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Chapter Introduction
Lesson 1 Mendel and His Peas
Lesson 2 Understanding Inheritance
Lesson 3 DNA and Genetics
Chapter Wrap-Up
What do you think?
Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements.
1. Like mixing paints, parents’ traits always blend in their offspring.
2. If you look more like your mother than you look like your father, then you received more traits from your mother.
3. All inherited traits follow Mendel’s patterns of inheritance.
Do you agree or disagree?
4. Scientists have tools to predict the form of a trait an offspring might inherit.
5. Any condition present at birth is genetic.
6. A change in the sequence of an organism’s DNA always changes the organism’s traits.
Do you agree or disagree?
Mendel and His Peas
• Why did Mendel perform cross-pollination experiments?
• What did Mendel conclude about inherited traits?
• How do dominant and recessive factors interact?
• heredity
• genetics
• dominant trait
• recessive trait
Mendel and His Peas
• Heredity is the passing of traits from parents to offspring.
• Gregor Mendel is known as the father of genetics—the study of how traits are passed from parents to offspring.
Early Ideas About Heredity
• Mendel studied genetics by doing controlled breeding experiments with pea plants.
• There are two types of pollination:
• self-pollination
• cross-pollination
Mendel’s Experimental Methods
• When a true-breeding plant self-pollinates, it always produces offspring with traits that match the parent.
• Mendel cross-pollinated pea plants himself and recorded the traits that appeared.
Mendel’s Experimental Methods (cont.)
Mendel’s Experimental Methods (cont.)
Why did Mendel perform cross-pollination experiments?
• Once Mendel had enough true-breeding plants for a trait he wanted to test, he cross-pollinated selected plants.
• Plants are called hybrids if they come from true-breeding parent plants with different forms of the same trait.
Mendel’s Results
hybrid
Science Use the offspring of two animals or plants with different forms of the same trait
Common Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor
Mendel’s Results (cont.)
• Mendel also cross-pollinated hybrid plants.
• He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio.
Mendel’s Results (cont.)
Mendel’s Results (cont.)
Mendel recorded traits of offspring from many hybrid crosses.
Mendel concluded that two factors, one from each sperm and one from each egg, control each inherited trait.
Mendel’s Conclusions
What did Mendel conclude about inherited traits?
Mendel’s Conclusions (cont.)
• A dominant trait is a genetic factor that blocks another genetic factor.
• A recessive trait is a genetic factor that is blocked by the presence of a dominant factor.
How do dominant and recessive factors interact?
Mendel’s Conclusions (cont.)
• Genetics is the study of how traits are passed from parents to offspring.
• Mendel studied genetics by doing cross-breeding experiments with pea plants.
• Mendel’s experiments with pea plants showed that some traits are dominant and others are recessive.
A. true breeding
B. self-pollination
C. cross-pollination
D. bees
What method did Mendel use to select which plants pollinated other plants?
A. 0
B. 1
C. 2
D. 1 or 2
How many dominant factors does a purple-flowering pea plant have?
A. 1 : 1
B. 2 : 1
C. 3 : 1
D. 4 : 1
What is the approximate ratio of dominant to recessive expression when both parents are hybrid?
1. Like mixing paints, parents’ traits always blend in their offspring.
2. If you look more like your mother than you look like your father, then you received more traits from your mother.
Do you agree or disagree?
• What determines the expression of traits?
• How can inheritance be modeled?
• How do some patterns of inheritance differ from Mendel’s model?
Understanding Inheritance
• gene
• allele
• phenotype
• genotype
• homozygous
• heterozygous
• Punnett square
• incomplete dominance
• codominance
• polygenic inheritance
Understanding Inheritance
• Mendel concluded that two factors—one from each parent—control each trait.
• Mendel’s “factors” are part of chromosomes which exist as pairs—one chromosome from each parent.
• Each cell in an offspring organism contains chromosomes from both parents.
What Controls Traits
• A gene is a section on a chromosome that has genetic information for one trait.
