16 Mutation, Variation and Genome Organisation Flashcards
(25 cards)
What was the first theory of inheritance?
Jean Baptiste de Lamarck
- Inheritance of acquired characteristics
- Organs that are used most grow bigger and offspring inherit these characteristics
e.g. Giraffes necks
What are mutations?
Failure to replicate genetic information faithfully
- Affect whole chromosomes or single genes
- Spontaneous or induced
- Source of all genetic variation
- Necessary for natural selection and evolution
What are the causes of mutation?
Induced mutations - radiation, UV, X-rays
Mutagen - any agent that increases the mutation rate
How many pairs of chromosomes do humans have?
23 pairs
46 chromosomes
What are the types of chromosomal variation?
Polyploidy
Aneuploidy
Translocations
Deletions
Inversions
What is polyploidy?
Greater than two sets of chromosomes e.g. caused by dispermy
- Results in 3 complete sets 3n = 69
- 1-3% of conceptions
- Always lethal
Common in higher plants
What is aneuploidy?
When one set of chromosomes is incomplete
e.g. chromosome missing or extra chromosome present
Monosomy - one member of pair missing - lethal
Trisomy - one extra - usually lethal
What is nullisomy?
Both members of the chromosome pair are missing
Lethal
What is Trisomy 21?
One extra chromosome on the 21st pair
Down’s Syndrome
40 years+ longevity
What happens with aneuploidy in the sex chromosomes?
Lacking a chromosome:
45X - Turner’s Syndrome, Infertile
45Y - Inviable
Extra chromosomes:
47XYY, 47XXY, 47XXX
- Minor effects
What are translocations?
Exchange of parts between non-homologous chromosomes
- Carriers are unaffected
- Offspring can have wrong number of copies of each chromosome - usually lethal
What are deletions?
Part of a chromosome is missing
- Patient has only one copy of each gene in that region
- Severity depends on size of missing region
What are inversions?
Paracentric
- Excludes the centromere
- Often no problems in meiosis
Pericentric
- Includes the centromere
- Possible problems in meiosis
- Chromosomes unable to pair correctly
What is the size of the human genome?
3x10^9 (3 billion) base pairs long
What was Crick’s second discovery?
The genetic code
- Three nucleotides are called a codon
- Every codon specifies one AA
- An AA can be encoded by more than one codon - the code is degenerate
How many genes are in the human genome?
20-30,000
What percentage of the human genome encode proteins?
1.5%
What are coding region mutations?
Substitutions
- One base substituted
Insertion/deletions
- Different protein encoded due to shift in open-reading frame
What are synonymous mutations?
Substitutions that code for the same amino acid
What are nonsynonymous mutations?
Substitutions that code for a different amino acid
What causes many phenotypic polymorphisms?
Simple mutations of one or just a few nucleotides
e.g. tyrosinase causes albinism,
Sickle Cell Anaemia
What are single nucleotide polymorphisms?
SNPs
Variation in non-coding regions of the genome
What is satellite DNA?
Microsatellites (or simple tandem repeats, STRs)
- Nearly always harmless
CACACACACACA
CACACACACA
CACACACA
CACACA
What is Satellite DNA used for?
Finding disease genes, conservation genetics, evolutionary genetics, agricultural improvement
