Questions and Answers
What is the difference between heterozygous and homozygous individuals?
All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ.
When constructing a Punnett square, the symbols on the outside of the boxes represent _______ while those inside the boxes represent _______.
gametes, progeny
The same phenotype can be produced by more than one genotype.
True
In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait.
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If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb?
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What percentage of the offspring from two mice heterozygous for albinism (Aa) would have an albino phenotype?
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What is the genotype of the plant whose phenotype appeared once out of every 16 offspring in a 9:3:3:1 ratio?
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What would be the genotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien?
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What would be the phenotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien?
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Which of these is a testcross?
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What would be the predicted phenotypic ratio of offspring from Sam (black eyes, green skin) and Carole (orange eyes, white skin)?
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A cross between an individual with orange eyes and green skin and an individual with black eyes and white skin is an example of a _____ cross.
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A phenotypic ratio of 9:3:3:1 in the offspring of a cross indicates that _____.
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What best explains the results of a BbGg x bbgg cross yielding a phenotypic ratio of approximately 5 black eyes, green skin : 5 orange eyes, white skin : 1 black eyes, white skin : 1 orange eyes, green skin?
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In a situation where genes assort independently, what is the ratio of the gametes produced by an AaBB individual?
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Study Notes
Genetic Principles
- Heterozygous vs. Homozygous: Homozygous individuals possess two identical alleles, while heterozygous individuals have two different alleles for a gene.
- Punnett Square Construction: The outer symbols of a Punnett square represent gametes, whereas the symbols inside represent the potential offspring (progeny).
Phenotypes and Genotypes
- Phenotypic Expression: A single phenotype can arise from multiple genotypes due to dominance; for example, both AA and Aa yield the dominant phenotype.
- Dominant Phenotype Expression: A dominant phenotype appears when at least one dominant allele is present, including in heterozygous individuals (Aa).
- Gamete Ratio from Genotype: For an organism with genotype AaBb, no gametes can be Bb due to the segregation of alleles.
Offspring Ratios
- Albinism in Mice: A cross between two heterozygous (Aa) mice yields approximately 25% albino (aa) offspring.
- Pea Plant Phenotypic Ratio: In a TtPp (tall, purple-flowered) self-pollination, the offspring exhibit a 9:3:3:1 phenotypic ratio, with ttpp plants (short and white) appearing once in 16 offspring.
Genetic Cross Examples
- Genotypic Ratio for Eye Color: A cross between a heterozygous black-eyed individual (Bb) and an orange-eyed individual (bb) results in a genotypic ratio of 0 BB : 1 Bb : 1 bb.
- Phenotypic Ratio for Eye Color: The same cross results in a phenotypic ratio of 1 black (Bb) : 1 orange (bb).
- Testcross Definition: A testcross (e.g., Aa x aa) reveals the genotype of an individual with a dominant phenotype.
Dihybrid Crosses and Ratios
- Dihybrid Cross Example: A cross involving orange eyes with green skin and black eyes with white skin is classified as a dihybrid cross.
- Heterozygous Ratio: A 9:3:3:1 ratio in offspring indicates that both parents are heterozygous (TtPp) for two traits.
- Phenotypic Ratio Variation: A BbGg x bbgg cross results in approximately 5:5:1:1 phenotypic ratios, suggesting Mendel's law of independent assortment may be violated.
Gamete Production
- Gamete Ratio for AaBB Individual: In independently assorting genes, an AaBB individual produces gametes in a 1 AB : 1 aB ratio.
Studying That Suits You
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Description
Test your knowledge with these flashcards covering key concepts from Biology Chapter 14. Explore topics such as genetic variations between heterozygous and homozygous individuals, and learn how to construct Punnett squares. This quiz is a great way to reinforce your understanding of genetics.
