bio lab exam
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Gene
the fundamental physical and functional units of heredity, consisting of specific segments of DNA located on chromosomes
Allele
Different forms of the same gene
Homozygous vs. Heterozygous
Homozygous is two identical letters (AA, or aa). Heterozygous is two different letters (Aa)
Genotype vs. Phenotype
Genotype refers to the genetic makeup (AA,Aa, or aa). Phenotype refers to the visible trait (purple or yellow)
Mendel’s Law of Segregation
In diploid organisms each individual carries two alleles for every gene, one from each parent. These alleles may be the same or different. During meiosis the two alleles of a gene separate so that each gamete receives only one allele.
AA × aa
Genotypes: 100% Aa Phenotypes: 100% dominant
Aa × Aa
Genotypes: 1 AA : 2 Aa : 1 aa Phenotypes: 3 dominant : 1 recessive
Aa × aa
Genotypes: 1 Aa : 1 aa Phenotypes: 1 dominant : 1 recessive
• Probability of dominant phenotype from • Probability of recessive phenotype from
• Aa x Aa = 3/4 • Aa x Aa = 1/4 For independent events, multiply probabilities. Example: Probability of two recessive offspring in a row (Aa × Aa): 1/4 × 1/4 = 1/16
Chi-Squared Test Formula what does O and E mean in the formula?
χ² = Σ (O − E)² / E O = observed E = expected
Degrees of freedom (df) =
number of categories − 1
For monohybrid crosses (2 phenotypes):
df = 1
Critical value (p = 0.05) =
3.84
Mendel’s Law of Independent Assortment
This law states that alleles of different genes are inherited independently of one another. This principle applies to unlinked genes: ● On different chromosomes ● Far apart on the same chromosome
Decision rule:
● If χ² < 3.84 → Data fit expected ratio ● If χ² ≥ 3.84 → Data do not fit expected ratio
Dihybrid Cross (AaBb × AaBb) Possible gametes:
AB, Ab, aB, ab Classic F2 phenotypic ratio: 9 : 3 : 3 : 1 ● 9/16 both dominant ● 3/16 dominant/recessive ● 3/16 recessive/dominant ● 1/16 both recessive
Product Rule Shortcut
Instead of a 16-box Punnett square: From Aa × Aa: ● Dominant phenotype = 3/4 ● Recessive phenotype = 1/4 Multiply probabilities for each trait. Example: Probability of both recessive traits: 1/4 × 1/4 = 1/16
Chi-Square for Dihybrid Cross
4 phenotype categories → df = 3 Critical value (df = 3, p = 0.05) = 7.815
Recognizing Patterns of Inheritance Autosomal Dominant:
● Appears in every generation ● Affected individuals have affected parent ● Males and females affected equally
Recognizing Patterns of Inheritance Autosomal Recessive:
● Can skip generations ● Affected individuals may have unaffected parents ● Males and females affected equally
Recognizing Patterns of Inheritance X-Linked Recessive:
● More males than females ● No father-to-son transmission ● Affected females must have affected father
Recognizing Patterns of Inheritance Y-Linked:
● Only males affected ● Affected father passes trait to all sons
What’s on a Pedigree?
• Males are represented by squares, females by circles • shaded symbols indicate affected individuals • Horizontal lines connecting a male and female indicate mating • vertical lines descending from aa couple indicate their offspring • Generations are indicated by Roman numerals, starting with the oldest generation at the top • Individuals within a generation are numbered in birth order from left to right.
Incomplete Dominance
Heterozygote shows intermediate phenotype. Example: Red × White → Pink