Question 1

Adrenoleukodystrophy (ALD)is a fatal disease that results from the inability of liver cells to transport very long chain fatty acids (VLCFAs)across the peroxisomal membrane.It is diagnosed by the presence of high levels of VLFCAs in the blood.The disease results in destruction of brain myelin leading to progressive cognitive impairment,coma,and death by the age of 14.ALD is an X-linked recessive condition,and there has never been a case of ALD described in girls.You have just started your internship at the Mayo clinic and a 10-year-old girl comes in who is in a coma and having seizures.Blood tests show she has extremely elevated levels of long-chain fatty acids.This looks like ALD,but a girl has never been afflicted.When you go to your supervisor to give your diagnosis,which of the following hypotheses do you present to support it?
A)Both her mother and father are recessive carriers of ALD.
B)Most of the Barr bodies in the affected girl's liver have a normal peroxisome gene.
C)Her mother is a carrier for ALD.
D)She has Turner syndrome.
E)Her mother is a carrier,and either the affected girl has only genetically normal Barr bodies in her liver or she has Turner syndromE.

Accepted Answer

ALD is an X-linked recessive disease, meaning it is carried on the X chromosome. As females have two X chromosomes, they are usually only carriers of the disease, as the healthy copy of the X chromosome can compensate for the defective one. However, in rare cases, females can exhibit symptoms of ALD if they have two copies of the defective X chromosome or if they have Turner syndrome, which results in only having one X chromosome. Therefore, the best choice is E, as it considers the possibility of the affected girl either having only genetically normal Barr bodies in her liver or having Turner syndrome, while also acknowledging that her mother is a carrier of the disease.

Question 2

Barr bodies are a diagnostic feature of X inactivation.

Accepted Answer

Barr bodies are a diagnostic feature of X inactivation, which is the process by which one of the two X chromosomes in females is inactivated to equalize gene expression between males and females.

Question 3

The karyotype of a young patient shows two Barr bodies per cell.What condition might this child have?
A)Turner syndrome
B)Triple X syndrome
C)Down syndrome
D)Klinefelter syndrome
E)This child is a normal femalE.

Accepted Answer

Triple X syndrome is a condition in which a female has three X chromosomes instead of the usual two. This can cause a variety of symptoms, including intellectual disability, developmental delays, and physical abnormalities. The presence of two Barr bodies per cell is a characteristic finding in Triple X syndrome.

Question 4

Mendel used garden peas to study inheritance patterns,but other plants would have worked as well.Study the characteristics of the plants below,and determine which would be the best model organism to study inheritance patterns.
A)Phalaenopsis orchids produce large,showy flowers once a year.They easily self-pollinate and produce thousands of minute seeds in their fruits.In order for orchid seeds to germinate,they must form a symbiosis with a fungus that provides it with carbohydrates,or they must be plated onto nutrient rich agar that provides a source of carbohydrates.Once germinated,plants will flower in approximately 5 years.
B)Papayas are dioecious;they produce separate male and female plants.They flower abundantly throughout the year,and female flowers give rise to large fruits with copious seeds.Once germinated,plants will flower and bear fruit in about 1 year.
C)Impatiens are common garden annuals that produce copious numbers of bright flowers throughout the growing season.Their flowers come in an array of different colors,they are self-fertile,and produce a fruit that is sensitive to the touch.When it is ripe,the lightest touch will cause the capsule to spring open and explosively release up to 100 seeds in all directions.This dramatic seed dispersal mechanism has given rise to its common name,touch-me-not.Impatiens have fast generation times,and a germinated seed can produce flowers in about 6 weeks.
D)Oak trees produce thousands of flowers every year.They are wind pollinated and many oak trees will all flower simultaneously,causing a yellow haze of pollen in the air and on the surface of lakes and ponds.The large sticky stigmas receive the airborne pollen and produce 1-seeded acorns.Once an acorn germinates,the new oak can begin to flower in 3-5 years.

Accepted Answer

Impatiens are the best choice as they have fast generation times, are self-fertile, come in an array of different colors, and the germinated seed can produce flowers in about 6 weeks. The explosive seed dispersal mechanism would be interesting to study in terms of inheritance patterns.

