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What are chromosomes? 4 of a cell that chromosome [KROH-muh-sohml: threadlike structures in the nucleus control heredity gamete: sex cell gene: part of a chromosome that controls inherited traits genetics Iiuh-NET-iksl: study of heredity 7 I F ( AZ’ H ” How “Mary has her mother’s eyes.” “Torn is built just like his father. often have you heard remarks like these? traits. All people resemble their parents in some ways. They have similar And it is no accident. Many traits are passed on from parents to The anoffspring. We say they are inherited. How are they inherited? swer is found in the cell nucleus. The nucleus has tiny bodies called chromosomes [KROH-muh-sohmsj. pairs. Most are rod-shaped. In body cells, chromosomes are found in Body cells are all the cells except sperm and egg cells. Each kind of organism has a specific number of chromosomes. For a example, every body cell of a fruit fly has S chromosomes (4 pairs); human has 46 (23 pairs); a garden pea has 14 (7 pairs). is a Along each chromosome there are many dark bands. Each band genes, many are many, small part of a chromosome called a gene. There of an at least one million in every nucleus. Genes determine the traits organism. the There are genes for height, genes for nose size and shape, genes for any color of hair, skin, and eyes. In fact, there are genes for most traits individual has. Some genes even affect traits like voice, intelligence and behavior. Genes also control the life processes of your cells. F H [1 genes) are In both asexual and sexual reproduction, chromosomes (and each passed from parents to offspring. During asexual reproduction, The cell. parent single a daughter cell receives chromosomes from the and sms organi daughter cell is an exact copy of the parent. Some body cells of ll organisms reproduce asexually. LI During sexual reproduction, an offspring receives chromosomes from cells, are jgj each parent cell. The chromosomes in gametes, or sex osomes paired. A sperm or an egg cell has only half the number of chrom cell and the egg as a body cell. When fertilization takes place, the sperm full number of the to up add cell unite. Together, their chromosomes or zygote, has egg, ed chromosomes found in body cells. The fertiliz both par from chromosomes from both of its parents. It also has traits ents. S U CHROMOSOMES AND GENES Every cell has a nucleus. C 1. Figure A shows an animal cell. a) Draw a line to the nucleus. b) Label it “nucleus.” Figure A 2. A nucleus contains tiny rod-shaped bodies. What are they called? nucleus 3. A chromosome is made up of even smaller bodies. What are they called? Figure B 4. Figure C shows a pair of chromo somes and their genes. a) The chromosomes are labeled 1S1 1*) ii SI eL_a Il b) Two genes are labeled 5. Why are genes important? *1 I1 i•I It! Figure C 9 Figure D shows what actual human chro mosomes look like. S p ‘ 1% V ai • Every body cell of a particular organ ism has the same chromosomes. • No two indjviduals that reproduce sexually have the same chromosomes. You have trillions of body cells. Each cell has the same chromosomes. No one else in the world has the same chromosomes. There is no “duplicate” of you—anywhere! ‘C Figure D Human chromosomes The study of traits and how they are passed on is called genetics [juh-NET-iks}. • All living things have traits. • All living things have genes. • Only living things have genes. Genes contain the “plans” for the traits an organism has. What are genes made of? Scientists have discovered that genes are made of a com plicated compound called DNA. DNA stands for deoxyribonucleic fdee-oks-ee ry-boh-noo-KLEE-ik] acid. Try to pro nounce it. Figure E 10 _ ____ _____ __________ FILL IN THE BLANK C Write your answers in the Complete each statement using a term or terms from the list below. spaces provided. Some words may be used more than once. genes pairs inherited specific 23 chromosomes 46 genetics traits 1. The characteristics an individual has are called way of saying this is 2. Traits are passed down from parents to offspring. Another “traits are 3. The study of heredity is called 4. The nucleus has tiny rod-shaped bodies called 5. A chromosome is made up of a chain of 6. Genes determine the of an individual. number of chromosomes. 7. Every organism has a 8. In body cells, chromosomes are found in 9. Each of your body cells has This is a total of 10. A human sperm or egg has pairs of chromosomes. single chromosomes. single chromosomes. MATCHING the correct letter in the Match each term in Column A with its description in Column B. Write space provided. Column A Column B 1. genes a) compound that makes up genes 2. chrowosomes b) made up of many genes 3. DNA c) have unpaired chromosomes 4. body cells d) pass on traits 5. gametes e) have paired chromosomes II ____ ____ ____ ____ - r WHAT DO THE PICTURES SHOW? from parent to offspring during asexual and The pictures below show how chromosomes are passed er the questions. sexual reproduction. Study Figures F and C. Then answ n Chromosomes Figure F Asexual reproduction cell in Figure F have? 1. How many chromosomes does the parent hter cell have? 2. How many chromosomes does each daug mosomes compare to the daughter cell’s 3. In Figure F, how do the parent cell’s chro chromosomes? duce? 4. Which Figure shows how body cells repro s does each sperm cell contain? 5. a. In Figure C, how many chromosome cell contain? b. How many chromosomes does each egg 6. Gametes have the half, twice chromosomes number of chromosomes as body cells. body cells 7. Fertilization produces a single cell. What is it d? calle 8. How many chromosomes does the zygote in ? have re Figu C 9. How many chromosomes will each body cell of the organism have? 10. The offspring will have traits of both the mother and father. Why? Figure C 12 Sexual reproduction ________ NUMBER, F: ( Fill in the missing number of chromosomes. Chromosomes In each body cell Organism Chromosomes in each sperm or egg 1. Human 46 2. Horse 60 3. Housefly 4. Dog 5. Grasshopper 7 6. Mosquito 3 7. Chicken 8. Apple 9. Spinach 10. 6 78 18 17 12 12 Lily the number of chromosomes that a body cell has. 11. A gamete has half, twice following? 12. How many pairs of chromosomes are there in each body cell of the a) horse d) lily b) mosquito e) human c) spinach 1) housefly ktnj — words and write Below are several scrambled words you have used in this Lesson. Unscramble the your answers in the spaces provided. I. NEEC 4 2. HERINIT 3. NEGITECS 4. ETEMAG 5. CHOMEOSORM 13 __________ __________ _________ ________ _________ TRUE OR FALSE in the space provided, write “true” if the sentence is true. Write “false” if the sentence is false. 1. Traits are the characteristics of living things. 2. Only animals have traits. 3. Traits are passed on from offspring to parents. 4. Traits are passed on by genes. 5. A cell has only a few genes. 6. Only animals have genes. 7. Different genes control different traits. 8. Genes form chromosomes. 9. Every organism has the same number of chromosomes. 10. Body cells have paired chromosomes. 11. Gametes have paired chromosomes. 12. A body cell and a sex cell have the same number of chromosomes. 13. Gametes have half the number of chromosomes of body cells. 14. A human body cell has a total of 23 chromosomes. 15. A human gamete has 23 single chromosomes. REACI-{LNC OUT Which organism would more closely resemble its parent, one produced by asexual reproduction, or one produced by sexual reproduction? Why? 14