Heredity

Heredity: The transfer of characters from one generation to next generation is called heredity.

Gene: A gene is tiny segment of DNA which determine particular character.

Alleles: An allele is one of the another gene present in a pair for eg,. in (Tt), T is allele fort.

Homozygous (pure) organism: An organism having two identical alleles (genes) in a pair that determines particular character are called homozygous. Eg (TT)

Heterozygous (hybrid) organism: An organism having two different alleles is called heterozygous organism. Eg. (Tt)

Phenotype: External appearance of an organism.

Genotype: Genetic makeup of an organism is called genotype.

First filial generation (F1): Offspring obtained by crossing between parents having pure characters are called F1 generation.

Second filial generation (F2): Offspring obtained from F1 generation are called F2 generation.

Dominant character: The character that appear in first generation when crossing is carried between parent having pure contrasting characters is called dominant characters.

Recessive character: The character that remain hidden in F1 generation when crossing is carried between the parents having pure contrasting characters.

Gregor John Mendel is known as father of genetics. It is because he was the first person to conduct detailed  study about variation and inheritance and discover laws. Mendel selected pea plant tone for his experiment due to following reasons:

1. Pea plant produce closed bisexual flower so it is easy to carry bath self and cross pollination.
2. Its life cycle completes in short period of time so result can be obtained quickly.
3. Many pairs of contrasting characters are found.
4. They produce large number of offsprings.

Some characters selected by Mendel:

1. Height of plant – Tall (TT) and dwarf (tt)
2. Position of flower – Axial (AA) and terminal (aa)
3. Color of flower – Red (RR) and white (rr)
4. Color of pod – Green (GG) and yellow (gg)
5. Shape of seed – Round (RR) and wrinkled (rr)
6. Color of seed – Yellow (YY) and Green (yy)

Mendel’s laws:

1. Law of dominance
2. Law of segregation
3. Law of independent assortment

1) Law of dominance: It states that “when crossing is carried between parents having pure contrasting characters, only one character appears in first generation.”

Q1. What will be the genotype and phenotype of offspring obtained in F1 and F2 generation when crossing is carried between a pure black dog (BB) and pure white dog (bb). Show with necessary chart.

For F1 generation,

Phenotype – All are black

Genotype – All are hybrid black

For F2 generation,

Phenotype – Black:White = 3:1

Genotype – Pure black:Hybrid black:Pure white = 1:2:1

Q2. What will be the genotype and phenotype of first and se filial generation when crossing is carried between pure and tall pea plant and pure dwarf pea plant show with necessary chart.

Here, let’s suppose Tall (TT)is dominant character.

For F1 generations,

Phenotype: All are tall

Genotype: All are hybrid tall

For F2 generations,

Phenotype: Tall:Dwarf = 3:1

Genotype: Pure tall:Hybrid tall:Pure dwarf = 1:2:1

Q3. What will be the phenotype and genotype F1 and F2 generation when crossing is carried by between pure green monkey and pure brown make show with necessary charts:

Here, Let’s suppose Green (GG) is a dominant character.

Phenotype:

F1 generation: All are green

F2 generation: 3 are green and one is browns i.e. Green:Brown=3:1

Genotype:

F1 generation: All ore hybrid tall

F2 generation: Pure green:hybrid green:pure brown = 1:2:1

Q4. The result obtained by crossing Red flowering pea plant and pure white flowering pea plant is given in table on the basis of it, answer it.

a. To which filial generation this result belong?

Second filial generation.

b. Which pair of genes, represent pure red?

RR

c. What is the percent of Red flowering pea plant?

75%

d. Write the genotype of the result obtained ?

Pure red: Hybrid Red: Pure white = 1:2:1

Q5. What will be the phenotype and genotype of F2 generation when crossing is called between a homozygous black rabbit and homozygous brown rabbit? Show with chart.

Let’s suppose black (BB) a dominant character.

Genotype – Pure black : Hybrid Black: Pure brown = 1:2:1

Phenotype – Black : brown = 3:1

Q6. What will be the genotype and phenotype of offspring obtained when cross is carried between hybrid black cat and pure white cat. show with necessary chart.

Phenotype – Black : White = 2:2

Genotype – Hybrid black : Pure white = 2:2

Q7. What will be phenotype and genotype of offsprings obtained when crossing is carried between hybrid red monkey and pure brown monkey. Show with chart.

