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Mendelian Inheritance
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Today, weโll explore Mendelian inheritance, starting with Gregor Mendel, who laid the groundwork for modern genetics. He discovered how traits are inherited using pea plants.
What are dominant and recessive alleles?
Great question! Dominant alleles can mask the expression of recessive alleles. For example, the brown eye allele is dominant over the blue eye allele.
So if someone has brown eyes, can we assume their genotype?
Not exactly! They could be homozygous (BB) or heterozygous (Bb). This brings us to homozygous and heterozygous genotypes.
What's the difference between those two?
Homozygous has two identical alleles, while heterozygous has two different ones. Can anyone recall a tool we can use to predict offspring traits?
Punnett Squares!
Exactly! Letโs visualize using a Punnett Square how a cross between BB and bb would result in Bb offspring.
Complex Inheritance Patterns
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Now that we understand Mendelian inheritance, letโs investigate more complex patterns such as incomplete dominance and codominance.
Whatโs incomplete dominance?
Incomplete dominance occurs when neither allele is fully dominant. For instance, if we cross red and white snapdragons, we get pink offspring. Can anyone think of another example?
Maybe AB blood types?
Correct! In codominance, both alleles contribute to the phenotype, as seen in AB blood types. What about traits like skin color?
That must involve multiple genes, right?
Absolutely, thatโs known as polygenic inheritance! Itโs a great example of how genetics can exhibit a range of phenotypes.
Introduction & Overview
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Quick Overview
Standard
Inheritance Patterns examines how traits are passed down from parents to offspring, explaining Mendelian inheritance principles, including dominant and recessive alleles, and discusses advanced concepts such as incomplete dominance, codominance, and polygenic inheritance, which showcase genetics' complexity.
Detailed
Inheritance Patterns
Inheritance Patterns analyze the basic tenets of genetics, primarily focusing on how traits are transmitted from one generation to the next. This section is grounded in the foundational work of Gregor Mendel, who established principles that govern heredity through his experiments on pea plants. Key concepts include:
Mendelian Inheritance
Dominant and Recessive Alleles
- Dominant alleles mask the expression of recessive alleles. For instance, in eye color genetics, the brown eye allele (B) is dominant over the blue eye allele (b).
Homozygous and Heterozygous
- Homozygous refers to individuals having two identical alleles (e.g., BB or bb), whereas heterozygous indicates two different alleles (e.g., Bb).
Punnett Squares
- A helpful tool for predicting the probability of inheritance of particular alleles. For example, when crossing a homozygous dominant (BB) with a homozygous recessive (bb) parent, all offspring will be heterozygous (Bb).
Beyond Mendelian Genetics
Incomplete Dominance
- This pattern occurs when neither allele is completely dominant, producing a blended phenotype (e.g., crossing red (RR) and white (WW) snapdragons yields pink (RW) offspring).
Codominance
- In codominance, both alleles are fully expressed in the phenotype. An example includes blood type AB, showcasing both A and B alleles.
Polygenic Inheritance
- Traits influenced by two or more genes, leading to continuous variation as seen in skin color.
Overall, understanding these patterns provides insight into the complexities of heredity and genetic diversity.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Mendelian Inheritance: Principles established by Mendel describing dominant and recessive traits.
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Homozygous and Heterozygous: Terms used to describe an individual's alleles for a trait.
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Punnett Squares: A tool for predicting the chances of offspring inheriting certain traits.
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Incomplete Dominance: A situation where neither allele fully dominates, leading to a mix of traits.
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Codominance: Both alleles contribute to the phenotype.
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Polygenic Inheritance: Multiple genes affecting a single trait.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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A Punnett Square shows that crossing a homozygous dominant (BB) and a homozygous recessive (bb) yields all heterozygous (Bb) offspring.
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In incomplete dominance, when red (RR) and white (WW) snapdragons are crossed, the resulting offspring (RW) are pink.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
๐ต Rhymes Time
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When genes donโt play fair, dominant will declare, recessive stay rare, in this genetic affair.
๐ Fascinating Stories
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Imagine a strong warrior (dominant allele) guarding a castle (trait) while a quiet villager (recessive allele) hides. The warriorโs strength can overshadow the villagerโs presence, displaying the battle of dominance.
๐ง Other Memory Gems
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Use the phrase 'Practical Cats' to remember: P - Punnett Square, C - Codominance, I - Incomplete Dominance, P - Polygenic Inheritance.
๐ฏ Super Acronyms
Remember 'HERC' for key genotypes
- H: - Homozygous
- E: - Express (dominant)
- R: - Recessive
- C: - Codominance.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Dominant Allele
Definition:
An allele that masks the expression of another allele.
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Term: Recessive Allele
Definition:
An allele that is masked by the presence of a dominant allele.
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Term: Homozygous
Definition:
Having two identical alleles for a specific trait.
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Term: Heterozygous
Definition:
Having two different alleles for a specific trait.
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Term: Punnett Square
Definition:
A grid used to predict the genotypes of offspring from parental genotypes.
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Term: Incomplete Dominance
Definition:
A hereditary pattern where neither allele is completely dominant, resulting in a blend of traits.
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Term: Codominance
Definition:
A genetic condition where both alleles are fully expressed in the phenotype.
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Term: Polygenic Inheritance
Definition:
A type of inheritance where multiple genes influence a trait.