The chromosomal basis of inheritance

The chromosomal basis of inheritance

The events of meiosis explain the behaviour of genes according to Mendel's laws

1) Law of segregation

An organism's characteristics are controlled by factors (genes) which are normally carried in pairs but which occur singly in the gametes

2) Law of independent assortment

Genes for different traits assort independently from each other in the formation of gametes

Parallel behaviour between genes and chromosomes in meiosis

Anaphase

• centromeres attach to spindle and are pulled to poles of cell
• homologous pairs pair up on either side of metaphase plate
• DNA replication has occured
• this is a random assortment

Telophase

• two cells form
• alternative form has equal probability of formation

Second anaphase

• new spindles form and centromeres finally divide

End of meiosis

• four cells are produced from each meiosis
• alternatives have equally likely chance of forming
• independent assortment

Genetic linkage and recombination by crossing over

• linked genes are close together on the same chromosome and are therefore inherited together
• unless they are separated by recombination (crossing over) at meiosis

Crossing over occurs during prophase I of meiosis

• homologous sequences of chromosome pairs are aligned
• crossing over - reciprocal exchange of chromatid segments…