Presentation on theme: "Section 1: Mendel’s Work"— Presentation transcript:
1 Section 1: Mendel’s Work What were the results of Mendel’s experiments, or crosses?What controls the inheritance of traits in organisms?
2 What is Genetics? Genetics: the study of heredity Heredity: the passing of physical characteristics from parents to offspring
3 The Father of GeneticsThe 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.
4 Crossing Pea PlantsGregor Mendel crossed pea plants that had different traits. The illustrations show how he did this.
5 Mendel’s ExperimentsIn 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.
6 Dominant and Recessive Alleles Mendel studied several traits in pea plants.
7 Dominant and Recessive Alleles Today, scientists use the word “gene” to describe a piece of DNA that controls a trait.
8 Dominant and Recessive Alleles The traits that Mendel studied in his pea plant experiments are controlled by different genes:GENESeed ShapeSeed colorSeed coat colorPod shapePod colorFlower positionStem height
9 Dominant and Recessive Alleles These genes usually have 2 or more alleles, or different forms of the gene:GENE ALLELE ALLELESeed Shape round wrinkledSeed color yellow greenSeed coat color gray whitePod shape smooth pinchedPod color green yellowFlower position side endStem height tall short
10 Dominant and Recessive Alleles Some of these alleles are known as dominant. Others are known as recessive:DOMINANT RECESSIVEGENE ALLELE ALLELESeed Shape round wrinkledSeed color yellow greenSeed coat color gray whitePod shape smooth pinchedPod color green yellowFlower position side endStem height tall short
11 Dominant and Recessive Alleles In a dominant allele, the trait always shows up as long as there is at least one dominant allele.KeyT = tallt = shortT T“pure tall”T t“hybrid tall”
12 Dominant and Recessive Alleles In a recessive allele, the trait only shows up if both alleles are recessive.KeyT = tallt = shortt t“pure short”
13 Dominant and Recessive Alleles Dominant alleles are always symbolized with capital letters. Recessive alleles are always symbolized with lower-case letters.Key for HeightT = tallt = shortKey for Seed ColorY = yellow seed colory = green seed colorKey for Pod ColorG = green pod colorg = yellow pod colorKey for Coat ColorA = gray coat colora = white coat color
15 Section 2: Probability and 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?
16 A Punnett SquareThe 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.
17 Probability and Genetics In a genetic cross, the allele that each parent will pass on to its offspring is based on probability.
18 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.
19 Practicing Punnett Squares Key for HeightT = tallt = shortT T x T Tt t x t tT t x T tKey for Seed ColorY = yellow seed colory = green seed colorKey for Pod ColorG = green pod colorg = yellow pod color
20 Practicing Punnett Squares Key for HeightT = tallt = shortY y x y yY Y x y yg g x G gG g x G gKey for Seed ColorY = yellow seed colory = green seed colorKey for Pod ColorG = green pod colorg = yellow pod color
21 Homozygous vs. Heterozygous Homozygous = 2 identical allelesalso called “pure” or “purebred”Examples: T T t tHeterozygous = 2 different allelesalso called “hybrid”Examples: T t
22 CodominanceIn codominance, the alleles are neither dominant nor recessive. As a result, both phenotypes are expressed in the offspring.
23 Incomplete DominanceIn 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”.
28 Section 3: The Cell and Inheritance What role do chromosomes play in inheritance?What events occur during meiosis?What is the relationship between chromosomes and genes?
29 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.
30 Punnett SquareA Punnett square is actually a way to show the events that occur at meiosis.
31 A Lineup of GenesChromosomes 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.
32 Human Chromosomes Humans have 23 pairs of chromosomes: 23 from their mother, and 23 from their father.
33 Human ChromosomesThe first 22 pairs are organized and named according to their size:Chromosomes #1 are the largest, #2 are the second largest, etc.
34 Human ChromosomesThe final pair of chromosomes (“X” and “Y”) are the sex chromosomes because they determine the gender of the person:XX = girlXY = boy
35 Sex Chromosomes Father Mother 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.FatherMother
37 Section 4: Genes, DNA, and Proteins What forms the genetic code?How does a cell produce proteins?How can mutations affect an organism?
38 The DNA CodeChromosomes 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.
39 How Cells Make Proteins During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.
40 MutationsMutations 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.
41 Damages Made by Mutation THEBIGBADCATATETHEBIGREDRAT