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Mendelian Genetics

Mendelian Genetics. The Pea Plant. Peas reproduce sexually (they produce two different gametes - male and female) Pollination = transfer of male pollen to pistil Fertilization = uniting of male and female gametes POLLEN + OVULE  SEED

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Mendelian Genetics

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  1. Mendelian Genetics

  2. The Pea Plant • Peas reproduce sexually (they produce two different gametes - male and female) • Pollination= transfer of male pollen to pistil • Fertilization= uniting of male and female gametes POLLEN + OVULE  SEED • Self-pollination= flower pollinates itself; male and female gametes come from same plant • Cross-pollination= male and female gametes come from different plants

  3. Gregor Mendel • 1850’s Austrian monk and gardner • “Father of Genetics” (study of heredity) • Heredity= passing on of traits from parent to offspring • Traits= characteristics that are inherited Mendel’s garden

  4. Mendel’s Experimental Methods • Mendel hand-pollinated flowers using a paintbrush • He could snip the stamens to prevent self-pollination • Covered each flower with a cloth bag • He traced traits through the several generations

  5. Mendel’s Studies • He first studied one trait at a time (the first trait he studied was the height of pea plants) • Monohybrid cross= mating between parents that only differ by ONE trait (Other traits he studied: flower position, flower color, seed color, pod color, seed shape, pod shape)

  6. Mendel’s Studies

  7. Mendel’s Studies Mendel tested 6 more traits. In every cross, one trait disappeared in F1, then reappeared in a ration of ¼ in the F2 plants. *Remember- a good science experiment must give reproducible results! P1 (Parent) Generation: X Cross-pollinate F1 (filial) Generation: Hybrids= offspring of parents with different forms of the same trait Self-pollinate F2 Generation:

  8. Mendel’s Laws From his pea plant experiments, Mendel came up with rules or “laws” about how traits are passed down from parent to offspring: • Rule of Heritable Factors: EACH ORGANISM HAS 2 COPIES OF A GENE THAT CONTROLS EACH TRAIT; ONE COPY CAME FROM THE MALE PARENTS AND ONE COPY CAME FROM THE FEMALE PARENT • Each chromosome has genes (a gene is a piece of DNA that controls a trait- ex. height)

  9. Mendel’s Laws • There can be different forms of the same gene; these different forms are called alleles. ex. For the height gene, the alleles are tall and short • The offspring can inherit any combination of alleles from the parents ex. Tall + tall, short + short, tall + short, or short + tall

  10. 2. Rule of Dominance ALLELES CAN BE DOMINANT OR RECESSIVE; THE DOMINANT ALLELE, IF PRESENT, COMPLETELY MASKS THE RECESSIVE ALLELE Dominant Trait- remained in the F1 generation (ex. tall) Recessive Trait- disappearned in F1 (ex. short) So we say that tall is dominant to short. When writing alleles, follow these rules: Use the same letter for different forms of the same gene. Use uppercase letter for dominant allele. Use lowercase letter for recessive allele. Always write dominant allele first. Example: height T = tall t = short A plant can be: TT tall Tt tall tt short Mendel’s Laws

  11. Punnett Square • Used to help solve genetics problems

  12. Mendel’s Laws 3. Law of Segregation THE TWO ALLELES THAT CONTROL EACH TRAIT WILL SEPARATE DURING GAMETE FORMATION TT X tt Result: Tt (all tall) Then Tt Tt X Result: TT, Tt (tall) and tt (short)

  13. Mendel’s Laws 4. Law of Independent Assortment TRAITS ON DIFFERENT CHROMOSOMES ARE INHERITED INDEPENDENTLY OF ONE ANOTHER • This can be seen in dihybrid crosses. For example, • Round Yellow seeded hybrid crossed with a Round, Yellow seeded hybrid (RrYy x RrYy)

  14. Other Important Information: • Phenotype = written description of appearance/behavior • Examples: tall and short BUT, two organisms can look the same but have different gene (or allele) combinations*: • Genotype = 2-letter gene combination • Examples: TT, Tt, tt *Note: TT and Tt are both genotypes for the same phenotype, tall

  15. Other Important Information: There are 3 different types of genotypes: homozygous dominant (TT) homozygous recessive (tt) heterozygous (Tt) Homo- means same Hetero- means different FYI: homozygous is the same as PUREBRED heterozygous is the same as HYBRID

  16. JUST A LITTLE PRACTICE

  17. Steps to Solving Genetics Problems-When solving genetics problems, ask yourself the following: • What’s dominant? • What letter do I use? What are my possible combinations? • What am I crossing? (What are parents’ genotypes?) • How do I set up my punnettsquare? • What is the answer to the problem I’m trying to solve?

  18. Example • Tall pea plants are dominant to short plants. A farmer crossed a homozygous tall plant with a short plant. How many of the offspring will be tall plants?

  19. Steps to Solving Genetics Problems • Identify the dominant trait. (ex. Tall is dominant to short.) • Use the first letter of the dominant trait to represent each possible combination of alleles in the problem. (TT= tall, Tt= tall, tt= short) • Identify the parents’ genotypes, and write out what the cross would be. (Homozygous tall crossed with short is TT x tt.) • Set up your punnett square. Put one parent’s alleles on one side, and the other parent’s on the other side. • Solve your punnett square. Answer the question. T T Tt Tt t 100% will be tall plants. t Tt Tt

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