Chapter 11 Review

Section Assessments

11-1

1. What are dominant and recessive alleles? Dominant alleles are the form of an allele whose trait always shows up if it is present; Recessive alleles are the form of an allele whose trait only shows up when the dominant allele is not present.

For plant Tallness: TT Tt tt

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2. What is segregation? What happens to alleles during segregation? Segregation is the separation of paired alleles;The alleles are sepatated during the formation of gametes with the result that each gamete only carries a single allele from the original pair.

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3. What did Mendel conclude determines biological inheritance? Mendel’s first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next.

Today, scientists call the chemical factors that determine traits genes.

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4. Describe how Mendel cross-pollinated pea plants.

Mendel cut away the the male parts of one flower, then dusted it with pollen from another flower.

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5. Why did only about one fourth of Mendel’s F2 plants exhibit the recessive trait?

Only one fourth of the possible gamete combinations did not have a dominant allele.

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6. Critical Thinking: Why were true-breeding pea plants important for Mendel’s experiments?

True-breeding pea plants have two identical alleles for a gene, so in a genetic cross each parent contributed only one form of a gene, making inheritance patterns more detectable.

11-2

1. How are the principles of probability used to predict the outcomes of genetic crosses?

The way in which the alleles segregate is random, and probability allows the calculation of the likelihood that a particular allele combination will occur in offspring.

11-2

2. How are Punnett squares used? To predict and compare the genetic

variations that will result from a cross.

3. What is probability? The likelihood that a particular event will

occur.

11-2

4. Define the terms genotype and phenotype. Genotype refers to the actual alleles

present for a trait or the genetic makeup. Phenotype refers to the visible expression

of the alleles, or the physical characteristics.

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5. Critical Thinking: An F1 plant that is homozygous for shortness is crossed with a heterozygous F1 plant. What is the probability that a seed from the cross will produce a tall plant?

t t T Tt Tt t tt tt

11-3

1. Explain what independent assortment means.

During gamete formation, pairs of alleles for different traits segregate, or separate, independently of one another.

11-3

2. Describe two inheritance patterns besides simple dominance.

Incomplete dominance- cases in which one allele is not completely dominant over another.

Codominance- in which both alleles contribute to the phenotype.

Multiple alleles- cases in which genes have more than two possible alleles.

Polygenic traits- traits that are produced through the interaction of several genes.

11-3

3. What is the difference between incomplete dominance and codominance?

In incomplete dominance, two alleles combine their effects to produce a single in-between phenotype.

In codominance, each allele is expressed in the offspring.

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4. Why are fruit flies an ideal organism for genetic research?

They are small, easy to keep in the laboratory, and produce large numbers of offspring in a short period of time.

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5. Critical Thinking: A geneticist studying coat color in animals crosses a male rabbit having the genotype CC with a female rabbit having genotype Ccch. The geneticist then crosses a ccch male with a Ccc female. In which of the two crosses are the offspring more likely to show greater genetic variation?

11-3 review of multiple alleles

Full Color: CC, Ccch, Cch, or CcChinchilla: cchch, cchcch, or cchcHimalayan chc or chch Albino: cc

Each individual only has two alleles. More than two alleles exist within the population.

11-3

Answer to #5

The offspring in the 2nd cross will show greater variation because 100 percent of the offspring from the first cross (CC x Ccch) will be full color.

11-4

1. Describe the main results of meiosis. From the original cell, Four haploid cells are

formed that are genetically different from one another.

2. What are the principle differences between mitosis and meiosis?

Mitosis produced two genetically identical diploid cells; Meiosis produces four genetically different haploid cells.

11-4

3. What do the terms diploid and haploid mean? Diplod = two sets of chromosomesHapolid = one set of chromosomes

4. What is crossing over? Homologous chromosomes pair up and form

tetrads, which may exchange portions of their chromatids, resulting in the exchange of alleles between the homologous chromosomes.

11-4

5. Critical Thinking: In human cells, 2N= 46. How many chromosomes would you expect to find in a sperm cell? In an egg cell? In a white blood cell? Explain.

Both sperm and egg cells have 23 chromosomes because they are gametes. A white blood cell has 46 chromosomes because it is a diploid body cell.

11-5

1. How does the principle of independent assortment apply to chromosomes?

It is the chromosomes that assort independently, not individual genes.

11-5

2. What are gene maps, and how are they produced?

A gene map shows the relative locations of genes on a chromosome. The frequency of crossing-over between genes is used to produce a map of distances between genes.

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3. How does crossing-over make gene mapping possible?

The farther apart two genes are, the more likely they are to be separated during a crossover in Meiosis. Therefore, the frequency of crossing-over is equal to the distance between two genes.

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4. Critical Thinking: If two genes are on the same chromosome but usually assort independently, what does that tell you about how close together they are?

The two genes are located very far apart from each other.

Exit Ticket

Take out a clean sheet of notebook paper. Put away any notes/ textbook.

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