Tools & Traits

 "Gene mapping" refers to the mapping of genes to specific locations on chromosomes.  It is a critical step in the understanding of genetic diseases.  There are two types of gene mapping  Genetic Mapping - using linkage analysis to determine the relative position between two genes on a chromosome.  Physical Mapping - using all available techniques or information to determine the absolute position of a gene on a chromosome.

 If two loci of a single chromosome are usually inherited together, they are said to be "linked".  genes on the same chromosome are less likely to be separated by crossing-over the closer they are to each other on the chromosome..  the more frequent recombination rates of genes of the same chromosome, or linkage group, would mean the further apart they existed on that chromosome

 This uses laboratory cultured cells and chromosomes isolated by mechanical means to study nucleotide sequences through a variety of techniques.  Restrictive enzyme analysis  Fluorescence techniques FISH  contigs

 Recombinant DNA  Cloning  Stem cells These techniques and tools have to date involved the use of bacteriophages and viruses to carry DNA/RNA segments to cells in culture.

 Karyotyping  A method of organizing the chromosomes of a cell in relation to number, size, and type.  Useful to see obvious abnormalities of chromosome structure and numbers.  Chromosomes are categorized and sorted by  Size of the chromosome  placement of the centromere  Relative lengths of arms

 A diagram shows inheritance patterns over several generations and can give many key clues as to the kind of inheritance a particular trait exhibits.  Based on physical expression or phenotypes  Ex: whether a trait is dominant / recessive or sex-linked Pedigrees are an important tool for understanding the pattern of inheritance of human genetic traits and disorders

Pedigree symbols Generations are numbered from the top of the pedigree in uppercase Roman numerals, I, II, III Individuals in each generation are numbered from the left in arab numerals 1, 2, 3

Draw the information one step at a time in a logical manner. Step 1 Begin with Alice, Bob and Charles. Step 2 Now add Alice's siblings and parents to the pedigree.

Step 3 Now add Gertrude's siblings to the pedigree. And David's siblings and his nephews and nieces Finally add Bob's side of the family

 Traits controlled by a single allele:  These traits are controlled by a single gene, or pair of alleles,  They may be dominant or recessive  Some traits may be controlled by more than a single pair of alleles.  3 or more alleles of the same gene may exhibit codominance  More than one gene may control expression as in polygenic trait

 Some traits are said to be sex-linked.  most often single allele recessive traits  carried on a sex chromosome  more rarely expressed.  Ex. Colorblindness and hemophilia.  Some traits are sex influenced.  The traits in this category are expressed differently in males and females  Influenced by sex hormones.  Ex. Pattern baldness.

 These genetic diseases are diseases caused by an error in a single gene.  Some examples of autosomal dominant diseases are Huntington's disease and achondroplasia (dwarfism).

 No carriers: Everyone who has the genetic error gets the disease,  Usually inherited: For a person to have the disease, one of the parents must have had the disease.  Parent-to-child transmission: The same probabilities apply as in the inheritance of any simple dominant gene  Vertical inheritance: Every generation is affected, called a "vertical" pattern, as seen on a family tree..  Gender bias: Male or females get the disease equally, because an autosomal error is unrelated to the sex chromosomes.

 These genetic diseases are diseases caused by an error in a single DNA gene.  Some examples are diseases are Cystic Fibrosis, Phenylketonuria, Sickle Cell Anemia, Tay Sachs, and Albinism.

 Parent – child transmission: Typical probabilities of recessive gene alleles apply.  Carrier: Any heterozygous state for a recessive allele constitutes a carrier state.  Gender bias: Male or females get the disease equally, because an autosomal error is unrelated to the sex chromosomes.  Horizontal Inheritance: patterns tend to be "horizontal", which a generation being affected (i.e. many siblings of the same parents), but not their parents nor their own children. Parents and next-generation children will usually be carriers.

 These genetic diseases are diseases caused by an error in a single gene located on a sex chromosome of pair #23.  Examples: red-green color blindness and hemophillia  May exhibit dominance or recessiveness although donimant sex-linked is very rare and usually lethal

 Sex-influenced inheritance is a pattern of inheritance in which the sex hormones of the animal affect the expression of a trait by the heterozygotes.  May be male dominant or female dominant  Example “pattern baldness” and the gene that controls the length of the index finger to be longer than the 3 rd finger

 A Mutation occurs when the DNA of a gene is damaged or changed in such a way as to alter the genetic message carried by that gene.  It may be inherited or acquired  A Mutagen is an agent of substance that can bring about a permanent alteration to the physical composition of a DNA gene such that the genetic message is changed.

Mutation In subtle or very obvious ways, the phenotype of the organism carrying the mutation will be changed the enzyme that is catalyzing the production of flower color pigment has been altered in such a way it no longer catalyzes the production of the red pigment. No product (red pigment) is produced by the altered protein.

 Chemical Mutagens  Radiation  Sunlight  Spontaneous

 Point mutations  small (but significant) changes. often in a single nucleotide base.  Deletions  remove information from the gene. A deletion could be as small as a single base or as large as the gene itself.  Insertions  occur when extra DNA is added into an existing gene  Frame shift mutations  either addition or deletion of one or two nucleotide bases. When this occurs the "reading frame" is changed so that all the codons read after the mutation are incorrect, even though the bases themselves may be still present

 Deletions  Due to chromosome breakage a piece may be lost thus losing information forever  Inversion  This is when a chromosome segment breaks off and the reattaches in an inverted orientation  Translocation  A chromosome segment breaks off and reattaches to a non-homologous chromosome.  Non-dysjunction  occurs during meiosis when homologous pairs fail to separate causing one gamete to have an extra chromosome and the other to have one less.

Non-dysjunction