Science 9 Q1 Heredity Inheritance and Variation PDF

Department of Education Region III DIVISON OF MABALACAT CITY Name: __________________________________ Grade & Section: ________________ School: ____________________________________________ Date: ________________...

Department of Education Region III DIVISON OF MABALACAT CITY Name: __________________________________ Grade & Section: ________________ School: ____________________________________________ Date: ________________ LEARNING ACTIVITY SHEET Science 9 (Q1 –Lesson 3) Heredity: Inheritance and Variation I. Introduction Genetics is the study of inheritance in which the traits from the parents are transferred to their offspring. In Grade 8, you have learned that one of the processes of cell division called Meiosis produces genetic variations in Mendelian patterns of heredity. You have learned how Gregor Mendel described the passing of traits from one generation to the next. His principles laid the foundation for the study of inheritance. The potential combinations of offspring from two parents of known genotype can now be determined. Traits can more easily be predicted. In Grade 9, we will focus on non-Mendelian patterns of heredity and describe the molecular structure of the DNA. The location and role of DNA in the transmission of traits from the parents to the offspring. This Learning Activity Sheets will help you discover more about inheritance and variations. Enjoy learning! II. Learning Competency This Learning Activity Sheets was designed and written with you in mind. It is here to help you explain the different patterns of non-Mendelian inheritance. (S9LT-Id-29). III. Objectives After going through this Learning Activity Sheets, you are expected to: 1. Explain the different patterns of Non-Mendelian genetics; 1  2. Describe the genotype and phenotype in incomplete dominance, codominance and multiple alleles; 3. Solve genetic problems involving non-Mendelian genetics; 4. Describe the location of genes in chromosome; and 5. Identify the components of DNA molecule. IV.Discussion Non-Mendelian Pattern of Inheritance Gregor Mendel was able to lay the foundation of genetics even before the discovery of genes. His principles form the bases for understanding heredity (similarities) and variation (differences). It follows the principle that a dominant trait will always be the one that is observable in the phenotype of the offspring when combined with a recessive trait. However, he was not able to discuss the factors in his laws of inheritance which lead other scientists to further investigate the science of heredity. As a result, a new pattern called non-Mendelian genetics was born which include incomplete dominance, codominance and multiple alleles. Incomplete Dominance In this pattern of inheritance, the resulting phenotype of the heterozygous offspring is in between the phenotypes of the parents. In other words, although both alleles are dominant, neither of the alleles of the parents will be dominant over the other. Hence, the traits of both parents will not be visible, instead a third phenotype will be observed on the offspring. For example a homozygous red (RR) flower plant is crossed with a homozygous white (WW) flower plant, following the principle of incomplete dominance, the resulting color of the heterozygous offspring will not be red or white but a third phenotype which is pink. This is because no allele from the parents is dominant over the other. Figure 1: A Punnett Square showing the possible genotypes and phenotypes in incomplete dominance. (Photo from www.pinterest.com) 2  Codominance In this pattern of inheritance, the contrasting alleles are equally expressed in the heterozygous offspring. It means that the characteristics of both of the father and mother will be visible on their offspring. For instance, a homozygous red (RR) flower plant is crossed with a homozygous white (WW) flower plant, following the principle of codominance, the resulting phenotype (color) of the heterozygous offspring will be red and white. Again both traits of the parents will be expressed equally since neither of them are dominant over the other. Figure 2: A Punnett Square showing the possible genotypes and phenotypes in codominance. Multiple Alleles In certain human traits, inheritance is controlled by a single gene but sometimes several or multiple alleles may exist. A typical example of this pattern of inheritance called multiple alleles is the human blood type. The blood type is determined by the presence of antigen on the surface of the red blood cells (RBCs). As previously discussed, persons with type A blood have an antigen A on the surface of their RBCs. Those with blood type B possess antigen B on the surface of their RBC’s. People with type AB blood have both antigens A and B on the surface of their RBC’s. When there is NO antigen A or B, then the person has a type O blood Figure 3: Some antigens found in the human blood which controls the blood type. 3  Figure 4: The possible genotypes and phenotypes of human blood. Type A blood contains Antigen A. Type B blood contains Antigen B. Type AB blood contains both Antigen A and B while Type O blood does NOT contain any antigen. Sex Determination In humans, there are a total of 23 pairs of chromosomes. One pair of these chromosome is called sex chromosomes which determines the gender of an individual. One of these chromosomes comes from the father and one from the mother. Females have a pair of XX chromosomes while males have a pair of XY chromosomes. An egg cell will always have an X-bearing cell while a sperm cell may be an X-bearing cell or Y-bearing cell. Limited, Sex Linked, and Sex-Influenced Figure 9: A pair of XY chromosomes results to a male offspring while a pair of XX sex chromosomes produces a female child. (Photo from www.funscience.in) Some traits are carried on the sex chromosomes, X and Y. Most traits carried are present on only the X-chromosome. The Y-chromosome is smaller, and so, very few genes are located on this chromosome. Sex traits can be categorized into three types of inheritance: sex- limited, sex-linked, and sex-influenced. 