Section 1: Chromosomes and Meiosis KEY CONCEPT Gametes have half the number of chromosomes that body cells have. VOCABULARY somatic cell autosome fertilization gamete sex chromosome diploid homologous chromosome sexual reproduction haploid meiosis MAIN IDEA: You have body cells and gametes. Fill in the blank with the word or phrase that best completes the sentence. 1. The two major groups of cell types in the human body are called and. 2. The gametes are located in the organs. 3. The number of chromosomes in a typical human body cell is. MAIN IDEA: Your cells have autosomes and sex chromosomes. Fill in the Concept Map below to summarize what you know about chromosomes. 46 chromosomes in human body cells half come from 4. include include 5. sex chromosomes 6. include 7. 8. include consist of 22 homologous pairs Holt McDougal Biology 1 Meiosis and Mendel Section 1: Chromosomes and Meiosis
continued 9. A person with two X chromosomes is female / male. 10. The X / Y chromosome carries the fewest number of genes. MAIN IDEA: Body cells are diploid; gametes are haploid. Circle the word or phrase that best completes the sentence. 11. During fertilization, the nuclei of the egg and sperm fuse / separate. 12. Germ / Somatic cells are haploid. 13. The haploid / diploid chromosome number in humans is 23. 14. Each human gamete has one autosome / sex chromosome. Read the descriptions in the table below and then decide which column should be labeled Mitosis and which column should be labeled Meiosis. 15. 16. Makes diploid cells. Makes genetically identical cells. Makes haploid cells. Makes genetically unique cells. Happens throughout an organism s life. Happens at specific times in an organism s life. Involved in asexual reproduction. Vocabulary Check 17. Circle all of the following statements that are true for homologous chromosomes. a. One is from the mother and one is from the father. b. They are a pair of chromosomes. c. They are fertilized gametes. Involved in sexual reproduction. d. They have the same genes, but they differ in length and appearance. e. They have the same genes, length, and overall appearance. Holt McDougal Biology 2 Meiosis and Mendel Section 1: Chromosomes and Meiosis
Section 2: Process of Meiosis KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells. VOCABULARY gametogenesis sperm egg polar body MAIN IDEA: Cells go through two rounds of division in meiosis. 1. After a chromosome is replicated, each half is called a sister chromatid / polar body. 2. Two chromosomes that are very similar and carry the same genes are called somatic / homologous chromosomes. In the space below, sketch the phases of meiosis I and II and write the name of each phase below it. Use Figure 2.3 to help you. Meiosis I 3. 4. 5. 6. Meiosis II 7. 8. 9. 10. Holt McDougal Biology 3 Meiosis and Mendel Section 2: Process of Meiosis
continued 11. In the diagram on the previous page, circle the phase in which homologous chromosomes separate, and put a box around the phase in which sister chromatids separate. MAIN IDEA: Haploid cells develop into mature gametes. 12. The sperm cell and the egg both contribute to an embryo. Place a check mark in the appropriate boxes below to indicate what each gamete contributes to the embryo. DNA Organelles Molecular building blocks Sperm cell Egg 13. Where are polar bodies made, in the male or in the female? 14. Complete the diagram of gametogenesis in the boxes below. Use Figure 2.4 to help you. Sperm Formation Egg Formation Vocabulary Check Fill in the blank with the word or phrase that best completes the sentence. 15. Genesis comes from a Greek word that means to be born. Therefore, gametogenesis is the of gametes. 16. Polar bodies are cells produced by in the female body. They contain little more than DNA and are eventually. Holt McDougal Biology 4 Meiosis and Mendel Section 2: Process of Meiosis
Section 3: Mendel and Heredity KEY CONCEPT Mendel s research showed that traits are inherited as discrete units. VOCABULARY trait purebred law of segregation genetics cross MAIN IDEA: Mendel laid the groundwork for genetics. Fill in the blank with the word or phrase that best completes the sentence. 1. Genetics is the study of biological patterns and variation in organisms. 2. A man named Gregor did early work that is the basis for much of our current understanding of genetics. 3. Mendel s views on inheritance differed from the views of many scientists of his time. Mendel recognized that are inherited as discrete units. MAIN IDEA: Mendel s data revealed patterns of inheritance. In designing his experiments, Mendel made three important choices that helped him see patterns of inheritance. The table below describes these choices and gives an example of how he put each choice into action. Match each choice with its example in the table. Mendel s Choices 4. Use of purebred plants 5. Study of either-or traits Example a. He removed the stamens and fertilized the pistil with pollen from a pea plant of his choice. b. He experimented with self-pollinating, purebred pea plants. 6. Control over breeding c. He looked at traits that did not have intermediate characteristics such as pea shape, pea color, flower color, pod shape, pod color, flower position, and plant height. Holt McDougal Biology 5 Meiosis and Mendel Section 3: Mendel and Heredity
