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Omar Bin Al-Khattab Sec. SchoolBiology Dept
InheritanceWorksheet 1
Name :
Introduction :
Inheritance is the passing of traits from parents to offspring. Genetics is the science that study inheritance and variation in living
organisms.
Mendel was the first person to study inheritance. He chose pea plants to
work on. Peas were an ideal choice because of the following :
1. __________________________________________.
2. __________________________________________.
3. __________________________________________.
4. __________________________________________.
He studied seven traits, each of which has two contrasting varieties.
Mendel started his experiment by pure-breeding plants, these are, plants
which when self fertilized produce identical offspring generation after
another.
One of Mendel`s experiments :
Mendel selected two pure-breeding plants with alternative varieties of a
particular trait
( one pure tall and the other pure short plant ).
He carried cross-pollination between them.
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He collected the seeds resulted and grew them to give
the first-generation offspring ( F1 )
He carried a self pollination for F1 plants and collected
the seeds, and grew them to give F2 generation.
What results he got?
1. ______________________________________________________________________
______.
2. ______________________________________________________________________
______.
3. ______________________________________________________________________
______.
Note : Mendel repeated his experiment on other traits and everytime he got the same results.
How Mendel explained these results?
He called the trait that appeared in F1 generation
______________________________________.
He called the trait that disappeared in F1 generation
______________________________________.
Every trait is controlled by ______________________________________.
Alleles separate during gamete formation. So, every gamete contains
___________________________,
Alleles of the dominant trait represented by capital letter. [ T : is the
factor for tallness ]
Alleles of the recessive trait represented by small letter. [ t : is the
factor for dwarf ]
An organism that has two similar alleles known as
_________________________________________.
An organism that has two different alleles known as
________________________________________.
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Dominantallele : an allele which has the same effect on the phenotype of
an organism weather the organism is homozygous or heterozygous for the
gene.
Recessivealleles : alleles which only shows in the phenotype when no
dominant allele is present.
So Mendel put his first law of inheritance ( Law of segregation ) :
For the previous example :
Tall plant contained 2 dominant alleles _____________
Short plant contained 2 recessive alleles _____________
When they were crossed, each plant formed gametes, so :
- The tall plant gave two similar gametes ______ and _______.
- The short plant gave two similar gametes ______ and _______.
We can represent the different possible combinations
of gametes using Punnette square.
All F1 were _____________________________________________.
In a heterozygous organism the dominant allele T masks the effect ofthe
recessive allele tso all plants appears Tall.
TT homozygous dominant. tall
Tt heterozygous dominant tall ( coz. T
masks t ).
tt homozygous recessive. Short
Genotypes phenotypes
Genotype :
_________________________________________________________________________.
gametes t t
T Tt Tt
T Tt Tt
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Characteristics of an organism are determined by
alleles which occur in pairs
Only one allele can be present in a single gamete.
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Phenotype :
_________________________________________________________________________.
Monohybrid inheritance :
Is the cross between two individuals to study the inheritance of a single
characteristic, one gene. ( Here 2 alleles are involved ).
What is the result of crossing a homozygous tall plant and a homozygous
short plant.
phenotype Homozygous tall X Homozygous short
Genotype ______ X ______
Gametes
At fertilization
All are tall plant
What is the result of crossing of two heterozygous tall plants.
phenotype ______________ X ______________
Genotype ________ X ________
Gametes
At fertilization
If a purple colored pea plant crossed with a white colored. All F1 were purple.
1. Which trait is the dominant ? ___________ . recessive? ____________.
2. Explain your answer in Q1 ? __________________________________.
Game
tes
Game
tes
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3. What is the genotype of the purple plant ? _______. of the white plant ?
_______.
4. What is the genotype of the F1 plants ? _______.
5. If two F1 plants were crossed, what will be the result? Calculate the ratio of
colors.
phenotype _________________ X ___________________
Genotype ______ X __________
Gametes
At fertilization
A tall pea plant was crossed with a short one. Half F1 were tall, and half shortWhat is the genotype
of both parents?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
________________________
In pea plants, the allele for yellow seeds is dominant to the allele of greenseeds. Predict the genotypicratio of offspring produced by crossing two parents heterozygous for this trait.
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
______________________________
If a two yellow seeds pea plant were crossed, the results were as
following :
Game
tes
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298 yellow seeds plant. 99 green seeds plant.
1. What is the most probably dominant trait ? ___________ recessive trait
? ____________ .
2. What is the expected genotype of the parents ? _______________ .
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