GENETICS AND INHERITANCE By Mrs. Ayesha Fareed ( Biology Teacher) DAMHS Ph-VII

1. GENETICS AND INHERITANCE By Mrs. Ayesha Fareed ( Biology Teacher) DAMHS Ph-VII

2. GENETICS: The branch of biology, that deals with the study of heredity and variations INHERITANCE: The process by which characters are transmitted from parents to their offspring

3. CHROMOSOME: Most cells in the human body have a nucleus containing 23 pairs of chromosomes. each chromosome carries hundreds of genes. Scientists have identified all the human genes and the complete set, of 20,000-25,000, is known as the human genome. Only some of the full set of genes is used in any one cell - some genes are "switched off".

4. Law of Segregation (The "First Law") “When any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy. A gamete will receive one allele or the other”. In meiosis the paternal and maternal chromosomes get separated and the alleles with the traits of a character are segregated into two different gametes.

5. DNA: Chromosomes are made from very long molecules of DNA. Each molecule is in a ladder-like shape, with the "rungs" being made from a pair of nitrogenous bases, known as Adenine, Thymine, Guanine and Cytosine, and the sides made from repeated pentose sugars and phosphate groups A group of one base, one pentose molecule and one phosphate together is known as a nucleotide and DNA can be regarded as a polymer of these nucleotides.

6. The bases are always paired A with T and G with C and it is the exact sequence of these base pairs in the DNA molecule that maps out the genetic code of the individual. The DNA molecule is twisted into a double helix and coiled so tightly, that the total length of the human genome, about 1.8m, fits inside a nucleus of diameter about 6 micrometres.

7. What are genes, and where are they found? There are genes in everything that lives, or has lived. There are genes in people, flies, ham, tomatoes, bacteria etc. A 200g steak contains 750,000,000,000,000 genes. A gene is a code that governs how we appear and what characteristics we have. There are, for example, genes which decide whether we have blue or brown eyes. We receive half of our genes from our mother, the other half from our father. Plants have genes too. Genes decide the colour of flowers, and how tall a plant can grow. Like people, the characteristics of a plant will be transferred to its children- the plant seeds, which grow into new plants.

10. IMPORTANT TERMS USED IN GENETICS

11. ALLELES The chromosomes in a pair carry the same genes at the same positions. One of each pair has come from the mother and the other from the father, so the genes are also in pairs and both code for the same characteristic. These alternative forms of one gene are called alleles Chromosomes showing matching genes with alleles shown in different colours An individual may have two alleles the same or two different alleles for any one gene. For example, there are two alleles of one of the genes controlling eye colour. They may both code for blue eyes or one may code for blue eyes and the other for brown eyes. If both alleles are the same (e.g. both for brown eyes) they are known as homozygousalleles and if they are different they are known as heterozygous When alleles are heterozygous it may be that one of the alleles is dominant and the other recessive. A dominant allele always shows its related characteristic in the individual.

12. Gregor Johann Mendel (July 20, 1822 – January 6, 1884) was an Augustinianpriest and scientist, who gained posthumous fame as the figurehead of the new science of genetics for his study of the inheritance of certain traits in pea plant Mendel showed that the inheritance of thesetraits follows particular laws, which were later named after him. The significance of Mendel's work was not recognized until the turn of the 20th century. The independent rediscovery of these laws formed the foundation of the modern science of genetics.

13. Gregor Mendel is considered to be the father of genetics, though his work was relatively unappreciated until the early 1900's He studied heredity and traits using simple pea plants. By tracing specific traits of a plant, such as pod shape and color, Mendel was able to devise several laws of heredity which applied to the passage of traits from one member of a species to another member of the same species. Between 1856 and 1863, he cultivated and tested some 29,000 pea plants. From these experiments he deduced two generalizations which later became known as Mendel's Principles of Heredity or Mendelian inheritance. He described these principles in a two part paper, Experiments on Plant Hybridization that he read to the Natural History Society of Brno on February 8 and March 8, 1865, and which was published in 1866. MENDELIAN INHERITANCE

14. EXAMPLE OF “LAW OF SEGREGATION” TONGUE ROLLING TRAIT IN HUMANS The above illustrations display each possible trait for tongue rolling a parent may have. The phenotypic expression of a gene is determined by dominance. For example, with tongue rolling if a parent had even one T in the pair, the T trait will be expressed- the parent can roll their tongue. Only in the case of entirely recessive inheritance, where both parents give their offspring the tt gene combination, will the tongue rolling trait not be expressed. The above illustration has a ratio of 3:1, meaning that there is a three in four chance that the dominant T gene will be expressed in the offspring, leaving a one in four chance that the offspring will not be able to roll their tongue.

