Genetic diversity Flashcards
(14 cards)
What are gametes ?
Haploid with only half the number of chromosomes present
How does meiosis produce gametes ?
Using two divisions:
Meiosis 1 is the reduction division due to separation of the homologous pair of chromosomes so the resulting nuclei are haploid
Meiosis 2 is similar to mitosis with the separation of sister chromatids
Four haploid cells are produced each with half the diploid number of chromosomes
What does meiosis produce ?
Genetic variation and so genetic diversity by crossing over and random segregation of homologous chromosomes
How does crossing over occur ?
Occurs in prophase 1 with the formation of chiasma
What is chiasma ?
Point of contact between two chromatids belonging to homologous chromosomes
How does chiasma form ?
Homologous pairs of chromosomes associate and form a bivalent
Chiasma to forms
Equal lengths of sister chromatids or alleles are exchanged
Producing new combination of alleles
Independent segregation of chromosomes (metaphase 1)
Independent segregation
Maternal and paternal chromosomes are reshuffled in any combination
Create new combinations of alleles
What are the other sources of variation
Fertilisation- random mating with random gametes this results in random fusion of gametes and new allele combinations
What are the differences with mitosis and meiosis ?
Mitosis has the same number of chromosomes whereas meiosis has half the number of chromosomes
Mitosis is genetically identical but meiosis is genetically different
Mitosis produces two cells whereas meiosis produces four
What is a mutation ?
Changes in the base sequence of chromosomes resulting in a new allele
What are the three types of mutations ?
Substitutions: one base is changed for another during dna replication
Deletion: one base is left out during dna replication this results in a frame shift
Insertion : an extra base is added during DNA replication and results in a frame shift
How can mutations not cause a change in a proteins structure ?
Mutation may be in an intron
The mutation may be in a recessive allele
The mutation may code for an amino acid with the same properties as the original one
How can a change in codon result in a change in a proteins structure
Amino acid sequence changes
The hydrogen/ionic/disulphide bonds between r groups change
Tertiary structure changes
What are chromosome mutations caused by
Non disjunction
