What is a mutation? Change in amount or structure of genetic material
•Mutations are spontaneous, random and rare. •Frequency varies •Most recessive, few are dominant •Mutagenic agents speed up mutation rate, e.g. radiation and chemicals (e.g. mustard gas)
2 types of mutation: 1.Gene mutation 2.Chromosome abnormality
Why are mutations bad?
Each time the information has Flossie now arriving changed, and the Flossie not arrivingSubstitution meaning has been altered. If this Please say where you are happens to genetic Please stay where you are code, the meaning Insertion changes, and the I will send my friend wrong protein is I will send my fiend Deletion made. How has the information been Bring thermos on outing altered each time? Bring mothers on outing Inversion
Gene mutations • Change in one or more nucleotides, altering amino acid sequence • 4 types: 1.Substitution – swapping one nucleotide for another 2.Inversion – nucleotides swapping places 3.Deletion – nucleotide removed 4.Insertion – nucleotide added
Original DNA strand: GAC TTG For each following sequence, state the type of mutation: GCT TG
Deletion
GAA CTT G Insertion GAC TGT Inversion GAC ATG Substitution How many amino acids are coded for in the original strand? How many will be affected after the mutations?
Point mutation •Only one amino acid altered •Substitution and inversion Frameshift mutation •Every amino acid after mutation is affected •Deletion and insertion •Can leave proteins non-functional •Can result in enzymes from metabolic pathways being omitted
Phenylalanine
1
tyrosine
2
Intermediate
3
Melanin
•Omission of enzyme 1 results in phenylketonuria (PKU) •Phenylalanine builds up, from which toxins are produced •Affects mental development
Phenylalanine
1
tyrosine
2
Intermediate
3
Melanin
•Omission of enzyme 3 results in albinism •Caused by lack of melanin
Cystic Fibrosis (not linked to pathway) •Mucus lining lungs and windpipe of affected individuals is abnormally thick leading to congestion •Mutation on chromosome 7
Chromosomal Abnormalities What is the end result of meiosis? What pulls chromosomes apart during meiosis, and what organelle in the cell produces these structures? What would happen if these structures failed?
• Non-disjunction – failure of a spindle fibre to separate chromosomes • Results in abnormal number of chromosomes in cells • If it occurs in meiotic division 1 – 2 gametes have extra chromosome, 2 lack a chromosome Fig. 13.3 p.98
http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Me
•Can also occur in 2nd meiotic division •Results in 2 normal gametes, 1 with extra chromosome, and one lacking a chromosome
http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Me
Down’s Syndrome •Occurs in mother egg cell •Non-disjunction of chromosome 21 •Zygote 2n = 47 •Associated with age of mother during pregnancy (Fig. 13.5 p,99) •Mental development and facial features are affected in the sufferer
Non-disjunction of Sex Chromosomes What is the normal chromosome number and sex chromosome present in egg cells? What is the normal chromosome number and sex chromosome present in sperm cells? If non-disjunction occurred in the sex chromosomes of the egg and sperm, what would their chromosome number, and sex chromosomes be?
Egg
Cells
Sperm
Cells
Normal
Abnormal
Normal
Abnormal
22 + X
22 + 0
22 + X
22 + 0
22 + XX
22 + Y
22 + XY
Turners Syndrome •Gametes which fuse = X and 0 •Chromosome complement = 2n = 44 + X0 •Sufferers are always female •Infertile and no secondary sexual characteristics Fig. 13.7 p.99
Kleinfelter’s Syndrome •Gametes which fuse = X and XY sperm, or XX egg and Y •Chromosome complement = 2n = 44 + XXY •Sufferers always male •Infertile, no secondary sexual characteristics Fig. 13.8 p.99