• The different forms of a gene are called alleles. Each chromosome has one allele for every gene on it.
• The two chromosomes in an offspring cell may have the same or different alleles.
What Controls Traits (cont.)
• Geneticists call how a trait appears, or is expressed, the trait’s phenotype.
• The two alleles that control the phenotype of a trait are called the trait’s genotype.
What Controls Traits (cont.)
What Controls Traits (cont.)
phenotype
from Greek phainein, means “to show”
• When the two alleles of a gene are the same, the genotype is homozygous.
• If the two alleles of a gene are different, the genotype is heterozygous.
What Controls Traits (cont.)
What Controls Traits (cont.)
How do alleles determine the expression of traits?
Scientists use uppercase and lowercase letters as symbols to represent the alleles in a genotype.
A Punnett square is a model used to predict possible genotypes and phenotypes of offspring.
Modeling Inheritance
A pedigree shows phenotypes of genetically related family members.
Modeling Inheritance (cont.)
• Sometimes traits appear to be blends of alleles.
• Alleles show incomplete dominance when the offspring’s phenotype is a blend of the parents’ phenotypes.
• Codominance occurs when both alleles can be observed in a phenotype.
Complex Patterns of Inheritance
Some traits, such as human ABO blood type, are determined by more than one allele.
Complex Patterns of Inheritance (cont.)
Polygenic inheritance occurs when multiple genes determine the phenotype of a trait.
Complex Patterns of Inheritance (cont.)
How does polygenic inheritance differ from Mendel’s model?
• An organism’s environment can affect its phenotype.
• Some examples of environmental factors that affect phenotype are soil type that a flower is growing in or time of year that a butterfly develops.
Genes and the Environment
• Geneticists use Punnett squares to predict the possible genotypes and phenotypes of offspring.
• In polygenic inheritance, traits are determined by more than one gene and have many possible phenotypes.
A. alleles
B. phenotypes
C. genotypes
D. chromosomes
What is the name for different forms of a gene?
A. heterozygous
B. dominant
C. homozygous
D. recessive
What is the genotype when two alleles of a gene are the same?
A. incomplete dominance
B. homozygous
C. polygenic
D. codominance
What occurs when both alleles can be observed in a phenotype?
3. All inherited traits follow Mendel’s patterns of inheritance.
4. Scientists have tools to predict the form of a trait an offspring might inherit.
Do you agree or disagree?
• What is DNA?
• What is the role of RNA in protein production?
• How do changes in the sequence of DNA affect traits?
DNA and Genetics
• DNA
• nucleotide
• replication
• RNA
• transcription
• translation
• mutation
DNA and Genetics
• Chromosomes are made of proteins and deoxyribonucleic acid, or DNA—an organism’s genetic material.
The Structure of DNA
• A gene is a segment of DNA on a chromosome.
DNA is shaped like a twisted ladder which is referred to as a double helix.
The Structure of DNA (cont.)
• A nucleotide is a molecule made of a nitrogen base, a sugar, and a phosphate group.
• Sugar-phosphate groups form the sides of the DNA ladder.
• The nitrogen bases, adenine (A), cytosine (C), thymine (T), and guanine (G), bond and form the rungs of the ladder.
The Structure of DNA (cont.)
A and T always bond together, and C and G always bonds together.
The Structure of DNA (cont.)
Replication is the process of copying a DNA molecule to make another DNA molecule.
• The DNA of each cell carries the complete set of genes that provide instructions for making all the proteins a cell requires.
• Proteins are made with the help of ribonucleic acid (RNA)—a type of nucleic acid that carries the code for making proteins from the nucleus to the cytoplasm.
Making Proteins
• RNA:
• is made of nucleotides.
• is single-stranded.
• has the nitrogen base uracil (U) instead of thymine (T), which is found in DNA.
Making Proteins (cont.)
Transcription—the process of making RNA from DNA—is the first step in making a protein.
Making Proteins (cont.)
