Transcript File
Mendelian Genetics 6A introduction to Genetics Mendel Austrian monk Father of modern genetics Law of Segregation Law of Independent Assortment Mendel’s Experiment Mendel performed experiments on garden pea plants Looked at the features shown in each plant generation after generation Mendel’s Experiment Found that features of one generation may not show up in the next generation, but may reappear in the 3rd generation Performed many experiments and came up with the basis for modern genetics Why did he use pea plants? Easy to grow, lots of offspring, simple traits that are easy to see and can control the pollination Mendel’s Peas When Mendel began his investigation, he cross-pollinated pea plants with purple flowers with a pea plants with white flowers This was his P generation The F1 generation then had ALL purple flowers Mendel’s Peas Not only did the F1 generation have all purple flowers… But when he allowed the F1 generation to self-pollinate, the F2 generation… Had both purple and white! Mendel’s Peas Being confused by why this happened, Mendel recorded data on 6 other characters Mendel’s Peas After many, many generations and lots a data, Mendel found that… For every character he observed, the ratio of one trait over another was 3:1 Three purple flowered plants to every 1 white flowered plant How do we explain this? More Vocabulary GENE Segment of DNA that codes for a protein and thus coded for a trait Gene for eye color Gene for height We get one copy of DNA from mom and one copy of DNA from dad Gene refers to all of the DNA needed for one trait (both mom and dad) Genes There are alternate forms of every gene Flower color – purple or white Allele One of the multiple forms of one gene One allele from mom and one allele from dad together make one gene Genes Meiosis Meiosis creates ___?___ cells HAPLOID Those haploid cells deliver the alleles from mom and alleles from dad to make up your genes Alleles Dominant Allele Describes an allele that is fully expressed whenever it is present Recessive Allele Describes an allele that is expressed only when a dominant allele is not present Dominant vs. Recessive Dominant Alleles = Capitol letters Recessive Alleles = Lowercase letters T = tall pea plant t = short pea plant NOTE: for plant height there is only one letter (T) capitol means tall, lowercase means short, but the letter is always T (not s for short) Dominant vs. Recessive Any time a dominant allele is present, that trait will be expressed TT (tall) Tt (tall) If NO dominant allele is present, the recessive trait will be expressed tt (short) Review Meiosis Diploid Haploid TT T TT T T T Review Meiosis Diploid Haploid tt t TT t T T Review Meiosis Diploid Haploid Tt T Tt t T t Review of Meiosis In meiosis, cells divide Start with DIPLOID, end with HAPLOID Homologous pairs separate Sister chromatids separate TWO copies of each gene. Sexually reproducing organisms have two copies of each gene. One from a female parent, one from a male. (Homologous Pairs) Mendel’s 1st Law Law of Segregation Parent has two alleles During meiosis, alleles separate into different gametes Each gamete produced has the same chance of receiving any given allele Alleles are separated randomly during meiosis Law of Segregation If dad is Tt… Any gamete produced, has the same chance as being T as it does being t. Separately randomly 50-50 chance either way Mendel’s 2nd Law Law of Independent Assortment Alleles separate during meiosis Different alleles for different traits do not affect how each other separate The alleles for seed color will not affect the alleles for seed shape Alleles can mix and match independently of each other Mendel’s Laws Law of Segregation Gametes have equal chances of receiving any given allele (T or t) Law of Independent Assortment Different alleles do not affect how each other separates during meiosis (T is not affected by R) Vocabulary Once two gametes are joined, fertilization occurs New organism now has one allele from each parent The two alleles now together form the organisms GENOTYPE Genotype is the specific alleles present TT or Tt or tt Vocabulary The resulting visible feature of the organism as a result of the two alleles is the PHENOTYPE Phenotype is what the organism looks like Phenotype – Physical looks Tall or short Vocabulary A pea plant’s genotype is Tt What the alleles are The same plant’s phenotype is tall What the plant looks like Phenotype is the result of the Genotype Practice 1. A pea plant is TT This is the plant’s (genotype or phenotype)? 