Summary IEB life science Genetics notes

GeneS : Dominant ,
Recessive & Alleles


other notes

Alleles https://www.studocu.com/en-za/a/18315301?


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·
Definition : One from a set of alternative characteristics found on the same locus of homologous chromosomes

·
Example : If Be
gene for brown hair 3 b gene for blonde
= hair , there are 3 possible Combinations of these alleles . (BB, bb or Bb)
·

Homozygous alleles are both the same (BB or bb)

·

Heterozygous alleles are two different Alleles (Bb)

· The Symbols BB , Bb or bb are called the
Genotype
·
A description of the condition produced e .


g blonde hair
. or brown hair is

called the phenotype.




Recessive Allele

·
Definition : An allele that is masked (not shown) in the phenotypeWhen found in the heterozygous condition CBb) It is.

only
expressed if both of the alleles are recessive (bb) ~




·
We use a lower case to represent the recessive gene, example 'b' for blonde if it is recessive to brown hair

·
Therefore we can always tell the
genotype of A person with two recessive alleles because the recessive alleles will be visible

in
phenotype example a , person with blonde hair must have genotype bb face to example before)

,Dominant Allele

· Definition : An allele that is expressed I shown) in the
phenotype when found in the heterozygous (T) and the homozygous
(TT) condition .




·
A Capital letter is used to represent the dominant allele , example if brown hair is dominant use B for brown .




·
A person with genotype BB or Bb will have brown hair .




Characteristic : Dominant : Recessive :




Eye Colour Brown Blue

Hair colour Brown Blonde

Hairline Shape Widow's peak Smooth hairline


Lip width Thick thin


Ear lobe attachment
freely hanging attached


Tongue rolling ability Can roll tongue Cannot role
tongue

, MENDEl-FATHER Of GENETICS
·
Full Name :
Gregor Mendel

·

Occupation : Austrian monk

·
Location lived : in a
monestary at Bino in Czech Republic

·
Discovery : Mendel made the first break through in understanding how characteristics were inherited
·
Method to
discovery D Choose
:



pea with observable traits . 2) Establishing purebred lines .
3) Cross-pollinating
and observing offspring. I Analyzing results
quantitatively .
of formulate hypothosis 6) Developed
. the laws .




·
Year : 1850




Experimental Setup :

· Mendel Choose pea plants for his experiments because :




-



They have easily observable traits

-

have short generation time


-
he could control pollination (cross or self)



·
He started with "true bredding" plants(plants that , when self-pollinated, always produced offspring with the same trait) he then :




D Cross-pollinated true-breeding plants with contrasting traits .




↳ this created the p generation

2) Observed the fe generation (offspring of the p generation

3) Allowed the fz generation to self-pollinate, the F2
creating generation




·
Conclusions :


② Law of Dominance

-

When two homozygous organisms with contrasting characteristics are crossed , all the individuals of the of the fi
generation will
display the


dominent trait .




-


An individual that is
heterozygous for a particular characteristics will have the dominant trait as the
phenotype .