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Class 12 Anthropology Chapter 2 Genetics
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Genetics
Chapter – 2
| QUESTIONS |
1. Who is the father of modern genetics?
Ans: The father of modern genetics is Gregor Johann Mendel.
2. What is heredity?
Ans: Heredity is the process by which traits and characteristics are passed from parents to offspring through genes.
3. For how many years Mendel carried out his experiment?
Ans: For 8 years Mendel carried out his experiment.
4. Where Mendel published his result?
Ans: Mendel published his research in the journal of the Natural History Society of Brunn.
5. Who rediscovered Mendel laws of inheritance?
Ans: Three European scientists Hugo de Vries, Carl Correns and Erich Von Tschermak rediscovered Mendel laws of inheritance.
6. What is Mendel’s monohybrid ratio?
Ans: Mendel’s monohybrid ratio is the result of a cross where only one trait is studied. He experimented with pea plants and crossed a pure tall (TT) plant with a pure dwarf (tt) plant. In the first generation (F₁), all plants turned out tall (Tt) because the tall trait was dominant. When these F₁ plants were crossed among themselves, the second generation (F₂) showed a pattern: 3 tall plants for every 1 dwarf plant. This 3:1 ratio is known as Mendel’s monohybrid ratio.
7. What is gene?
Ans: A gene is a small unit of DNA that carries instructions for a specific trait, like eye color or height. It acts like a blueprint for making proteins that control how our body works. Genes are passed from parents to offspring, which is why children inherit traits from their parents.
8. What is Mendel’s dihybrid ratio?
Ans: Mendel’s dihybrid ratio is the result of a cross where two traits are studied at the same time. He crossed pea plants with yellow round seeds (YYRR) and green wrinkled seeds (yyrr). In the first generation (F₁), all plants had yellow round seeds (YyRr) because these traits were dominant. When these F₁ plants were crossed, the second generation (F₂) showed a ratio of 9 yellow round : 3 yellow wrinkled : 3 green round : 1 green wrinkled. This 9:3:3:1 dihybrid ratio proved Mendel’s Law of Independent Assortment, which states that different traits are inherited independently of each other.
9. What is eugenics?
Ans: The eugenics is the science of bringing into the world only the good germplasm or improving the genic qualities of individuals yet to be born by exercising selective mating. Eugenics involves the improvement of human genetic traits through the promotion of higher reproduction of people with desired traits or reduced reproduction and or sterilization of people with less-desired or undesired traits or both.
10. Who is the father of eugenics?
Ans: Charles Daewin is the father of Eugenics.
11. What are the two types of eugenics?
Ans: The two types of eugenics are Positive eugenics and negative eugenics.
12. What is another name for down syndrome?
Ans: Another name for down syndrome is Mongoloid Idiocy.
13. What is the number of chromosomes in a female having Turner syndrome?
Ans: When one of the X chromosomes is missing, partially or completely. Such individuals possess only 45 chromosomes instead of the normal 46 chromosomes.
14. Who discovered Klinefelter syndrome?
Ans: Dr. Henry Klinefelter discovered Klinefelter syndrome.
15. Write a short note on down syndrome.
Ans: Down syndrome was first detected by Longdon Down in 1866 and is accordingly named after him. This syndrome is characterised by such clinical symptoms as short stature, stubby hands and feet, peculiarity of the palm prints, fissured tongue, Mongoloid eye fold and mental retardness. The abnormality is often referred to as “Mongolism” due to the presence of a peculiar eye fold similar to that of Mongoloids, although it has no relation with the population. The Mongoloid idiots are cheerful and friendly to autosomal abnormality in man, its Karyotype showing 47 chromosomes instead of the normal number of 46 chromosomes.
16. Write short note on:
(a) Turner syndrome.
Ans: Turner syndrome, also referred to as congenital ovarian hypoplasia syndrome, was first described by Henri Turner, an Oklahoma physician in 1938. It is the most common sex chromosomal abnormality found in females. It results when one of the X chromosomes is missing, partially or completely. Such individuals possess only 45 chromosomes instead of the normal 46. This condition occurs due to numerical aberration in of sex chromosomes and hence their chromosomal constitution is XO. In spite of the presence of half the normal component of sex chromosomes (a single x), the individual cannot be treated as male. Such an individual is treated as female with an abnormal genotype and more properly speaking an incomplete female due to the fact that she should have been the normal female and she has been endowed with another X chromosome.
(b) Klinefelter syndrome.
Ans: Klinefelter syndrome was discovered in 1950. Dr. Henry Klinefelter identified this syndrome and in 1959, it was first demonstrated than men with Klinefelter syndrome have an additional X chromosome resulting in a 47 chromosome (44+xxy).The Klinefelter syndrome or the testicular dysgenesis as it is called due to the under development of testes is a condition in which the so-called males develop small breasts as in the adolescent female (gynaecomastia). The testicles of such persons remain small and produce no spermatozoa. Thus, they remain sterile throughout their lives. The patients of this syndrome are characterized by the external male genitalia with small testes incapable of spermatozoa production, sparse body hair, female like breast development and unusually long-legged.
(c) Eugenics.