Phenotype – Red:Brown = 2:2

Genotype: Hybrid red : Pure brown = 2:2

Q8. Is it possible have child with blue eyes if both parents are having brown eyes show with necessary chart.

It is possible only when both parents have hybrid brown(Bb) eyes.

Monohybrid cross: When crossing is carried by taking only one pair of contrasting characters under observation, it is called monohybrid cross. For eg, cross between tall pea plant and dwarf pea plant.

Dihybrid cross: When crossing is carried by taking two pairs of contrasting characters under observation, it is called dihybrid cross.

2) Law of segregation or law of purity gamete: It states that “In hybrid of first generation genes for both dominant and recessive characters remains together but they don’t intermix and separates at time out forming gametes.” Since gamete formed are always pure for that particular character. It is called law of purity of gametes.

3) Law of independent assortment: It states that “When crossing is carried between parents having two pairs of contrasting characters, inheritance of one character is independent to another character.”

Some dominant and recessive characters in human beings.

Variation: The physiological differences among the individuals of same species which gives them personal identity is variation. They are of 2 types:

a. Hereditary variation:  Variation seen in an organism do to change in structure and function of genes present in chromosomes is called  hereditary variation. Crossing over that takes place at the time of forming gametes during sexual reproduction is responsible for this type of variation.

b. Environmental variation: Varieties seen in an organism due to environmental factors like temperature, light, food etc is called environmental variation.

On the basis of degree of differences there are 2 types of variety variations:

1. Continuous variation: Slow and gradual change seen in organism is called continuous variation. Oregon. change in height, skin .color etc
2. Discontinuous variation: Sudden and sharpe changes seen in an organism is called discontinuous variation. It’s also called mutation.

Mutation: Sudden and sharp change in genetic characters of an organism is called mutation. For eg, A boy with 6 fingers in one hand, sheep without horn, cow with 3 legs etc. Radiations likes x-rays, UV rays. B-rays, use of chemical like drugs etc are responsible for mutation

Answer the following questions

a. Two black parents have given birth of white child. The father result to accept the baby and case is filed in court. The decision from court was in favour of mother. Explain the cause with suitable illustration.

This is possible when both the parents are hybrid black.

b. Mendel selected a pea plant but he didn’t select a frog.

Due to following reasons:

1. Pea plant produces bisexual flower where self-pollination is possible but frogs are unisexual.
2. Life cycle of pea plant completed in short time period than that of frog so, result obtained in short time.

c. Average height of pea isn’t seen on crossing tall and dwarf peas.

According to law of segregation, genes for dominant and recessive character don’t intermix and separate at the time of forming gamete due to which average height of pea isn’t seen on crossing tall and dwarf peas.

d. Some people have deformity in organs.

It is due to the mutation which brings sharp change in genetic character of an organism.

e. Two tall pea plants were crossed Result is given.

i. Fill up the table?

ii. What is the percentage of pure tall pea plant?

Percentage of pure tall pea plant is 25%.

iii. What is the ratio of tall pea plant to dwarf one?

Ratio of tall pea plant dwarf pea plant is 3:1.

iv. Of which generation result does it belong to?

It belongs to second filial generation.

v. Which Mendel’s law does it explain? State the law.

It explains Mendel’s law of segregation which states that, “In hybrid of first filial generation genes for both dominant and recessive characters remain together but they don’t intermix and separate at time at forming gametes.”

f. Write difference between variation and mutation.

g. What is monohybrid cross? When peas with pure round seeds are crossed with pure wrinkled seeds and the resulting progeny were self fertilized, what types of progeny will be produced ? Show it in a filial chart.

When crossing is carried between pair of contrasting character under observation, it is called monohybrid cross.

Suppose round is dominant (RR)

Genotype = Pure round : Hybrid round : Pure wrinkled = 1:2:1

Phenotype = Round : Wrinkled = 3:1

h. When the mating between black and brown guinea pig occurs, there appears only black guinea pig in first filial generation, but not the brown one. Explain with the chart why brown guinea pigs were not produced

Let the dominant character be black (BB).

Brown guinea pigs weren’t produced as it was a recessive character. According to law of segregation.