8.1 Origins Of Genetic Variation Flashcards
The three sources of genetic variation
Meiosis (crossing over and independent assortment)
Mutation
Random fertilisation
Crossing over
H chromosomes line up next to each other (Meiosis 1 prophase)
Tangle at specific loci (chiasmata)
Crossing over occurs, alleles are swapped
Gene number and location is still the same
Same genes and different combination of alleles
Independent assortment
Each pair of homologous chromosomes is arranged completely randomly
- each pair lines up independently
The daughter cells contain a different assortment of chromosomes (paternal, maternal or both)
The gametes carry the same genes but different number of alleles
Gametes are bi genetically identical
Mutation definition
A mutation is a change in amount or structure of DNA. There are two types of mutations:
- a gene or point mutation
- a chromosome mutation
point mutation
change in bases sequence of a gene which alters polypeptide chain
change occurs in DNA replication
changes a single amino acid and can effect whole protein
chromosome mutation
change in number or structure of chromosomes
caused by errors in cell division
deletion
a portion of chromosomes is lost
involves the loss of genes
often lethal
duplication
a portion of chromosome is doubled
results in repetition of a portion of gene sequence
inversion
a portion of chromosome is repeated the reattached in an inverted position
the sequence of genes in this portion is reversed
translocation
a portion of chromosome becomes deleted and rejoins on a different point of the same chromosome or a different chromososome
random fertalisation
fusion of two haploid gametes to form a diploid zygote
as meiosis results in two genetically different gametes, random fertilisation of egg and sperm will always produce a different zygote
