Chromosomal Disorders What happens when meiosis goes wrong?

What is a mutation? Mutations involve a change in the number of chromosomes, or the structure of a chromosomes or a nucleotide in the DNA Can lead to disorders OR be beneficial to the organism.

Karyotype

Human Chromosomes Humans have 46 chromosomes arranged in 23 pairs Two sex chromosomes- determine an individual’s sex Females have two copies of the large X chromosome Males have one X and a smaller Y chromosome

Human Chromosomes The remaining 44 chromosomes are known as autosomal chromosomes or autosomes Males and females are born in a roughly 50:50 ratio All human egg cells carry a single X Half of all sperm carry an X and the other half carry a Y

Male or Female???

Types of Mutations Mutations effects vary. One factor is the type of cell if affects…read about the two types now… GERM CELLS- Cells that undergo meiosis to produce egg and sperm cells (in ovaries and testes) SOMATIC CELLS- All the “other” body cells that only do mitosis

How would this affect the person differently?

Gene/DNA Mutations Gene/DNA mutations involve changes in ONE nucleotide Ex’s- Point and Frameshift Mutations

Types of Mutations Chromosomal mutations involve changes in either the number chromosomes or structure of chromosomes (A “chunk” of a chromosome is mutated)

Chromosomal Mutations Examples: Entire chromosome mutation = nondisjunction “chunk” of a chromosome mutation= listed to the right in diagram (insertion, deletion…)

Chromosomal Mutations Entire chromosomes encounter mutations as well There are two main types Nondisjunction Structural four types: Deletion Inversion Insertion Translocation A B C D E Chromosome Gene

Deletion Before mutation After mutation A B C D E A C D E Occurs when a single break causes a chromosome to lose an end piece or when two simultaneous breaks lead to loss of internal segment

Inversion Before mutation After mutation A B C D E A B C E D Occurs when a part of the chromosome breaks off and is reinserted backwards

Insertion (aka duplication or repeat) Before mutation A B C D E After mutation B C A B C B C D E Occurs when a part of the chromosome breaks off & re-attaches to the same chromosome resulting in a duplication of genes

Translocation Before mutation A B C D E F G H After mutation F A B C D E G H Occurs when a part of one chromosome breaks off & attaches to a non-homologous chromosome F G H F G H F G H

Can you spot what is wrong with this karyotype?

Nondisjunctions create… Remember: Normal diploid cells have 2 copies of each chromosome creating homologous pairs… After a nondisjunction , zygote cells will have: Trisomy: when a cell has 3 copies of a chromosome or Monosomy: when a cell has only 1 copy of a chromosome

Creates gametes with the wrong number of chromosomes! Nondisjunction Creates gametes with the wrong number of chromosomes! Two ways it can occur: Homologous chromosomes fail to separate during meiosis I Sister chromatids fail to separate during meiosis II OR

DNA/GENE MUTATIONS

DNA/Gene Mutations Protein synthesis does encounter errors Errors in final sequence of amino acids can be traced to errors in the original strand of DNA Can effect the primary protein structure and ultimately the final shape and function of the protein Two types: point mutations and frameshift mutations

Lets see what happens! Look at A on the handout and locate the substitution Transcribe that part of the gene into the codon it will code for. What amino acid should be there normally? What amino acid is there now?

Point Mutations Involve the substitution of one nucleotide for another Three types of substitution: Silent mutation Nonsense mutation Missense mutation Effects vary from going unnoticed to completely changing shape of final protein

Silent Mutation NORMAL STRAND OF DNA: T A C T T C G A C G T G A C T SUBSTITUTED BASE PAIR: T A C T T T G A C G T G A C T In normal strand: TTC  In substituted strand: TTT  Same amino acid, so there is no change in protein structure DNA mRNA Amino Acid AAG = lysine DNA mRNA Amino Acid AAA = lysine

Nonsense Mutation T A C T T C G A C G T G A C T NORMAL STRAND OF DNA: T A C T T C G A C G T G A C T SUBSTITUTED BASE PAIR: T A C A T C G A C G T G A C T In normal strand: TTC  In substituted strand: ATC  Substituted base codes for a stop codon which can have disasterous effects because the protein isn’t finished DNA mRNA Amino Acid AAG = lysine DNA mRNA Amino Acid UAG = stop

Missense Mutation NORMAL STRAND OF DNA: T A C T T C G A C G T G A C T SUBSTITUTED BASE PAIR: T A C T C C G A C G T G A C T In normal strand: TTC  In substituted strand: TCC  Different amino acid, so there is a change in protein structure DNA mRNA Amino Acid AAG = lysine DNA mRNA Amino Acid AGG = arginine

Frameshift Mutations Caused by either the addition or removal of one or more nucleotides in the original strand of DNA Two types: Insertion Deletion Called frameshift because the addition or removal shifts the “frame” that is read for the amino acid codes

Insertion C NORMAL STRAND OF DNA: T A C T T C G A C G T G A C T T A C TT C C G A C G T G A C T By inserting one base, the entire DNA strand is read differently and can result in a different final protein shape & function C

Deletion NORMAL STRAND OF DNA: T A C T T C G A C G T G A C T DELETION: T A C T T C G AG TG A C T By deleting one base, the entire DNA strand is read differently and can result in a different final protein shape & function C