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Holt McDougal

46 chromosomes inhuman body cells

halfcome from

4.

includeinclude 5.

sex chromosomes 6.

include include

7. 8.consist of

22 homologous pairs

1 Meiosis and Mendel Section 1: Chromosomes

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Holt McDougal 2 Meiosis and

Mendel Section 1: Chromosomes

Section 1: Chromosomes and Meiosis

Study Guide AKEY CONCEPTGametes have half the number of chromosomes that body cells have.

VOCABULARY

somatic cell autosome fertilizationgamete 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.

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Holt McDougal 1 Meiosis and

Mendel Section 1: Chromosomes

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Holt McDougal 2 Meiosis and

Mendel Section 1: Chromosomes

Circle the word or phrase that best completes the statement.

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 haploid cells.

Makes genetically identical cells. Makes genetically unique cells.

Happens throughout an organism’s life. Happens at specific times in an organism’s life.

Involved in asexual reproduction. Involved in sexual reproduction.

Vocabulary Check17. 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.d. They have the same genes, but they differ in length and appearance.e. They have the same genes, length, and overall appearance.

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Study Guide A

3. 4. 5.

6.

7. 8. 9.

Section 2: Process of Meiosis

Study Guide AKEY CONCEPTDuring meiosis, diploid cells undergo two cell divisions that result in haploid cells.

VOCABULARY

gametogenesis eggsperm polar body

MAIN IDEA: Cells go through two rounds of division in meiosis.Circle the word or phrase that best completes the statement.

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 calledsomatic / 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

Meiosis II

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Holt McDougal Biology Study Guide A

3 Meiosis and Mendel Section 2: Process of Meiosis

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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 checkmark in the appropriate boxes below to indicate what each gamete contributes to the embryo.

Sperm cell Egg

DNA

Organelles

Molecular building blocks

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

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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 .

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Holt McDougal Biology Study Guide A

4 Meiosis and Mendel Section 2: Process of Meiosis

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Study Guide A Section 3: Mendel and Heredity

Study Guide AKEY CONCEPTMendel’s research showed that traits are inherited as discrete units.

VOCABULARY

trait purebred law of segregationgenetics 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 Example

4. Use of purebred plants

a. He removed the stamens and fertilized the pistil with pollen from a pea plant of his choice.

5. Study of “either-or” traits

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.

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Holt McDougal Biology Study Guide A

5 Meiosis and Mendel Section 3: Mendel and Heredity

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Circle the word or phrase that best completes the statement.

7. Mendel used pea plants, because they reproduce quickly / slowly, and he could control how they grow / mate.

8. Mendel bred flowers resulting in F1 generation with dominant / recessive phenotype. He then allowed the F1 generation offspring to self-pollinate. This resulted in an F2 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 CheckCircle the word or phrase that best completes the statement.

11. Segregation means “separation.” In Mendel’s law of segregation, it is thegametes / genes that are segregated, or separated.

12. “Purebred” means a line of organisms that has uniform genetics / phenotype.

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Holt McDougal Biology Study Guide A

6 Meiosis and Mendel Section 3: Mendel and Heredity

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Study Guide A Section 4: Traits, Genes, and Alleles

Study Guide AKEY CONCEPTGenes encode proteins that produce a diverse range of traits.

VOCABULARY

gene heterozygous phenotypeallele genome dominant

homozygous genotype recessive

MAIN IDEA: The same gene can have many versions.Circle the word or phrase that best completes the statement.

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).

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Holt McDougal Biology Study Guide A

7 Meiosis and Mendel Section 4: Traits, Genes, and Alleles

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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.

Definition Analogy

Genotype

Phenotype

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 CheckFill 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 .

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Holt McDougal Biology Study Guide A

8 Meiosis and Mendel Section 4: Traits, Genes, and Alleles

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A a

A

a

Section 5: Traits and Probability

Study Guide AKEY CONCEPTThe inheritance of traits follows the rules of probability.

VOCABULARY

Punnett square testcross law of independent assortmentmonohybrid 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.

1. 3.

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.

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AA Aa

Aa aa

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9 Meiosis and Mendel Section 5: Traits and Probability

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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 ofa. 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.Circle the word or phrase that best completes the statement.

10. Probability predicts the average / exact number of occurrences, not theaverage / 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 CheckCircle the word or phrase that best completes the statement.

12. A testcross is done between an organism with a dominant / recessivephenotype and an organism with a(n) known / unknown genotype.

13. In the law of independent assortment, allele pairs / gene pairs are independent.

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Holt McDougal Biology Study Guide A

10 Meiosis and Mendel Section 5: Traits and Probability

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Study Guide A Section 6: Meiosis and Genetic Variation

Study Guide AKEY CONCEPTIndependent assortment and crossing over during meiosis result in genetic diversity.

VOCABULARY

MAIN IDEA: Sexual reproduction creates unique gene combinations.Circle the word or phrase that best completes the statement.

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.

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Holt McDougal Biology Study Guide A

11 Meiosis and Mendel Section 6: Meiosis and Genetic Variation

crossing over genetic linkage

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Study Guide A 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 meiosisII. 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.

7.

Location of genes A and B

On separate, nonhomologous

Will they follow Mendel’s law of independent assortment? (Yes or No)

Explanation (a, b, or c)

8.

chromosomes

At opposite ends on the same

9.

chromosome

Very close together on thesame chromosome

Vocabulary CheckFill 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 .

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Holt McDougal Biology 12 Meiosis and MendelStudy Guide A Section 6: Meiosis and Genetic Variation