Biology Heredity Practice Questions PDF

Kuala Lumpur, Malaysia SEMESTER I NAME: _______________________ REF: 2024-25/ SCI /STD 10/ HO 10 CLASS: _______________ SUBJECT: Biology DATE: 4/10/2024...

Kuala Lumpur, Malaysia SEMESTER I NAME: _______________________ REF: 2024-25/ SCI /STD 10/ HO 10 CLASS: _______________ SUBJECT: Biology DATE: 4/10/2024 Topic: Heredity Introduction Reproduction is the process of producing new organisms. Individuals in a species resemble one another and organisms maintain continuity by producing individuals similar to themselves but with slight differences. Similarities between organisms is due to heredity and differences between organisms is due to variations. What is heredity? Heredity is the transmission of genetically based characteristics from parent to offspring. All organisms arise from common ancestors. Heredity ensures that relations continue to exist between successive generations. Traits are carried from generation to generation and continuity of features between generations is ensured by heredity. What is a trait? A trait is any characteristic that is transferred from parent to offspring. It is the continuity of features from the prior generation to the next which is present in the fertilized egg or zygote. That zygote develops into an organism of a particular type. What is Genetics? Genetics is that branch of biology which deals with transmission of body features both similarities and differences from parents to offspring and the laws related to such transmissions. It is the study of heredity and variation. ‘Genetics ‘word was coined by Bateson in 1905. Gregor Johann Mendel is the ‘Father of Genetics’. Variation and its importance The differences in the characters/traits between the parent and offspring is called Variation. No two individuals in a species is exactly identical. Types of Variations Variation are of two types: (i) Somatic Variation (ii) Gametic Variation Page 1 of 10 Copyright © Global Indian International School Somatic Variation/Acquired traits It takes place in the body cell. They are developed /experienced during the lifetime of individuals. It is neither inherited nor transmitted. It cannot undergo direct evolution. It is also known as acquired traits. Examples: cutting tails in dogs, swimming, dancing, etc. Gametic Variation/ Inherited traits Takes place in the gametes/Reproductive cells. Inherited as well as transmitted. Can undergo direct evolution. Also known as inherited traits. Example: human height, skin colour. Accumulation of Variation during Reproduction Variation occurs during reproduction whether organisms multiply sexually or asexually. Variations produced in successive generation gets accumulated in organism. Variations show up only if it continues to be inherited by offspring for several generations. Variations in Asexual Reproduction Variations are fewer. Occurs due to small inaccuracies in DNA copying. Variations in Sexual Reproduction Variations are large. Occurs due to independent assortment and crossing over during meiosis, random union of gametes during fertilization and mutation. Importance of Variation Depending upon the nature of variations, different individuals would have different kinds of advantage. Example, a heat resistant trait that develops in a bacterial colony accumulate in some bacteria. When there is sudden change in temperature the entire bacterial colony will get killed except for those individuals who have developed the new heat resistant trait. When there is genetic variation natural selection acts on it. Main advantage of variation in species is that it increases the chances of its survival in a Page 2 of 10 Copyright © Global Indian International School changing environment. The survival and reproductive success of individuals is related to the way inherited traits function in context to the environment. Survival of individual depends on whether the genes that produce a particular trait are well adapted to the environment. Free ear lobes and attached ear lobes are two variants found in human populations. Variation leads to organic evolution. Evolution is an orderly change of various forms through slow but continuous process. Evolution gives rise to complex body designs even as simpler ones flourish. Carriers of Heredity Gametes are the carriers of heredity that carry traits from parent to offspring. They form the link between one generation and another. Chromosomes present in the nucleus of a cell carry hereditary traits. Chromosomes are rod like structures seen in dividing cells. Chromatin fiber’s are seen as a network in nucleus of undividing cells. Chromosomes contain 40% DNA and 60% histone proteins. Extra Information Chromosomes are made up of DNA (Deoxy ribonucleic acid) and histone proteins. DNA carry genetic code. DNA is a double helix structure formed of 2 strands of polynucleotide chains. James. D. Watson and Francis H.C. Crick discovered the double helix structure of DNA. DNA is made up of nucleotides that contain 3 molecules namely – Nitrogenous bases (Purines- Adenine, Guanine, Pyrimidines- Cytosine and Thymine), a pentose sugar and a phosphate group. The bases complement each other Adenine bonds with Thymine and Cytosine with Guanine. Number of Chromosomes: Number of Chromosomes are constant in the cells of each species. Based on number of chromosomes cells are: 1. Haploid: Cells in which all types of chromosomes are present in a single set. 2. Diploid cells: Cells that contain two sets of all types of chromosomes. Example: Dog and Fowl have 78 chromosomes, Human has 46, Mouse has 40, Gorilla has 48, Cray fish has 200 chromosomes while Ascaris has 2 chromosomes. Page 3 of 10 Copyright © Global Indian International School Characters in an individual and complexity of organisms do not depend on the number of chromosomes. Homologous Chromosomes Two chromosomes of one pair are exactly similar in shape, size and structure and bear genes that control the same characteristics. One out of each homologous chromosome is shared by each parent to the offspring. Genes are specific part of the chromosome composed