1. Chromosomal Disorders
What happens when meiosis goes wrong?

2. 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.

3. Karyotype

4. 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

5. 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

6. Male or Female???

7. 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

8. How would this affect the person differently?

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

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

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

12. 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

13. 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

14. 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

15. 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

16. 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

17. Can you spot what is wrong with this karyotype?

18. 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

20. 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

21. DNA/GENE MUTATIONS

22. 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

23. 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?

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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