Mutations and other genetic issues Genetics Unit

Mutations Changes in the genetic material. Any deviation from the normal chromosomal compliment Two types: Spontaneous mutations-occur randomly; no cause can be determined Induced mutations are caused by some traceable artificial factor: exposure to chemicals, alcohol, drugs, radiation

Mutations Mutations that produce changes in a single gene are gene mutations. Mutations that produce changes in a whole chromosome are chromosomal mutations.

Gene Mutations Point mutation-change in one or just a few nucleotides. So named because it occurs at a single point. Substitutions Deletions Insertions

Gene Mutations Frameshift mutation—shift the reading frame of the genetic code Can alter a protein so much that it can’t perform its job.

Chromosomal Mutations Involve a change in the number or structure of the chromosome Some change the location of some genes on the chromosome Some may change the number of copies of some genes.

Chromosomal Mutations Four main types of mutations: Deletion Duplication Inversion translocation

Deletion The permanent loss of a segment of chromosome Can be found anywhere on the chromosome Can be caused by heat, radiation, viruses, chemicals, errors

Deletion

Duplication Doubles a segment of chromosome Can be fatal Can be caused by uneven crossing over during meiosis or replication error before meiosis

Duplication

Causes of abnormalities Nondisjunction The failure of the chromosome pairs to separate during Meiosis I or Meiosis II Result will be a zygote with too many or too few chromosomes Two types: Primary and secondary nondisjunction

Primary Nondisjunction

Secondary Nondisjunction

Types of Genetics Tests When trying to determine a genetic problem, we can use non-invasive tests such as Pedigrees Karyotypes

Pedigrees A pedigree follows a specific trait through several generations Resembling a type of map, the pedigree uses symbols to represent certain elements

Pedigree key

Pedigree

Karyotypes A photographic inventory of an individual’s chromosomes Can show the individual’s gender and any abnormalities in chromosome number or structure

Karyotypes

Karyotypes

Amniocentesis An invasive test that obtains amniotic fluid surrounding the fetus using a needle

Amniocentesis Pros and Cons Able to determine fetus’ gender and/or any abnormalities Can’t be done before 16th week of pregnancy Can cause infection to mother and/or fetus Can cause premature delivery and birth

Chorionic Villus Sampling (CVS)

CVS Pros and Cons Can determine fetus gender and any genetic abnormalities Can be done after 10 weeks Can cause leakage of amniotic fluid Can cause premature labor and delivery

Recessive Disorders Must be inherited from BOTH parents Autosomal recessive disorders (non-sex cells) Tay-Sachs PKU Cystic fibrosis

Recessive Disorders Tay-Sachs—lipid accumulation in the brain; mental deficiency; blindness, death in early childhood PKU-phenylketonuria—accumulation of phenylalanine in tissues; lack of normal skin pigment; mental retardation Cystic fibrosis—excess mucus in lungs, digestive tract, liver; increased susceptibility to infections; often die young

Dominant Disorders Can get the disorder by inheriting only one dominant allele Huntington’s disease Achondroplasia

Dominant Disorders Huntington’s Disease Achondroplasia Mental deterioration and uncontrollable movements Doesn’t appear until middle age Achondroplasia One form of dwarfism

Sex Linked Disorders Is there a pattern of inheritance for genes located on the X or Y chromosome? YES especially on the X Many times it is male children that inherit these disorders from their mothers because . . . They inherit their X from their mom’s Many sex linked genes are on the X Colorblindness Hemophilia Duchenne Muscular Dystrophy

Sex Linked Disorders Colorblindness Most often found in males Females have to inherit from both parents 1 in 100 females Most common is red-green colorblindness

Sex Linked Disorders Hemophilia Two genes on the X chromosome control blood clotting Many times it is male children that inherit this from their mom’s X chromosome 1 in 10,000 males A bleeding disorder; can cause death in severe cases

Sex Linked Disorders Duchenne Muscular Dystrophy 1 in 3000 males Progressive weakening and loss of skeletal muscle Caused by defective version of gene that codes for a muscle protein

Genetic Disorders Trisomy Downs Syndrome (extra chromosome 21) Edwards Syndrome (extra chromosome 18) Patau Syndrome(extra chromosome 13)

Downs Syndrome (Trisomy 21)

Edwards Syndrome (Trisomy 18)

Patau Syndrome (Trisomy 13)

Turner’s Syndrome

Turner’s Karyotype

Klinefelter’s Syndrome