Podcast
Questions and Answers
In a dihybrid cross, what principle of inheritance is demonstrated?
In a dihybrid cross, what principle of inheritance is demonstrated?
- Law of Dominance: One allele masks the effect of another.
- Law of Independent Assortment: Genes assort independently during gamete formation. (correct)
- Law of Segregation: Alleles separate during gamete formation.
- Law of Uniformity: Offspring of similar parents are identical.
If a plant has the genotype AaBb, and these genes are on different chromosomes, what are the possible allele combinations that could be present in its pollen grains (male gametes)?
If a plant has the genotype AaBb, and these genes are on different chromosomes, what are the possible allele combinations that could be present in its pollen grains (male gametes)?
- Aa, Bb
- AA, bb
- AaBb only
- AB, ab, Ab, aB (correct)
Why are Punnett squares less practical for analyzing crosses involving more than three genes?
Why are Punnett squares less practical for analyzing crosses involving more than three genes?
- The number of possible gamete combinations becomes too large, making the square unwieldy. (correct)
- Mendel's laws do not apply to more than three genes.
- The probability of inheritance becomes zero.
- Trihybrid crosses are impossible to perform.
What is the primary purpose of a Punnett square?
What is the primary purpose of a Punnett square?
What component is crucial for constructing a Punnett square?
What component is crucial for constructing a Punnett square?
In genetics, what distinguishes a dominant allele from a recessive allele?
In genetics, what distinguishes a dominant allele from a recessive allele?
If a heterozygous individual (Ll) mates with a homozygous recessive individual (ll) for the lactase gene, what is the probability that their offspring will be lactose intolerant?
If a heterozygous individual (Ll) mates with a homozygous recessive individual (ll) for the lactase gene, what is the probability that their offspring will be lactose intolerant?
In the context of a Punnett square, what do the edges of the square and the inner boxes represent, respectively?
In the context of a Punnett square, what do the edges of the square and the inner boxes represent, respectively?
A lactose-tolerant woman (LL) has children with a man who is also lactose-tolerant (Ll). What is the probability their child will be lactose-intolerant?
A lactose-tolerant woman (LL) has children with a man who is also lactose-tolerant (Ll). What is the probability their child will be lactose-intolerant?
Why is it important to know the genotypes of the parents before constructing a Punnett square?
Why is it important to know the genotypes of the parents before constructing a Punnett square?
In a cross where one parent is heterozygous (Mm) for a dominant trait and the other is homozygous recessive (mm), what is the probability that their offspring will inherit the dominant trait?
In a cross where one parent is heterozygous (Mm) for a dominant trait and the other is homozygous recessive (mm), what is the probability that their offspring will inherit the dominant trait?
A couple, both heterozygous carriers (Ff) for cystic fibrosis, have two children. One child has cystic fibrosis (ff), and the other does not. What is the probability that their next child will have cystic fibrosis?
A couple, both heterozygous carriers (Ff) for cystic fibrosis, have two children. One child has cystic fibrosis (ff), and the other does not. What is the probability that their next child will have cystic fibrosis?
An individual with Marfan syndrome (Mm) has children with someone who does not have Marfan syndrome (mm). What is the probability that their child will NOT inherit Marfan syndrome, assuming Marfan syndrome is a dominant trait?
An individual with Marfan syndrome (Mm) has children with someone who does not have Marfan syndrome (mm). What is the probability that their child will NOT inherit Marfan syndrome, assuming Marfan syndrome is a dominant trait?
In a Punnett square analyzing a monohybrid cross, what does each box within the square represent?
In a Punnett square analyzing a monohybrid cross, what does each box within the square represent?
What is the purpose of determining the genotypes of potential offspring when constructing a Punnett square?
What is the purpose of determining the genotypes of potential offspring when constructing a Punnett square?
Flashcards
Punnett Square
Punnett Square
A graphical tool to calculate possible genotypes and phenotypes in offspring.
Law of Segregation
Law of Segregation
Each individual has two alleles for each gene, which separate during gamete formation.
Law of Independent Assortment
Law of Independent Assortment
The inheritance of one gene doesn't affect the inheritance of another gene.
