Examples of recessive lethal in the following topics:
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- An inheritance pattern in which an allele is only lethal in the homozygous form and in which the heterozygote may be normal or have some altered non-lethal phenotype is referred to as recessive lethal.
- For crosses between heterozygous individuals with a recessive lethal allele that causes death before birth when homozygous, only wild-type homozygotes and heterozygotes would be observed.
- In other instances, the recessive lethal allele might also exhibit a dominant (but not lethal) phenotype in the heterozygote.
- For instance, the recessive lethal Curly allele in Drosophila affects wing shape in the heterozygote form, but is lethal in the homozygote.
- However, just as the recessive lethal allele might not immediately manifest the phenotype of death, dominant lethal alleles also might not be expressed until adulthood.
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- This low genetic diversity means they are often susceptible to disease and often pass on lethal recessive mutations; only about 5% of cheetahs survive to adulthood.
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- In a heterozygote, the allele which masks the other is referred to as dominant, while the allele that is masked is referred to as recessive.
- One allele can be dominant to a second allele, recessive to a third allele, and codominant to a fourth.
- If a genetic trait is recessive, a person needs to inherit two copies of the gene for the trait to be expressed.
- Thus, both parents have to be carriers of a recessive trait in order for a child to express that trait .
- Recessive traits are only visible if an individual inherits two copies of the recessive allele
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- Therefore, recessive alleles can be "carried" and not expressed by individuals.
- However, the results of a heterozygote self-cross can still be predicted, just as with Mendelian dominant and recessive crosses.
- Mendel implied that only two alleles, one dominant and one recessive, could exist for a given gene.
- The variant may be recessive or dominant to the wild-type allele.
- Discuss incomplete dominance, codominance, and multiple alleles as alternatives to dominance and recessiveness
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- Hemizygosity makes the descriptions of dominance and recessiveness irrelevant for XY males because each male only has one copy of the gene.
- In an X-linked cross, the genotypes of F1 and F2 offspring depend on whether the recessive trait was expressed by the male or the female in the P1 generation.
- Because human males need to inherit only one recessive mutant X allele to be affected, X-linked disorders are disproportionately observed in males.
- Females must inherit recessive X-linked alleles from both of their parents in order to express the trait.
- The son of a woman who is a carrier of a recessive X-linked disorder will have a 50 percent chance of being affected.
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- Mendel's experiments with peas revealed the presence of dominant and recessive traits in the filial generations.
- He called these, respectively, dominant and recessive traits.
- Recessive traits become latent, or disappear, in the offspring of a hybridization.
- The recessive trait does, however, reappear in the progeny of the hybrid offspring.
- For this same characteristic (flower color), white-colored flowers are a recessive trait.
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- The recessive yellow genotype is epistatic to the B gene: mating two heterozygotes (BbEe) results in a 9:3:4 ratio of black (B_E_) to brown (bbE_) to yellow (__ee) offspring.
- A mouse with a recessive c allele at this locus is unable to produce pigment and is albino regardless of the allele present at locus A.
- Finally, epistasis can be reciprocal: either gene, when present in the dominant (or recessive) form, expresses the same phenotype.
- When the genes A and B are both homozygous recessive (aabb), the seeds are ovoid.
- The recessive c allele does not produce pigmentnand a mouse with the homozygous recessive cc genotype is albino regardless of the allele present at the A locus.
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- Many metabolites are toxic and can even be lethal to animals that ingest them.
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- If the pattern of inheritance (dominant or recessive) is known, the phenotypic ratios can be inferred as well.
- Therefore, the two possible heterozygous combinations produce offspring that are genotypically and phenotypically identical despite their dominant and recessive alleles deriving from different parents.
- In a test cross, the dominant-expressing organism is crossed with an organism that is homozygous recessive for the same characteristic.
- Alternatively, if the dominant expressing organism is a heterozygote, the F1 offspring will exhibit a 1:1 ratio of heterozygotes and recessive homozygotes.
- In the P generation, pea plants that are true-breeding for the dominant yellow phenotype are crossed with plants with the recessive green phenotype.
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- Because of independent assortment and dominance, the 9:3:3:1 dihybrid phenotypic ratio can be collapsed into two 3:1 ratios, characteristic of any monohybrid cross that follows a dominant and recessive pattern.
- Round/green and wrinkled/yellow offspring can also be calculated using the product rule as each of these genotypes includes one dominant and one recessive phenotype.
- For instance, for a tetrahybrid cross between individuals that are heterozygotes for all four genes, and in which all four genes are sorting independently in a dominant and recessive pattern, what proportion of the offspring will be expected to be homozygous recessive for all four alleles?
- We know that for each gene the fraction of homozygous recessive offspring will be 1/4.
- Therefore, multiplying this fraction for each of the four genes, (1/4) × (1/4) × (1/4) × (1/4), we determine that 1/256 of the offspring will be quadruply homozygous recessive.