15. “LAW OF INDEPENDENT ASSORTMENT” “Members of one pair of genes separate from each other during gamete formation independent of the members of the other pair of genes and are assorted at random in the resulting gametes.” While Mendel's experiments with mixing one trait always resulted in a 3:1 ratio between dominant and recessive phenotypes, his experiments with mixing two traits (dihybrid cross) showed 9:3:3:1 ratios. But the 9:3:3:1 table shows that each of the two genes are independently inherited with a 3:1 ratio. Mendel concluded that different traits are inherited independently of each other, so that there is no relation, for example, between a cat's color and tail length. This is actually only true for genes that are not linked to each other.

16. EXAMPLE OF “LAW OF INDEPENDENT ASSORTMENT”

17. EXAMPLE OF “LAW OF INDEPENDENT ASSORTMENT “

18. Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck (1 August 1744,Bazentin, Somme – 18 December 1829), often just known as "Lamarck", was a Frenchsoldier, naturalist, academic and an early proponent of the idea that evolution occurred and proceeded in accordance with natural laws. Lamarck fought in the Pomeranian War with Prussia, and was awarded a commission for bravery on the battlefield. At his post in Monaco, Lamarck became interested in natural history and resolved to study medicine. He retired from the army after being injured in 1766, and he returned to his medical studies. Lamarck developed a particular interest in botany, and later, after he published a three-volume work Flora française, he gained membership of the French Academy of Sciences in 1779. In the modern era, Lamarck is remembered primarily for a theory of inheritance of acquired characters, called soft inheritance or Lamarckism. However, his idea of soft inheritance was, perhaps, a reflection of the folk wisdom of the time, accepted by many natural historians. Lamarck's contribution to evolutionary theory consisted of the first truly cohesive theory of evolution, in which an alchemical complexifying force drove organisms up a ladder of complexity, and a second environmental force adapted them to local environments through use and disuse of characteristics, differentiating them from other organisms.

19. LAMARCK’S THEORY OF EVOLUTION ( LAMARCKISM ) • This theory explains Lamarck assumptions for evolution based on the following two natural biological principles by whch the organ evolves or degenerates altogether called organic evolution. • Environmental factors and development of organs • Inheritance of acquired characteristics • Environmental factors and development of organs: Use and disuse – Individuals lose characteristics they do not require (or use) and develop characteristics that are useful. According to Lamarck, the organs that brought into greater use become more effiecient and enlarged while disused organs progressively degenerate; result of which some modifications appear in body structure. In this way the changed climate and overall environment of the new habitat influences on the development of body structure of animals called acquired characters. II. Inheritance of acquired characteristics: Individuals inherit the traits of their ancestors. According to Lamarckism the acquired characters are transmitted to some extend in the next generation. By repeating the inheritance of similar acquired characters and accumulating such small modifications through a very large number of generations the forth coming population of the same parents is transformed into a new species.

20. EXAMPLES OF LAMARCKISM Giraffes stretching their necks to reach leaves high in trees (especially Acacias), strengthen and gradually lengthen their necks. These giraffes have offspring with slightly longer necks (also known as "soft inheritance"). Example of disuse of organs: KIWI: Like other reptiles, ancestors of snakes had four limbs to move on land but to escape from their enemies they had to use their bellies instead of limbs. As a result of disuse of limbs generation after generation, the snakes lost their limbs Wings of flying birds declined in the future generations

21. OBJECTIONS ON LAMARCK’S THEORY • Acquired characters are not inherited, because • these are changes in somatic cells and not in the germ cells. Numbers of examples are cited to disprove the inheritance of acquired characters, as shown below. i) The boring of ear lobes has been practiced by Indians for several generations but offsprings with bored ear lobes are yet to be born. ii) Artificially maintained small feet in Chinese women are not inherited. iii) August Weismann’s experiment on mice. B) Theory does not explain the evolution of all forms of life. ( flying birds transformed into kiwi but how??????) • Somewhere it only explains forward evolution • (Giraffes) but somewhere it explains backward evolution only (Kiwi). D) The muscles of the shoulder of blacksmith develops much due to its constant use during hammering but it is not inherited in their offsprings.