Human GeneticsTools & Traits

Gene Maps

"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.

Linkage analysis

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

Physical mapping

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

Managing the genes

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.

Tracking Human Inheritance 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

Pedigree

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 isdominant / 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 1Begin with Alice, Bob and Charles.

Step 2Now add Alice's siblings and parents to the pedigree.

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

Genetic Traits & Disorders

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

Genetic Traits & Disorders

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.

Autosomal Dominant

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.

Autosomal Recessive

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.

Sex linked

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

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 3rd finger

Mutations

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.

Types of Mutagens

Chemical Mutagens

Radiation

Sunlight

Spontaneous

Categories of Gene Mutations

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

Chromosome mutations

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.

Chromosome mutations

Non-dysjunction