2. The pea plant is tall This is the plant’s (genotype or phenotype)? TT, Tt, tt Different genotypes have different terms to describe them Hetero means different Homo means same Zygous zygotic (fertilized) Zygote = fertilized egg TT, Tt, tt Heterozygous genotype - plant height Tt 2 different alleles Homozygous genotype – plant height TT or tt 2 of the same alleles TT, Tt, tt Homozygous = TT or tt Differentiate between the two… What is different? TT = homozygous dominant tt = homozygous recessive TT, Tt, tt Homozygous Dominant TT Heterozygous Tt Homozygous Recessive tt Punnett Squares A model that predicts the likely outcomes of a genetic cross The simplest is a monohybrid cross One trait Punnett square for one trait uses four boxes Probability The likelihood of an event actually occurring Probabilities can be expressed as fractions (1/2, 3/4) or as percentages (25%, 50%) Probability Probability is calculated by: Number of one kind of possible outcome Total number of all possible outcomes Practice Problems Genotype vs. Phenotype Yellow (Y) vs. Green (y) Pea Plants Genotype Homozygous dominant Heterozygous Homozygous recessive Phenotype Genotype vs. Phenotype Purple (P) vs White (p) Flowered Pea Plants Genotype Homozygous dominant Heterozygous Homozygous recessive Phenotype Genotype vs. Phenotype Round (R) vs Wrinkled (r) Pea Plant Seed Shape Genotype Homozygous dominant Heterozygous Homozygous recessive Phenotype Genotype vs. Phenotype Smooth (S) vs Wrinkled (s) Pea Plant Pod Shape Genotype Homozygous dominant Heterozygous Homozygous recessive Phenotype Probability of Genotype for a Heterozygous Cross Ratio % TT T Tt T t tt t Probability of Phenotype for a Heterozygous Cross Ratio % TT T Tt T Tall t tt Short t Probability of Genotype & Phenotype for a Homozygous Cross Ratio % TT T Tt T Tall T tt Short T Spongebob & Friends Scientists at Bikini Bottoms have been investigating the genetic makeup of the organisms in this community. Use the following information to test your knowledge of genetics. Spongebob Yellow body color is dominant to blue What is Spongebob’s phenotype? Yellow What is Spongebob’s possible genotype? YY or Yy Patrick Tall head is dominant to short head. What is Patrick’s phenotype? Tall What is Patrick’s possible genotype? TT or Tt Spongebob Spongebob Squarepants recently met SpongeSusie Roundpants at a dance. Spongebob is heterozygous for his squareshape, but Susie is round. What are the possible genotypes if they had children? Draw a Punnett Square Spongebob What are the chances of a child with a square shape? ___ out of ___ ___% What are the chances of a child with a round shape? ___ out of ___ ___% Patrick Patrick recently met Patti at a dance. Both of them are heterozygous for their pink skin color which is dominant over yellow. What are the possible genotypes if they had children? Draw a Punnett Square Patrick What are the chances of a child with pink skin? ___ out of ___ ___% What are the chances of a child with yellow skin? ___ out of ___ ___% Squidward Squidward’s family has light blue skin, which is the dominant trait for body color. His family brags that they are a “purebred” line. He recently married a nice girl with light green skin, which is a recessive trait. What are the possible genotypes if they had children? Draw a Punnett Square Squidward What are the chances of a child with blue skin? ___ out of ___ ___% What are the chances of a child with green skin? ___ out of ___ ___% Mr Krabbs Mr Krabbs and his wife recently had a Lil’ Krabby, but it has not been a happy occasion. Mrs. Krabbs has been upset since she first saw her baby who had short eyeballs. She claims that the hospital goofed and mixed up her baby with someone else’s baby. Mr. Krabbs is homozygous for his tall eyeballs, while Mrs. Krabbs is heterozygous. Draw a Punnett Square to figure out if the hospital made a mistake.