4  Figure 5: X chromosome is bigger than the Y chromosome. (Photo from www.flicker.com) Sex-limited traits are traits that are visible only within one sex. For instance, lactation or production of milk is only Figure 6: Baldness can affect both limited to female cows. Beard growth is sexes but more frequent in men. only limited to men, women does not grow (Photo from www.quora.com) a beard but may pass the genes of heavy beard growth to her sons. Sex-linked traits are traits that are controlled by a gene or an allele located on the sex chromosome. They are said tobe linked because more males (XY) develop these traits than females (XX). This is because the females have a second X gene to counteract the recessive trait. Thus, the trait is more likely to be visible in the male. Examples are sickle cell anemia, color blindness and hemophilia. These traits do not affect female; however, they may be carrier or may pass the genes to their offspring. If the mother is a carrier and she has a son, then her son would manifest the trait of colorblindness, sickle- cell anemia or hemophilia. Sex-influenced traits are autosomal traits that are influenced by sex. These traits are expressed in both sexes but more frequently in one sex than the other. If a male has one recessive allele, he will show that trait, but it will take two recessives for Figure 7: An example of sex-limited trait. the female to show that same trait. One Beard only appears on men. such gene is baldness which is more (Photo from www.reddit.com) common to men than women. Deoxyribonucleic Acid (DNA) Deoxyribonucleic acid (DNA) is a biomolecule that contains the genetic information of an individual. It also holds the instruction an organism 5 needs to develop, live and reproduce. The physical appearance, the kind of organism, the behavior will all depend on the DNA of that species. We share 99% percent of our DNA with other humans, the 1% percent remaining makes us unique from other people because no two persons can have 100% exact DNA. Figure 8: A model of a DNA molecule. DNA Structure 1. DNA has double helix structure. 2. A molecule of a DNA is composed of chains of nucleotides. 3. Each nucleotide is made of a deoxyribose (sugar), phosphate group and a nitrogenous base. 4. There are four types of nitrogenous bases, namely: cytosine, guanine, adenine and thymine. 5. Cytosine pairs only with guanine while adenine pairs only with thymine. Parts of a Nucleotide Figure 9: Twisted and Step-ladder Figure 10: A nucleotide is made up of model of DNA. phosphate group, deoxyribose (sugar) and nitrogenous base. Figure 11: The four nitrogenous bases in DNA. Adenine only pairs with Thymine; Cytosine only pairs with Guanine 6  DNA is composed of chain of nucleotides built on sugar and phosphate backbone and wrapped around each other in the form of a double helix. The backbone supports four bases: Guanine and Cytosine are complementary, always appearing opposite each other on the helix, as are Adenine and Thymine. This is critical in the reproduction of the genetic material, as it allows a strand to Figure 12: A DNA molecule composed of divide and copy itself, since it only needs eight nucleotides, four on the left and four on the right. The sides are made up of half of the material in the helix to alternating phosphate group and sugar duplicate successfully. which support the nitrogenous bases. The difference in the base arrangement of the nucleotides results to a difference in DNA code. Figure 13: Two different DNA samples. The first DNA has a sequence of ACGT on the left and TGCA on the right. The second DNA has a sequence of TCGT on the left and AGCA on the right side. V. Activities Activity # 1: Phenotypes and Genotypes in Incomplete Dominance Read the given problem and using a Punnett Square, answer the questions. Problem 1. In a pink snapdragon flowering plant, R is the allele for red color and W is the allele for white color. Two heterozygous pink (RW) flower plants are crossed. Questions 1. What are the possible genotypes of the offspring? 2. What are the possible phenotypes of the offspring? 3. What is the genotype of the heterozygous offspring? 4. What is the phenotype of the heterozygous offspring? 7 Problem 2. In a pink snapdragon flowering plant, R is the allele for red color and W is the allele for white color. If a homozygous red (RR) snapdragon flower plant is crossed with a homozygous white (WW) snapdragon flower plant, here are the questions: Questions 1. What is the genotype of the a. male flower plant? b. female flower plant? 2. What is the phenotype? of the a. male flower plant? b. female flower plant? 3.What are the possible genotypes of the offspring? 