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BIO207H5 Lecture Notes - Lecture 11: Sickle-Cell Disease, Penetrance, Bone Marrow

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School
UTM
Department
Biology
Course
BIO207H5
Professor
Fiona Rawle

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Document Summary

Interpretation of genotypic and phenotypic ratios is based on the assumption that there is a strict correlation between phenotype and genotype: however, in some cases different phenotypes can result from the same phenotype. Incomplete penetrance and variable expressivity can complicate interpretation of genotypic and phenotypic ratios. Incomplete penetrance: an organism is pentrant for a trait when the phenotype is consistent with the genotype, an organism which does not produce the phenotype generally associated with the genotype is nonpentrant. Traits for which nonpentrant individuals routinely occur are said to display incomplete penetrance. Incomplete penetrance: polydactyly: polydactyly is an autosomal dominant condition, in which affected individuals have more than 5 fingers and toes. The dominant allele is nonpenetrant in about 25 30% of individuals carrying it. In variable expressivity individuals who carry the alleles for a trait show a phenotype but to a varying degree of severity: waardenburg syndrome has four principle features.

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Related Questions

1. A species of flowering plant includes plants with blooms that range from bright golden yellow to very pale yellow; no flowers carrying the yellow pigment allele appear white. The allele for yellow flower color:

a. must be a suppressor of another allele.
b. demonstrates incomplete penetrance.
c. demonstrates variable expressivity.
d. must be a modifier of another allele.
e. demonstrates variable penetrance.

2. Coat color in mice is determined by two alleles acting at a single locus: B is dominant and results in mice with black coats, and b is recessive and results in mice with white coats. In a litter of 12 mice, nine are black (B/–) and three are white (b/b). What is the penetrance of the B coat color allele?

a. zero
b. 25 percent
c. 50 percent
d. 75 percent
e. 100 percent

3. Semisterility in nearly 50 percent of the progeny they produce is often an indication that:

a. the parents are translocation heterozygotes.
b. both parents carry pericentric inversions.
c. both parents carry polytene chromosomes.
d. one of the parents carries a chromosomal deletion that removes a telomere.
e. one of the parents carries a chromosomal deletion that removes a chromosome's centromere.

4. A researcher is studying melanoma cells derived from a patient's skin tumor. He determines that all melanoma cells are 2n + 1, but the chromosome number in all normal skin cells is 2n. The 2n + 1 melanoma cells likely arose from:

a. mitotic nondisjunction.
b. meiotic nondisjunction.
c. mitotic recombination.
d. parthenogenesis.
e. colchicine treatment.

5. Why won't a balancer chromosome in Drosophila produce viable crossover products when paired with a wild-type chromosome?

a. Balancer chromosomes contain multiple inversions.
b. Balancer chromosomes contain multiple deletions.
c. Balancer chromosomes have no centromere.
d. Balancer chromosomes have no telomeres.
e. None of the answers is correct.

6. A doctor notes that a patient's genome contains 100 potentially harmful recessive mutations; however, the patient is heterozygous for all of the loci considered and thus does not demonstrate any abnormal phenotypes. The 100 recessive mutations the doctor discovered represent the patient's:

a. bivalents.
b. monosomy.
c.genetic load.
d. amphidiploidy.
e.nondisjunction.

7.The term describing the relationship between the number of copies of a gene and how much product is made from the gene is:

gene-dosage effect.
gene balance.
dosage compensation.
transcription.
aneuploidy.

8. The gene for upright ears in rabbits has two alleles. The E allele is dominant and results in upright ears, and the recessive e allele results in droopy ears. Of 100 rabbits surveyed, 87 had a genotype for upright ears (E/–). However, only 72 of these 87 rabbits had upright ears; the remaining 15 rabbits had completely droopy ears. This suggests that the allele for upright ears:

a. has incomplete penetrance.
b. has complete penetrance.
c. demonstrates variable expressivity.
d. is lethal.
e. is incompletely dominant.

9. A researcher has selfed an autotetraploid plant with the genotype D/D/d/d, and in the resulting progeny she observes a 35:1 phenotypic ratio. What can she conclude from this observation?

a. The progeny from this cross do not demonstrate a standard Mendelian phenotypic ratio.
b. In the 35:1 phenotypic ratio, the 1 represents the phenotype of the d/d/d/d progeny.
c. During meiosis in the D/D/d/d parent plant, it is likely that only bivalents, no quadrivalents or trivalents, formed.
d. It is likely that in this plant species, gametes associate with one another randomly.
e. All of the answers are correct.

10. A researcher is studying fur color in a new species of bats. He notices that fur color, which is due to the presence of a dominant allele (G), ranges from light gray to very dark gray. In addition, some bats that carry a G allele have no fur pigmentation whatsoever; their coats appear white. This is an example of:

a. only variable expressivity.
b. only incomplete penetrance.
c. both variable expressivity and incomplete penetrance.
d. recessive allele lethality.
e. pleiotropy.

