Class 10 Science Chapter 9 Heredity and Evolution. In this chapter, we are going to learn about the concept of heredity and evolution. As in the previous chapter, we learned about the variations. In this chapter, we are going to learn about how these variations create and transfer to new generations.
All the new generation inherit some common things from their parents such as body design and some variations. Now, 2nd generations can get the variation from 1st generations and also some variations from the parent generation of 1st generation.
Variations: Small differences between individuals due to inheritance.
Class 10 Science Chapter 9 Heredity and Evolution
In this section of Class 10 Science Chapter 9 Heredity and Evolution, we are going to learn about the variations and about heredity.
# Accumulation of variations during reproduction
Q. How did variations created?
It is created due to small inaccuracies in DNA copying.
Different variations in different organisms have different advantages and disadvantages in them. In the whole population if a common feature is found in most of them, then it means that feature comes early in the population’s as compared to the feature which is found in less number in the population.
# Heredity
Transmission of genetically based characteristics from parents to offspring. In other words, the passing down of characters from parents to offspring is termed heredity. It is also controlled by Genes.
Character: Any inheritable feature is called character.
Traits: Alternate forms of character are called traits, like the color of eyes, the shape of the hair, types of eyebrows, etc.
Q. Name some human traits that show variation?
Color of the eye, Shape of external hairs, Blood group, skin color, air lobe, Lips, etc.
# Rules for the inheritance of traits – Mendel’s Contribution
Both parents produce an equal amount of genetic material like 23 chromosomes in sperm and 23 chromosomes in egg cells or ovum which contains DNA. Thus, in each child, there would be 2 versions.
Gene: It is a specific part in the DNA, which carries information.
Class 10 Science Chapter 9 Heredity and Evolution
In this section of Class 10 Science Chapter 9 Heredity and Evolution, we are going to learn about the experiment of Mendel.
Mendel’s Experiment
1st he took pea plants and observe the visible character, such as round wrinkled seeds, tall/short plants, white/violet flowers, etc.
Now, he took 2 pea plants such as short and tall pea plants, and produce progeny (Offspring) using cross-pollination.
In its conclusion, there would be no medium height plants found it means only 1 of the parent trait seen instead of a mixture.
Now, to see if the height of the tall parent plant is the same as the 1st generation tall plant. He uses self-pollination in both of them, so, as a result, the tall parent plant produces all tall plants but the F-1 generation (1st generation) produces both tall and short plants.
So, it means the F-1 generation contains both of its parent plants traits but only expressed 1 of them. So, if both genes are the same in an organism then it is known as homozygous, however, if both the genes are different then it is known as heterozygous.
Conclusion
So, in the experiment, he named the tall plant as “T” and the small plant as “t”. So, TT is tall plants, and Tt is also tall plants. While only tt is a small plant. So, if a plant contains “T” in it, then it may become tall, however, if a plant contains “tt” in it, then it may become small.
Explanation
T → Tall
t → short
Parent Generation: TT (Tall) x tt (Short)
Parent Gamete: T and t
| Parent Gamete (T x t) | t (short) |
|---|---|
| T (Tall) | Tt (Tall) |
F1 Generation: Tt (Tall) x Tt (Tall)
F1 Gamete: T, t, T, and t
| F1 Gamete (T, t x T, t) | T (Tall) | t (short) |
|---|---|---|
| T (Tall) | TT (Tall) | Tt (Tall) |
| t (Short) | Tt (Tall) | tt (Short) |
F2 Generation: TT (Tall), Tt (Tall), Tt (Tall), tt (short)
Genotype: It is a combination of genes in an organism. Its ratio is done on the basis of genes. Like in the F2 generation there is 1 TT, 2 Tt, and 1 tt so, the ratio will be ( 1:2:1).
Phenotype: Observable characteristics which are genetically controlled. Its ratio is done on the basis of visibility. Like in the F2 generation there are 3 tall plants and 1 short plant so, the ratio will be ( 3:1).
Class 10 Science Chapter 9 Heredity and Evolution
In this section of Class 10 Science Chapter 9 Heredity and Evolution, we are going to learn about Mendel’s law and traits expressed.
Before we learn about Mendel’s law let’s learn about the different traits, such as Dominant traits and Recessive traits.
Dominant trait: It occurs more in number in the plants.
Recessive trait: It occurs less in number in the plants.
Example:
- TT → Pure dominant variety
- tt → Pure recessive variety
Monohybrid Cross: When pair between 2 plants and having only 1 pair of feature or contrasting characters in the zygote.
Di-hybrid Cross: When pair between 2 plants and having 2 pairs of feature or contrasting characters in the zygote.
So, according to the experiment, we can have 3 Mendel’s laws. Let’s learn about each of them.
- Law of Dominance: When there are 2 traits for a character and only 1 of them is expressed it is known as the Law of dominance.
- Law of Segregation: During the formation of gamete the factors for a character are separated it is known as Law of segregation.
- Law of Independent Assortment: When we are contrasting 2 characters, then any character can be mixed with any other character it is known as the law of independent assortment.
# How do these traits get expressed?
As we know, DNA contains the information source for a protein and a section of DNA known as a gene. So, the amount of hormone in the plant depends on the efficiency of the process. Thus, genes control the characteristics or traits.
So, it means in the experiment each pea plant has 2 sets of genes in it. Hence, the gene which is present in an organism is in the form of pieces called chromosomes.
As we know human being contains 23 pairs of chromosomes in it. There are 2 types of chromosomes in human beings i.e. Autosomes (1-22) and Sex-chromosome (23).
During sexual reproduction, a female gamete fuses with a male gamete which is a haploid to form a zygote. A zygote is a diploid that contains 23 chromosomes from the mother and 23 from the father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.
Class 10 Science Chapter 9 Heredity and Evolution
In this section of Class 10 Science Chapter 9 Heredity and Evolution, we are going to learn about sex determination.
# Sex Determination
Whether the child becomes a girl or a boy it is decided on the genes of the parents which they inherit. Although, not all chromosomes of humans are paired. This means all the 44 chromosomes contain exact pair of 1 chromosome from mother and 1 from father also known as Autosome.
But the sex-chromosome doesn’t have a perfect pair in it. However, the girl always has a perfect pair of chromosomes i.e. XX but the male doesn’t have a pair in it i.e. XY. In other words, in the girl gamete, it contains X and X but in the male gamete, it contains X and Y in it.
So, if a male produces X and the female produces X, then the zygote becomes XX (Female). If the male produces Y and the female produces X, then the zygote becomes XY (Male). So, the sex of a child only depends on the father.
Let’s understand this concept clearly down in the table.
| Male Gamete | Female Gamete | Result |
|---|---|---|
| X | X | XX (Female) |
| Y | X | XY (Male) |
This is all this chapter is worth in this term. As evolution is reduced from your syllabus for this time. To see Class 10 Science Chapter 9 Heredity and Evolution blueprint down in the table.
| Class 10 Science Chapter 9 Heredity and Evolution | |
|---|---|
| 1 Marker | 1 question |
| 2 Marker | 1 question |
| Total questions | 2 |
| Total marks | 3 |
| Class 10 Science Chapter 9 Heredity and Evolution Blueprint 2021-22 | |
The total worth of Class 10 Science Chapter 9 Heredity and Evolution in terms of the board exam. According to the table, this chapter contains 1 mark for 1 question, 1 mark for 1 question. Please note that this marking scheme may vary in board exams.
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