What is the role of RNA in protein production?
A change in the nucleotide sequence of a gene is called a mutation.
Mutations
mutation
from Latin mutare, means “to change”
• The 46 human chromosomes contain between 20,000 and 25,000 genes that are copied during replication.
• Mutations can be triggered by exposure to X-rays, ultraviolet light, radioactive materials, and some kinds of chemicals.
Mutations (cont.)
There are several types of mutations. Three types of mutations are substitution, insertion, and deletion.
Mutations (cont.)
• In a deletion mutation, one or more nitrogen base is left out of the DNA sequence.
• In an insertion mutation, one or more nitrogen bases is added to the DNA.
• In a substitution mutation, one nitrogen base is replaced by a different nitrogen base.
• The effects of a mutation depend on where in the DNA sequence the mutation happens and the type of mutation.
• Some mutations in human DNA cause genetic disorders.
Mutations (cont.)
Mutations (cont.)
How do changes in the sequence of DNA affect traits?
• DNA is a complex molecule that contains the code for an organism’s genetic material.
• An organism’s nucleotide sequence can change through the deletion, insertion, or substitution of nitrogen bases.
A. DNA
B. mutations
C. mRNA
D. protein
What is created through transcription?
A. adenine
B. cytosine
C. thymine
D. uracil
In DNA, which of the following is paired with guanine?
A. insertion
B. substitution
C. transgression
D. deletion
Which of the following describes the mutation that occurs when three base pairs are added?
5. Any condition present at birth is genetic.
6. A change in the sequence of an organism’s DNA always changes the organism’s traits.
Do you agree or disagree?
Key Concept Summary
Interactive Concept Map
Chapter Review
Standardized Test Practice
Genetic information is passed from generation to generation by DNA. DNA controls the traits of an organism.
• Mendel performed cross-pollination experiments to track which traits were produced by specific parental crosses.
• Mendel found that two factors—one from a sperm cell and one from an egg cell—control each trait.
• Dominant traits block the expression of recessive traits. Recessive traits are expressed only when two recessive factors are present.
Lesson 1: Mendel and His Peas
Lesson 2: Understanding Inheritance
• Phenotype describes how a trait appears.
• Genotype describes alleles that control a trait.
• Punnett squares and pedigrees are tools to model patterns of inheritance.
• Many patterns of inheritance, such as codominance and polygenic inheritance, are more complex than Mendel described.
• DNA contains an organism’s genetic information.
• RNA carries the codes for making proteins from the nucleus to the cytoplasm. RNA also forms part of ribosomes.
• A change in the sequence of DNA, called a mutation, can change the traits of an organism.
Lesson 3: DNA and Genetics
A. 1
B. 2
C. 3
D. 4
According to Mendel, how many factors controlled each trait?
A. phenotype
B. codominance
C. genotype
D. polygenic inheritance
Which of the following describes alleles that control a trait?
A. transcription
B. replication
C. translation
D. mutation
Which of the following describes an error made during the copying of DNA?
A. 25%
B. 50%
C. 75%
D. 100%
If parents have the genotypes RR and Rr, what percentage of offspring will have a Rr genotype?
A. translation
B. transcription
C. replication
D. mutation
Which of the following describes the process of making a protein from RNA?
A. 25 percent C. 75 percent
B. 50 percent D. 100 percent
In fruit flies, the allele for red eyes (R) is dominant over the allele for white eyes (r). If parents have the genotypes Rr and Rr, what percentage of offspring will have red eyes?
A. chromosomes
B. genes
C. genotype
D. all of the above
Heredity is associated with which of the following?
A. polygenic inheritance
B. mutation
C. environmental influence
D. codominance
Which occurs when multiple genes determine the phenotype of a trait?
A. adenine bonds with guanine
B. cytosine bonds with adenine
C. thymine bonds with adenine
D. none of the above
In DNA, which of the following is true?
A. DNA
B. RNA
C. mRNA
D. proteins
What is the product of replication?
