Changes in Genetic Material Genetic and Chromosomal Mutations

Genetic Mutations  Changes in a single gene.  Types of genetic mutations: 1. Point mutations 2. Frameshift mutations

Point Mutations  Change in one or a few nucleotides of DNA or RNA.  Types of point mutation:  1. Substitutions  2. Insertions  3. Deletions

Point Mutations: Substitutions A substitution is a mutation that exchanges one base for another (i.e., a change in a single “chemical letter” such as switching an A to a G).

Point Mutations: Insertions  Insertions are mutations in which extra base pairs are inserted into a new place in the DNA.

Point Mutations: Deletions  Deletions are mutations in which a section of DNA is lost, or deleted.

Frameshift Mutations  If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings are shifted for every codon that follows. These changes are called frameshifts.  For example, consider the sentence, “The fat cat sat.” Each word represents a codon. If we delete the first letter and keep the order of the sentence in the same way, it doesn’t make sense.

Chromosomal Mutations  Changes in the number or structure of a whole chromosomes.  Types of chromosomal mutations: 1. Deletions 2. Duplications 3. Inversions 4. Translocations 4. Translocations

Deletion of a Gene  Genes of a chromosome are permanently lost 1. Normal chromosome before mutation 2. Genes not attached to centromere become loose and lost forever 3. New chromosome lacks certain genes which may prove fatal depending on how important these genes are

Duplication of Genes  Genes are displayed twice on the same chromosome  Can be an advantageous mutation as no genetic information is lost or altered and new genes are gained 1. Normal chromosome before mutation 2. Genes from the homologous chromosome are copied and inserted into the genetic sequence 3. New chromosome possesses all its initial genes plus a duplicated one, which is usually harmless

Inversion of Genes  The order of a particular sequence of genes are reversed 1. Normal chromosome un-altered 2. The connection between genes break and the sequence of these genes are reversed 3. The new sequence may not be viable to produce an organism, depending on which genes are reversed. Advantageous characteristics from this mutation are also possible

Translocation of Genes  Information from one of two homologous chromosomes breaks and binds to the other  Usually this sort of mutation is lethal 1. An un-altered pair of homologous chromosomes 2. Translocation of genes has resulted in some genes from one of the chromosomes attaching to the opposing chromosome

Review of Chromosomal Mutations  Click here:  Animated Mutation Review Animated Mutation Review Animated Mutation Review

Self-Check Quiz  Name the type of mutation that is occurring in each illustration.  Is it a genetic point mutation, genetic frameshift mutation, or a chromosomal mutation?

Duplication/Chromosomal mutation

Deletion/Genetic point mutation

Frameshift/Genetic mutation

Translocation/ Chromosomal mutation

Deletion/Chromosomal mutation

Substitution/ Genetic point mutation

Insertion/ Genetic point mutation

Inversion/ Chromosomal mutation

Human Chromosome Analysis Karyotypes

How are chromosomes analyzed?  Cell biologists photograph cells in mitosis, when the chromosomes are easy to see.  Then the chromosomes are cut out of the photograph and grouped in pairs.  This arrangement is called a karyotype.

 46 chromosomes indicates that this is a human karytope  Result of a haploid sperm and a haploid egg (23 chromosomes each)  The X and Y chromosomes determine the sex and are called sex chromosomes.  Females have two X chromosomes. Males have an X and a Y chromosome.  Is this karyotype from a male or a female?

 The remaining 44 chromosomes are known as autosomal chromosomes, or autosomes.  Biologist summarize the total number of chromosomes in a human cell like this: 46,XX (for females) or 46,XY (for males)

Sex-linked Genes  There is a special pattern of inheritance located on X or Y chromosomes.  More than 100 sex-linked disorders have been mapped on the X chromosome.  The Y chromosome is much smaller than the X and appears to contain only a few genes.

Colorblindness  Three human genes associated with color vision are located on the X chromosome.  In males, if any of theses genes are defective, colorblindness is produced.  The most common form, red- green colorblindness, is found in about 1 in 10 males is the U.S.  Colorblindness is rare among females-only about 1 in 100 has colorblindness.  This is because males have only one X chromosome.

