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Name: __________________________________________________ Genetics I. Chromosomes: A) Humans have 46 chromosomes, or 23 homologous pairs. 1. Homologous: chromosomes with the same size, shape and genes. B) Chromosome pairs carry genes for the same traits. We all have 2 alleles for each gene. 1. Most organisms have two genes for each trait - 1 from each parent, 1 on each member of the homologous pair. C) Sex chromosomes – In humans, females are XX and males are XY 1. The Y chromosome is much smaller than the X, so it is missing many genes. This means many genes on the X chromosome do not have a “partner” so: If a male has a recessive trait on the X chromosome, the Y chromosome will not be able to “hide” it with a dominant gene, so... This makes males more likely to have some traits (like color blindness). These are called sex linked traits. D) Autosomes the 22 chromosome pairs that are not sex chromosomes. E) Common mistake: “Humans have 23 chromosomes (or 46 pairs of chromosomes, or some other incorrect number).” Wrong! These numbers are often confused. You must memorize them correctly. F) We have 23 pairs, 46 total! II. Chromosomes and Genes A) Each chromosome has hundreds or thousands of genes. B) Each gene codes for a particular protein. 1. Common mistake: “Genes/DNA are made from protein.” Genes carry the instructions to make protein. The genes themselves are made from nucleic acids. 2. While genes determine our traits, the environment can affect expression of genes. ( Identical twins with different freckle patterns.) III. DNA A) DNA is the chemical that makes up your genes and chromosomes. 1 B) C) D) E) 1. Analogy: If your genes and chromosomes are the “instruction manual” for your body, DNA would be the paper it is printed on. The shape of a DNA molecule is a double helix, which resembles a twisted ladder. The shape of DNA allows it to replicate (copy) itself almost perfectly. DNA is made up of many nucleotides. Each nucleotide contains a phosphate, a deoxyribose sugar, and a nitrogen base. DNA is made of 4 nitrogen bases: A, T, C and G 1. Base pairs: A - T and C- G in RNA the pairs are A - U and C- G DNA – Always Tired, Constantly Grumpy RNA- Always Ugly, Constantly Grumpy IV. Protein Synthesis: This is how genes control your body: 2 A) A codon is a sequence of three bases in DNA. Each codon represents a specific amino acid. Ribosomes assemble amino acids in the same order that they are listed in the DNA codons. The amino acids will make a protein. The order of the amino acids (determined by the DNA sequence) determines the shape of the protein. The shape of a protein determines its function. Therefore: The sequence of bases in DNA will determine the functions of all the proteins in the body. The proteins build and run the body. B) RNA carries the genetic code to ribosomes. 1. m RNA gets copied in the nucleus. 2. m RNA moves from the nucleus into the cytolplasm, and then to the ribosome. 3. t RNA transfers the amino acid to the m RNA where protein synthesis occurs (in the ribosome) The order of DNA bases in your genes determines the order of amino acids in your proteins, which determines the proteins’ shape, which determines the proteins’ function, and the proteins build and run your body. Therefore: How your body functions depends on the order of the bases in your genes! 3 V. Mutations: Any change in the genetic material of an organism. A) Can only be passed on if they occur in reproductive cells (sperm or egg). B) Common mutagenic agents include radiation, chemicals and viruses. 1. Mutagenic agent: Any environmental factor that causes a mutation. C) Gene mutations may cause a change in a gene which can change the shape of a protein. This will have an effect on the way the protein works (if it still works at all). 1. Gene mutations are caused when DNA bases are in some way changed. D) Chromosome mutations are usually caused when a person inherits too many or too few chromosomes. 1. Chromosome mutations affect many genes at once. Most are lethal 2. Down’s Syndrome: Non lethal mutation, caused by inheritance of an extra copy of chromosome 21. (Note – only chromosome 21 can cause Down Syndrome). VI. Genetic technology: A) Selective breeding: Breeding organisms to produce offspring with desired traits. (disease resistance, larger fruit, more meat or milk, specific colors) 1. Inbreeding – Breeds organisms with the same traits ( ex: beagle x beagle) 2. Outbreeding – Breeds organisms with different traits ( ex: horse x donkey = mule) 3. Cannot be used to breed completely unrelated species. B) Genetic engineering: Inserts a gene from one organism into the DNA of a different organism. 1. Restriction enzymes are used to cut the DNA segments. 2. Organism that receives the new gene will begin to make the protein coded for by that gene. 3. The new protein/enzyme/hormone will be exactly the same as the one produced by the original organism. 4. Bacteria are often used because they are cheap, simple, and reproduce quickly. 5. The example of gene splicing you MUST know: Bacteria have been engineered to make insulin for diabetics. Bacteria have been engineered to make human growth hormone. 4 In both cases the engineered hormones are safe to use because they are identical to normal human hormones. C) New technologies (karyotyping, DNA fingerprinting) are making it easier to diagnose and treat genetic disease, though we cannot yet cure them. 1. Karyotype: A photograph of an organism’s chromosomes. Can determine if a person has a chromosome disorder such as Down Syndrome. 2. DNA finerprinting, or gel electrophoresis, creates banded patterns based on a person’s DNA base sequence. Each fingerprint is unique, so it can be used to identify people. Fingerprints of relatives are similar to each other, so can be used to determine genetic relationships between two people, or even two groups of organisms. D) Genetic research has posed many ethical problems (ie right and wrong) that science alone cannot answer. 