PCB 3063 Complete Exam 1 Set 2025

Autosomal dominant - - -appear in every generation -males & females equally affected -all affected individuals have an affected parent -most affected individuals are heterozygotes Autosomal recessive - --skips generations -males & females equally affected -all affected individuals are homozygous recessive -unaffected parents of affected offspring are obligate heterozygotes -occurs more often in consanguineous matings Law of independent assortment - -the law that states that genes separate independently of one another in meiosis What is independent assortment? A. That in diploids, two alleles exist on independent chromosomes B. That the two homologous chromosomes separate and become independent of each other during meiosis C. That the two alleles for a single gene can be crossed over during prophase 1 independently of one another D. That nonhomologous chromosomes move independently of one another in meiosis E. That the two stages of meiosis are independent of one another - -d. That nonhomologous chromosomes move independently of one another in meiosis As seen in the figure, how one homologous pair separates does not influence how a different homologous pair separates. For unlinked genes, this leads to variations in alleles in the gametes. What is the probability that two parents who are heterozygous for the recessive trait of albinism will have two albino offspring? A. 1/2 B. 1/4 C. 1/8 D. 1/16 E. 1/32 - -d. 1/16 For each birth, the probability that the couple will have a homozygous recessive child is 1/4. Using the product law, the probability of having two such offspring is 1/4 x 1/4 = 1/16. PCB 3063 PCB 3063 Law of segregation - -mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete Law of dominance - -in many traits one allele is dominant over the other allele. The "weaker (recessive" allele is only expressed when it is paired with another recessive allele Mendel's third postulate is "during the formation of gametes, the paired unit factors separate, or segregate, randomly so that each gamete receives one or the other with equal likelihood." when does this segregation occur? A. In g1 B. In mitotic anaphase C. In meiotic anaphase i D. In meiotic anaphase ii E. In both meiotic anaphase i and anaphase ii - -c. In meiotic anaphase i The alleles separate ("segregate") from one another when the homologs are separated. The two homologs migrate to opposite poles at anaphase i. How many different types of gametes can be formed by the genotype aabbcc? A. 3 B. 4 C. 8 D. 16 E. 32 - -c. 8 First, you must determine the number of different heterozygous gene pairs (n) involved. Once n is determined, 2n is the number of different gametes that can be formed. Here, there are three heterozygous genes, so the correct formula is 2^3 = 8. The possible gametes are as follows. P genotype: aabbcc Gametes: abc, abc, abc, abc, abc, abc, abc, abc X-linked dominant - --disorders caused by mutations in genes on the x chromosome, -in females (who have two x chromosomes), a mutation in one of the two copies of the gene in each cell is sufficient to cause the disorder. -in males (who have only one x chromosome), a mutation in the only copy of the gene in each cell causes the disorder. -males experience more severe symptoms of the disorder than females -no male to male transmission PCB 3063 PCB 3063 X-linked recessive - --disorders caused by mutations in genes on the x chromosome. -in males (who have only one x chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. -in females (who have two x chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder. -affect males more frequently -no male-to-male transmission Mitochondrial inheritance - --no transmission from m -maternal inheritance -potential for the disease to affect both sons and daughters of affected f Homozygote - -an individual with 2 identical alleles for a gene Heterozygote - -an individual with 2 different alleles for a gene Mendel's first postulate is "genetic characters are controlled by unit factors existing in pairs in an individual." what is a modern term for "unit factors?" A. Genes B. Chromosomes C. D n a D. Phenotypes E. Alleles - -a. Genes If the green pea pod allele (g) is dominant to the yellow allele (g), a cross between two heterozygous plants would be expected to produce _____. A. All green B. 1/4 green and 3/4 yellow C. 1/2 green and 1/2 yellow D. 3/4 green and 1/4 yellow E. All yellow - -c. 3/4 green and 1/4 yellow The cross is expected to produce offspring in the genotypic proportions of 1/4 gg, 2/4 gg, and 1/4 gg. Since g is dominant to g, 1/4 gg and 2/4 gg = 3/4 green and 1/4 gg is yellow. Hemizygote - -a male positive for an x-linked mutation Sex-linked gene - --all sons of an affected mother are affected -all daughters of an affected male are carriers -no male-to-male transmission of trait -males more often affected than females PCB 3063 PCB 3063 Sex-limited traits - -a characteristic controlled by autosomal genes that is phenotypically exhibited in only