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GENETICS Ch. 12 *Definition: the study of heredity

GENETICS Ch. 12 *Definition: the study of heredity. ~ heredity : the passing of traits from parent to offspring. Gregor Mendel the “Father of Modern Genetics” 12.1. Austrian monk 1860’s used garden pea plants  why? 3 reasons:

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GENETICS Ch. 12 *Definition: the study of heredity

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  1. GENETICS Ch. 12*Definition: the study of heredity ~heredity: the passing of traits from parent to offspring.

  2. Gregor Mendelthe “Father of Modern Genetics”12.1 • Austrian monk • 1860’s • used garden pea plants  why? 3 reasons: 1. the structure of the pea flowers (usually self-pollinates). 2. the presence of contrasting traits. 3. rapid reproductive cycle (~90 days).

  3. *Mendel studied 7 distinct characters (physical features that are inherited; ex. flower color)…pg. 268 • Trait: one of several possible forms of a character; ex. purple or white • Mendel’s experiments used monohybrid crosses in order to study one pair of contrasting traits (ex. purple vs. white for flower color). • P generation  F1  F2 (true-breeding parents) (1st filial) (2nd filial) ***LEAVE SOME SPACE HERE IN YOUR NOTES 

  4. -VOCAB- • ~purebred: an organism that receives the same genetic traits from both of its parents (*self-pollination in plants). • ~hybrid: an organism that receives different forms of a genetic trait from each parent (purple X white).

  5. Mendel and Modern Genetics 12.2 • gene: sections of a chromosome that code for a trait. *most organisms have 2 copies of every gene and chromosome (1 from each parent) …remember “homologous chromosomes” from meiosis AND the karyotype activity? • allele: different versions of a gene (ex. tall vs. short for plant height)…T and t • dominantallele: the expressed form of a gene when 2 different alleles are present. *ex. Tt (T is dominant; the plant is tall) • recessiveallele: a form of a gene that is not expressed when the dominant allele is present (masked). *ex. Tt…tall; short is only expressed when in the form of tt

  6. genotype: the set of alleles an individual has for a character. *genetic makeup -includes both genes in a homologous pair of chromosomes. -ex. Rr, rr, RR • phenotype: the trait that results from a set of alleles. • *-ex. tall, short, purple, white. • Genotype determines phenotype!

  7. homozygous: 2 alleles in a gene pair are identical. • heterozygous: 2 alleles in a gene pair are different. • Punnettsquare: shows the expected outcomes of a genetic cross. *shows all possible combinations of gametes. (ch.12.3) • Probability: the likelihood that a specific event will occur. • --can be written as a %, fraction, ratio, or in words) • EXAMPLES

  8. Test Cross: used to determine an organism’s genotype. -done by breeding the organism whose genotype is unknown with a homozygousrecessive organism (known genotype). -ex. G = green (dominant) g = yellow (recessive) -Question: what is the genotype of a plant with green peas?...to find the answer, we can perform a test cross.

  9. Mono vs. Dihybrid Crosses • http://images.google.com/imgres?imgurl=http://www.gwu.edu/~darwin/BiSc150/One/codominance.GIF&imgrefurl=http://www.gwu.edu/~darwin/BiSc150/One/genetics.htm&h=177&w=391&sz=3&hl=en&start=4&um=1&tbnid=7ny9gScMBApx-M:&tbnh=56&tbnw=123&prev=/images%3Fq%3Dcodominance%26svnum%3D10%26um%3D1%26hl%3Den%26sa%3DN • Monohybrid Cross: predicts the offspring of a cross for onetrait (ex. plant height). • Dihybrid Cross: predicts the offspring of a cross for twotraits (ex. plant height and seed shape).

  10. Patterns of Inheritance 12.4 • Sex-linked genes: genes that are located on the sex chromosomes (X or Y)…mostly found on the X chromosome; ex. Colorblindness • Polygenic inheritance: when more than 1 gene controls a character; ex. eye color, height, skin color. • Multiple alleles: when genes have 3 or more possible alleles; ex. blood type (3 alleles with 4 different blood types).

  11. Continued… • Incomplete dominance: occurs when neither allele is completely dominant over the other; neither allele is fully expressed; ex. red snap dragon X white snap dragon = ? • Codominance: when both alleles for the same gene are fully expressed; ex. AB blood type

  12. Weekend Homework: • Explain the genetic basis for Mendel’s laws of segregationandindependent assortment. (hint: think about meiosis and gamete formation…answers are found in chapter 12!) • Due Monday…no late papers accepted. • Start studying NOW 

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