Monohybrid Cross
Monohybrid Cross
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Dihybrid Cross
Dihybrid Cross
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Alleles
Alleles
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Dominant Allele
Dominant Allele
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Recessive Allele
Recessive Allele
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Genotype
Genotype
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Phenotype
Phenotype
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Homozygous
Homozygous
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Heterozygous
Heterozygous
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Recessive Genetic Disease
Recessive Genetic Disease
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Study Notes
- A Punnett square is a graphical tool to determine possible outcomes of a genetic cross, showing the odds of maternal and paternal gene combinations.
- Parental gametes are placed on the top and side, with offspring combinations inside the square, quantifying potential outcomes from a single cross.
Monohybrid Cross
- Monohybrid crosses model the inheritance of one gene, demonstrating Mendel's Law of Segregation where each individual has two alleles per gene.
- Alleles segregate into separate gametes, each containing only one allele.
Dihybrid Cross
- Dihybrid crosses analyze the inheritance of two genes, illustrating Mendel's Law of Independent Assortment.
- The segregation of one gene does not affect the segregation of another.
- Punnett squares can work for up to trihybrid crosses (3 genes.)
- Scientists use computer programs and bioinformatics for more than 3 genes.
Genotype and Phenotype
- Alleles: Alternative gene forms producing different traits (e.g., LCT gene for lactose digestion).
- Dominant alleles (e.g., LCT) are expressed even with one copy; recessive alleles (e.g., lct) are only expressed with two copies.
- Genotype: The combination of alleles (e.g., LCT/lct).
- Phenotype: How the genotype is expressed physically (e.g., lactose tolerance).
- Homozygous: Alleles are the same (LL or ll).
- Heterozygous: Alleles are different (Ll).
- Heterozygous individuals display the dominant phenotype.
How to Construct a Punnett Square
- Determine parental genotypes
- Identify possible gametes for each parent (containing half the genetic information)
- Arrange gametes along the Punnett square's edges
- Fill in offspring squares by combining gametes
- Interpret results as ratios, percentages, or fractions.
Homozygous Example: Marfan Syndrome
- Marfan syndrome is a dominant disorder affecting connective tissues.
- Affected individuals are usually heterozygous (Mm) for the Marfan syndrome allele.
- Unaffected individuals are homozygous recessive (mm).
- A cross between an affected heterozygous man (Mm) and an unaffected woman (mm) yields a 50% chance of offspring having Marfan syndrome.
Heterozygous Example: Cystic Fibrosis
- Cystic fibrosis is a recessive genetic disease; 1 in 35 people are carriers.
- Individuals with the condition must inherit two recessive alleles (ff).
- Parents who are carriers (Ff) have a 25% chance of having a child with cystic fibrosis.
Dihybrid Crosses Explained
- Dihybrid crosses examine the inheritance of two genes simultaneously
- They uUse different letters to represent each gene.
- Gametes contain two alleles (one per gene), and offspring genotypes have four letters.
- The five steps remain the same.
Dihybrid Cross Example: Lactose Intolerance & Cystic Fibrosis
- Cross example: A llFf father and a LlFf mother.
- Father's gametes: lF, lf.
- Mother's gametes: LF, Lf, lF, lf.
- This creates a 2x4 Punnett square with eight offspring possibilities.
- The ratio for this llFf x LlFf cross is 3:3:1:1
- 3 lactose tolerant, no cystic fibrosis (dominant dominant)
- 3 lactose intolerant, no cystic fibrosis (dominant recessive)
- 1 lactose tolerant, with cystic fibrosis (recessive dominant)
- 1 lactose intolerant, with cystic fibrosis (recessive recessive)
- The probability of a child being lactose intolerant with cystic fibrosis is 1/16 or 6.25%.
Fully Heterozygous Dihybrid Crosses
- Crosses where both parents are heterozygous (e.g., LlFf x LlFf) result in a 9:3:3:1 phenotypic ratio
- 9 lactose tolerant, no cystic fibrosis (dominant dominant)
- 3 lactose intolerant, no cystic fibrosis (dominant recessive)
- 3 lactose tolerant, with cystic fibrosis (recessive dominant)
- 1 lactose intolerant, with cystic fibrosis (recessive recessive)
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Description
Explore dihybrid crosses, allele combinations, and Punnett square applications. Understand dominant vs. recessive alleles and predict offspring genotypes via Punnett squares. Learn about inheritance principles and genetic probabilities.
