OCR A-Level Biology Inheritance and Variation Summary

variation occurs due to both
genetic and environmental factors
:


.




Continuous
Polygenetic Characteristic Height/weight
·



spectrum or range
:
-
on a


Discontinuous Monogenetic characteristic with discrete values <Blood Group
·
:




Simple Genetic Cross monogenetic :
characteristics
*
-
a
aa
3 :l phenotypioratio
Heterozygous parents
codominance Both dominant
:

aueles can be expressed ie :




flower colour
↳
Blood Type A :
IP I or I Io Blood Type B I IP or :
II
Type O I I
O
·


II
*

Blood Type AB :



Blood :


*:
I Antigen A produced IP Antigen
:
B produced I: No antigen is produced

Sex Linkage located 23rd
Any gene on the chromosome
:




↳ Recessive conditions occur more females to have unaffected
in males as are more
likely an


dominant X auele ie .

haemophilia or Colour blindness




Dihybrid inheritance :
Inheritance of two characteristics

YyRr x YyRr
tr d
YR
d
F
Yo
2

Y ya ye yo yR
YR YryR yr
YR
YyRR YyR
YR R Ratio 9: 3 3
YyRr Phenotypic 1
:

Yr :
Yyrr
:




yR YyRR YyRr yyRR yyRr ↳
yo YyRr Yyor yyrR yyrr may differ due to mutations or
linkage

Autosomal
linkage Genes are found on the same chromosome
:




↳ No
independent assortment unless separated by chiasmata
↳ Inherited
together
Crossing Over Can :

cause
autosomally linked
genes to Separate
↳ leads to recombinant
offspring Have a different aude combination to parents
:




Recombination
frequency :
Recombinant offspring/ total offspring
↳ <50 %: No linkage