1. Part 2: Genetics, monohybrid vs. Dihybrid crosses, Chi Square

2. Genes Alleles Genotype Phenotype F1 generation F2 generation
Section of DNA that codes for a specific protein
Alleles
Dominant: allele that has an affect in a heterozygous organisms
Recessive: allele that does not have an affect in heterozygous organism
Symbols:
Use letters where capital letter looks different than lowercase letter
Genotype
Homozygous (organism has TWO identical alleles for a gene…dominant or recessive)
Heterozygous
Phenotype
Observable characteristics of an organism; determined by genotype
F1 generation
Offspring resulting from cross between organism with a HOMOZYGOUS Dominant parent and a HOMOZYGOUS recessive parent
F2 generation
Offspring resulting from cross between two F1 generation (heterozygous organism)

3. Co-dominant Multiple Alleles Sex Inheritance
Both alleles express their characteristic at the same time
Multiple Alleles
When a gene has more than two versions (alleles)
Ex. Blood groups
Caused by genetic mutation: base substitution, deletion, insertion, etc.
Sex Inheritance
Alleles found on sex chromosomes (pair 23)
Sex-linked gene  gene found on X chromosome and not matched on Y chromosome
Use X chromosome as gene symbol with superscript
Mother can be carrier
Male either has allele or does it have allele
Ex. FACTOR VIII
Gene that codes for production of protein needed for blood clotting
Dominant allele  produces protein (H)
Recessive allele  does NOT produce protein (h)

6. Genetic Diagrams
Standard way of showing the genotypes of offspring that might be expected from two parents
Monohybrid Crosses
Diagrams showing inheritance of ONE gene
Test Cross
Cross organism showing dominant phenotype with organism that is homozygous recessive
Phenotypes of offspring will guide you to determine the phenotype of Dominant parent (homozygous or heterozygous)

8. Dihybrid Crosses Diagrams that show inheritance of TWO genes at once
Independent assortment
Two ways in which 2 pairs of chromosomes can line up along equator during METAPHASE 1
Many cells going through meiosis  chromosomes in half will line up one way and the other half will line up the other way
Predict gametes formed from heterozygous cells appear in equal numbers): AD Ad aD ad

11. Interaction between LOCI
Same Locus Interactions
Dominant alleles
Dominant & recessive alleles
Multiple Alleles
Different Loci Interactions
Genes at one loci affect inheritance of genes at another loci

16. Autosomal Linkage
When two or more gene loci are on the same chromosome
Do not sort independently
Inherited together (usually)

17. Crossing Over Prophase 1 of meiosis 1
A bivalent (pair of homologous chromosomes) joined by CHIASMATA
Chromatids of bivalent can break and reconnect to another NON-SISTER CHROMATID
Leads to exchange of gene loci between maternal and paternal chromosome
Cross-over value
Percentages of offspring that belong to recombinant class
Measure of the distance apart of two gene loci on chromosome
Smaller cross-over value = closer gene loci are
Chance of crossing over DIRECTLY related to distance apart
Farther apart = higher chance of crossing over

19. Chi-Squared Test
Statistical test that allows comparison of observed results with expected results to determine if there is a significant difference between the two
Ratios from genetic diagrams represent PROBALITLITIES of phenotypes
Do NOT always come out to that ratio
Expected phenotypic ratio vs. actual phenotypic ratio

20. Stage 1 of Chi-squared Test
Complete dihybrid cross for expected results
Record expected results on table
Observe and record your actual observed results onto table
Calculate difference between each set of results
Squaring gets rid of negative signs (irrelevant)
Divide each square difference by expected value
Add up all answers for x2 value
Finding expected value with ratio:
(using 9:3:3:1)
Take ratio (9/16) and multiply by total number of organisms actually produced
Take ratio (3/16) and multiply by total number of organisms actually produced
Take ratio (1/16) and multiply by total number of organisms actually produced

21. Stage 2 of Chi-Squared Test
Degrees of Freedom of Results
Takes into account the number of comparisons made
Calculation of degrees of freedom:
Degrees of Freedom = # of classes of data – 1
For dihybrid cross, we have 4 possible resulting phenotypes (classes of data)
Degrees of freedom = 4-1 = 3
Look at table of X2 probabilities
Probabilities in table are the probabilities that the differences between our respected and observed results are due to chance
Probability of 0.05 is CRITICAL in biological investigations
If X2 value represents probability of 0.05 or larger = differences b/t observed and expected results are due to chance
When x2 value is LESS than critical value for that specific degree of freedom, it is GOOD!
NOT SIGNIFICANT DIFFERENCE
If X2 value represents probability smaller than 0.05 = differences b/t observed and expected results are SIGNIFICANT, reconsider assumptions about cross
Probability 0.1 means 1 in 10 chance
Critical value tells us how often we expect to see difference between observed and expected result
0.05 means 5%

22. Hypothesis vs. Null Hypothesis
Null hypothesis is always what is expected to be.
Looking at a dihybrid cross, our null hypothesis would be our expected results.
“There is NO significant difference between the observed and expected frequencies”
Hypothesis: The loss of my homework is due to an alien abduction.
Null Hypothesis: The loss of my homework has nothing to do with an alien abduction.
When X2 is LESS than critical value, null hypothesis is accepted (GOOD!)
When X2 is MORE than critical value, null hypothesis is NOT accepted (it is REJECTED)
Something other than chance causing observed results
We want Chi-squared value to be LESS than critical value!