Inheritance Ws1

Omar Bin Al-Khattab Sec. School Biology Dept

Inheritance Worksheet – 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. 1

 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 every time 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. 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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[ t : is the



Dominant allele : an allele which has the same effect on the phenotype of an organism weather the organism is homozygous or heterozygous for the gene.



Recessive alleles : alleles which only shows in the phenotype when no dominant allele is present.

So Mendel put his first law of inheritance ( Law of segregation ) : Characteristics of an organism are determined by alleles which occur in pairs Only one allele can be present in a single gamete.

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 _______. gametes t  We can represent the different possible combinations T Tt of gametes using Punnette square. T Tt -

t Tt Tt



All F1 were _____________________________________________.



In a heterozygous organism the dominant allele T masks the effect of the recessive allele t so all plants appears Tall.

TT  homozygous dominant.

tall

Tt  heterozygous dominant

tall ( coz. T

masks t ). tt

 homozygous recessive.

Genotypes

Short phenotypes

Genotype : _________________________________________________________________________.

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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

Genotype

X

______

X

Homozygous short ______

Gametes At fertilization Game All are tall plant

tes

What is the result of crossing of two heterozygous tall plants. phenotype

______________

Genotype

________

X X

______________ ________

Gametes At fertilization

Game tes

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

_________________

Genotype

X

______

___________________ X

__________

Gametes At fertilization

Game tes

A tall pea plant was crossed with a short one. Half F1 were tall, and half short. What is the genotype of both parents? _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ _____________________________________________________________________ ________________________ In pea plants, the allele for yellow seeds is dominant to the allele of green seeds. Predict the genotypic ratio 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 : 5

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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