continued 7. Mendel used pea plants, because they reproduce quickly / slowly, and he could control how they grow / mate. 8. Mendel bred flowers resulting in F 1 generation with dominant / recessive phenotype. He then allowed the F 1 generation offspring to self-pollinate. This resulted in an F 2 generation with dominant phenotypes only / both dominant and recessive phenotypes. 9. Mendel concluded that traits are inherited as discrete units. Today, we call these discrete units gametes / genes. 10. Mendel s law of segregation has two conclusions: i. Organisms inherit one copy / two copies of each gene, one from each parent. ii. Genes segregate during gamete formation, so organisms donate one copy / two copies of each gene in their gametes. Vocabulary Check 11. Segregation means separation. In Mendel s law of segregation, it is the gametes / genes that are segregated, or separated. 12. Purebred means a line of organisms that has uniform genetics / phenotype. Holt McDougal Biology 6 Meiosis and Mendel Section 3: Mendel and Heredity
Section 4: Traits, Genes, and Alleles KEY CONCEPT Genes encode proteins that produce a diverse range of traits. VOCABULARY gene heterozygous phenotype allele genome dominant homozygous genotype recessive MAIN IDEA: The same gene can have many versions. 1. There is a relationship between genes and proteins: A gene / protein provides instructions for a cell to make a certain gene / protein. 2. An allele is any of the alternative forms of a gene / genome that may occur at a specific locus / trait. 3. If a pair of alleles is the same, they are called heterozygous / homozygous. If a pair of alleles is different, they are called heterozygous / homozygous. 4. Homologous chromosomes are two chromosomes (one from the mother and one from the father) that have the same length, overall appearance, and alleles / genes, although the alleles / genes may differ. 5. In the space below, draw a pair of homologous chromosomes. On the chromosomes, draw and label one set of genes with homozygous alleles (Gene A, Gene A). Draw and label another set of genes with heterozygous alleles (Gene B, Gene b). Holt McDougal Biology 7 Meiosis and Mendel Section 4: Traits, Genes, and Alleles
continued MAIN IDEA: Genes influence the development of traits. 6. Genotype and phenotype differ. Use the statements below to fill in the definition and an analogy for each one in the table. a. The observable traits of an organism. b. The underlying genetics of an organism. c. A person s thoughts that you can t read. d. A person s words that tell you what they re thinking about. Genotype Phenotype Definition Analogy Fill in the blank with the word or phrase that best completes the sentence. 7. Alleles are represented on paper by letters. Uppercase letters indicate alleles, and lowercase letters indicate alleles. 8. An organism s phenotype is affected both by alleles and by. Complete the table by filling in the following terms: dominant, recessive, TT, Tt. Genotype Phenotype Alleles homozygous dominant dominant 9. homozygous recessive 10. tt heterozygous 11. 12. Vocabulary Check Fill in the blank with the word or phrase that best completes the sentence. 13. An organism with a QQ genotype has alleles. 14. An alternative form of a gene is called an. 15. The opposite of homozygous is. The opposite of dominant is. Holt McDougal Biology 8 Meiosis and Mendel Section 4: Traits, Genes, and Alleles
Section 5: Traits and Probability KEY CONCEPT The inheritance of traits follows the rules of probability. VOCABULARY Punnett square testcross law of independent assortment monohybrid cross dihybrid cross probability MAIN IDEA: Punnett squares illustrate genetic crosses. Identify what each of the numbered parts represents in the Punnett square below. Then draw lines from each of the parents alleles to the corresponding alleles in the offspring. 2. A a A AA Aa 1. 3. a Aa aa 1. Circle the parts of the Punnett square that represent the parents alleles. 2. What are the possible genotypes of the offspring in this cross? Fill in the blank with the word or phrase that best complete the following sentence. 3. Each parent contributes only one allele to the offspring, because the alleles segregated during gamete formation, which is called. During this process, the chromosomes separated. Holt McDougal Biology 9 Meiosis and Mendel Section 5: Traits and Probability