Question 5

Barr bodies
A)are formed in females
B)are formed only in males
C)cause an increased production of X-linked gene products
D)inactivate Xic on autosomes
E)are formed only in males and inactivate Xic on autosomes

Accepted Answer

Barr bodies are formed in females and are a condensed, inactive X chromosome that is visible in the nucleus. This allows females to balance out the gene expression from their two X chromosomes.

Question 6

The frequency of crossing over varies along the length of the chromosome.

Accepted Answer

The frequency of crossing over is not uniform along the length of the chromosome. It is affected by factors such as chromosomal structure, physical location, and the distance between genes. Therefore, some regions of the chromosome may show a higher frequency of recombination compared to others.

Question 7

In biparental inheritance,paternal and maternal gametes provide chloroplasts to the zygote.

Accepted Answer

Biparental inheritance is a type of inheritance pattern seen in plants where both the maternal and paternal gametes contribute chloroplasts to the zygote. This is different from uniparental inheritance, where only one parent contributes chloroplasts.

Question 8

If a male cat with orange fur produces female offspring with calico fur,what color was the mother cat?
A)orange
B)black
C)calico
D)black or calico
E)orange or calico

Accepted Answer

The coloration of calico cats is a result of X-chromosome inactivation, which is a phenomenon that occurs in female mammals. Since male cats (XY) with orange fur can only pass on the orange gene (O) or a non-orange gene (o), and since calico cats are typically female (XX) with a combination of orange (O) and black (B) fur, the mother must provide the black fur gene. Therefore, the mother could be either black or calico, as calico females also carry the black fur gene.

Question 9

Two genes that are close together on the same chromosome will cross over more frequently than two genes that are further apart.

Accepted Answer

Two genes that are close together on the same chromosome are less likely to be separated by crossover during meiosis, so they cross over less frequently than two genes that are further apart.

Question 10

In cats,a fur color gene is on the X chromosome.At this locus,cats can have a black allele or an orange allele.Cats who are homozygous for the black allele have black fur,cats who are homozygous for the orange allele have orange fur,and cats who are heterozygous at this locus are tortoiseshell.What offspring would you expect from a cross between an orange female and a black male?
A)orange females and black males
B)black females and orange males
C)tortoiseshell females and orange males
D)tortoiseshell females and black males
E)tortoiseshell females and tortoiseshell males

Accepted Answer

An orange female (X^O X^O) crossed with a black male (X^B Y) will produce tortoiseshell females (X^O X^B) and orange males (X^O Y).

Question 11

A human cell with a Barr body always comes from a female.

Accepted Answer

The answer of A human cell with a Barr body...

Question 12

Two identical twins were separated at birth,one grew up in a prosperous home with ample food and time for rest.The other twin was tragically abandoned and grew up in and out of foster homes and living on the streets.After more than 20 years,the two twins were reunited,but despite their identical genomes,the twins looked very different.The most noticeable difference was their difference in stature,the prosperous twin was tall and well built,while the abandoned twin was short and scrawny.How can you explain these differences?
A)The twins actually have different genotypes.
B)The poor twin was undernourished as a child,and as a result his genes that control height and stature were mutated,resulting in a different phenotype.
C)The poor twin was undernourished as a child,and as a result he was unable to reach the full potential of his genes.
D)Traits such as height and stature are are not controlled by a person's genes,rather they are determined by environmental factors,such as nutrition,rest,and exercise.
E)Twins often have different phenotypes,because one twin gets more resources in the womb than the other.

Accepted Answer

The poor twin was undernourished as a child, which is likely to have resulted in malnourishment, leading to stunted growth, which means that the poor twin may not have reached their full potential for height and stature. Identical twins have the same genotype, so option A is incorrect. While some genetic mutations can lead to different phenotypes as stated in option B, it is unlikely to occur in both height and stature. Option D is incorrect because genes play a crucial role in determining traits such as height and stature, but environmental factors can also affect them. Option E is incorrect because twins usually get equal resources in the womb.

Question 13

A mitochondrion has its own genome,so it can live independently from a eukaryotic cell.

Accepted Answer

Although a mitochondrion has its own genome, it cannot live independently from a eukaryotic cell because it relies on the cell for many essential functions and resources.

