Testing Deviations from Mendel

What is linkage

• Alleles on the same gene have a higher chance of being inherited together

  • as chromosomes have many genes

• independent assortment (mendels second law stating that genes are passed on independently of other genes) can only occur when alleles are on different chromosomes

• If genes on same chromosome then are linked and are likely be inherited together

  • so most of offspring will inherit parental phenotypes

• Complete linkage is where genes for characteristics are so close together on the same chromosome that they are always inherited together

What is recombination of linked genes

• when alleles on chromosome further apart, crossing over in P1 can lead to different combinations of A/a and B/b

  • called incomplete linkage and the product is recombinant chromosomes

How to know if deviations from Mendel’s ratios are significant

• fertilisation random so can be big difference between observed ratios compared to expected ratios

  • even if genes on different chromosomes so can do independent assortment

• can be tested using Chi squared test, compares observed and expected results to determine if difference is due to chance or if it has a cause

When is Chi squared test used

• When data is nominal (can be given categories like different phenotypes)

• have actual observations not percentages or fractions

• able to calculate expected values

What does a null hypothesis state

• there is no statistically significant difference between observed and expected results

• needs to be formulated before calculating chi squared statistic

what probability should be used with degrees of freedom to find critical value?

0.05 (5%)