Mutations
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What are mutations?
Any change in the genetic composition of an organism.
Why does a mutation occur
-could occur by chance -could occur as a result of mutagens
What are mutagens
-physical or chemical agents that cause mutations.
When can gene mutations be transferred to children
Only mutations that occur in the sexual organs can be passed on
What are the 2 types of mutations
-Gene mutations -chromosomal mutations
What are gene mutations?
-A change in the nucleotide sequence
When can gene mutations occur?
They can occur during: - DNA replication - Transcription of DNA and RNA - Crossing over during prophase of meiosis
What are the four types of gene mutations?
-Substitution -deletion -insertion -inversion
A change in the nucleotide sequence. As a result…
As a result the code for protein synthesis changes and forms a faulty protein.
What happens in substitution?
-One nitrogenous base is replaced by another -results in the alterations of one amino acid -point mutation
What happens in deletion?
-one or more nitrogenous bases are lost -results in a frame shift - all base triplets are altered and consequently all the amino acids are
What happens during insertions?
-one or more nitrogenous bases are inserted -all base triplets are altered and consequently also the amino acids. -frame shift
How does a chromosomal mutation occur?
• it occurs when Meiosis doesn’t proceed properly which results in changes in one chromosome number or structure.
What is Aneuploidy?
• extra chromosomes or missing chromosomes in a cell.
Give examples of Aneuploidy.
• Down syndrome - 47 chromosomes. • Turner Syndrome - only one sex chromosomes (XO) • Klinefelter syndrome- extra sex chromosomes (XXY)
How does Down syndrome occur?
Occurs during the production of eggs during Meiosis when chromosomes number 21 doesn’t separate during Anophase 1
What is a zygote?
It is a fertilised egg cell that is formed when a female gamete and a male gamete join.
What is trisomy 21?
A genetic chromosome 21 disorder causing developmental and intellectual delays. -Also known as Down syndrome.
What are the characteristics of Down syndrome? (9)
• small almond eyes • ears situated lower down the head • flat forehead • short, stubby toes • poor muscle tone • flat nose bridge • large tongue • predisposed to heart disease • mental retardation
What is the Maternal Age Effect?
• After the age of 35 the risk of complications like miscarriage, congenital disorders and high blood pressure.
What gender does the turner syndrome effect and what happens with the chromosomes?
• effects the development of females • only one X chromosome (XO)
How many people develop turner syndrome?
1 out of 40 zygotes develop turner syndrome
What are the characteristics of turner syndrome? (7)
• abnormal growth - short in stature • lack of female secondary sexual characteristics. • sterile • slight mental retardation • webbed neck • heart defects • low hairline
What are Somatic Mutations.
They are mutations that occur in body cells and are not transmitted to the next generation. It can cause cells to become malignant.