Ch. 5 - Beyond Mendel's Laws Flashcards
In the parental generation, a male fruit fly with a gray body (BB) and straight wings (CC) was crossed with a female fruit fly with a black body (bb) and curved wings (cc). The F1 flies all had gray bodies and straight wings. A female F1 fly was crossed with a male fly that was homozygous recessive for both traits. The female fly had the B and C alleles on one chromosome and the b and c alleles on the other chromosome. Because the genes are linked, the expected ratio in the F2 generation would be 50% with gray bodies and straight wings and 50% with black bodies and curved wings. But four different phenotype combinations appear in the offspring, with two expected, but there were also offspring with gray bodies and curved wings and offspring with black bodies and straight wings. Which of the following best explains what happened?
A recombination occurred during the formation of the F1 female’s egg cells
I^AI^A
Blood type A
I^BI^B
Blood type B
I^AI^B
Blood type AB
ii
Bloody type O
When a genotype is _____ , some individuals with the genotype do not have the associated phenotype.
Incompletely penetrant
The severity or extent to which a phenotype is expressed is its _____.
Expressivity
The same phenotype may result from different genotypes due to _____.
Genetic heterogeneity
An environmentally caused condition whose symptoms are similar to those of a known inherited disorder is called a(n) _____.
Phenocopy
A(n) _____ allele may result in a phenotypic class that does not survive long enough to reproduce.
Lethal
Which of the following statements describe mitochondrial DNA?
Fewer types of DNA repair than nuclear DNA
Inherited from the mother only
No crossing over
High exposure to oxygen free radicals
Carries 37 genes
In epistasis, the blocked gene is expressed normally, but the product of the modifier gene inactivates it.
True
An allele combination that produces a phenotype in everyone who inherits it is not penetrant.
False
A phenotype is variably expressive if symptoms vary in intensity among different people.
True
On a molecular level, genetic heterogeneity occurs when a single protein affects different body parts, participates in more than one biochemical reaction.
False
Phenocopies are genetically caused traits that appear to be inherited.
False
What is the best explanation for the inheritance pattern shown in the pedigree below?
Mitochondrial inheritance
An investigator determines that gene c and gene f are linked on chromosome 5 of the honeybee genome. Bees that are homozygous for the dominant wild type alleles have long stingers (c+c+) and bi-lobed wings (f+f+). Bees that are homozygous for the recessive mutant alleles have short stingers (cc) and tri-lobed wings (ff). The parent generation was composed of homozygous dominant male bees (c+c+f+f+), and homozygous recessive females (ccff), which produced a heterozygous F1 generation. Male bees from the F1 generation (c+cf+f) were mated in a testcross with homozygous recessive females (ccff). The testcross produced the F2 generation. The resulting phenotypic ratios in the F2 generation were as follows: Long stingers and bi-lobed wings (362); short stingers and tri-lobed wings (348); long stingers and tri-lobed wings (151); and short stingers and bi-lobed wings (139). Based on the recombination frequency of this cross, what is the map distance between the c and f genes?
29 map units
When the cystic fibrosis gene was discovered in 1989, only one mutation was described, and a diagnostic test was developed to detect it. Over the years, as more mutations were discovered, they were added to the test panel. Today, most pregnant women are offered a CF test that detects 100 or so alleles, although more than 1600 mutations have been discovered. Which of these is reflected by the given facts?
The presence of multiple alleles
In humans, the melanocortin 1 receptor (MC1R) is a key protein involved in human skin and hair color. Several versions of the MC1R gene with changes in single nucleotides have been reported. One of these has the amino acid histidine where the amino acid aspartate normally is found at a certain location in the MC1R protein. Another version has a tryptophan where an arginine should be. Both of these versions of the gene are associated with red hair, whereas the wild type version of this gene is associated with dark hair. What phenomenon is occurring with these genes?
Multiple alleles
You are working in the lab, studying what you suspect to be a mitochondrial disease. You isolate mitochondria from a child with this disease, and sequence the mitochondrial genome. You also sequence the mitochondrial genomes of the parents. You are surprised to find that the child has a mutation in a very important mitochondrial gene, but that neither of her parents have this mutation. Further, both parents are healthy. What most likely explains this finding?
