Lecture 3 Mendelian Genetics Flashcards
Exam 1/2
What is Mendel’s model organism? Why are they considered model organisms?
- Easy to grow
- True-breeding strains
- Controlled matings: self-fertilization or cross-fertilization
- Grow to maturity in one season
- Observable characteristics with two distinct forms
Mendel kept _____ records with visible features
QUANTITATIVE
What were the seven pairs of CONTRASTING FEATURES of Mendel’s monohybrid crosses?
- Seed Shape: round/wrinkled
- Seed color: yellow/green
- Pod shape: full/constricted
- Pod color: green/yellow
- Flower color: violet/white
- Flower position: axial/terminal
- Stem height: tall/dwarf
P1 generation means what?
Original Parents
What is the ratio of the contrasting trait reappearing in the F2 generations?
1/4
Geneticists recognized Mendel had discovered what? Define that term!
- The basis for the transmission of hereditary traits.
- Transmission genetics: How genes are transmitted from parents to offspring
Explain Monohybrid Crosses
- True-breeding
- Involve a SINGLE pair of contrasting traits.
- P1(parent), F1 (First filial), etc
In F2 generations, they are the offspring of F1 generation which occur due to what process?
Self Fertilization: “Selfing”
Explain the ratio discovered by Mendel in the F2 generation
- 3/4 of plants exhibit the same trait as F1 generation (either one of the contrasting trait)
-1/4 exhibit the contrasting trait that was lost in the F1 generation. - Essentially a 3:1 ratio phenotypically or 1:2:1 genotypically
NOTE: Dominant generation is the trait that typically took over even if heterozygous.
In a Punnett square is the horizontal portion male or female?
- Horizontal: Male
- Vertical: Female
Define Reciprocal crosses
- Crosses made in both directions
- breeding experiment where the sex of the parents is reversed between two separate crosses
- Allowing researchers to test if the inheritance pattern of a trait is influenced by which parent is male or female
- AKA is a trait sex-linked by comparing the offspring produced when the mother carries the trait versus the father
Define Particulate Unit Factor (genes) as proposed by Mendel
- Basic units of heredity
- Are passed unchanged from generation to generation
- Determine various traits expressed by each individual plant
What were Mendel’s 3 Postulates/Rules
- Unit factors exist in pairs (figured it out with F2 when the missing trait came back up, meaning, he thought it existed in a silent expression)
- Dominance/Recessiveness (one unit is dominant, the other is recessive)
- Segregation (Paired unit factors segregate independently during gamete formation)
Define Phenotype
Physical expression of a trait
Define Gene
Unit of Inheritance
Define Allele
Alternative form of a single gene
Define Genotype
- Genetic makeup of individual
- Alleles written in pairs (DD, Dd, dd)
- Organism inherits two alleles (one from each parent)
Define Homozygous
Both alleles are the same (DD or dd)
Define Heterozygous
Alleles are different (Dd)
Explain Punnett Square
- Reginald C. Punnett devised this approach
- Genotypes and phenotypes resulting from combining gametes can be visualized
- Displays all possible random fertilization events
True Genotype means what?
- Both alleles are the same
- Homozygous dominant or Homozygous recessive
Explain Testcross: One Character
- Determines if an individual displaying a dominant phenotype is homozygous or heterozygous for a trait.
- Cross between dominant phenotype and homozygous recessive
Ex.) DD x dd OR Dd x dd
What is a Dihybrid cross?
- Two pairs of contrasting traits
- Generates unique F2 generation
Chromosomal Theory of Inheritance
- Genetic material in living organisms contained in chromosomes
- Separation of chromosomes during meiosis served as the basis for Mendel’s principles of segregation and independent assortment
- Independent Assortment = Leads to extensive genetic variation
What is the criteria for classifying two chromosomes as homologous pairs?
- Both are the same size and exhibit IDENTICAL centromere locations
- Excludes X and Y chromosomes in mammals
- Form pairs of synapses during stages of meiosis
- Contain identical linear order of gene loci
- One member of each pair is derived from the maternal parents and one from the paternal parent.
Independent Assortment leads to extensive ________ ________
GENETIC VARIATION
Define Product Law
- Calculates the probability of outcomes occurring together
- Ex.) Coin toss of penny (P) and nickel (N) to see if heads or tails of each occur at the same time. AKA 50% chance. LOOK AT NOTES IF CONFUSED
Define Sum Law
- Calculates the probability of outcomes INDEPENDENT of each other
When predicting genetic outcomes, two factors in analyzing or predicting genetic outcomes include what?
- Sample size: Average deviation decreases as sample size increases
- Independent Assortment: Subject to random fluctuations due to chance deviations
Define Null hypothesis
- Assumes data will fit given the ratio
- Assumes there is NO REAL DIFFERENCE between measured values and predicted values
- Apparent difference attributed purely to chance
Define Chi-Square
- Goodness of fit of null hypothesis
- Analysis used to test how well the data fit the null hypothesis
- Analysis of observed vs. expected deviations
What is Degrees of Freedom (df)
- Equal to n-1
- n: number of different categories into which data points may fall (different outcomes)
- 3:1 ratio means n=2 and df=1
- 9:3:3:1 ratio means n=4 and df=3
Define Probability Value (p)
- When the number of degrees of freedom is determined
- x^2 value can be interpreted in terms of a corresponding probability value (p)
Define Pedigree
- Family tree concerning given trait
- Pedigree analysis reveals patterns of inheritance of human traits
- For example, are certain traits due to dominant or recessive alleles
MUST KNOW HOW TO READ A PEDIGREE
LOOK AT CH 3 NOTES!
Define Mendel’s Fourth Postulate
- INDEPENDENT ASSORTMENT
- Unit factors (traits) assort independently during gamete formation
- All possible gamete combinations form with EQUAL frequency
Trihybrid Crosses have an easier method than making a 64 Punnett square. What is it?
Forked-line method (Branch diagram)
Mendel suggested heredity resulted in what type of variation?
- DISCONTINUOUS
- A dominance-recessive relationship
Darwin and Wallace subscribed to the theory of what variation?
- CONTINUOUS
- Offspring were a blend of parental phenotypes
