Mendel's Laws and Meiosis Flashcards
What is a haploid cell?
A cell containing one set of chromosomes (n), like gametes (egg or sperm cells)
What is a diploid cell?
A cell containing two sets of chromosomes (2n), like body cells
What’s the difference between genotype and phenotype?
Genotype is the genetic makeup (e.g., Aa), while phenotype is the physical appearance/observable traits
State Mendel’s Law of Segregation
Alleles separate during gamete formation, and each gamete receives only one allele of each gene. Example: Aa separates into A and a gametes
What is Independent Assortment?
Different genes sort independently during meiosis, allowing new combinations of traits in offspring. Location of one gene doesn’t affect inheritance of another
What is a monohybrid cross?
A cross involving one gene pair (e.g., Tall pea TT × short pea tt)
What ratio appears in F2 generation of a monohybrid cross?
3:1 phenotype ratio (dominant:recessive)
What is a dihybrid cross?
A cross involving two gene pairs (e.g., Purple, round PPRR × white, wrinkled pprr)
What ratio appears in F2 generation of a dihybrid cross?
What ratio appears in F2 generation of a dihybrid cross?
What is a testcross?
A cross with a homozygous recessive individual to determine unknown genotype of another individual
What’s the difference between F1 and F2 generations?
F1 is the first generation offspring from parent (P) cross; F2 is the second generation from F1 × F1
What is a pure-breeding organism?
An organism that always produces offspring identical to parents for specific traits
What makes an allele dominant?
It’s expressed even when only one copy is present, often coding for functional proteins that can work alone
What makes an allele recessive?
It’s only expressed when two copies are present, often producing non-functional proteins or resulting in loss of function
How does meiosis create segregation?
Homologous chromosomes separate in Anaphase I, and sister chromatids separate in Anaphase II, resulting in each gamete getting one allele
How does meiosis demonstrate independent assortment?
How does meiosis demonstrate independent assortment?
What is the probability rule for independent events?
Multiply probabilities for independent events (e.g., getting both dominant alleles = 1/2 × 1/2 = 1/4)
What are the possible gametes from a dihybrid heterozygote (AaBb)?
Four types: AB, Ab, aB, ab, each with 25% probability
What is the Product Rule used for?
A: - Used for independent events occurring SIMULTANEOUSLY
- Multiply probabilities together
- Makes events LESS likely
- Use when you need BOTH things to happen
Example: P(rolling two 4s) = 1/6 × 1/6 = 1/36
What is the Sum Rule used for?
A: - Used for mutually exclusive events
- Add probabilities together
- Makes events MORE likely
- Use when you need EITHER event to happen
Example: P(rolling 4 OR 5) = 1/6 + 1/6 = 1/3
Q: List the key characteristics of recessive inheritance
A: - Most genetic diseases are recessive
- Disease can skip generations
- Carriers (heterozygotes) appear normal
- Unaffected parents can have affected children
- Need two copies of mutant allele (aa) to show trait
- More common in consanguineous marriages
List the key characteristics of dominant inheritance
A: - Disease appears in every generation
- Affected child must have at least one affected parent
- No carriers exist
- Only need one copy of mutant allele to show trait
- Both heterozygotes (Aa) and homozygous mutants (AA) show trait
What are the possible outcomes of a mutant allele?
A: A mutant allele may result in:
1. No protein production
2. Non-functional protein
3. Partially functional protein
4. Abnormally functional protein
Why is Cystic Fibrosis recessive at molecular level?
A: - CF+ (normal) allele makes functional CFTR protein
- CF (mutant) allele makes non-functional/no CFTR protein
- One working copy (CF+) is enough for normal function
- Need both copies broken (CF/CF) to show disease
What are the key symbols in pedigree analysis?
A: □ = Male
○ = Female
■/● = Affected individual
Empty symbol = Unaffected
═ = Marriage
Line through symbol = Deceased
Double line = Consanguineous marriage
How can you identify a recessive trait in a pedigree?
A: Look for:
- Disease skipping generations
- Unaffected parents having affected children
- Higher frequency in consanguineous marriages
- Both parents must be carriers to have affected child
What steps should you take when analyzing a new pedigree?
A: 1. Identify pattern (dominant vs recessive)
2. Label known genotypes
3. Determine possible genotypes for key individuals
4. Consider probabilities for future offspring
5. Look for consanguineous marriages
6. Consider if trait is rare in population
When calculating probability of multiple events, how do you choose between Product and Sum rules?
A: - Use Product Rule (multiply) when you need BOTH events
- Use Sum Rule (add) when you need EITHER event
- Ask yourself: “Do I need both things or just one of them?”
- Remember: AND = multiply, OR = add
What is meant by “wild-type vs. mutant” allele?
A: Wild-type:
- Common in population
- Makes functional product
- Usually designated with “+”
Mutant:
- Rare variant
- May be non-functional/altered function
- Usually designated without “+”
What is penetrance in genetic inheritance?
A: - The proportion of individuals with a particular genotype who exhibit the phenotype
- Complete penetrance = 100% of individuals with genotype show trait
- Incomplete penetrance = Some individuals with genotype don’t show trait
