitrogen-containing bases 3. nitrogen bases are classified into purines (adenine, guanine) and pyrimidines (cytosine, guanine) 4. within the double helix, the base adenine pairs with (is complementary to) thymine, cytosine pairs with guanine 5. Watson and Crick are given credit for discovering the structure of DNA (1953) B. DNA replication 1. the double helix is unwound and unzipped (helicase) 2. each of the two strands serves as a template for the addition of new nucleotides (DNA polymerase) 3. two identical DNA molecules are formed, each containing one strand of parental DNA and one strand of new daughter DNA (semi-conservative replication)

BCPS Summer 2003 3 Genetics Unit Outline

C. Protein synthesis 1. a sequence of nucleotides codes for the production of proteins 2. protein synthesis relies on a chemical cousin of DNA called RNA a. RNA contains the sugar ribose, instead of deoxyribose b. RNA is single-stranded c. the base uracil replaces thymine 3. types of RNA a. messenger RNA (mRNA) b. transfer RNA (tRNA) c. ribosomal RNA (rRNA) 4. transcription a. one strand of DNA serves as a template for the synthesis of RNA (helicase, RNA polymerase) b. in RNA, the base uracil pairs with DNA’s adenine, instead of thymine 5. translation a. mRNA travels to the ribosome, the site of protein synthesis b. three consecutive bases in mRNA (codon) are “read” as one amino acid c. tRNA carries the amino acids to the ribosome and has an anti-codon that is complementary to the mRNA codon d. rRNA combines with certain proteins to make up the structure of the ribosome e. while the tRNA is temporarily bonded to the mRNA, amino acids are connected via a peptide bond to form a protein f. the genetic “code” for amino acids is essentially universal among all organisms D. How mutations change traits 1. a mutation is a change in the DNA sequence of a gene 2. a change in a DNA nucleotide will change the mRNA codon a. if the new mRNA codes for the same amino acid, the protein does not change, and neither will the trait b. if the new mRNA codes for a different amino acid, the protein will change 1. if only one amino acid changes, the trait might not change 2. the new protein may change the trait a. harmful effect b. beneficial effect Essential vocabulary: adenine double helix ribonucleic acid (RNA) anticodon* guanine rRNA codon mRNA thymine cytosine nucleotide transcription deoxyribonucleic acid (DNA) purine* translation deoxyribose pyrimidine* tRNA

* denotes higher level vocabulary

BCPS Summer 2003 4 Genetics Unit Outline

IV. Application of DNA Science A. Genetic engineering 1. combines DNA from two different organisms to produce traits different from those of the unmodified organism 2. restriction enzymes are used to cut DNA into fragments 3. fragments from two different organisms are sealed together forming recombinant DNA (ligase, DNA splicing) 4. new DNA is transferred into the host organism (vector, plasmid, transformation – in prokaryotes, creates a transgenic organism) 5. cells/organisms with the desired traits are cloneD 6. uses of genetic engineering by society a. producing human proteins for pharmaceutical purposes, including diabetes and vaccines b. characteristics such as pest resistance, drought tolerance, and increased vitamin content have been added to major agricultural crops c. gene therapy B. Cloning 1. nuclear transfer a. nuclear material from host cell is transferred to a denucleated cell b. the new cell divides and develops into a clone of the donor organism 2. mitotic cloning / vegetative propagation a. cells are isolated from the organism to be cloned b. cells are cultured under special conditions and develop into clones of the parent organism or clones of parent tissues 3. uses of cloning a. mass production of plants such as agricultural crops and flower species such as orchids b. production of specialized cells such as skin cells for skin grafts c. potential for endangered species conservation d. potential for supply of organs for transplantation e. medical research

BCPS Summer 2003 5 Genetics Unit Outline

C. Electrophoresis 1. DNA samples are obtained from blood, skin cells, hair, semen, saliva, etc. 2. DNA is cut, and fragments are separated by size using a gelatinous material and electricity 2. DNA fragments migrate toward the positive end of the gel 3. the smallest fragments travel the furthest 4. DNA bands from each sample within the gel are then compared 5. uses of electrophoresis a. identifying criminals b. evidence in paternity suits c. population studies

Essential vocabulary: cloning plasmid* DNA fragment recombinant DNA gel electrophoresis restriction enzyme gene splicing transformation* genetic engineering vector*

* denotes higher level vocabulary

BCPS Summer 2003 6