**Please answer ALL 10 QUESTION**

1. A species of flowering plant includes plants with blooms that range from bright golden yellow to very pale yellow; no flowers carrying the yellow pigment allele appear white. The allele for yellow flower color:

a. must be a suppressor of another allele.

b. demonstrates incomplete penetrance.

c. demonstrates variable expressivity.

d. must be a modifier of another allele.

e. demonstrates variable penetrance.

2. Coat color in mice is determined by two alleles acting at a single locus: B is dominant and results in mice with black coats, and b is recessive and results in mice with white coats. In a litter of 12 mice, nine are black (B/–) and three are white (b/b). What is the penetrance of the B coat color allele?

a. zero

b. 25 percent

c. 50 percent

d. 75 percent

e. 100 percent

3. Semisterility in nearly 50 percent of the progeny they produce is often an indication that:

a. the parents are translocation heterozygotes.

b. both parents carry pericentric inversions.

c. both parents carry polytene chromosomes.

d. one of the parents carries a chromosomal deletion that removes a telomere.

e. one of the parents carries a chromosomal deletion that removes a chromosome's centromere.

4. A researcher is studying melanoma cells derived from a patient's skin tumor. He determines that all melanoma cells are 2n + 1, but the chromosome number in all normal skin cells is 2n. The 2n + 1 melanoma cells likely arose from:

a. mitotic nondisjunction.

b. meiotic nondisjunction.

c. mitotic recombination.

d. parthenogenesis.

e. colchicine treatment.

5. Why won't a balancer chromosome in Drosophila produce viable crossover products when paired with a wild-type chromosome?

a. Balancer chromosomes contain multiple inversions.

b. Balancer chromosomes contain multiple deletions.

c. Balancer chromosomes have no centromere.

d. Balancer chromosomes have no telomeres.

e. None of the answers is correct.

6. A doctor notes that a patient's genome contains 100 potentially harmful recessive mutations; however, the patient is heterozygous for all of the loci considered and thus does not demonstrate any abnormal phenotypes. The 100 recessive mutations the doctor discovered represent the patient's:

a. bivalents.

b. monosomy.

c.genetic load.

d. amphidiploidy.

e.nondisjunction.

7.The term describing the relationship between the number of copies of a gene and how much product is made from the gene is:

a. gene-dosage effect. gene balance.

b. dosage compensation.

c. transcription.

d. aneuploidy.

8. The gene for upright ears in rabbits has two alleles. The E allele is dominant and results in upright ears, and the recessive e allele results in droopy ears. Of 100 rabbits surveyed, 87 had a genotype for upright ears (E/–). However, only 72 of these 87 rabbits had upright ears; the remaining 15 rabbits had completely droopy ears. This suggests that the allele for upright ears:

a. has incomplete penetrance.

b. has complete penetrance.

c. demonstrates variable expressivity.

d. is lethal.

e. is incompletely dominant.

9. A researcher has selfed an autotetraploid plant with the genotype D/D/d/d, and in the resulting progeny she observes a 35:1 phenotypic ratio. What can she conclude from this observation?

a. The progeny from this cross do not demonstrate a standard Mendelian phenotypic ratio.

b. In the 35:1 phenotypic ratio, the 1 represents the phenotype of the d/d/d/d progeny.

c. During meiosis in the D/D/d/d parent plant, it is likely that only bivalents, no quadrivalents or trivalents, formed.

d. It is likely that in this plant species, gametes associate with one another randomly.

e. All of the answers are correct.

10. A researcher is studying fur color in a new species of bats. He notices that fur color, which is due to the presence of a dominant allele (G), ranges from light gray to very dark gray. In addition, some bats that carry a G allele have no fur pigmentation whatsoever; their coats appear white. This is an example of:

a. only variable expressivity.

b. only incomplete penetrance.

c. both variable expressivity and incomplete penetrance.

d. recessive allele lethality.

e. pleiotropy.

These all relate to exceptions to the inheritance patterns encountered by Mendel.​

Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?

Select the four correct statements.

-When an essential gene is mutated, it can result in a lethal phenotype. There are no classic Mendelian monohybrid and dihybrid ratios.
-In the case of codominance, heterozygotes produce gene products from both alleles of a gene. Classic Mendelian monohybrid and dihybrid ratios are modified by codominance.
-In the case of incomplete dominance, the phenotype of the heterozygote is distinct from and often intermediate to the phenotypes of homozygous individuals. Classic Mendelian monohybrid and dihybrid ratios are modified by incomplete dominance.
-Genes exist in a large number of allelic versions and a diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.
-When an essential gene is mutated, it can result in a lethal phenotype. This results in a modification of classic Mendelian ratios.
-The phenotype of the heterozygous genotype is distinct from and often intermediate to the phenotypes of the homozygous genotypes. The joint expression of both alleles in a heterozygote is called codominance. There are no classic Mendelian monohybrid and dihybrid ratios.
-Genes exist in a large number of allelic versions, but in a diploid organism, only one allele of the gene can occupy one homologous gene loci. Classic Mendelian inheritance cannot explain this phenomenon.
-Each gene produces a unique gene product. The effect of one allele in a heterozygote completely masks the effect of the other. Classic Mendelian genetics cannot explain this phenomenon.