chapter 5 genetics: the science of heredity what were the results of mendel’s experiments, or...
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Chapter 5 Genetics: The Science of Heredity
• What were the results of Mendel’s experiments, or crosses?
• What controls the inheritance of traits in organisms?
Section 1:Mendel’s Work
Chapter 5 Genetics: The Science of Heredity
What is Genetics?
Genetics: the study of heredity
Heredity: the passing of physical characteristics from parents to offspring
Chapter 5 Genetics: The Science of Heredity
The Father of Genetics
The field of Genetics was founded by Gregor Mendel, an Augustinian priest.
Between 1856 and 1863, Mendel cultivated and tested almost 30,000 pea plants.
The importance of Mendel's work was not discovered until almost 30 years after Mendel died.
Chapter 5 Genetics: The Science of Heredity
Crossing Pea Plants
Gregor Mendel crossed pea plants that had different traits. The illustrations show how he did this.
Chapter 5 Genetics: The Science of Heredity
Mendel’s Experiments
In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Mendel studied several traits in pea plants.
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Today, scientists use the word “gene” to describe a piece of DNA that controls a trait.
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
The traits that Mendel studied in his pea plant experiments are controlled by different genes:
GENE
Seed Shape
Seed color
Seed coat color
Pod shape
Pod color
Flower position
Stem height
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
These genes usually have 2 or more alleles, or different forms of the gene:
GENE ALLELE ALLELE
Seed Shape round wrinkled
Seed color yellow green
Seed coat color gray white
Pod shape smooth pinched
Pod color green yellow
Flower position side end
Stem height tall short
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Some of these alleles are known as dominant. Others are known as recessive:
DOMINANT RECESSIVE
GENE ALLELE ALLELE
Seed Shape round wrinkled
Seed color yellow green
Seed coat color gray white
Pod shape smooth pinched
Pod color green yellow
Flower position side end
Stem height tall short
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
In a dominant allele, the trait always shows up as long as there is at least one dominant allele.
Key
T = tallt = short
T t“hybrid tall”
T T“pure tall”
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
In a recessive allele, the trait only shows up if both alleles are recessive.
Key
T = tallt = short
t t“pure short”
Chapter 5 Genetics: The Science of Heredity
Dominant and Recessive Alleles
Dominant alleles are always symbolized with capital letters. Recessive alleles are always symbolized with lower-case letters.
Key for Height
T = tallt = short
Key for Seed Color
Y = yellow seed colory = green seed color
Key for Pod Color
G = green pod colorg = yellow pod color
Key for Coat Color
A = gray coat colora = white coat color
Chapter 5 Genetics: The Science of Heredity
End of Section: Mendel’s Work
Chapter 5 Genetics: The Science of Heredity
What is probability and how does it help explain the results of genetic crosses?What is meant by genotype and phenotype?What is codominance?
Section 2: Probability and Heredity
Chapter 5 Genetics: The Science of Heredity
A Punnett Square
The diagrams show how to make a Punnett square. In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele.
Chapter 5 Genetics: The Science of Heredity
Probability and Genetics
In a genetic cross, the allele that each parent will pass on to its offspring is based on probability.
Chapter 5 Genetics: The Science of Heredity
Phenotypes and Genotypes
An organism’s phenotype is its physical appearance, or visible traits. An organism’s genotype is its genetic makeup, or allele combinations.
Chapter 5 Genetics: The Science of Heredity
Practicing Punnett Squares
1) T T x T T
2) t t x t t
3) T t x T t
Key for Height
T = tallt = short
Key for Seed Color
Y = yellow seed colory = green seed color
Key for Pod Color
G = green pod colorg = yellow pod color
Chapter 5 Genetics: The Science of Heredity
Practicing Punnett Squares
1) Y y x y y
2) Y Y x y y
3) g g x G g
4) G g x G g
Key for Height
T = tallt = short
Key for Seed Color
Y = yellow seed colory = green seed color
Key for Pod Color
G = green pod colorg = yellow pod color
Chapter 5 Genetics: The Science of Heredity
Homozygous vs. Heterozygous
Homozygous = 2 identical alleles
also called “pure” or “purebred”
Examples: T T t t
Heterozygous = 2 different alleles
also called “hybrid”Examples: T t
Chapter 5 Genetics: The Science of Heredity
Codominance
In codominance, the alleles are neither dominant nor recessive. As a result, both phenotypes are expressed in the offspring.
Chapter 5 Genetics: The Science of Heredity
Incomplete Dominance
In incomplete dominance, the contributions of both alleles are visible and do not overpower each other in the phenotype. As a result, both phenotypes look “mixed”.
Chapter 5 Genetics: The Science of Heredity
Dihybrid Cross
Chapter 5 Genetics: The Science of Heredity
Dihybrid Cross
Key for Height
T = tallt = short
Key for Seed Color
Y = yellow seed colory = green seed color
Key for Pod Color
G = green pod colorg = yellow pod color
Chapter 5 Genetics: The Science of Heredity
Dihybrid Cross
Chapter 5 Genetics: The Science of Heredity
End of Section: Probability and Heredity
Chapter 5 Genetics: The Science of Heredity
What role do chromosomes play in inheritance?What events occur during meiosis?What is the relationship between chromosomes and genes?
Section 3: The Cell and Inheritance
Chapter 5 Genetics: The Science of Heredity
MeiosisDuring meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.
Chapter 5 Genetics: The Science of Heredity
Punnett Square
A Punnett square is actually a way to show the events that occur at meiosis.
Chapter 5 Genetics: The Science of Heredity
A Lineup of Genes
Chromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others.
Chapter 5 Genetics: The Science of Heredity
Human Chromosomes
Humans have 23 pairs of chromosomes:
23 from their mother, and 23 from their father.
Chapter 5 Genetics: The Science of Heredity
Human Chromosomes
The first 22 pairs are organized and named according to their size:
Chromosomes #1 are the largest, #2 are the second largest, etc.
Chapter 5 Genetics: The Science of Heredity
Human Chromosomes
The final pair of chromosomes (“X” and “Y”) are the sex chromosomes because they determine the gender of the person:
XX = girl
XY = boy
Chapter 5 Genetics: The Science of Heredity
Sex Chromosomes
Father
Mot
her
The father is who determines the gender of the child since males need a “Y” chromosome, and only males have “Y” chromosomes.
The mother can only give out an “X”, and both boys and girls have at least 1 “X” chromosome.
Chapter 5 Genetics: The Science of Heredity
End of Section: The Cell and Inheritance
Chapter 5 Genetics: The Science of Heredity
• What forms the genetic code?• How does a cell produce proteins?• How can mutations affect an organism?
Section 4: Genes, DNA, and Proteins
Chapter 5 Genetics: The Science of Heredity
The DNA Code
Chromosomes are made of DNA. Each chromosome contains thousands of genes. The sequence of bases in a gene forms a code that tells the cell what protein to produce.
Chapter 5 Genetics: The Science of Heredity
How Cells Make Proteins
During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.
Chapter 5 Genetics: The Science of Heredity
Mutations
Mutations can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism’s trait, or phenotype, may be different from what it normally would have been.
Chapter 5 Genetics: The Science of Heredity
Damages Made by Mutation
THEBIGBADCATATETHEBIGREDRAT
Chapter 5 Genetics: The Science of Heredity
End of Section: Genes, DNA, and Proteins