inheritance ws1

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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 ? __________________________________.

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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 :

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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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