Presentation on theme: "CHAPTER 11 MENDEL & HEREDITY SC STANDARD B 4: The student will understand the molecular basis of heredity."— Presentation transcript:
CHAPTER 11 MENDEL & HEREDITY SC STANDARD B 4: The student will understand the molecular basis of heredity.
E SSENTIAL Q UESTION How does segregation of alleles contribute to genetic variation?
O RIGINS OF H EREDITARY S CIENCE Mendel Breeding Experiments Genetics: is the science of heredity &the mechanism by which traits are passed from parents to offspring Mendel born 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
M ENDEL S E XPERIMENTS Mendel spent 2 years preparing his control plants to insure they were true breeders describes organisms that are homozygous for a specific trait so always produce offspring that have the same phenotype for that trait
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
M ENDEL S E XPERIMENTS male parts were removed from 1 st flower pollen taken from male parts of 2 nd flower pollen from 2nd brushed onto female parts of 1 st flower
M ENDEL S E XPERIMENTS 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
M ENDEL S E XPERIMENTS 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
M ENDEL S E XPERIMENTS 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 grow 1. Matures quickly 2. Needs little care 3. Produces many offspring
M ENDEL S E XPERIMENTS Monohybrid Cross: 3 Steps 1. Produced a true-breeding parent generation (P generation) 2. Produced 1 st filial generation ( F 1 generation) 3. Produced 2 nd filial generation ( F 2 generation)
M ENDEL S E XPERIMENTS True breeding purple True breeding white
M ENDEL S E XPERIMENTS Step 2: cross pollinated parents F 1 generation all purple Self-pollinated F 2 generation 3 : 1 purple to white
M ENDEL S E XPERIMENTS 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
Ratios in Mendels Results F 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
M ENDEL S T HEORY Explains simple patterns of inheritance 2 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
M ENDEL S T HEORY 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 pre sent
M ENDEL S T HEORY 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
M ENDEL S T HEORY : L AW OF S EGREGATION OF A LLELES
M ENDEL S T HEORY GENOTYPE: a specific combination of alleles in an individual….. the genes an individual has example: AA, Aa, or aa PHENOTYPE : the detectable trait or traits that result from the genotype of an individual….. the physical appearance an individual has example: normal, normal, albino
M ENDEL S T HEORY GENOTYPE DETERMINES PHENOTYPE !
M ENDEL S T HEORY The genotype of each of the peas is ____________.
M ENDEL S T HEORY The phenotype of each of the following is _____.
M ENDEL S T HEORY Homozygous: describes an individual that carries two identical alleles of a gene Example: PP or pp Heterozygous: describes an individual that carries two different alleles of a gene Example: Pp
M ENDEL S T HEORY Mendels 2 nd Experiments Dihybrid crosses: involves test crossing two characters Law of Independent Assortment: during gamete formation, the alleles on non-homologous chromosomes segregate independently
P ROBLEM S OLVING : P RODUCING T RUE -B REEDING S EEDS Textbook page 271 Work in table groups Define the problem Organize information Create solution Present to class
M ENDEL S T HEORY When genes are close together on same chromosome they will rarely separate independently so are said to be linked.
M ODELING M ENDEL S L AWS Punnett Square: a graphic used to predict the results of a genetic cross
M ODELING M ENDEL S L AWS A Punnett Square shows all the genotypes that could possibly result from any given cross match.
M ODELING M ENDEL S L AWS Monohybrid Homozygous Cross Draw 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 Cross Draw a Punnett Square crossing 2 plants that are heteroygous for Y What is the ratio of yellow to green seeds?
M ODELING M ENDEL S L AWS Test Cross: used to test an individual whose phenotype for a given characteristic is dominant but its genotype is unknown Individual 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
M ODELING M ENDEL S L AWS Using Probability Probability: the likelihood that a specific event will occur; expressed in mathematics Probabilities are used to predict the likelihood that specific alleles will be passed down to offspring
Q UICK L AB : P ROBABILITIES : PAGE 268 Notebook: page 15 Everyone completes this: Follow procedure Answer analysis questions 1 - 2
M ODELING M ENDEL S L AWS 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
M ODELING M ENDEL S L AWS Pedigrees can help answer 3 aspects of inheritance: 1. Sex linkage 2. Dominance 3. Heterozygocity
M ODELING M ENDEL S L AWS 1. Sex-Linked Gene 1. Gene located on either the X or Y chromosomes 2. 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
M ODELING M ENDEL S L AWS 2. Dominant or Recessive? If a child shows a trait and neither parent shows the trait it is likely a recessive trait
M ODELING M ENDEL S L AWS 3. Heterozygous or Homozygous? Recessive trait in a child shows parents had to be heterozygous for the trait
B EYOND M ENDELIAN H EREDITY Polygenic Character: a character influenced by more than 1 gene includes many characters in humans Eye color Skin color Height
B EYOND M ENDELIAN H EREDITY Incomplete Dominance: the phenotype for a heterozygous individual is intermediate between the homozygous dominant phenotype and the homozygous recessive phenotype
B EYOND M ENDELIAN H EREDITY Genes that are said to have 3 or more possible alleles are said to have multiple alleles Example: humans ABO blood types
B EYOND M ENDELIAN H EREDITY Codominance: a condition in which both alleles for a gene are fully expressed in the phenotype
B EYOND M ENDELIAN H EREDITY Genes Affected by the Environment Nutrients available or temperature can affect the expression of the genotype Examples Some animals have fur that changes color with the seasons
B EYOND M ENDELIAN H EREDITY 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)