Bio1233 Chp 7 – Flashcards
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Most genes come in alternative forms called:
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alleles.
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Traits that are determined by a single gene:
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are common in humans.
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Pea plants were well suited for Mendel's breeding experiments for all of the following reasons:
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peas exhibit variations in a number of observable characteristics, such as flower color and seed shape; Mendel and his staff could control the pollination between different pea plants; it is easy to obtain large numbers of offspring from any given cross; many of the characteristics that vary in pea plants are not linked closely on the same chromosome.
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The law of segregation states that:
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each of two alleles for a given trait segregate into different gametes.
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In pea plants, purple flower color is dominant to white flower color. If two pea plants that are true-breeding for purple flowers are crossed, in the offspring:
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all of the flowers will be purple.
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Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from a cross between purple-flowered, round-seeded individuals will have both white flowers and round seeds?
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3/16
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The test-cross:
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makes it possible to determine the genotype of an individual of unknown genotype that exhibits that dominant version of a trait; is a cross between an individual whose genotype for a trait is not known and an individual homozygous recessive for the trait; sometimes requires the production of multiple offspring to reveal the genotype of an individual whose genotype is unknown (but who exhibits the dominant phenotype).
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Pedigree analysis:
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darkened squares or circles always represent individuals with the trait being traced.
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All the offspring of a black hen and a white rooster are gray. The simplest explanation for this pattern of inheritance is:
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incomplete dominance.
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A woman with type B blood and a man with type A blood could have children with which of the following phenotype?
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A, B, AB, or O
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Which trait shows a polygenic method of inheritance?
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skin color in humans
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The impact of a single gene on more than one characteristic is called:
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pleiotrophy
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A rare, X-linked dominant condition in humans, congenital generalized hypertrichosis, is marked by excessive hair growth all over a person's body:
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the son of a woman with this disease has just slightly more than a 50% chance of having this condition; the daughter of a man with this condition has a 100% chance of having this condition; the daughter of a woman with this disease has just slightly more than a 50% chance of having this condition; males with this condition almost always have a more severe phenotype, because women usually have at least one normal allele that dilutes the effect of the mutated allele.
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Because of Mendel's law of independent assortment:
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the alleles coding for one trait do no usually influence the inheritance pattern for another trait.
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Thousands (or even tens of thousands) of different traits make up an individual. For this reason:
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in a species with 23 different chromosomes, some traits must be coded for by genes on the same chromosome.
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Traits that are controlled by genes on the sex chromosomes are called:
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sex-linked traits.
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A diploid individual with two identical alleles for a particular gene is said to be:
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homozygous for that gene.
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An allele:
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can be dominant or recessive; will assort independently from alleles on other chromosomes; can be identical to or different from its sister allele for any gene in a somatic cell; can be one of several alternative forms of a gene.
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Autosomal dominant traits:
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appear in equal frequency in males and females; do not skip generations
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How can an individual carry a defective gene but not exhibit the defective phenotype?
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Individuals carry two copies of gene instructions, and one dominant allele could mask the presence of a recessive defective allele.