Ans: The eugenics is the science of bringing into the world only the good germplasm or improving the genic qualities of individuals yet to be born by exercising selective mating. Eugenics involves the improvement of human genetic traits through the promotion of higher reproduction of people with desired traits or reduced reproduction and or sterilization of people with less-desired or undesired traits or both.Genetics are greatly concerned with the science of being “Well born” the word derived from Greek word Eu means well and genes or born. This separate discipline, Eugenics, was established in 1883 by Sir Francis Galton, an English statistician, demographer and ethnologist and he was a cousin of Charles Darwin. He was the father of Eugenics.
Galton has defined eugenics as “The study of eugenics under social control which may improve the racial qualities of future generations, both physically and mentally with the application of principles of genetics”. Galton believed that eugenics could control human evolution and development.
(d) Gene and allele.
Ans: A gene is a segment of DNA that carries instructions for a specific trait, such as eye color or blood type. Genes are found on chromosomes and are passed from parents to offspring, determining inherited characteristics. An allele is a different form of the same gene. For example, the gene for eye color may have alleles for brown, blue, or green eyes. Each person inherits two alleles for a gene, one from each parent. Some alleles are dominant, meaning they express their trait even if only one copy is present, while others are recessive and show their effect only when both copies are the same.
(e) Genotype and phenotype.
Ans: The above 1:2:1 ratio is based on the genotypes of the plants. By the term genotype the total gene component in an organism is meant, while phenotype is the external appearance of an organism resulting from the interaction of its genotype and its environment. Thus the ratio 3:1 is based on the phenotype of the plants.
A T(D) plant is said to be in heterozygous condition Because it possesses two different alleles – D for dwarfners and T for tallness: while D and T plants are homozygous plants as in both the cases two alleles are alike. A D plants have two genes, both being responsible for dwarfners. Similarly a T plan has two genes of tallness. In man wooly hair is dominant over straight hair. Each of the A and B blood group genes is dominant over 0 genes. But neither A is dominant over B nor B is over A. This condition is called co-dominant. In the MN blood group system M & N are co-dominant.
(f) Homozygous and heterogeneous.
Ans: Homozygous and heterozygous are terms used to describe the genetic makeup of an organism for a specific trait. An individual is homozygous when they have two identical alleles for a gene, either dominant (AA) or recessive (aa). For example, a plant with TT (tall) or tt (dwarf) genes is homozygous for height. On the other hand, an individual is heterozygous when they have two different alleles for a gene, such as Tt, where one allele is dominant and the other is recessive. In this case, the dominant trait (tall) is expressed, but the organism still carries the recessive allele. Homozygous individuals always pass down the same allele to their offspring, while heterozygous individuals can pass either of the two alleles. These concepts play a crucial role in understanding how traits are inherited in genetics.
17. Describe Mendel’s monohybrid ratio with a neat diagram.
Ans: Mendal carried his experiment by crossing varieties of garden peas and recording his results. In pea he found a number of contrasting characters e.g. tall or dwarf plants, purple or white flowers and yellow or green, wrinkled or smooth seeds. In one series of experiments he selected dwarfness and tallness of plans. Pure breed of tall plants were found out by breeding tall plants with tall for several generations which had produced tall plants only. Similarly, dwarf plants were also collected. The experiment was started by breeding tall plants with dwarf plants. This generation is known as the parental generation. When tall plants of pure strains were crossed with dwarf plants of pure straints it was found that all the plants were tall. This generation is called the first filial of F₁ generation or hybrid generation. Thus all the plants of the F₁ generation resembled only one part, the tall one. Next, the numbers of F₁ generation were crossed with each other and different results were obtained. The second or the F₂ generation gave rise to a mixed generation of tall and dwarf (but no intermediate) in the ratio 3 : 1. When the dwarf plants were crossed with one another, it was found that all the plants were dwarf and this was true for every drawf tested. But with the tall it was not so. Though the tall plants were indistinguishable in appearance, some of them bred true to type, that is, they gave rise to tall plants only, while others behaved like the original tall/hybrid, splitting up into tall and dwarf in the ration of 3:1.
18. Describe Mendel’s dihybrid ratio.
Ans: Mendel considered the pair tall dwarf (of which tall is dominant) and the pair round-wrinkled (of which round is dominant) at a time. He selected one pure tall pea plant with pure round seed and a pure dwarf plant with pure wrinkled seed. The four unit characters were involved in the dihybrid ratio.
By artificial method the two plants were crossed. In F, generation all plants were crossed. In F₁ generation all plants were tall with round seeds. But when the plants of the F, generation were allowed to cross, the resulting generation of F, generation exhibited segregation of character showing all possible combinations in the following proportion 9 round tall : 3 wrinkled tall: 3 round dwarf: 1 wrinkled dwarf. Thus the dihybrid ratio is 9:3:3:1. Here dominant gene for round is represented as R and the recessive gene for wrinkled as r, the dominant for tall T and the recessive for dwarf at t. This the formula for hybrid peas Rs Tt and that for pure recessive is rrtt and that for the pure dominant is RRTT. The pure recessive type can produce only one kind of gamete, rt and the pure, dominant type only RT. But the hybrid plants equal number -RT, Rt, rT, rt.
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