continued MAIN IDEA: A monohybrid cross involves one trait. 4. You know a ratio is a comparison that tells how two or more things relate. Therefore, a genotypic ratio is a comparison that tells the proportion of offspring that have a particular. A phenotypic ratio is a comparison that tells the proportion of offspring that have a particular. 5. What is the genotypic ratio of the offspring in Figure 5.3? 6. What is the phenotypic ratio of the offspring in Figure 5.4? MAIN IDEA: A dihybrid cross involves two traits. 7. A dihybrid cross examines the inheritance of a. two testcrosses. b. four testcrosses. c. two traits. d. four traits. 8. Suppose an organism has the genotype AABb. Two types of gametes could result from this allele combination: and. 9. What is the phenotypic ratio that results from a dihybrid cross between two organisms that are heterozygous for both traits? See Figure 5.5 for help. MAIN IDEA: Heredity patterns can be calculated with probability. 10. Probability predicts the average / exact number of occurrences, not the average / exact number of occurrences. 11. To calculate the probability that two independent events will happen together, divide / multiply the probability of each individual event. Vocabulary Check 12. A testcross is done between an organism with a dominant / recessive phenotype and an organism with a(n) known / unknown genotype. 13. In the law of independent assortment, allele pairs / gene pairs are independent. Holt McDougal Biology 10 Meiosis and Mendel Section 5: Traits and Probability
Section 6: Meiosis and Genetic Variation KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity. VOCABULARY crossing over genetic linkage MAIN IDEA: Sexual reproduction creates unique gene combinations. 1. Sexual reproduction helps create and maintain genetic diversity by independent assortment of chromosomes during meiosis / mitosis and by deliberate / random fertilization of gametes. 2. Sexual reproduction creates new alleles / new combinations of alleles. 3. The production of unique genetic combinations is a(n) advantage / disadvantage to organisms and species, because the resulting organisms have unique phenotypes, which increases / decreases the likelihood that some will survive under changing conditions. MAIN IDEA: Crossing over during meiosis increases genetic diversity. 4. When crossing over occurs, chromosomes are in a(n) duplicated / unduplicated state. 5. Use sketches to illustrate how crossing over contributes to genetic diversity. Use Figure 6.2 for reference. 1. Draw a cell with four chromosomes in the first box. Make one pair of chromosomes large and the other pair small. Color in one large chromosome and one small chromosome. 2. In the next box, draw the cell in prophase I. Have each pair of homologous chromosomes line up together large with large, small with small. 3. In the third box, show crossing over between each pair of homologous chromosomes. 4. In the last box, show what the chromosomes look like as a result of crossing over. Holt McDougal Biology 11 Meiosis and Mendel Section 6: Meiosis and Genetic Variation
continued 6. Refer to your cell sketch in the last box on the previous page. Also refer to Figure 2.3 (in Section 2) if necessary. 1. In the first box below, show what your cell would look like at the end of meiosis I. Remember, the result will be two cells that have one duplicated chromosome from each homologous pair. 2. In the second box, show what your cell would look like at the end of meiosis II. Remember, the result will be four cells that have one (unduplicated) chromosome from each homologous pair. In the following table, indicate whether or not genes A and B will follow Mendel s law of independent assortment. Place the letter of each explanation listed below into the appropriate box. a. The chromosomes carrying those genes will line up randomly and separate randomly during meiosis. b. The genes are likely to be linked and to travel together during meiosis. c. The genes will be far enough from each other that crossing over is very likely to occur between them. Location of genes A and B 7. On separate, nonhomologous chromosomes 8. At opposite ends on the same chromosome 9. Very close together on the same chromosome Vocabulary Check Fill in the blank with the word or phrase that best completes the sentence. 10. The exchange of chromosome segments between homologous chromosomes is called. 11. The tendency for two genes that are located close together on a chromosome to be inherited together is called. Will they follow Mendel s law of independent assortment? Explanation (Yes or No) (a, b, or c) Holt McDougal Biology 12 Meiosis and Mendel Section 6: Meiosis and Genetic Variation