Mutations and other genetic issues

Genetics Unit

Mutations

Changes in the genetic material.Any deviation from the normal

chromosomal complimentTwo 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.SubstitutionsDeletions Insertions

Gene Mutations

Frameshift mutation—shift the reading frame of the genetic codeCan 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:DeletionDuplication 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 chromosomeCan be fatalCan be caused by uneven crossing over

during meiosis or replication error before meiosis

Duplication

Causes of abnormalities

NondisjunctionThe failure of the chromosome pairs to

separate during Meiosis I or Meiosis IIResult will be a zygote with too many or too

few chromosomesTwo 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

PedigreesKaryotypes

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 weeksCan cause leakage of amniotic fluidCan cause premature labor and delivery

Recessive Disorders

Must be inherited from BOTH parentsAutosomal recessive disorders (non-sex

cells)Tay-SachsPKUCystic 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 alleleHuntington’s diseaseAchondroplasia

Dominant Disorders

Huntington’s DiseaseMental deterioration and uncontrollable

movementsDoesn’t appear until middle age

AchondroplasiaOne 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

ColorblindnessMost often found in males

1 in 10 malesFemales have to inherit from both parents

1 in 100 femalesMost common is red-green colorblindness

Sex Linked Disorders

HemophiliaTwo genes on the X chromosome control

blood clottingMany times it is male children that inherit

this from their mom’s X chromosome1 in 10,000 malesA bleeding disorder; can cause death in

severe cases

Sex Linked Disorders

Duchenne Muscular Dystrophy1 in 3000 malesProgressive weakening and loss of skeletal

muscleCaused by defective version of gene that

codes for a muscle protein

Genetic Disorders

TrisomyDowns 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