BIO 1 Chapter 11 Introduction to Genetics 11

BIO 1 Chapter 11 Introduction to Genetics

11 -1 The Work of Gregor Mendel § Gardener in Austrian monastery § Born 1822 § Called the “Father of Genetics” § Used pea plants because 1. Traits exist as clearly different forms ex: flower is white or purple 2. Both Male & female parts in plants, so self-fertilization can occur or can cross-pollinate 3. Small, grow easily, mature quickly You. Tube - Mendel - From the Garden to the Genome

§Heredity- passing on of characteristics from parents to offspring §Genetics- study of heredity or traits & characteristics

Mendel used “Selfpollinating” peas to produce future offspring § Knew that each flower produces both male (sperm –found in pollen) and female (egg) gametes § Fertilized flower’s egg with its own sperm § Produced what he called “true breeding” § Offspring would be genetically identical

Cross Pollination

Trait – specific characteristic that varies from one individual to the next § Important that Mendel used traits that were unambiguous

Monohybrid crosses- cross 1 pair of contrasting traits § P generation- parents, first two crossed § F 1 generation- first offspring, Px. P § F 2 generation- F 1 x F 1 §Plants that were products of cross -pollination are known as “hybrids. ”

Mendel’s Hypothesis 1. For each inherited trait, an individual has 2 copies of the gene, one from each parent 2. There alternative versions of genes = alleles (purple, white) 3. When two different alleles occur together, one of them may be expressed, while one is covered up

Definitions Mendel concluded that heredity is dictated by chemical factors called genes (about 100 years later before Watson & Crick and the whole DNA thing) §Genes have alternate forms depending on the plant § These alternate versions of the same gene are called alleles Plant height = gene Short and tall = alleles §Both alleles are present. §One type (recessive) can only be expressed if the other (dominant) is not present

Definitions § Dominant- expressed trait (D) § Recessive- not expressed (d) § Homozygous- both letters are same, either both capital or both lowercase (DD or dd) § Heterozygous- one of each, dominant allele is expressed (Dd) § Genotype- set of alleles (DD or Dd or dd) § Phenotype- physical appearance (purple or white flowers)

Laws § Law of Segregation- the 2 alleles separate when gametes are formed § Law of Independent Assortment- one trait doesn’t affect the inheritance of another (purple/white flowers has nothing to do with smooth/rough pod)

11 -2 Probability and Punnett Squares §Probability – likelihood of an event to take place § What are the chances for a coin to be flipped heads three times in a row? ½ X ½ = ⅛ §Probability explains everything in predicting outcomes of genetic crosses

Rules for combining probabilities 1. Probability that one event out of a set of mutually exclusive events will occur is the sum of their probabilities. (Mutually exclusive events cannot occur together. ) (Look for the word “or”. ) Ex. What is the probability of rolling a 3 or a 6 on a 6 -sided dice? p = 1/6 + 1/6 = 2/6 or 1/3

2. Probability that both of two independent events will occur is the product of the independent probabilities of the single events. (Independent events do not affect each other. )(Look for the word “and”. ) Ex. What is the probability that I roll a 1 and a 3 when rolling two 6 -sided dice? p = 1/6 x 1/6 = 1/36

Punnett Squares § 1 pair of traits: The letters represent alleles < Homozygous recessive Homozygous dominant All offspring are heterozygous

Genotypic Ratio ? 1. 2. 3. 4. Phenotypic Ratio?

7. A heterozygous round seeded plant (Rr) is crossed with a homozygous round seeded plant (RR). What percentage of the offspring will be homozygous (RR)? ______ 8. A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. What are the genotypes of the parents? _____ x _____ What percentage of the offspring will also be homozygous? ____

9. In pea plants purple flowers are dominant to white flowers. If two white flowered plants are cross, what percentage of their offspring will be white flowered? _______ 10. A white flowered plant is crossed with a plant that is heterozygous for the trait. What percentage of the offspring will have purple flowers? _______ 11. Two plants, both heterozygous for the gene that controls flower color are crossed. What percentage of their offspring will have purple flowers? _______ What percentage will have white flowers? ______

12. In guinea pigs, the allele for short hair is dominant. What genotype would a heterozygous short haired guinea pig have? _______ What genotype would a purebreeding short haired guinea pig have? _______ What genotype would a long haired guinea pig have? ____ 13. Show the cross for a pure breeding short haired guinea pig and a long haired guinea pig. What percentage of the offspring will have short hair? _____

14. Show the cross for two heterozygous guinea pigs. What percentage of the offspring will have short hair? ____ What percentage of the offspring will have long hair? _______ 15. Two short haired guinea pigs are mated several times. Out of 100 offspring, 25 of them have long hair. What are the probable genotypes of the parents? ____ x ______ Show the cross to prove it!