of DNA; they are the units of heredity and are responsible for inheritance. The expression of characteristics is contained in genes. Different traits are formed by different genes. The gene carries the genetic code for a particular characteristic. Genetic Code: Genes contain Genetic Code for protein synthesis. Proteins control specific traits in organisms. For example, if a plant/animal has inherited the gene for tallness, then the gene will instruct the plant/animal to produce more GH and make the plant grow tall. The complexity and the character of an individual organism depends on the type of gene present in the chromosome. Alleles: A pair of genes code for a particular trait. They are slightly different forms of the same gene. For example: one allele for hair colour produces black colour another allele produces brown colour hair. Alleles are alternate form of the same gene occupying the same position on a homologous chromosome and affecting the same character in two different ways. E.g. there are two alleles for the height gene, one is short, and one is tall. The offspring may inherit the same alleles from both parents or two different alleles from them. Expressing allele of a gene: 1. Homozygous: In a true breeding dwarf or tall variety of pea plant the allele pair for height is identical or homozygous. e.g., tallness(TT) dwarfness (tt) 2. Heterozygous: Hybrid plants contain alleles that express contrasting characters and are called heterozygous (Tt). How are traits transferred from parents to offspring? Genetic information is carried within chromosomes; the chromosomes are found in the nucleus of a cell. Long coiled molecules of DNA make up chromosomes. The genes are contained in the DNA; they are the units of heredity and are responsible for inheritance. The expression of characteristics is contained in genes. Different traits are formed by different genes. The gene carries the genetic code for a particular characteristic. The height of a person, the facial features such as nose or jaw line are all controlled by different genes. The inheritance of characteristics in an organism is contributed equally by the mother and father. The mother and father provide equal amounts of genetic material to their offspring. Therefore, each trait has two factors, one that comes from the mother and the other that comes from the father. DNA have the information source for making proteins in the cell. A section of DNA that provides information for one protein is called the gene for that protein. Page 4 of 10 Copyright © Global Indian International School For example: Plant height depends on the amount of a particular plant hormone that is secreted. The amount of the hormone made will depend on the efficiency of the process for making it. Cellular DNA (Information source) → For synthesis of Proteins (Enzyme) → Works efficiently → More Hormone → produced Tallness of plant. Terminologies Locus: is the position on the chromosome where the allele of a given trait occurs. Dominant Gene: is the gene that expresses itself even if there is a contrasting trait in the pair. Heterozygous (Tt). Dominant gene is the one that expresses itself in F1 generation. The dominant trait is denoted using capital letters. Recessive gene: The gene that is unexpressed and can express itself only if present on both the chromosomes, the alleles are identical, homozygous (tt). Recessive trait is denoted using small letters. Genotype Genotype is the description of the genes present in an organism represented by a pair of letters. Each letter stands for a trait that is inherited from each parent (as a result of sexual reproduction). One code of the trait comes from the father and the other comes from the mother. Dominant gene is represented by capital letter and recessive gene by small letter. Therefore, there are always three possibilities with genotypes. For eg. For the height of an offspring, it can be HH, Hh or hh. Phenotype Phenotype is the visible expression of characteristics of an organism. The characters that one can observe in an organism are known as the phenotype. Colour of the eyes, the hair etc.. First filial Generation: When true breeding plants are crossed a progeny /offspring produced is called first filial generation (F1 generation). Second filial Generation: When the first filial generation is crossed among themselves to produce offspring. The offspring produced is called second filial generation or F2 generation. Punnett Square: A graphical representation to calculate the probability of all possible genotype of offspring in a genetic cross. Possible gametes are written on the two sides, top row and left column. Possible combinations are represented in the boxes in the square. Genome: The complete set of genes or genetic material present in a cell or organism. Page 5 of 10 Copyright © Global Indian International School Mendel and his work on Inheritance Gregor Johann Mendel (1822 & 1884) started his experiments on plant breeding and hybridization. He proposed the laws of inheritance in living organisms. Mendel was known as Father of Genetics Plant selected by Mendel: Pisum sativum (garden pea). He used 14 true breeding pea plants varieties as pairs which were similar except for one character that had a contrasting trait. True breeding plant: Plants that has undergone continuous self-pollination and shows stable traits inheritance and expressions for several generations. Seven pairs of contrasting characters in Garden Pea Why was Garden Pea (Pisum sativum) chosen for his experiment? Availability of many contrasting traits of several characters. True breeding varieties were available. Short reproductive span of the plant. Flowers are bisexual and normally self-pollinate, by removing either the stamen or carpel self-pollination could be prevented. Cross-pollination could also be carried out easily due to the size of the flower. Large no. of seeds produced. Page 6 of 10 Copyright © Global Indian International School Mendel’s Experiments: Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time). Inheritance of one gene In his hybridization