CHAPTER 11 MENDEL & HEREDITY SC STANDARD B 4: The student will understand the molecular basis of...
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CHAPTER 11MENDEL & HEREDITYSC STANDARD B 4:
The student will understand the molecular basis of heredity.
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ESSENTIAL QUESTION
How does segregation of alleles contribute to genetic variation?
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ORIGINS OF HEREDITARY SCIENCE
Mendel” Breeding ExperimentsGenetics: is the science of heredity
&the mechanism by which traits are passed from parents to offspring
Mendelborn in Austrian Empire (today Czech Republic) in 1822
Studied physics & mathematics @ University of Vienna
Joined monastery in 1843 where he was put in charge of the gardens
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MENDEL’S EXPERIMENTS
Mendel spent 2 years preparing his control plants to insure they were true breedersdescribes organisms that are homozygous for a specific trait so always produce offspring that have the same phenotype for that trait
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MENDEL’S EXPERIMENTS
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MENDEL’S EXPERIMENTS
crossed true breeding, purple blossomed pea plants with true breeding, white blossomed pea plants and all the offspring had purple flowers
Then let the offspring self-pollinate and some of the plants in that generation had purple flowers & some had white
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MENDEL’S EXPERIMENTS
male parts were removed from 1st flower
pollen taken from male parts of 2nd flower
pollen from 2nd brushed onto female parts of 1st flower
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MENDEL’S EXPERIMENTS
Vocabulary:
- character: a recognizable inherited feature or characteristic of an individual- trait: one of two or more possible forms of a character
~ phenotype: physical characteristics
~ genotype: genetic makeup , what alleles an organism has
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MENDEL’S EXPERIMENTS
Vocabulary:
- hybrid: the offspring of a cross between parents that have contrasting traits- generation: the entire group of offspring produced by a given group of parents
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MENDEL’S EXPERIMENTS
3 reasons why the garden pea plant was good choice:
1. Several characters appear in contrasting forms
2. These flowers can self-pollinate because each flower has both male & female parts
3. Plant is easy to grow1. Matures quickly2. Needs little care3. Produces many offspring
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MENDEL’S EXPERIMENTS
Monohybrid Cross
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MENDEL’S EXPERIMENTS
Monohybrid Cross: 3 Steps
1. Produced a true-breeding parent generation (P generation)
2. Produced 1st filial generation ( F 1 generation)
3. Produced 2nd filial generation ( F 2 generation)
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MENDEL’S EXPERIMENTS
True breeding purpleTrue breeding white
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MENDEL’S EXPERIMENTS
Step 2: cross pollinated parents
F 1 generation all purpleSelf-pollinated
F 2 generation 3 : 1 purple to white
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MENDEL’S EXPERIMENTS
Mendel repeated these experiments with 7 different traits in pea plants:For each of the 7 characters he found a similar 3 : 1 ratio of contrasting traits in the F 2 generation
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MENDEL’S EXPERIMENTS
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MENDEL’S EXPERIMENTS
Ratios in Mendel’s ResultsF 1 generation expressed the
same trait for any of the 7 characteristics he studied
When F 1 plants allowed to self-pollinate he always saw a 3 : 1 ratio of contrasting traits
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MENDEL’S THEORY
Explains simple patterns of inheritance2 of several versions of a gene combine & result in 1 of several possible traits
Allele: one of two or more alternative forms of a gene each leading to a unique trait
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MENDEL’S THEORY
Dominant: describes an allele that is fully expressed whenever the allele is present
Recessive: describes an allele that is expressed only when there is no dominant allele present
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MENDEL’S THEORY
Law of Segregation of Alleles:
When an organism produces gametes, each pair of alleles on homologous chromosomes separate in Meiosis I and each gamete has an equal chance of receiving either one of the alleles
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MENDEL’S THEORY: LAW OF SEGREGATION OF ALLELES
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MENDEL’S THEORY
GENOTYPE: a specific combination of alleles in an individual….. the “genes” an individual hasexample: AA, Aa, or aa
PHENOTYPE : the detectable trait or traits that result from the genotype of an individual….. the “physical appearance” an individual hasexample: normal, normal,
albino
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MENDEL’S THEORY
GENOTYPE DETERMINES PHENOTYPE !
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MENDEL’S THEORY
The genotype of each of the peas is ____________.
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MENDEL’S THEORY
The phenotype of each of the following is _____.
