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OCR A-Level Biology Inheritance and Variation Summary
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Handwritten Summary by an Oxford Medical Student which covers all content necessary for an A* in Inheritance and Variation at OCR Biology A-Level.
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variation occurs due to bothgenetic 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
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