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Chapter 10: Mendel and Meiosis

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Chapter 10: Mendel and Meiosis 0250-0251 UO4 BDOL-829900 8/4/04 6:16 PM Page 250 1863 Lincoln writes the Emancipation Proclamation. 1865 Mendel discovers the rules of inheritance. Genetics What You’ll Learn Chapter 10 Mendel and Meiosis Chapter 11 DNA and Genes Chapter 12 Patterns of Heredity and Human Genetics Chapter 13 Genetic Technology Unit 4 Review BioDigest & Standardized Test Practice Why It’s Important Physical traits, such as the stripes of these tigers, are encoded in small segments of a chromosome called genes, which are passed from one generation to the next. By studying the inheritance pattern of a trait through several generations, the probability that future offspring will express that trait can be predicted. Indiana Standards The following standards are covered in Unit 4: B.1.8, B.1.21, B.1.22, B.1.23, B.1.24, B.1.25, B.1.26, B.1.27, B.1.28, B.1.29, B.1.30, B.2.4 Understanding the Photo White tigers differ from orange tigers by having ice-blue eyes, a pink nose, and creamy white fur with brown or black stripes. They are not albinos. The only time a white tiger is born is when its parents each carry the white- coloring gene. White tigers are very rare, and today, they are only seen in zoos. 250 in.bdol.glencoe.com/webquest (t)Science Photo Library/Photo Researchers, (crossover)Tom Brakefield/CORBIS 0250-0251 UO4 BDOL-829900 8/4/04 3:08 PM Page 251 1950 1964 The Korean War begins The Beatles make when North Korea their first appearance invades South Korea. on American TV. 1910 1952 2000 Scientists determine that genes Alfred Hershey and 1953 Most of the reside on chromosomes. Martha Chase show Watson, Crick, human DNA conclusively that DNA Wilkins, and sequence is is the genetic material. Franklin determine completed. 1944 the structure 1990 Scientists suggest genetic of DNA. The Human Genome material is DNA, not protein. 1961 Project begins to map The results are not accepted. The genetic code and sequence the entire is cracked. human genome. (tl)Omikron/Science Source/Photo Researchers, (tr)CNRI/Phototake, NYC 251 0252 C10Open BDOL-829900 8/3/04 9:47 PM Page 252 Mendel and Meiosis What You’ll Learn ■ You will identify the basic concepts of genetics. ■ You will examine the process of meiosis. Why It’s Important Genetics explains why you have inherited certain traits from your parents. If you understand how meiosis occurs, you can see how these traits were passed on to you. Understanding the Photo Zebras usually travel in large groups, and each zebra’s stripes blend in with the stripes of the zebras around it. This confuses predators. Rather than seeing individual zebras, predators see a large, striped mass. Zebra stripe patterns are like human fingerprints—they are geneti- cally determined, and every zebra’s stripe pattern is unique. Visit in.bdol.glencoe.com to • study the entire chapter online • access Web Links for more information and activities on genetics and meiosis • review content with the Interactive Tutor and self- check quizzes 252 Dr. G.G. Dimijian/Photo Researchers 0253-0262 C10S1 BDOL-829900 8/3/04 8:45 PM Page 253 Mendel’s Laws of Heredity 10.1 Indiana Standards Standard B.1.22 Understand and explain the genetic basis for Mendel’s laws of segregation and independent assortment. SECTION PREVIEW Objectives Heredity Make the following Foldable to help you Relate Mendel’s two laws organize information about Mendel’s laws of heredity. to the results he obtained in his experiments with garden peas. STEP 1 Fold one piece of paper STEP 2 Fold the paper Predict the possible off- lengthwise into thirds. widthwise into fifths. spring of a genetic cross by using a Punnett square. Review Vocabulary experiment: a procedure that tests a hypothesis by the process of col- lecting data under con- STEP 3 STEP 4 trolled conditions (p. 13) Unfold, lay the paper length- Label your table wise, and draw lines along the folds. as shown. New Vocabulary heredity Describe in Give an Mendel Your Words trait Example Rule of genetics unit factors gamete Rule of fertilization dominance zygote Law of pollination segregation Law of hybrid independent allele assortment dominant recessive Make a Table As you read Chapter 10, complete the table describing law of segregation Mendel’s rules and laws of heredity. phenotype genotype homozygous heterozygous Why Mendel Succeeded law of independent assortment People have noticed for thousands of years that family resemblances are inherited from generation to generation. However, it was not until the mid-nineteenth century that Gregor Mendel, an Austrian monk, carried out important studies of heredity—the passing on of characteristics from parents to offspring. Characteristics that are