one gender Sex-influenced traits - -an autosomal trait that is influenced by the presence of male or female sex hormones (ess) Duchenne muscular dystrophy is caused by a recessive x-linked allele. A man with this disorder _____ A. Could have inherited it from either parent B. Must have inherited it from his mother C. Must have inherited it from both parents D. Can pass it along to all of his children E. Can pass it along to only his sons - -b. Must have inherited it from his mother The man must carry only one copy of the allele on his x chromosome, which he must have inherited from his mother. He would have inherited a y chromosome from his father. He would pass that x chromosome on to only his daughters. In chickens, cock-feathering is a sex-limited recessive trait. What ratio of offspring would you get from an hh-hen feathered hen x hh-cock feathered rooster? A. 1:1 hen-feathered hens: cock-feathered roosters B. All hen-feathered C. All cock-feathered D. 3:1 hen-feathered hens: cock-feathered roosters E. Unable to predict from this information - -a. 1:1 hen-feathered hens: cock-feathered roosters All offspring from this cross are hh, but since the trait is sex-limited, only the roosters will have cock-feathering, while the hens will have hen-feathering. Heteroplasmy - -presence of two or more distinct variants of dna within the cytoplasm of a single cell. Sister chromatid - -one of a pair of identical chromosomes created before a cell divides Homologous chromosome - -chromosomes that have the same sequence of genes and the same structure Variable expressivity - -individuals who carry alleles for a trait show a phenotype, but to a varying degree of severity (waardenburg syndrome) PCB 3063 PCB 3063 If one hot summer, you shaved a small patch from your himalayan rabbit's brown paw, and then let it grow back while the rabbit played outdoors, what color would the fur grow back? A. White B. Brown C. Light brown D. Depends on the animal's genotype E. Depends on the animal's nutrition - -a. White The white fur in himalayans is due to a temperature-sensitive allele: the encoded protein does not function to produce brown pigment at elevated temperatures. Therefore, if the rabbit was exposed to hot temperatures while the fur grew back, the pigment would not be produced and you would have a white patch. Penetrance - --percentage of a population with a particular genotype that show the expected phenotype -can be complete (100%) or incomplete (e.g., retinoblastoma penetrance is 75%). Anticipation - -a phenomenon where the symptoms of a genetic disorder become apparent at an earlier age with each generation (huntington's_ Paternal transmission bias - -like anticipation but for paternal Dynamic mutation - -a type of mutation in which a repeated sequence, such as three nucleotides, can readily increase in number from one generation to the next. Pleiotropy - -a single gene having multiple effects on an individuals phenotype Genotype - -the specific alleles of genes in dna Phenotype - -observable/measurable physical traits Haplotype - -a group of alleles of different genes on a single chromosome that are closely enough linked to be inherited usually as a unit Karyotype - -organized picture of chromosomes in the cell Diploid - -2 copies of each chromosome Haploid - -1 copy of each chromosome Kinetochore - -protein complexes that assemble on the centromeric regions of the chromosomes Centriole/centrosome - -produce spindle fibers during cell division PCB 3063 PCB 3063 Chiasmata - -points at which crossovers occur The result is an exchange of genetic material between homologous chromosomes and creation of novel combinations of alleles in offspring. Nondisjunction - -error in meiosis in which homologous chromosomes fail to separate. Consanguinity - -blood relationship Maternal effect genes - -a gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the genotype. Mendelian monohybrid - -based on law of segregation A cross of one observable trait with 2 alleles Assuming both parents are heterozygotes: Genotypic ratio: 1:2:1 Phenotypic ratio: 3:1 (if the phenotypic ration is 2:1 there is probably a recessive lethal allele) Mendelian dihybrid - -based on law of segregation and law of independent assortment A cross between two different lines/genes that differ in two observed traits Assuming both parents are heterozygotes: Phenotypic ratio: 9:3:3:1 Incomplete dominance - --f1 hybrids that differ from both parents express an intermediate phenotype - "blending". -neither allele is dominant or recessive to the other. -phenotypic ratios are same as genotypic ratios - 1:2:1 Codominance - --f1 hybrids express the phenotypes of both parents equally. -neither allele is dominant or recessive to the other. -phenotypic ratios are same as genotypic ratios. - 1:2:1 In a plant species, if the b allele (blue flowers) and the b allele (white flowers) are incompletely dominant (b b is light blue), what offspring ratio is expected in a cross between a blue-flowered plant and a white-f