Genetics Ch. 3

• Mendel's Experiments

  • Monohybrid cross
  • Mendel's 1st Law
  • Test Cross
• Gene

  an inherited factor (region of DNA) that helps determine a characteristic; genetic encoding region; sequence of nucleotides that encode for a specific product
• Allele

  A specific form of a gene
• Locus

  Specific location on a chromosome occupied by an allele
• Phenotype

  A specific trait or characteristic that is observed
• Characteristic

  an attribute or feature possessed by an organism
• Trait

  Each variant for a character, such as purple or white color for flowers
• Monohybrid cross

  A cross (mating) between two parents that differ in a single characteristic (homozygous individuals)
• Mendel's First Law (Principle of segregation)

  Each individual diploid organism possesses two alleles for any given characteristic, These two alleles segregate when gametes are formed, and one allele goes into each gamete
• Concept of Dominance

  When two different alleles are present in a genotype, only the trait encoded by one of them―the "dominant" allele―is observed in the phenotype
• Backcross

  Used to test the theory of inheritance of dominant traits; going back to the original parent and crossing it with a heterozygous offspring (F1)- either parent is fine to use
• Predicting the outcomes of genetics crosses easy with a PUNNETT SQUARE
• Testcross

  taking an unknown with a known genotype; to determine the genotype of the mystery individual, homozygous recessive is ideal; if the offspring displays the recessive phenotype then the mystery parent must be heterozygous
• Probability

  Mathematical calculation of the likelihood of the occurrence of a particular event
• Addition rule


  To calculate the probability of two independent events occurring separately, add the probabilities of those events together
• Multiplication rule


  To calculate the probability of two independent events occurring together, multiply the probabilities of those events together
• The key word for the addition rule is "OR"
• The key word for the multiplication rule is "AND"
• Conditional probability

  Probability that is modified by additional information that another event has occurred
• Wild type

  Most common allele, usually indicated by "+" sign, any deviation is "-"
• Dihybrid cross

  Examine two traits at a time
• Principle of independent assortment

  Cross between individuals that are heterozygous for 2 different characteristics
• Mendel's second law of inheritance

  • crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters
  • dihybrid cross, can determine whether two characters are transmitted to offspring as a package or independently
• Dihybrids

  Crossing two true-breeding parents differing in two characters produces heterozygous individuals for both characters in the F1 generation
• Law of independent assortment

  Each pair of alleles segregates independently of every other pair of alleles during gamete formation; the law only applies to genes on different, nonhomologous chromosomes
• Genes on different/far apart chromosomes

  Tend to be inherited independently
• Genes located near each other

  Tend to be inherited together
• Branch diagrams

  Another way to show phenotypes, genotypes and determine probability
• Chi-square goodness-of-fit test

  Determines if observed differences are due to random chance or some other factor
• Hypothesis testing

  Cannot prove hypothesis is true, but can give confidence that observed difference is not due to random chance
• Null hypothesis

  Difference between expected and observed is due to random chance
• Alternative hypothesis

  Difference between expected and observed is not due to random chance
• Using chi-square to test hypothesis

  1. Step 1: Determine expected results

  2. Step 2: Record observed results

  3. Step 3: Write out expected and observed results

  4. Step 4: Calculate chi-square value

  5. Step 5: Determine p-value from chi-square table
• With p-value between 0.025 and 0.01, we reject the null hypothesis
• Success of Mendel's Experiments was do to?

  • Proper experimental model in the pea plant
  • Used an experimental approach and analyzed results mathematically (started pure breeding)
  • Used Stats to understand his results
  • Studied easily differentiated characteristics (came up with patterns of the traits)
• Genotype

  set of alleles possessed by an individual organism; what is encoded
• Heterozygote

  two different alleles at a locus
• Homozygote

  two of the same alleles at a locus
• What is encoded and what is seen is not always the same.
• Character/Characteristic

  a heritable feature that varies among individuals (such as flower color)