Modern Genetics III Gene Mutations Karyotypes

What is a mutation? A mutation is any change in the sequence of an organism’s DNA. Any change from the normal.

Benefits of mutations Those populations that are comprised of individuals who are different and diverse have a greater chance of survival. This means that if we were all the same genetically, we would have less of a chance of survival from one generation to the next. Recombination and genetic mutations are what allow for this diversity.

Impact Some gene mutations or new gene combinations can little or no effect on the organism. Others produce organisms that are better suited to their environments; others can be deleterious, or deadly.

Causes Carcinogens are environmental agents that cause mutations to occur. Over exposure to UV, X-rays, chemicals etc are all carcinogens

Causes Mutations can also be caused by genetic factors such as non-disjunction of chromosomes, and random errors in the genetic code.

Mutation Types There are two types of mutations: Chromosomal mutations Which are errors in the chromosomes Gene mutations Which are errors in the gene sequence

Gene Mutations These mutations occur as a result in a random error in the genetic code. This can occur during replication or be inherited from a parent. There are several types of gene mutations including: Deletions, additions, substitutions, and rearrangements

Deletions Normal: the old man saw the dog Deletion: the old mns awt hed ogh This is when one or more bases are deleted from the original DNA sequence.

Addition Normal: the old man saw the dog Added: the old man saw ath edo This is when one or more bases are added to a DNA sequence.

Substitution Normal: the old man saw the dog Substituted: the old man saw the hog This is when one or more bases are substituted in the DNA sequence.

Rearranged Normal: the old man saw the dog Rearranged: the old man saw the god This is when one or more bases have been rearranged to produce a new sequence.

The Outcome When a base is altered, rearranged, added or deleted it will affect the DNA sequence. It is from this sequence that all proteins are derived. So if there is an error in the DNA sequence it is likely there will also be an error in the protein chain produced.

Point vs. Frame-shift Mutations Point mutations- occur when only one amino acid is effected after the mutation. Frame-shift mutations- occur when the entire sequence is altered after the mutation.

15copyright cmassengale

Chromosomes 16copyright cmassengale

Chromosome Number All cells in the human body (SOMATIC CELLS) have 46 or 23 pairs of chromosomes Called the DIPLOID or 2n number These cells reproduce through the process of mitosis GAMETES (eggs & sperm) have only 23 chromosomes Called the MONOPLOID or 1n number These cells reproduce through the process of meiosis 17copyright cmassengale

Chromosome Types Sex Chromosomes are the chromosomes that tell the gender of the organism. In females the sex chromosomes are XX IN males the sex chromosomes are XY

Nondisjunction Non-disjunction is when chromosomes fail to separate during meiosis Resulting gametes may have too few or too many chromosomes This in turn, leads to chromosomal mutations 19copyright cmassengale

The result of too few or too many chromosomes causes: Chromosomal Disorders such as Down Syndrome (Trisomy 21 – 3 Chromosomes on #21) Sex chromosome disorders can also occur: Turner Syndrome: XO (missing sex chromosome) Klinefelter Syndrome: XXY, XXXY, and even XXXXY (extra sex chromosome) no reported cases born just “Y”

Karyotypes We use a karyotype (a picture of chromosomes) to study the human genome (the sequence of our DNA) Photograph cells during mitosis (easiest time to see) Cut out chromosomes from photographs Group homologous chromosomes in pairs Label pairs 1 – 23 (1-22 are autosomes, 23 are sex chromosomes)

Normal Male 22 2n = 46 copyright cmassengale

Normal Female 23 2n = 46 copyright cmassengale

Male, Trisomy 21 (Down’s) 24 2n = 47 copyright cmassengale

Female Down’s Syndrome 25 2n = 47 copyright cmassengale

What is Down Syndrome? Common physical signs include: Decreased muscle toneDecreased muscle tone at birth Excess skin at the nape of the neck Flattened nose Separated joints between the bones of the skull (sutures) Single crease in the palm of the hand Small ears Small mouth Upward slanting eyes Wide, short hands with short fingers White spots on the colored part of the eye (Brushfield spots) Physical development is often slower than normal. Most children with Down syndrome never reach their average adult height. Children may also have delayed mental and social development. Common problems may include: Impulsive behavior Poor judgment Short attention span Slow learning

Klinefelter’s Syndrome 27 2n = 47 copyright cmassengale

What it is Klinefelter’s Syndrome? Abnormal body proportions (long legs, short trunk, shoulder equal to hip size) Abnormally large breasts (gynecomastia)gynecomastia Infertility Sexual problems Less than normal amount of armpit, and facial hair Tall height

Turner’s Syndrome 29 2n = 45 copyright cmassengale

What is Turner Syndrome? Possible symptoms in young infants include: Swollen hands and feet Wide and webbed neck A combination of the following symptoms may be seen in older females: Absent or incomplete development at puberty, including small breasts Broad, flat chest shaped like a shield Drooping eyelids Dry eyes Infertility No periods (absent menstruation) Short height

Cri-du-Chat

What is Cri-du-chat? Cri-du-chat. Babies with the cry of the cat syndrome have a cry which sounds like that of a cat in distress: because the infant's larynx is improperly developed. The cause of this condition is a deletion of about half of the short arm of chromosome number five. Cri-du-chat babies are severely mentally retarded, round face, low set ears, heart disease, and have a small cranium. The incidence of this syndrome is 1/1,000,000 live births. Karyotype: 46XX or 46 XY with one chromosome #5 upper arm deletion.

DNA Technologies We have seen various ways that a change in DNA can impact an organism. But what happens when we manipulate this code?

DNA Impact There is a great potential for the use and misuse of the information that we have gained from DNA. We can develop drugs like insulin that treat diabetes. We can create pest resistant fruits and vegetables. But what happens when the science is not used for good?

Eugenics: A misuse of heredity Eugenics is a pseudo-science of selective procreation that was practced in the 20 th century. Eugenics is the idea that only select individuals should be allowed to procreate to ensure the most fit individuals for society.

Genetic Research The process of producing genetically identical offspring from a single cell of an organism is called cloning.

Cloning Vegetative propagation of plants (when plants send out their shoots to become new plants) and regeneration (when parts of an animal regrows after being lost) of animals are examples of cloning that occur naturally. Clones of frogs have been produced experimentally from the nuclei of cells in blastula stage of an embryo. Mice and sheep have also been cloned.

Cloning

Bacterial Transformation Bacterial transformation occurs when cultures of two strains of bacteria are mixed, portions of the DNA of one strain may enter the cells of second strain. The bacteria of the second culture are then able to synthesize proteins that only the first strain could produce before the transfer. This process is called bacterial transformation.

Examples of Transformation Resistance to antibiotics can be transferred from one bacterial cell to another. Directions on how to make hormones that can later be used for human medications such as insulin and human growth hormone. We use transformed bacteria to lower the cost medications.

Bacterial Transformation

Engineered Transformation

Genetic Engineering By means of bacterial transformation and other techniques, it is possible to transfer genes from one organism to another, producing what is called recombinant DNA. The recipient organism then produces the protein specified by the transferred gene.

Genetic Engineering, Cont. This process, called genetic engineering or “gene splicing” has been used to produce strains of bacteria that can synthesize useful substances, such as insulin, growth hormones and interferons. In the future, these techniques may make it possible to correct genetic defects in individuals.

Where are we going with what we know? The Human Genome Project is a project that is an effort to map out all of the human base sequence or genome. This information is long sought after and is a world wide effort because its completion would be key in the prevention, treatment and detection of many genetic diseases.

Ethics Should we be trying to decode our genetic code? What might the impact to society be?