Notes: Mendelian Genetics - Center Grove Elementary School
Homework: Finish Monohybrid Cross Lab IN.S.S. Core Standard 8.3 * I can explain the predictability of characteristics being passed down from parent to offspring. Agenda 1. TradeNGrade Genetic Profile
2. Mendel and Genetics Notes 3. Begin Monohybrid Cross Lab THURSDAY 04.11.13 WEEK 3 Reproduction Review Reproduction Review
Hint: Use your Chapter Review from Last Unit! Mitosis copying and splitting of cells Meiosis the creation of 4 haploid sex cells
Fertilization the combination of 2 haploid sex cells to create a zygote Zygote the single diploid cell with complete set of chromosomes, from mom, and from dad. Homologous a certain set of chromosomes (from mom and dad) Haploid single set of chromosomes Diploid full set of chromosomes Meiosis Replication occurs. Each
chromosome is copied to prepare for division. Here is one set of chromosomes. For example, the two sets of chromosome #5. These are homologous chromosomes. and it is a diploid (2n) cell. The light blue came from this organisms mother, and the dark blue was from dad.
Crossing over occurs. The first division: Homologous chromosomes separate. We now have haploid (n) cells with replicated chromosomes. The second division occurs and the replicated chromosomes separate. We end with 4 haploid
(n) cells with unreplicated chromosomes. Notes: Mendelian Genetics Heredity is passing characteristics from one generation to the next. Genetics is the study of heredity.
Who was Gregor Mendel? Gregor Mendel is the Father of Modern Genetics. He was an Austrian monk who studied heredity in pea plants. His work was published in 1865. He described factors that were passed between generations of plants. We now know the factors are genes: chemical factors that determine characteristics.
Mendel observed true-breeding pea plants produced genetically identical offspring. ex. Tall plants produced tall offspring, short produced short. True-breeding plants self-pollinate. (have both male and female parts) Mendels Peas Mendel studied seven different traits in pea plants. - Traits are inherited characteristics that vary
from individual to individual. oEach trait each had two different forms or alleles. oPea plant height can be either tall (T) OR short (t). oAllele the different possible forms of a trait Mendels Peas Homozygous means to have 2 identical alleles for a trait. Ex. TT or tt True-breeding pea plants are
homozygous. Heterozygous means to have 2 different alleles for a trait. Ex. Tt Hybrid plants are heterozygous. Generations of Pea Plants P = Parent generation = your parents F1 = First generation offspring. = you Produces hybrids = crosses between parents with different traits (Tall x short)
(TT x tt) F2 = Second generation offspring. = your kids Formed from hybrid x hybrid. (Tt x Tt) (F1 x F1) Mendels Experiment: TT x tt Question: True-breeding tall x true breeding short? (P generation) Hypothesis: Mendel expected medium-sized plants in F1 generation.
Method: He cross-pollinated plants, taking pollen from one flower onto another. Results: F1 generation = hybrid generation All plants were TALL, not medium as expected. Mendels Experiment: TT x tt Genotypic ratio (genetic makeup): 0TT: 4 Tt : 0 tt Phenotype
(physical appearance): 4 Tall : 0 short Conclusion: Principle of Dominance: some alleles are dominant and others are recessive T T
t Tt Tt t Tt Tt
Principle of Dominance Dominant traits are expressed if only one allele is present. (capital letter, first letter of trait ex. Tall= T) Ex - Tall allele (T) is dominant and short allele is recessive (t) F1 generation = All plants were tall even though Tt both TT and Tt plants are Tall
Principle of Dominance Recessive traits are expressed when the dominant allele not present. Two alleles are needed for the recessive trait to be expressed. (lower case letter) Ex from pea plants- short allele is recessive (t) Only tt plants are short. Principle of Dominance The Principle of Dominance explains why
genotype differs from phenotype. Genotypes for plant height are TT, Tt, tt. Genotypes can be heterozygous or homozygous. Phenotypes for plant height are tall or short. TT and Tt genotypes both expressed the tall phenotype because the T is dominant to t. Only the tt genotype expressed the short phenotype. Mendels Experiment: Tt x Tt
Question: Have the recessive alleles disappeared? Hypothesis: The F2 generation will be all tall plants. Method: F1 x F1 Tt x Tt = Mendel allowed the hybrids to self-pollinate T
t T TT Tt t
Tt tt Mendels Experiment: Tt x Tt Result: F2 Generation genotypic ratio: 1 TT : 2 Tt : 1 tt phenotypic ratio: 3 tall: 1 short The recessive alleles
reappeared and were expressed. T t T TT
Tt t Tt tt Mendels Experiment: Tt x Tt Conclusion: Principle of Segregation: 2 alleles for a trait separate
during meiosis. Each gamete receives only one allele. * The alleles are on separate homologous chromosomes. T and t separated (segregated) during meiosis, and each gamete received only T or t. Principle of Segregation During fertilization, a t gamete fertilized a t gamete 1/4 of the time, resulting in tt short plants. This accounts for new combinations of
alleles that were not present in either parent. Principle of Segregation TT T Tt T
T tt t GAMETES t t
Principle of Segregation Punnett Squares A Punnett square is a diagram that predicts outcomes of genetic crosses. use dominance to determine phenotype from genotype Ex. #1 In humans, having dimples is dominant to not having dimples. Predict the genotypic and phenotypic ratios of a cross between a man heterozygous for dimples and a woman without dimples.
D = dimples d = no dimples Equation: Dd x dd Genotypic ratio: 0DD: 2 Dd: 2 dd Phenotypic ratio: 2 dimples: 2 no dimples D
d d Dd dd d
Dd dd Summary Genotype genetic makeup of individual (letters) Phenotype physical expression of individual Allele the different forms of a trait Dominant the trait is expressed with only one allele
Recessive = the trait is only expressed if both alleles are present Link: Mendel Rap Lryics:
The answers in my garden where Ive planted different peas And sprinkled pollen as I pleased then counted out the progeny. What did you discover in your garden with your peas? About those factors we cant see but which explain our family trees? Heres the news. They come in twos. They separate. Its up to fate. If an egg or a sperm has a trait that will dominate. And when they join together, my forecastings most impressive. Bet you, three times out of four Im right unless theyre both recessive. But where these hidden factors are well that I cannot fathom.
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