Question 14

The actions of Xist result in an organism that is a phenotypic mosaic.

Accepted Answer

Xist is a gene involved in X chromosome inactivation in females. Its actions result in the silencing of one X chromosome in each cell, which leads to a mosaic pattern of gene expression in female individuals. Due to X chromosome inactivation, different cells in the female body can express different sets of X-linked genes, resulting in a phenotypic mosaic. This pattern can be observed in female calico cats, for example, which have patches of different coat colors due to X chromosome inactivation.

Question 15

Paternal inheritance occurs in plants but not animals because plants have chloroplasts instead of mitochondria.

Accepted Answer

Paternal inheritance can occur in both plants and animals but it is relatively rare. In plants, chloroplasts can be inherited from the male parent along with other genetic material. In animals, mitochondrial DNA is usually inherited solely from the maternal parent.

Question 16

You examine the chromosomes from a somatic cell nucleus of a human individual.That nucleus contains a Y chromosome and a Barr body.Which of the following is ACCURATE?
A)The individual is a female because there is a Barr body
B)The individual is a male because there is a Y chromosome
C)The individual has Klinefelter Syndrome
D)The individual is a male with Klinefelter Syndrome
E)The individual is a female with Klinefelter Syndrome

Accepted Answer

The presence of a Y chromosome indicates that the individual is male, and the presence of a Barr body suggests that there is a second X chromosome that has been inactivated. This combination could be seen in individuals with Klinefelter Syndrome, which occurs when a male has an extra X chromosome (XXY genotype), and one of the X chromosomes is inactivated to form a Barr body. Therefore, choice D is the most accurate option.

Question 17

The agouti gene,when expressed in mice,makes them obese,ravenous,yellow,and prone to diabetes.The agouti phenotype is dominant.During ovulation an agouti mouse is given a drug that methylates (or shuts off the agouti gene).She is then bred to another mouse and gives birth to a litter of baby mice,none of whom have the agouti phenotype.Which of the following is accurate?
A)an epigenetic change in the mother was passed to her offspring
B)her offspring inherit the methylated form of the agouti gene
C)the agouti gene will be inactivated for the entire lives of her offspring
D)all of these are correct

Accepted Answer

The drug methylated the agouti gene in the mother, which was then passed on to her offspring. The methylated form of the gene is inactive, so the offspring do not have the agouti phenotype. The epigenetic change in the mother was passed to her offspring, and the offspring inherit the methylated form of the agouti gene. The agouti gene will be inactivated for the entire lives of her offspring.

Question 18

Environment can have an influence on the range of phenotypes seen in a population.

Accepted Answer

Environmental factors such as temperature, availability of resources, and predation pressure can affect the expression of different traits in a population, leading to a wider range of phenotypes. This is known as phenotypic plasticity.

Question 19

Which of the following is evidence supporting the Lyon hypothesis of X inactivation?
A)Female mammals that are heterozygous for X-linked traits are phenotypic mosaics.
B)A highly condensed structure is consistently observed in female cells,but not in normal male cells.
C)A female cat that is homozygous for coat color cannot have a calico phenotype.
D)Calico patterns of coat color are never exactly the same.
E)All of these are correct

Accepted Answer

The Lyon hypothesis of X inactivation is supported by all the given options. A) Female mammals exhibit phenotypic mosaicism for X-linked traits due to random inactivation of one of the X chromosomes in each cell. B) The Barr body, a highly condensed X chromosome, is observed in female cells, supporting X inactivation. C) A homozygous female cat for coat color cannot be calico because the calico phenotype requires different alleles on the X chromosomes, which is an example of X inactivation leading to mosaic patterns. D) The unique calico patterns in cats are due to random X inactivation, resulting in different expressions of coat color genes in different areas.

Quiz 14: Patterns of Inheritance

Barr bodies are a diagnostic feature of X inactivation.

The karyotype of a young patient shows two Barr bodies per cell.What condition might this child have?

Mendel used garden peas to study inheritance patterns,but other plants would have worked as well.Study the characteristics of the plants below,and determine which would be the best model organism to study inheritance patterns.

Barr bodies