experiment one pure breeding tall and one pure breeding dwarf plant was crossed. He grew the first hybrid generation of plants (F1) First filial generation. All plants produced were tall. No dwarf plants were seen. He repeated the experiment with other traits and each time the F1 progeny resembled either one of the parent and the other parent trait was not seen. Law of Dominance The factor/allele that expresses itself phenotypically in the presence of a contrasting allele is called dominant and the other that does not express itself is called recessive. On selfing the F1 generation, the plants produced in the F2 generation were 75% tall and 25% dwarf in the ratio 3:1. The trait that was not seen in F1 generation was expressed in F2 generation. Explanation of Monohybrid cross: 1. When two pure breeding pea plants were crossed. The F1 generation produced identical offspring that only showed the dominant trait (Tall) of either of the parent. The character of only one parent was shown while the character of the other parent was not seen. 2. On selfing (self-fertilization) the F1 plants, the F2 generation showed the parent trait that was not expressed in F1 generation, both tall and dwarf plants were produced in the ratio 3:1. 3. Traits expressed in F2 generation were identical to the parent trait there was no mixing/blending. None of the offspring showed intermediate trait. 4. The dwarf plants were possible from the F1 tall plants only because: a. The gene of dwarfness had segregated or separated from the gene of tallness. b. Gene of tallness did not blend or influence the gene of dwarfness. 5. Phenotypically dominant individuals can be homozygous (TT) or heterozygous (Tt) but recessive plants are always homozygous(tt). Law of Segregation: Mendel postulated this law based on the Monohybrid cross. Two factors or genes controlling one-character separate /segregate without blending or influencing each other during the formation of gametes so that each gamete receives one factor or gene for each character. Gametes are pure. Page 7 of 10 Copyright © Global Indian International School Inheritance of two or more traits Laws of Independent Assortment Factors /genes controlling different characteristics assort independently without influencing each other during the formation of gametes. Dihybrid Cross Mendel explained the Law of independent assortment using the dihybrid cross. He considered inheritance of two different characters simultaneously. For example, Mendel chose colour and shape of the seed, one having Round Yellow seeds and the other Wrinkled Green seeds. In the F1 generation all plants produced were round and Yellow seeds. By selfing the F1 plants, the F2 generation that was raised showed four combinations in the following ratios: (Round Yellow) 9: (Round Green) 3: (Wrinkled Yellow) 3: (Wrinkled green) 1 Page 8 of 10 Copyright © Global Indian International School Note: The above picture is for Illustration only. Follow the steps of doing the Monohybrid and Dihybrid cross as done in school. Human Blood Group Inheritance: ABO blood groups are controlled by a gene which is denoted by symbols IA, IB and IO (sometimes also denoted as i). The genes IA and IB show no dominance over each other (they are codominant, i.e., both expresses themselves independently). Both genes are dominant over the gene IO. Therefore, blood group of a person depends on the type of genes present, e.g. 1. Blood group A has the following gene types: IA IA OR IAIO 2. Blood group B has the following gene types: IB IB OR IBIO 3. Blood group AB has the following gene types: IA IB 4. Blood group O has the following gene types: IO IO Rh Factor The Rhesus monkey factor, or Rh factor, is a certain type of protein found on the outside of blood cells. People are either Rh-positive (they have the protein) or Rh-negative (they do not have the protein). This distinction mostly matters when you are Rh-negative and your child is Rh-positive. Determining sex of a newborn individual genetically: In human beings the sex of the individual is determined genetically. There are 23 pairs of chromosomes of which 22 are similar in male and female and are known as autosomes. The remaining one is sex chromosome which is XY in males and XX in females. Males produce two types of sperms X and Y, while female produces one type of egg X. If X type of sperm fertilizers the egg then the sex of baby will be female (XX). If Y type of sperm fertilizers the egg then the sex of the baby will be male (XY). Ovum has equal chance of being fertilized by a sperm bearing x/y chromosome. Sex is determined at the time of fertilization. Page 9 of 10 Copyright © Global Indian International School In some animals sex is determined by the environment factors: Reptiles: temperature at which fertilized egg is incubated before hatching determines the sex of the offspring. Turtles: High incubation temperature leads to development of female offsprings. Lizard: high incubation temperature leads to male progeny. Snails: Individuals change sex. Answer the following Questions 1. We cannot pass on our experience and educational qualification to our progeny’. Justify this statement. 2. How did Mendel’s experiment show that traits are inherited independently? 3. ‘It is possible that a trait is inherited but may not be expressed’ Give suitable example to explain the statement. 4. Different species use different strategies (Environmental or genetically) to determine the sex of the newborn individual. Explain with examples both the strategies. 5. How did Mendel interpret his results to show that traits may be dominant or recessive? Describe briefly. 6. “Genes control traits”. Explain this statement with example. 7.The genotype of green stemmed tomato plant is denoted by GG and purple stemmed tomato plants as gg. When these two are crossed: [a] What colour stem will be expressed in F1 generation? [b]Give the percentage of purple stemmed plants when F1 generation is self- fertilized. [c] What ratio will the green and purple stemmed plants be in F2 progeny? Page 10 of 10 Copyright © Global Indian International School