Ch. 2 - Transmission Genetics

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Non è quello che usi tu?Cambia libro di testo

Sanders 3rd Edition

Ch. 2 - Transmission Genetics

Problema 8f

Capitolo 2, Problema 8f

Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.
If a woman is heterozygous for albinism, an autosomal recessive condition that results in the absence of skin pigment, the proportion of her gametes carrying the allele that allows pigment expression is expected to be 75%.

Guida verificata passo dopo passo

Step 1: Understand the genetic basis of albinism. Albinism is an autosomal recessive condition, meaning that an individual must inherit two recessive alleles (aa) to express the condition. A heterozygous individual (Aa) carries one dominant allele (A) and one recessive allele (a).

Step 2: Recall the concept of gamete formation during meiosis. In a heterozygous individual (Aa), the alleles segregate equally during gamete formation, resulting in 50% of the gametes carrying the dominant allele (A) and 50% carrying the recessive allele (a).

Step 3: Analyze the statement provided. The statement claims that the proportion of gametes carrying the allele for pigment expression (dominant allele A) is 75%. This is inconsistent with Mendel's law of segregation, which states that alleles segregate equally.

Step 4: Revise the statement to make it correct. The correct proportion of gametes carrying the allele for pigment expression (A) in a heterozygous individual (Aa) is 50%, not 75%.

Step 5: Conclude that the statement is false and provide the corrected information: If a woman is heterozygous for albinism, the proportion of her gametes carrying the allele that allows pigment expression is expected to be 50%.

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Heterozygosity

Heterozygosity refers to the presence of two different alleles at a specific gene locus. In the context of albinism, if a woman is heterozygous, she has one normal allele (for pigment production) and one recessive allele (for albinism). This genetic makeup influences the types of gametes she can produce, specifically affecting the expression of traits in offspring.

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05:15

Inversions

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait is expressed only when an individual has two copies of the recessive allele. In the case of albinism, an individual must inherit the recessive allele from both parents to exhibit the condition. If only one recessive allele is present, the dominant allele will mask its effect, leading to normal pigmentation.

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Autosomal Pedigrees

Gamete Formation and Allele Distribution

During gamete formation, specifically through meiosis, alleles segregate so that each gamete receives only one allele from each gene pair. For a heterozygous individual (e.g., Aa), the gametes will carry either the dominant allele (A) or the recessive allele (a) in equal proportions, resulting in 50% of the gametes carrying the allele for pigment expression, not 75%.

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Formation of Plant Gametes

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Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.

The outcome of a trihybrid cross is predicted by the law of segregation.

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Reciprocal crosses that produce identical results demonstrate that a strain is pure-breeding.

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Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.

The progeny of a trihybrid cross are expected to have one of 27 different genotypes.

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In the datura plant, purple flower color is controlled by a dominant allele, P. White flowers are found in plants homozygous for the recessive allele p. Suppose that a purple-flowered datura plant with an unknown genotype is self-fertilized and that its progeny are 28 purple-flowered plants and 10 white-flowered plants.

Use the results of the self-fertilization to determine the genotype of the original purple-flowered plant.

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Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.

A test cross between a heterozygous parent and a homozygous recessive parent is expected to produce a 1:1 genotypic and phenotypic ratio.

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Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.

If a dihybrid plant is self-fertilized,

(1) 9/16 of the progeny will have the same phenotype as the F₁ parent.

(2) 1/16 of the progeny will be true-breeding.

(3) 1/2 of the progeny will be heterozygous at one or both loci.

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