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Basic Agricultural Genetics - Agricultural Sciences Grade 12 Revision Guide and Frequently Asked Questions
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- *Monohybrid cross /monohybridism= when a single factor is involved in cross breeding. Eg Tallness x shortness
- *Dihybrid cross /dihybridism = when two factors are involved in cross breeding. eg Tall &Light x short & dark
- *Phenotype ======= physical/outward appearance of an organism
- *Genotype ======= genetic composition of an organism
- *Alleles ======= alternate forms of genes/pairs of
Genes (TT, Tt, tt, WW, Ww, ww) - *Homozygous alleles== similar/identical pairs of
Genes (TT, tt ,WW, ww, BB, bb) - *Heterozygous alleles== dissimilar pairs of genes(Tt, Ww, Bb Zz, Ll, Dd)
- *Prepotency======= ability of an organism/individual to transmit its characteristics to the offspring/progeny.
- *Atavism======== Reappearance of ancestral characteristics
- MONOHYBRID CROSS
-when a single factor is involved in cross breeding- WITH DOMINANCE (COMPLETE DOMINANCE)
T=tall, t=short
Pure bred (very) tall===
Hybrid (medium) tall==
Reccessive (very) short - WITHOUT DOMINANCE (INCOMPLETE DOMINANCE)
*Mendell used flowers of different colours
eg Red flowers(R) and a White flower(r)
For you to do:
Give the ratio of each of the following:
Phenotype=
Genotype=
Give the % of :
Red flowers=
Pink flowers=
White flowers=
- WITH DOMINANCE (COMPLETE DOMINANCE)
- CO-DOMINANCE
- There is NO Recessiveness
- Both characteristics (colours) are dominant
- Both colours of the parents will equally appear in the offspring
- The offspring will have a Roan colour
SUMMARYDOMINANCE
INCOMPLETE DOMINANCE
CO-DOMINANCE
COLOUR OF OFFSPRING
* One colour is dominant and the other is recessive.
*The offspring resembles one of the parents
* There is no dominance
* None of the parents’ colours will be visible to the offspring
* The offspring has one colour which is completely different from its parents
* There is no recessiveness
* Both colours are dominant
* Both colours of the parents equally appear in the offspring
* This colour of the offspring is called a Roan colour (White and Black spots/patches)
- DIHYBRID CROSS
-Two factors are involved in cross breeding
Mendell used seeds
Punette Square- F1RY
ry
ry
ry
Ry
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
Punette Square
RATIO: Phenotype:RY
Ry
rY
ry
RY
Ry
rY
Ry
Round &Yellow
Round & green
wrinkled & Yellow=
wrinkled & green=
MENDELL’S LAWS OF INHERITANCE- First Law : When Mendell discovered GENES
- Genes are transmitted from one generation to the next. - Second Law : Dominance and Recessiveness
-Some genes are dominant and others are recessive - Third Law : Law of Segregation
- During meiosis pairs separate to form gametes
eg:
- Fourth Law: Independent assortment /Dihybrid cross /Dihybridism
-Independent pairs of genes are released during meiosis
eg:
- First Law : When Mendell discovered GENES
