Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Inheritance

Topic 10
...
H
...
2

Biology HL 

Horizontal bars = homologous chromosomes 
■

Show that the locus of G is on the same chromosome as L 

➢ Sometimes crossing over can interfere with the linkage 
➢ Outcomes of genetic crosses should typically follow Mandelian ratios of 3:1 for an 
F2 monohybrid cross and 9:3:3:1 for a dihybrid cross 
➢ There is nothing alarming about a slight variation, but if there is a significant 
deviation it suggests that independent assortment is not happening and instead 
the genes of the traits being observed are linked 
 
Chi-squared tests (x​2​) 
➢ A sample size is far smaller than the whole population studied and therefore the 
ratios found in experiments are rarely equal to the theoretical ratios 
➢ Chi-squared test ​is a statistical test that biologists use to see whether the 

difference between an observed result and an expected result is statistically 
significant 

 
➢ The chi-squared value is compared to a table 
○
○

The ​degrees of freedom​ is the number of ​data classes minus 1 
In biology the probability 0
...
2

Biology HL 

➢ Partly explains the difficulty in finding out which genes are responsible for traits 
whose genetic components are not understood 
 
Continuous and discrete variation  
➢ Monogenic traits show d
​ iscrete variation 
○

The different characteristics can easily be distinguished from each other 
■

○

Either this or that 

Examples:  
■

Cystic fibrosis 

■

Haemophilia  

■

Sickle cell anaemia 

➢ Polygenic traits show ​continuous variation 
○

A gradual change of the characteristic can be seen in a population 

○

An array of possible phenotypes can be produced 

○

A discontinuous variation can be displayed as bar charts 

○

Examples:  
■

Height  

■

Body shape 

■

Eye colour  

■

Skin colour 

➢ These characteristics can be influenced by environmental factors, like height and 
nutrition 
 
 
  

3 



---