Genetics
Concepts
Genetics
Alleles
The science of inheritance
Versions of genes that differ from each other in their nucleotide
sequences
Genotype
Types of alleles that a single individual has
Phenotype
Expression of alleles in the individual's size, shape, or
metabolism
Mutations make varying genotypes and phenotypes
Replication of DNA
DNA is replicated during the S phase of the cell cycle
Doubles the amount of DNA
Each gene exists in at least two copies
One on each of the two chromatids
When it begins, chromatin 1st becomes less compact
Opening sufficiently to allow entry of the necessary replicating
factors
DNA does not release from the histones
1 strand of DNA double helix is cut and the two strands seperate
Form a small bubble called replicon
DNA polymerase
Primer RNAs act as substrates for the DNA-synthesizing enzyme
Semiconservative replication occurs next
Replication fork
As DNA uncoils and then separates, it has a forked appearance
Ligated
MutationsDefiniton
Any change however large or small
Point mutation
Smallest mutation affecting the least amount of DNA
Deletion
A piece of DNA is lost
Insertion
The addition of extra DNA
Inversion
DNA becomes tangled and breaks, and during repair it is put in
backwards
Causes of Mutations Mutagen
Something that causes mutations
Several important ones
Certain chemicals
Ultraviolet light
X-rays
Radiation from radioactive substances
Many mutagenic chemicals are man made
Over time are increasing in our environment
Transposable elements have two basic forms
Insertion sequences
Transposon
Only a few thousand base pairs long Contain the genes that code for the enzyme actually involve in
cutting the insertion sequence out and splicing it into DNA
somewhere else
Like an insertion sequence except that it may be much longer Carries genes that code for proteins not associated with
transposition
Effects of Mutation
Significance depends on its nature, position, and extent
If happening in spacer DNA between two genes, it may have no
effect
Statistically mutations are always harmful
All mutations are not harmfull
Somatic mutations
Happen in cells that never lead to sex cells
Cross
Sexual reproduction between two individuals
Monohybrid cross
Only a single character is analyzed and studied
Homozygous
Have two identical alleles
Heterozygous
Has two different alleles
Punnett square
Heterozygote is like that of the parent with two effective
alleles The trait is said to be dominant over the other version which is
recessive