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Class X    CH – 9   Health and Heredity

Syllabus of Heredity and evolution: Heredity; Mendel's contribution- Laws for inheritance of traits: Sex determination: brief introduction; Basic concepts of evolution.

1. HEREDITY-  It is also known as biological inheritance. It is passed from parent to offspring through the reproductive process and offspring's organism or cells have inherited genetic information from their mother and father. We look like our parents because of heredity.
2. DNA ( Deoxyribose nucleic acid) and RNA (Ribonucleic acid) are genetic materials in all organisms.
3. DNA contains the genetic instructions for the development and function of living things It is the source of making protein in a cell.
4. The rules of heredity determine the process by which traits and characteristics are reliably inherited.
5. Gene - Gene is a part of DNA and controls the expression of a particular trait.
6. Rules for the Inheritance of Traits – Mendel’s Contributions -  The laws of inheritance of such traits in humans are related to the fact that both father and mother make practically equal amounts of the genetic contribution to the child. Each trait can be affected by both paternal and maternal DNA. Thus, for each attribute, each child will have two versions.
7. The first study of inheritance was done by Gregor Mendel on the garden pea.
8. Mendel was educated in a monastery and went to the University of Vienna to study science and mathematics.
9. Mendel's law of inheritance is
   Law of dominance
   Law of segregation
   Law of independent assortment.
10. During monohybrid cross:
    i. When tall pea plants are crossed with short pea plants only tall plants are obtained in the F1 generation and these F1 tall plants reproduce by self-pollination.
    i. Second generation F2, F1 tall plant offspring are not all tall. Instead, one-quarter of them are short. This indicates that both elongation and shortness traits were inherited in F1 plants, but only the elongation characteristic was expressed.
    iii. In a dihybrid cross, two pairs of contrasting characters wear considered. The tall plant crosses with round seeds and the shorter plant with wrinkled seeds. The progeny are all long and have round seeds. The tall and round seeds are thus the dominant features. F1 progeny are tall plants with round seeds, and some were short plants with wrinkled seeds. However, there will also be some F2 progeny who showed new mixtures. Some of them will be tall, but have wrinkled seeds, while others will be short, but round seeds. Thus, long/short traits and round seed / wrinkled seed traits are independently inherited.
11. In sexual reproductive organisms, differentiation occurs due to factors such as a recombination of genes, mutation, and crossing of the environment.
12. The mechanism of heredity- Heredity is a fact of passing traits from parents to their offspring undergoing reproduction and it is the mechanism of heredity. 
13. Proteins control the characteristics  -  Plants have hormones that help in growth and growth depends on the amount of a particular plant hormone. The production of plant hormones depends on an enzyme that is more efficient which is important for the process by which a lot of hormones will be made, and the plant will grow longer. Genes that carry the instructions for making proteins that help metabolism by acting as an enzyme.
14. According to Mendelian experiments- both parents should contribute equally to the offspring's DNA during sexual reproduction.
15. Chromosomes - The chromosomes are present in the nucleus. It is a thread-like structure. It is made up of proteins and consists of a single molecule deoxyribonucleic acid (DNA) that is passed from parents to offspring. In humans, each cell normally has 23 pairs of chromosomes. DNA is tightly packed into chromosomes within the nucleus.
16. Sex Determination - The process of sex determination is different in different species. It depends on environmental signals. In some animals, the temperature at which fertilized eggs are laid determines whether the animals that develop into eggs will be male or female.
17. Snails can individually alter sex and indicate that sex is not genetically determined.
18. The genotype is a composition of genes present in an organism and the phenotype is its characteristics which are visible in an organism.
19. Women have a perfect pair of sex chromosomes XX  and men have a mismatched pair of sex chromosomes in which one is a normal-sized X and the other is a short size Y. Therefore women are XX, while men are XY.
20. The sex of the children will be determined by what they inherit from their father. A child will be a girl if she inherits an X chromosome from her father and a child will be a boy if he inherits a Y chromosome from his father.
21. EVOLUTION - Evolution is the change in the genetic characteristics of biological species from a few generations. These characteristics are passed on through genes from parents to offspring during reproduction.
22. Darwin’s theory of evolution is the first theory of evolution given by Jea Baptiste Lamark.
23. The "origin of species" theory proposed by Darwin is popularly known as Darwinism's theory of natural selection.
24. Changes in DNA during reproduction are the main cause of evolution.
25. There are three types of evolution:
    i. Convergent evolution
    ii. Divergent evaluation and
    iii. Parallel evolution.
26. In populations of living things, natural selection manages evolution. This happens to better fit the environment of the population of living things.
27. We all come from Africa. A few thousand years ago, some of our ancestors left Africa, while others stayed. While the inhabitants spread to Africa, migrants gradually spread throughout the planet - from Africa to West Asia, then to Central Asia, Eurasia, South Asia, East Asia. He traveled the islands of Indonesia and the Philippines to Australia and took the Bering Land Bridge to the US. All other species on the planet, they were exposed to an accident of evolution, and they were trying to live their lives to the best.
28. The process by which new species develop from the existing species is known as speciation.
29. The factors which lead to speciation are: 
    i. Genetic drift.
    ii. Geographical isolation
    iii. Natural selection.Gene flow.
    iv. Reproductive isolation.

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