Because mitochondrial DNA mutates much more quickly than nuclear DNA, the girl likely incurred a new mutation in her mitochondrial DNA
Imagine that the genes for eyelash length and hair texture are on the same chromosome. A man with long eyelashes and straight hair has one chromosome with the E gene and the S gene, and a second chromosome with the recessive genes, e and s. Assuming crossing over does not occur in meiosis, what combinations of genes should you see in his gametes?
ES and es
A pair of college sweethearts do a DNA test to find out their respective ancestries. They are shocked to find that they share nearly 1% of their genome. What is their likely relationship?
Third cousins
You identify a rare purple plumed parrot. When you cross the parrot to a true breeding white parrot, you get 1/2 white and 1/2 purple parrots. When you cross two purple parrots you get 1/3 white parrots and 2/3 purple parrots. Which of the following best explains this result?
The purple allele is lethal in the homozygous state
Familial hypercholesterolemia illustrates incomplete dominance in humans because _____.
Heterozygotes have an intermediate number of low-density lipoprotein receptors on their liver cells
Epistasis and multiple alleles differ in that _____.
Epistasis is an interaction between two genes, and multiple alleles are variants of the same gene
Marbles is a Manx cat whose tail is so short that she appears not to have one. The genotype for short tail in Manx cats is heterozygous (Mm). Cats that are genotype mm have normal length tails, but cats that are genotype MM die before birth due to highly abnormal brains and spinal cords. Marbles has one copy of a dominant _____ allele.
Lethal
Several members of the Fitzsimmons family have polydactyly, and they differ in their numbers of extra fingers and toes. Yet, certain relatives who should have extra digits don’t, such as Megan Fitzsimmons. She has two children, a son with two extra fingers and a daughter with an extra toe, and her father has an extra digit on each hand and foot. Polydactyly in this family is _____.
Variably expressive and incompletely penetrant
Hairlessness in dogs is inherited from a single dominant allele. Inheriting two dominant alleles is lethal for an embryo. Penelope, a hairless dog mates with Arnold, a dog with hair. The probability Penelope will have hairless puppies is _____.
1/2
A gene may have many alleles, but a person has only two alleles for a gene, because _____.
A gene can be altered in many ways, but a person has only two copies of any gene
A man who has normal hearing and has a recessive deafness allele on chromosome 17 marries a woman who also has normal hearing and also has a recessive deafness allele, but this allele is on chromosome 3. The probability that their children will be deaf due to either of these mutated genes is closest to _____.
0%
Some combinations of recessive alleles cause problems so severe that a fetus may cease to develop. Such lethal allele combinations appear to alter Mendelian ratios because _____.
Homozygotes for the lethal allele do not appear as a progeny class
Zuzu is a white cat. She is genotype Ww for the “white masking gene” that reduces the number of melanocytes (pigment-containing cells). As a result, her body makes pigment, but it cannot get into the cells where it would color the fur. Zuzu’s white masking gene is _____ to the melanin pigment gene because it prevents full expression of the pigment.
Epistatic
Mitochondrial disorders are probably very rare because _____.
The oocytes with harmful mitochondrial mutations do not have sufficient energy to survive
The mitochondrial genome consists of _____ genes.
37
Mitochondrial DNA differs from nuclear DNA in that it _____.
Is poorer at DNA repaid
Mitochondrial disorders tend to cause great fatigue because _____.
Muscle cells are normally filled with mitochondria
LOD (logarithm of the odds) scores are used to indicate linkage between genes. A LOD score of _____ or greater is a strong indicator of linkage.
3
A, B, and C are linked genes. Recombination between A and B is 3%; between A and C is 6%; and between B and C is 9%. What is the order of these genes on the chromosome?
B-A-C
Geneticists construct linkage maps of chromosomes by _____.
Calculating the percent recombination between two genes on the same chromosome
Genes that are situated close on a chromosome _____.
Do not assort independently
In common English, “linkage” refers to one event that tends to occur when another does. In genetics, linkage has a precise meaning. It refers to the transmission of _____.
Two genes on the same chromosome
Types of genetic markers include _____.
Places in the genome where a base varies among individuals in a population
