Mutations - 7.2 Flashcards
(21 cards)
What are mutations?
Changes in the nucleotide sequence of DNA
May occur in somatic cells or gametes
Where may mutations occur?
In somatic cells and gametes
Somatic mutations aren’t passed to offspring; gamete mutations can be
What is the evolutionary significance of mutations?
Rates of mutation generally high, leading to a high load of deleterious mutations
What types of mutations are there?
Gene mutations and chromosome mutations
Gene mutations include base-pair substitutions; chromosome mutations involve changes in chromosome number
What are base-pair substitutions?
Caused by chance errors during synthesis or repair of DNA
Leads to new alleles which may or may not change phenotypes
What are the four types of chromosome mutations?
- Deletion
- Inversion
- Duplication
- Translocation
What happens during a deletion mutation?
A piece of a chromosome is lost
Caused by breakage
Describe an inversion mutation.
A chromosome segment breaks off, flips around backwards, and reattaches
What occurs during a duplication mutation?
A gene sequence is repeated
What is a translocation mutation?
Part of one chromosome is transferred to another chromosome
Involves two chromosomes that aren’t homologous
What is a gene mutation?
Change in the nucleotide sequence of a gene
May only involve a single nucleotide
What is nondisjunction?
Failure of homologous chromosomes to separate during meiosis
What is Down’s Syndrome caused by?
Nondisjunction in chromosome 21
Results in an abnormal zygote (2n = 47)
What is Turner’s syndrome?
Gamete with no sex chromosomes fuses with a normal X gamete
Zygote has chromosome complement 2n = 45
What is Klinefelter’s syndrome?
Zygote has chromosome complement 2n = 47 (44 + XXY)
Always male and normally infertile
What is complete nondisjunction?
All spindle fibres in a gamete mother cell fail
Results in abnormal diploid gametes
What is polyploidy?
Formation of mutant plants with complete extra sets of chromosomes
What is the economic significance of polyploid plants?
They are larger than diploid relatives and give greater yields
Examples include apples, strawberries, tomatoes, and wheat
What are the effects of mutations?
Almost all mutations are neutral, but chemicals and UV radiation can cause them
How can mutations lead to big changes?
- Accumulation of many small mutations, each with a small effect
- Accumulation of several small mutations, each with a large effect
- One large mutation with a large effect
What can mutations in regulatory sequences affect?
Regulation of development