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MENDEL’S THEORY
Homozygous: describes an individual that carries two identical alleles of a geneExample: PP or pp
Heterozygous: describes an individual that carries two different alleles of a geneExample: Pp
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MENDEL’S THEORY
Mendel’s 2nd ExperimentsDihybrid crosses: involves test
crossing two characters
Law of Independent Assortment: during gamete formation, the alleles on non-homologous chromosomes segregate independently
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MENDEL’S THEORY
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PROBLEM SOLVING: PRODUCING TRUE-BREEDING SEEDS
Textbook page 271Work in table groupsDefine the problemOrganize informationCreate solutionPresent to class
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MENDEL’S THEORY
When genes are close together on same chromosome they will rarely separate independently so are said to be “linked”.
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MODELING MENDEL’S LAWS
Punnett Square: a graphic used to predict the results of a genetic cross
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MODELING MENDEL’S LAWS
A Punnett Square shows all the genotypes that could possibly result from any given cross match.
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MODELING MENDEL’S LAWS
Monohybrid Homozygous CrossDraw a Punnett Square crossing homozygous Y (for yellow seed color) with homozygous y (for green seed color)
What is the ratio of yellow to green seeds ?
Monohybrid Heterozygous CrossDraw a Punnett Square crossing 2 plants that are heteroygous for Y
What is the ratio of yellow to green seeds?
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MODELING MENDEL’S LAWS
Test Cross: used to test an individual whose phenotype for a given characteristic is dominant but its genotype is unknownIndividual is crossed with a
known homozygous recessive If unknown is homozygous dominant all offspring will show dominant phenotype
If unknown heterozygous for the trait then ½ the offspring will show dominant phenotype & ½ will show recessive trait
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MODELING MENDEL’S LAWS
Using ProbabilityProbability: the likelihood that a specific event will occur; expressed in mathematicsProbabilities are used to predict the likelihood that specific alleles will be passed down to offspring
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QUICK LAB: PROBABILITIES: PAGE 268
Notebook: page 15 Everyone completes this:
Follow procedureAnswer analysis questions 1 - 2
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MODELING MENDEL’S LAWS
Pedigree: a diagram that shows the occurrence of a genetic trait in several generations of a family
Genetic Disorder: an inherited disease that is caused by a mutation in a gene or by a chromosome defect
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PEDIGREES
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PEDIGREES
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PEDIGREES
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MODELING MENDEL’S LAWS
Pedigrees can help answer 3 aspects of inheritance:1. Sex linkage2. Dominance3. Heterozygocity
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MODELING MENDEL’S LAWS
1. Sex-Linked Gene1. Gene located on either the X or
Y chromosomes2. Females have 2 X
chromosomes so rarely show the recessive phenotype; males have just 1 X chromosome so will show the trait for a single recessive allele for genes on the X chromosome
3. If find a trait that is more common in males than females it is likely sex-linked
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GENES ON SEX CHROMOSOMES
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Sex-Linked
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MODELING MENDEL’S LAWS
2. Dominant or Recessive? If a child shows a trait and neither parent shows the trait it is likely a recessive trait
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MODELING MENDEL’S LAWS
3. Heterozygous or Homozygous?
Recessive trait in a child shows parents had to be heterozygous for the trait
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BEYOND MENDELIAN HEREDITY
Polygenic Character: a character influenced by more than 1 geneincludes many characters in humansEye colorSkin colorHeight
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BEYOND MENDELIAN HEREDITY
Incomplete Dominance: the phenotype for a heterozygous individual is intermediate between the homozygous dominant phenotype and the homozygous recessive phenotype
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BEYOND MENDELIAN HEREDITY
Genes that are said to have 3 or more possible alleles are said to have multiple allelesExample: human’s ABO blood
types
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BEYOND MENDELIAN HEREDITY
Codominance: a condition in which both alleles for a gene are fully expressed in the phenotype
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BEYOND MENDELIAN HEREDITY
Genes Affected by the EnvironmentNutrients available or
temperature can affect the expression of the genotype
ExamplesSome animals have fur that changes color with the seasons
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BEYOND MENDELIAN HEREDITY
During meiosis, genes that are close together on the same chromosome are less likely to be separated than genes that are far apart
Genes that are close together and the traits they determine are said to be linked (not just sex-linked)
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BEYOND MENDELIAN HEREDITY
Linked Genes