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Mendel and Heredity

Learn about Gregor Mendel and the principles of heredity and genetics, including terms like alleles, genotype, phenotype, and Punnett squares. Explore topics such as dihybrid crosses, sex-linked genes, incomplete dominance, and DNA structure and replication.

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Mendel and Heredity

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  1. Mendel and Heredity

  2. Mendel and Heredity Terms • Gregor Mendel- “Father of Genetics” • Traits- characteristics that are inherited • Ex. Eye color, hair color • Genetics- study of biological inheritance patterns • Purebred- offspring inherit all of parents characteristics, genetically uniform

  3. Mendel and Heredity Terms • Cross- mating of two organisms • Gene- piece of DNA that provides a set of instruction to a cell • Allele- any alternative form of a gene that may occur

  4. Mendel and Heredity Terms • Homozygous- two of the same alleles • Heterozygous- two different alleles

  5. Mendel and Heredity Terms • Genotype- genetic makeup of a specific set of genes • Phenotype- physical characteristics or appearance of an organism • Dominant- allele is expressed when two different alleles are present • Recessive- allele is expressed only when two copies are present

  6. Genetics • In the 1800’s, Gregor Mendel laid the groundwork for modern genetics • He crossed many pea plants and observed traits of offspring • Discovered that • Organisms inherit two copies of each gene, one from each parent

  7. Genetics • Peas either: • Round (dominant) • Wrinkled (recessive) • GenotypesPhenotypes • RR (homozygous dominant) -round • Rr (heterozygous) -round • rr (homozygous recessive) -wrinkled

  8. Genetics • Another example: • Brown (dominant) vs. black (recessive) • Genotypes? Phenotypes?

  9. Genetics • Mendel’s discoveries led to the Punnett square • Developed by R.C. Punnett • Used to predict genotypes of offspring • Example: • Straight (dom.) vs. curly (rec.) • Dad-heterozygous • Mom-homozygous recessive

  10. Dihybrid Punnett Square • Predicting more than one trait • EX. Cross a tall pea plant with green leaves with a short pea plant with yellow leaves. • Determine parent genotypes. • Find combinations of alleles. • Fill out Punnett square. • Determine phenotypes of offspring.

  11. Dihybrid Punnett Square • EX. Cross a tall (homozygous) pea plant with green (heterozygous) leaves with a short pea plant with yellow leaves. (Tall is dominant to short, green is dominant to yellow)

  12. Dihybrid Practice • Cross the parents SsYy x SsYy SY Sy sY sy SY Sy sY sy Smooth/Yellow __9____ Smooth/Green ___3___ Rough/Yellow ____3__ Rough/Green _____1_

  13. Bellringer:Complete both questions in your notebook • 1. In one particular species of cats, long hair is dominant to short hair. If a heterozygous male is crossed with a homozygous recessive female, what is the probability that one of the offspring has long hair? • 2. A homozygous dominant flower is crossed with a homozygous recessive flower. Purple flowers are dominant to red flowers. What are the genotypes and phenotypes of the offspring?

  14. Sex-linked Genes • Sex-linked genes- genes located on the sex chromosomes • Female (XX), Male (XY) X Y X X

  15. Incomplete Dominance • Alleles that show incomplete dominance show both the dominant and recessive traits • Neither allele is completely dominant or recessive • Ex. If a homozygous red flower and homozygous white flower cross, the offspring have pink flowers

  16. Codominance • Both the dominant and recessive alleles are expressed • Ex. Red and white flower are crossed, the offspring will be red and white

  17. Exit Slip • Sex linked genes are located ______________. 2. A dog that shows the phenotypes of both his mother and father would be an example of (incomplete or codominance). 3. A blue flower crosses with a yellow flower to produce a green flower. This is an example of (incomplete or codominance).

  18. Pedigree • Pedigree- chart that can help trace phenotypes and genotypes in a family • Helps to determine if people carry the recessive allele

  19. Pedigree

  20. Pedigree • Reading a pedigree

  21. Example ○ □ □ ○ □ How many boy children? How many girl children? Is the oldest child a boy or girl?

  22. Griffith Experiment

  23. DNA Structure • DNA is a polymer made of monomers called nucleotides • Each nucleotide is made of: • A phosphate group • Deoxyribose (sugar) • Nitrogen containing base

  24. Types of Nucleotides • C – Cytosine Pyrimidines • T – Thymine • A – Adenine Purines • G – Guanine

  25. Base-Pairing Rules • Nucleotides always pair in the same way • Thymine (T) always pairs with Adenine (A) • Cytosine (C) always pairs with Guanine (G) • Ex. TTACGTAG AATGCATC

  26. DNA Structure • DNA is in the shape of a double helix • Each nucleotide is paired

  27. Exit Slip • Thymine is an example of a _____________. • nucleotide 2. The shape of DNA is known as a ___________. • Double helix 3. Write the DNA base pair: TCGGAATCCACGTG _______________ • AGCCTTAGGTGCAC

  28. DNA Replication • Replication is a process by which DNA is copied • Occurs during the S stage of the cell cycle

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