1. Ethics: Study of what is morally right or wrong. A karyotype shows all 23 pairs of human chromosomes. Note the last pair identifies this as a male. 5 Genetics Unit Review These are the vocabulary words that you need to know for the genetics unit. You need to study them and quiz yourself using the castlelearning flashcard assignment that is posted. acquired characteristic A characteristic developed during an individuals lifetime. These are not passed on to succeeding generations. addition The adding of DNA nucleotides to a chromosome. allele A procedure that removes amniotic fluid containing fetal cells for analysis to determine the presence of genetic defects. artificial selection A breeding practice by which organisms are purposely mated to produce offspring with specific desirable traits. One of the two or more possible genes autosomes for a trait. They are always at the same Chromosomes that are not sex position (loci) on homologous chromosomes. chromosomes. amino acid The basic building block of proteins. They contain an amine group and a carboxyl group. centromere amniocentesis 6 The region where the chromatids of a Inheritance in which both of the double-stranded chromosome are held alleles are expressed. The hybrid is a together. blend of both. chromatid Codon One of the two strands of a replicated chromosome. A sequence of three nitrogenous bases in the messenger RNA sequence that are specific for one amino acid. chromosomal mutation Any change in the number or structure common ancestors of the chromosomes. Organisms from which closely related chromosome organisms have evolved. A structure found in the nucleus that is complementary made of DNA and protein. It contains Being the complement of the other, the hereditary information. the result of specific pairing. cloning The production of genetically identical organisms. crossing-over codominance The equal exchange of genetic material by homologous 7 chromosomes during the synapsis of meiosis. deletion environmentally influenced traits Traits that are not expressed unless the environmental conditions are correct. A chromosomal abnormality in which a portion of the chromosome has been gametes lost. Monoploid sex cells produced in gonads by meiotic cell division. diploid Sperm and egg. The 2n number. The normal number of chromosomes for a particular species. gel electrophoresis The human diploid number is 46 A method used to separate DNA DNA (deoxyribonucleic acid) fragments on the basis of their size. The nucleic acid that stores the hereditary information, that is, the genetic material. gene A section of DNA on a chromosome that codes for a particular trait. gene mutation Any change in the sequence of bases in DNA. double helix gene-chromosome theory The shape of the DNA molecule, the spiral shape formed by the parallel strands. The theory that states that genes are arranged in a linear sequence in definite locations (loci) on 8 chromosomes. Genes for the same trait are located at the same loci on homologous chromosomes. The study of DNA and how the hereditary information is transmitted from one generation to the next. genetic genotype Pertaining to DNA, the hereditary material. The genetic makeup of an individual; ex. hybrid tall. genetic engineering heredity The process which transfers genes to another organisms DNA resulting in recombinant DNA. The sum total of genetically inherited characteristics which are passed from parents to offspring. heterozygous genetic screening The analysis of body fluids such as blood or urine to detect the presence of a genetic disease. genetically Having to do with the chromosomes and how traits are inherited. genetics Hybrid. The pair of genes for a trait are not alike; for example Tt. homologous chromosomes A pair of chromosomes of the same size and shape that carry genes for the same trait. homozygous Pure. The pair of genes are the same; for example TT. identical twins 9 Two individuals formed from a single fertilized egg. They have the same genetic makeup. independent assortment Different traits that are carried on different chromosomes are inherited independently from one another. inherited Coming from ancestors. insertion at enlarged images of them arranged on a grid according to size. male An organism that has XY sex chromosomes or produces sperm cells. Mendel A mathematician and monk who developed the hereditary principles of dominance, segregation, and independent assortment. A mutation that is caused by the placement of a DNA nucleotide into an existing gene. messenger RNA An RNA molecule with a specific code for a polypeptide. This code is A hormone produced by the Islands of determined by the sequence of bases Langerhans in the pancreas. It lowers of the DNA molecule in the nucleus. blood sugar levels. mutagenic agents karyotyping Any substance that can change the The process by which an individual’s structure of the DNA, causing a chromosomes are examined by looking mutation. Insulin 10 mutation recessive traits A change in the genetic material. Traits that do not appear if the dominant gene is present. nitrogenous bases Adenine, thymine, uracil, cytosine and guanine. recombinant DNA nucleotide The DNA of an organism has been changed usually by the addition of a gene. The basic unit of nucleic acids. It consists of a 5-carbon sugar bonded to a phosphate and a nitrogenous base. recombination The formation of new combinations of genes. This can be the result of The appearance of an organism; how it crossing over during meiosis. looks. replication protein The copying of the exact base An organic compound made of amino sequence of the DNA. acids. ribosome protein synthesis The organelle that is the site of The making of a protein from amino protein synthesis in the cell. acids by matching the anticodon of the transfer RNA to the codon of the messenger RNA. phenotype 11 A group of organisms that can interbreed and produce fertile offspring. sperm selective breeding The manipulation of reproductive processes to produce offspring with specialized traits; choosing mates or crossing traits to produce offspring that have desired traits. Methods of selective breeding include inbreeding, artificial selection, hydridization, and vegetative propagation. For example, dog breeds such as the Dalmatian are the result of selective breeding. sex chromosomes The pair of genes that determines the sex of the individual, with XX being female and XY being male. The male monoploid (n) gamete, sex cell. Tay-Sachs A fatal recessive genetic disease which is characterized by the deterioration of nerve tissue due to the accumulation of fatty material. It is most frequent in Jews of Central European descent. Template A guide for the assembly of products to assure their uniformity. sex determination In humans, the male determines the sex. XX is female XY is male. species Tetrad The structure formed when the homologous double stranded 12 chromosomes (4 chromatids) come together during the synapsis of meiosis. Trait A characteristic of an organism. transfer RNA vegetative propagation A form of asexual plant reproduction that produces identical new plants as undifferentiated tissue divides by mitosis. The resulting cells specialize providing the needed tissues. The type of nucleic acid that contains an anticodon three nucleotides long. It carries a specific amino acid to the Watson and Crick mRNA at the ribosome during protein The scientists who discovered the synthesis. structure of the DNA molecule. tumor An abnormal mass of cells. 13