inherited are called traits. Mendel was the first person to succeed in predicting how traits are trans- ferred from one generation to the next. A complete explanation requires the careful study of genetics—the branch of biology that studies heredity. heredity from the Mendel chose his subject carefully Latin word hered-, Mendel chose to use the garden pea in his experiments for several rea- meaning “heir”; Heredity describes sons. Garden pea plants reproduce sexually, which means that they produce the way the gene- male and female sex cells, called gametes. The male gamete forms in the tic qualities you pollen grain, which is produced in the male reproductive organ. The receive from your ancestors are female gamete forms in the female reproductive organ. In a process called passed on. fertilization, the male gamete unites with the female gamete. The resulting fertilized cell, called a zygote (ZI goht), then develops into a seed. 10.1 MENDEL’S LAWS OF HEREDITY 253 0253-0262 C10S1 BDOL-829900 8/3/04 8:46 PM Page 254 The transfer of pollen grains from a male reproductive organ to a female reproductive organ in a plant is called Observe and Infer pollination. In peas, both organs are Looking at Pollen Pollen grains located in the same flower and are are formed within the male tightly enclosed by petals. This pre- anthers of flowers. What is vents pollen from other flowers from their role? Pollen contains the male gametes, or sperm cells, entering the pea flower. As a result, peas needed for fertilization. This Anther normally reproduce by self-pollination; means that pollen grains carry that is, the male and female gametes the hereditary units from male parent plants to female parent Pistil come from the same plant. In many of plants. The pollen grains that Mendel’s experiments, this is exactly Mendel transferred from the Stamens what he wanted. When he wanted to anther of one pea plant to the breed, or cross, one plant with another, female pistil of another plant carried the hereditary traits that he so carefully observed in the next generation. Mendel opened the petals of a flower and removed the male organs, as shown Procedure in Figure 10.1A. He then dusted the ! Examine a flower. Using the diagram as a guide, locate the female organ with pollen from the plant stamens of your flower. There are usually several stamens he wished to cross it with, as shown in in each flower. Figure 10.1B. This process is called @ Remove one stamen and locate the enlarged end—the cross-pollination. By using this tech- anther. nique, Mendel could be sure of the par- # Add a drop of water to a microscope glass slide. Place the ents in his cross. anther in the water. Add a coverslip. Using the eraser end of a pencil, tap the coverslip several times to squash the Mendel was a careful researcher anther. $ Observe under low power. Look for numerous small round Mendel carefully controlled his structures. These are pollen grains. experiments and the peas he used. He studied only one trait at a time to con- Analysis trol variables, and he analyzed his data 1. Estimate Provide an estimate of the number of pollen mathematically. The tall pea plants he grains present in an anther. worked with were from populations of 2. Describe What does a single pollen grain look like? plants that had been tall for many 3. Explain What is the role of pollen grains in plant generations and had always produced reproduction? tall offspring. Such plants are said to be true breeding for tallness. Like- wise, the short plants he worked with were true breeding for shortness. Figure 10.1 A B Pollen In his experiments, grains Mendel often had to transfer pollen from one plant to another plant with different traits. This is called Transfer making a cross. Remove pollen Describe How did male parts Female part Male parts Mendel make a cross? Cross-pollination 254 MENDEL AND MEIOSIS 0253-0262 C10S1 BDOL-829900 8/3/04 8:47 PM Page 255 Mendel’s Monohybrid The original parents, the true- breeding plants, are known as the P1 Crosses generation. The P stands for “parent.” What did Mendel do with the tall The offspring of the parent plants and short pea plants he selected? He are known as the F1 generation. crossed them to produce new plants. The F stands for “filial”—son or Mendel referred to the offspring of daughter. When you cross two F1 this cross as hybrids. A hybrid is the plants with each other, their offspring offspring of parents that have differ- are the F2 generation—the second fil- ent forms of a trait, such as tall and ial generation. You might find it eas- short height. Mendel’s first experi- ier to understand these terms if you ments are called monohybrid crosses because mono means “one” and the two parent plants differed from each other by a single trait—height.
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