Hemophilia  Sex-linked disorder where a protein that is necessary for normal blood clotting is missing.  Affects about 1 in every 10,000 males  Person can bleed to death from minor cuts or suffer internal bleeding from bumps or bruises  Can be treated by protein injections

Duchenne muscular dystrophy  Sex-linked disorder that results in the progressive weakening of skeletal muscle.  1 in every 3000 males are born with this condition in the U.S.  Caused by defective gene that codes for muscle protein  Research is being done to find a cure

Chromosomal Disorders  A mistake in meiosis occurs when homologous chromosomes fail to separate is known as nondisjunction (“not coming apart”).  This results in an abnormal number of chromosomes in gametes.  There may also be mistakes in sex chromosomes, which will also cause disorders.

Down Syndrome  If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of a chromosome.  This is known as trisomy.  Three copies of chromosome 21 is called Down Syndrome.

Down Syndrome  In the U.S., about 1 in 800 babies are born with Down syndrome.  Down syndrome produces mild to severe mental retardation.  Also increases susceptibility to many diseases and a higher frequency of some birth defects.

CYSTIC FIBROSIS

CYSTIC FIBROSIS Leads to: _________ and _________ complications, increased susceptibility to infections; “__________” is a symptom “__________” is a symptom More common in ____________ but can affect all races. 30,000 people in U.S. have cystic fibrosis 1 in 31 people are carriers Caucasians respiratorydigestive Salty skin

HUNTINGTON’S DISEASE ______________________ CAUSE: Extra ______________ at end of gene on chromosome 4 The _____________... the more __________ the symptoms. severe CAG repeats more repeats AUTOSOMAL DOMINANT

HUNTINGTON’S DISEASE Causes progressive _____ of ________________ and ___________function loss muscle control mental 1 in 10,000 people in U.S. have Huntington’s disease Huntington’s brain Normal brain

A person with Huntington’s disease has a _____ chance of passing the disorder on to their offspring. Problem: Symptoms of disorder usually don’t show until ____________... so you don’t know you have it until ________ you have had children. 50% MIDDLE AGE AFTER

SICKLE CELL DISEASE CAUSE: T changed to A in gene for __________________ (protein in red blood cells that carries oxygen in blood) HEMOGLOBIN

SICKLE CELL DISEASE SYMPTOMS: _____________ become sickle shaped in persons with ______ sickle cell ________ RED BLOOD CELLS TWO ALLELES

SICKLE CELL DISEASE Circulatory problems Cells stick in capillaries Loss of blood cells (anemia) Organ damage (brain, heart, spleen) Can lead to DEATH

SICKLE CELL DISEASE More common in _________________ 1 in 500 = have sickle cell disease 1 in 500 = have sickle cell disease 1 in 10 = carriers for allele 1 in 10 = carriers for allele Also affects persons of _______________ and _________________ descent Why do so many African Americans carry the sickle cell allele? AFRICAN AMERICANS MEDITERRANEAN MIDDLE EASTERN

SICKLE CELL DISEASE Many can trace their ancestry to west central Africa where ___________, a serious parasitic disease that infects red blood cells is common. Images from: MALARIA Watch a video about sickle cell and malaria

_______________are diagrams that show how are ____________ on __________ over several generations PEDIGREES genes are passed in families

Drawing a pedigree chart

Y-LINKED GENES: Genes ______________ chromosome Genes ______________ chromosome EXAMPLE: Hairy pinna _________genes _____ show up _______ Y linked in males carried on Y ONLY

Turner syndrome ____  1 in 5000 births  Females have only one X chromosome  Small size  Slightly decreased intelligence  35% have heart abnormalities  Hearing loss common  Broad chest  Reproductive organs don’t develop at puberty  Can’t have children XO

Klinefelter syndrome  1 in 1000 births  Males have extra X chromosomes (Can be XXy, XXXy, or XXXXy)  Average to slight decrease in intelligence  Small testes/can’t have children  Usually not discovered until puberty when don’t mature like peers

X-chromosome Inactivation In female cells ______ chromosome is randomly ________________ It condenses and forms a dense region in the nucleus called a _____________ _____________ BARR BODY ONE X SWITCHED OFF

In some female cells the X with the allele for orange spots is switched off and in some cells the X with the allele for black spots is switched off, so cat has different colored spots. CAT COLOR In cats, a gene that controls the _____________ is carried on the ____________________ X chromosome SPOT COLOR See a video

_________ cats have only one X chromosome, so they can only have ____________ of spots! CAT COLOR Male one color THINK ABOUT IT? How many colors of spots could a male cat with Klinefelter syndrome have?