11 -3 Exploring Mendelain Genetics A. Independent Assortment 1. The Two-Factor Cross: F 1 2. The Two-Factor Cross: F 2 B. A Summary of Mendel’s Principles C. Beyond Dominant and Recessive Alleles 1. 2. 3. 4. Incomplete Dominance Codominance Multiple Alleles Polygenic Traits D. Applying Mendel’s Principles E. Genetics and the Environment

Dihybrid Crosses- § “FOIL” method § Aa. Bb x Aa. Bb

P X P F 1 generation= 100% Rr. Yy

F 1 X F 1 = F 2 generation 9 round, yellow: 3 round, green: 3 wrinkled yellow: 1 wrinkled, green

Practice RRBb X Rrbb

Practice rr. Bb X Rr. BB

3. A male rabbit with the genotype Gg. Bb. Determine the gametes produced by this rabbit (the sperm would have these combinations of alleles) Hint there are 4 combinations. 4. A female rabbit has the genotype gg. Bb. Determine the gamets (eggs) produced by this rabbit.

5. Use the gametes from #4 and #5 to set up the punnett square below. Put the male's gametes on the top and the female's gametes down the side. Then fill out the square and determine what kind of offspring would be produced from this cross and in what proportion.

Science Starter: An aquatic arthropod called a Cyclops has antennae that are either smooth or barbed. The allele for barbs is dominant. In the same organism, resistance to pesticides is a recessive trait. A Cyclops that is resistant to pesticides and has smooth antennae is crossed with one that is heterozygous for both traits. Show the genotypes of the parents and then complete a punnett square showing the results: _______ x ________ have barbed antennae and are not resistant to pesticides ______ have barbed antennae and are resistant to pesticides. _______ have smooth antennae and are not resistant to pesticides _______ have smooth antennae and are resistant to pesticides

8. Set up a punnett square for the cross. 9. What are the phenotypic ratios of the offspring?

Beyond Dominance and Recessiveness §Not all genes show simple patterns of dominant and recessive alleles. Genetics is more complicated. §The majority of genes have more than 2 alleles. §Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

Incomplete Dominance § A cross between two 4 -o’clock plants: § Red flowered RR § White flowered WW § Which is dominant? § Incomplete Dominance: Cases in which one allele is not completely dominant over another

Incomplete Dominance Examples § In horses, some of the genes for hair color are incompletely dominant. Genotypes are as follows: brown horses are BB, white horses are WW and a WB genotype creates a yellow-tannish colored horse with a white mane and tail, which is called “palomino”. Show the genetic crosses between the following horses and record the genotypic and phenotypic percentages: § 1. Brown x white § 2. Brown X palomino § 3. Palomino X palomino

Codominance §Similar to incomplete dominance however both traits are actually visual instead of blended § Chickens with speckled black spots on white feathers § Humans have gene for protein controlling cholesterol – if heterozygous two forms are made

§Multiple Alleles §When there are more than two alleles for a particular gene § Blood type (also demonstrates some codominance) Polygenic traits §Traits controlled by many genes § § § § Height SLE (Lupus) Weight Eye Color Intelligence Skin Color Many forms of behavior

Applying Mendel’s Principles §Good animal to test was fruit fly § Drosophilia melanogaster §Fast reproductive rate/life cycle and produced many offspring

Environmental impact on gene expression • Environmental factors/conditions may alter gene expression. § Example: Soil p. H and flower color.

11 -4 Meiosis A. Chromosome Number B. Phases of Meiosis 1. 2. Meiosis II C. Gamete Formation D. Comparing Mitosis and Meiosis

Meiosis §Process of turning diploid somatic cells into haploid gametes §Must reduce chromosome number so when fertilization takes place we re-establish the regular chromosome number § Humans § Hapolid – sex cells N = 23 § Diploid – somatic cells 2 N = 46

Figure 11 -15 Meiosis Section 11 -4 Meiosis I Go to Section:

Figure 11 -17 Meiosis II Section 11 -4 Meiosis II Prophase II Metaphase II Anaphase II Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Go to Section: Telophase II Meiosis II results in four haploid (N) daughter cells.

Crossing Over § Parts of chromosomes “switch places § A tetrad forms in prophase 1 § 4 chromosomes to a tetrad

Gamete Formation § Figure 11 -17 on page 278 § Males § Animals = sperm § Flowering plants = pollen § 4 equal sized gametes § Females § Animals = egg § Flowering plants = ovule § Only 1 large egg results from meiosis, the other 3 cells are called polar bodies and not involved in reproduction.

Mitosis VS. Meiosis Mitosis Purpose Location in Body Number of Daughter Cells Change in chromosome number Number of phases Number of Cell Divisions Difference in DNA between parent cell and daughter cell Meiosis

11 -5 Linkage and Gene Maps §Found that some genes were linked to other ones § Seems to violate the rule of independent assortment § Ex: fruit flies – red eyes and miniature wings §Mendel missed this…. § He thought the genes independently assorted § Actually it was the chromosomes that do! § Why did he miss it? § 6 of the 7 genes he studied in peas were on separate chromosomes § The two that were on the same chromosome were so far apart they independently assorted

Gene Maps §Do two genes on the same chromosome mean they are forever linked? § No! Crossing over may put them on separate chromosomes §The further apart genes are the more likely they could be separated during meiosis §Low rate of separation and then recombination means genes are close to one another.