4.What are the possible phenotypes of the offspring? 5. What is the genotype of the heterozygous offspring? 6. What is the phenotype of the heterozygous offspring? Activity # 2: Phenotypes and Genotypes in Codominance Read the given problem and using a Punnett Square, answer the questions. Problem 1. In a roan cow, R is the allele for red color and W is the allele for white color. Two heterozygous roan (RW) cows are crossed. Questions 1. What are the possible genotypes of the offspring? 2. What are the possible phenotypes of the offspring? 3. What is the genotype of the heterozygous offspring? 4. What is the phenotype of the heterozygous offspring? Problem 2. In a cow, R is the allele for red color and W is the allele for white color. If a pure breed red cow (RR) is crossed with a pure breed white (WW) cow, here are the questions: Questions 1. What is the genotype of the a. father cow? b. mother cow? 2. What is the phenotype? of the a. father cow? b. mother cow? 3. What are the possible genotypes of the offspring? 4.What are the possible phenotypes of the offspring? 5. What is the genotype of the heterozygous offspring? 6. What is the phenotype of the heterozygous offspring? 8 Activity # 3: Part A: Sex Determination in Humans (Adapted from Science 9 Learner’s Module) Read the given problem and using a Punnett Square, answer the questions. Problem 1. Males have XY sex chromosomes why females have XX sex chromosomes. Questions 1. What will be the sex produced in a child when an egg cell is fertilized by a sperm that has Y chromosome? 2. What type of sperm must fertilize an egg to result in a female child? 3. Based on the Punnett Square, what is the percentage for a child to have the male sex? 4. Which sex chromosomes is present in both male and female? 5. Infer which sex chromosome determines a person’s sex. Activity # 4: DNA: The Genetic Material Part A: Name the parts of a nucleotide. 1. P _ _ _ P H _ _ _ 2. D_ O _ _ _ _ _ _ S _ 3. B_ _ _ Part B: Complete the DNA molecule. Use the following Letters. A=Adenine C=Cytosine P=Phosphate Group T=Thymine G=Guanine S=Deoxyribose (sugar) 9 What is: 4.___________ 12.________19. Thymine pairs with _________________ 5.___________ 13._______ 20. Guanine pairs with _________________ 6.___________ 14._______ 21. Adenine pairs with _________________ 7.___________ 15.________22. Cytosine pairs with _________________ 8.___________ 16.________23. Will there always be equal number of guanine and cytosine? 9.___________ 17.________24. Will there always be equal number of adenine and thymine? 10.__________ 18.________25. Which part of the nucleotide always differs? 11.__________ VI. Assessment Direction: Choose the letter of the best answer. Write your answer on a separate sheet of paper. 1. A pattern of inheritance wherein the resulting phenotype of the offspring is somewhat between the phenotypes of the parents. A. Codominance C. Multiple alleles B. Incomplete dominance D. Mendelian genetics 2. Which part of the nucleotide always differs? A. base B. phosphate group C. sugar D. none of the above 3. How many strands does DNA have? A. one B. two C. three D. four 4. The chromosomes are found inside the ______ of the cell. A. cytoplasm B. mitochondrion C. Membrane D. nucleus 5. What do you call the biomolecule that contains the genetic information of an individual? A. carbohydrates C. ribonucleic acid B. deoxyribonucleic acid D. none of the above 6. What do you call a pattern of inheritance where the phenotypes of the parents are equally expressed in the resulting phenotypes of the offspring? A. Codominance C. Multiple alleles B. Incomplete dominance D. Mendelian genetics 10 7. A type of trait that is exclusive only in one sex is called ________ A. Sex-influenced traits C. Sex-limited traits B. Sex-linked traits D. None of the above 8. ABO blood type in humans is an example of which pattern of inheritance? A. Codominance C. Multiple alleles B. Incomplete dominance D. Mendelian genetics 9. A normal human will have how many sex chromosomes? A. 1 B. 2 C. 3 D. 4 10. Which sex chromosome determines the sex of a person? A. X B. Y C. Both X & Y D. None of the above 11-15. Is there a possibility for a blond-haired couple to produce offspring/s that is/are black-haired? Show your complete solution. VII. Reflection Many times, you may have heard other people tell you that you have your mother’s eyes or your father’s height. While you know that these are characteristics you inherited from your parents, you also know that they did not literally give you their eyes, height, skin, hair, or any other traits. What then, is actually inherited? How are these traits inherited? Based from the knowledge you gained from this lesson, what is the most significant characteristics or traits you inherited from your parents that you are so grateful or proud of? Make a short poem about how thankful you are from your inheritance. (at least 2-3 stanza only) in your activity sheet. 11 VIII. Reference Grade 9 Science Learners’ Module. Department of Education. Exploring Life through Science SERIES. Phoenix Publishing House Inc. 2014. Josefina Ma. Ferriols-Favico, John Doonie A. Ramos, Anna Cherylle Morales- Ramos, Airste V. Bayquen, and Angeline A. Silverio Images http://clipart-library.com www.flickr.com www.genetics.thetech.org www.myoclinic.org www.pinterest.com www.funscience.in www.reddit.com www.quora.com 12