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Transcript
Genetics Chapter 11 Gregor Mendel Austrian monk that had an interest in science Worked with pea plants at the monastery Had a background in math and science Proved valuable research in heredity Gregor Mendel Taught high school science Kept a garden plot of pea plants Observed 7 characteristics of pea plants Each trait had 2 possible outcomes Gregor Mendel Recorded plant seeds and planted them Noticed purple plants all came from purple seeds White plants also grew from these seeds Noticed a pattern in height Began his study on controlling pollination Pollination • When pollen grains produced by male part of a flower are transferred to female part of the flower Self-Pollination • When pollen is transferred from anthers to stigma of same plant or another flower on same plant Cross Pollination • When pollen is transferred between two plants Gregor Mendel • To control the pollination, Mendel removed the anther of the pea plants • Used pollen from anthers to cross pollinate and control traits passed to next generation Mendel’s Experiments • True-breeding plants • Plants that only produce offspring with same characteristics every time • • Ex: true-breeding yellow pod plants only produced yellow pods in next generation Mendel used true-breeding plants to test for passed on traits P Generation • Mendel himself cross-pollinated pairs of plants that were true-breeding parents • Known as P generation F1 Generation • Mendel recorded next generation of pea plants characteristics • Known as F1 generation F2 Generation • The F1 generation were able to self-pollinate to make a new generation • Known as F2 generation Mendel’s Results • Recessive and Dominant Traits • Dominant traits were seen more often • These traits mask or dominate other traits • Ex: Brown eyes are dominant over blue • Recessive traits are seen less often https://www.youtube.com/watch?v=mnSkz8s-b44 Mendel’s Results • Law of Segregation • Law states that pair of factors is separated during formation of gametes (meiosis) • Making gametes (sperm and egg) produces haploid cells with only one half the amount of chromosomes Mendel’s Results • Law of Independent Assortment • Traits do not necessarily appear together • The trait for pod seed color is not associated with the flower color • They are independent traits • Random separation during meiosis Mendel’s Conclusions • Molecular genetics • Study of heredity on the chromosomal level • Factors that Mendel was testing are known as alleles on a chromosome • Area of a chromosome that determines a specific trait https://www.youtube.com/watch?v=Mehz7tCxjSE Alleles • Alleles are represented with letters • Ex: Dominant (P) recessive (p) Genotype/Phenotype Genotype: bb • Genotype: BB, Bb Genotype • Genetic makeup of an organism • Consists of 2 allele letters • Can determine phenotype from genotype • Ex: Brown eyes (BB or Bb), blue eyes (bb) Genotype/Phenotype Phenotype: blue eyes • Phenotype: brown eyes Phenotype • Physical appearance that is seen • Phenotypes cannot always tell you the genotype • Ex: brown or blue eyes Genotype/Phenotype • • Homozygous • When the two alleles are the same • Ex genotype: BB or bb Heterozygous • When the two alleles are different • Ex genotype: Bb Probability Punnett Squares • Monohybrid Cross • Cross of one characteristic from two organisms • Ex: eye color Mom: BB (brown) Dad: bb (blue) Example 1 • Homozygous x Homozygous • Ex: Homozygous purple plants x homozygous white plants • Genotypes: P = purple p = white Example 2 • Homozygous x Heterozygous • Ex: Homozygous black guinea pigs x heterozygous black guinea pig • Genotypes: B = black b = white Example 3 • Heterozygous x Heterozygous • Ex: Heterozygous black coat rabbit x Heterozygous black coat rabbit • Genotypes: B = black b = white Testcross • To test for unknown genotype • Unknown individual is crossed with a homozygous recessive individual • If the results are only phenotype dominant, unknown individual is homozygous dominant • If the results show some phenotype recessive, unknown individual is heterozygous Dihybrid Crossing • Dihybrid Cross • Cross of 2 characteristics • Harder to predict because more possible results Example 1 • Homozygous x Homozygous Ex: Homozygous wrinkled, green peas x homozygous round, yellow Genotypes: Example 2 • Heterozygous x Heterozygous Ex: Heterozygous round, yellow peas x Heterozygous round, yellow peas Genotypes: Example 5 • Incomplete dominance • When the phenotype of a heterozygous individual is an in between of the two parents • Ex: four o’clock flowers RR RW WW Example 6 • Codominance • When both alleles are expressed at the same time • Three possible phenotypes • Both alleles are dominant • Ex: Red & white flowers Codominance • Blood Typing • There are 4 possible blood types • A, B, AB, & O • A and B are both dominant • O is recessive • Use letter I to show genotype Polygenic Inheritance • A trait that is influenced by many genes • Poly = many • Genic = genes • Usually show degrees of variation • Ex: skin color, height http://www.tate.org.uk/context-comment/video/tateshots-roman-ondak-measuring-universe Multiple Alleles • Genes with 3 or more alleles • • Ex: Blood types (IAIB,IAIA, IBIB, IAi, IBi, ii) This shows both codominance and multiple alleles Chromosomes • Thomas Hunt Morgan • Worked with fruit flies (Drosophila) and noticed they have 4 pairs of chromosomes • Males and females have one pair of different sized chromosomes (X and Y chromosomes) Meiosis • • • Process of making gametes • Males = sperm • Females = eggs Gametes are haploid cells • 23 chromosomes (no pairs!) End result is 4 nonidentical daughter cells Meiosis I • Prophase I • DNA condenses to chromosomes • Spindle fibers from centrioles appear • Homologous chromosomes pair up called a synapse • Pair of homologous chromosomes is called a tetrad Meiosis I • Prophase I • Tetrads exchange genetic info to mix up possible genes • Called crossing over • When tetrads cross over, they create recombinant DNA • This is the reason why daughter cells are non-identical Meiosis I • Metaphase I • Tetrads line up randomly along middle of cell Meiosis I • Anaphase I • Tetrads separate to opposite poles of the cell • This is a RANDOM process • Random assortment of genes Meiosis I • Telophase I & Cytokinesis I • Chromosomes reach opposite side of the cell and cytokinesis begins • Creates 2 non-identical daughter cells Meiosis II • Prophase II • Nucleus disappears • Chromosomes begin to move • Spindle fibers form • NO DUPLICATION OF CHROMOSOMES! Meiosis II • Metaphase II • Chromosomes line up in the middle of the cell • Anaphase II • Chromosomes split apart to sister chromatids Meiosis II • Telophase II & Cytokinesis II • Nuclear membrane forms • Chromosomes break down to chromatin • Creates 4 non-identical daughter cells that are haploid • Only one sister chromatid of each chromosome Sexual Reproduction • Production of offspring through meiosis and the union of a sperm and egg • After fertilization, the egg is called a zygote • The zygote undergoes division and becomes a new organism Mitosis vs. Meiosis