1. _______ is a human hereditary disease that is caused by a dominant allele but does not show up in affected individuals until they are in middle age. Huntington's disease

2. . A human female with only one X chromosome is said to have a condition called Turner syndrome.

3.

. A person who has lost a large amount of blood but is still alive is found in a wrecked automobile under a highway bridge. Several people are helping the paramedics load the victim into the ambulance. After the ambulance has departed for the hospital, you overhear the following conversation from the persons who helped the paramedics. "I am certain that when that guy gets to the hospital, they will transfuse him with any blood that they have in the blood bank since he has lost so much blood." The other person says, "Yeah, I bet you're right!" Having had a biology course, you know which blood could be safely given to anyone. Select it below.

O

4. . After fertilization, the resulting zygote develops by which of the following processes? mitosis

5.

. Children born in areas where proper nutrition is not available to them do not always realize their full growth potential. These children have the genes for normal growth of bones. Which of the following statements can best explain this situation?

Since nutrition is necessary for proper development and is a part of the environment, it is a clear case of environmental effect on the phenotype.

6. . In humans, if a non-disjunction event led to an individual with a genotype of XO, they would

be female because they do not have a Y chromosome

7. . In the human, the body cells (non-sex cells) contain two sets of chromosomes totaling 46

8.

. In white tigers, the absence of fur pigmentation is caused by a recessive allele. This allele also causes the tigers to be cross-eyed. If two tigers heterozygous for this allele mate and produce offspring, what percentage can be expected to be white and/or cross-eyed?

25% will be white and the same 25% will be cross-eyed.

9. One of the most likely explanations for the evolutionary origin of sexual reproduction is that

DNA replication errors could be corrected by recombination.

10.Organisms generally have many more genes that assort independently than the number of chromosomes. This phenomenon is due to

crossing over

11. The allelic make up of an individual is referred to as its Genotype.

12. Which of the following cell functions are maintained by cell division growth and reproduction

13. Which offspring will inherit all their mitochondria DNA from their mother and none from their father? both sons and daughters

14.

1. Eukaryotic chromosomes are composed of a complex of 60% protein and 40% DNA. The name of this chemical complex is a

chromatin

15. 6. _________ is that portion of the cell cycle in which the chromosomes are invisible under the light microscope

6. Interphase

because they are not yet condensed.

7. Prophase is the first stage of mitosis characterized by the _________ of the chromosomes.

8. __________ is the stage of mitosis characterized by the alignment of the chromosomes in a ring along the inner circumference of the cell.

9. The stage of mitosis characterized by the physical separation of sister chromatids is called __________.

10. The last stage of mitosis is characterized by the disassembly of spindle apparatus, the reestablishment of the nuclear membrane, and the decondensation of the chromosomes into invisible threads. This stage is known as _________.

7condensation

8Metaphase

9anaphase

10telophase

16.

11. The progress of mitosis is regulated by ______ and their dependent kinases.

12. Binary fission in prokaryotes concludes with the accumulation of _______ protein at the midpoint of the cell which facilitates septum formation.

13. Normally _____ functions in the cell to stop cell division if the cell has experienced extensive DNA damage.

11cyclins

12FtsZ

13p53

17. Which of the following is not a checkpoint for cell cycle control in a eukaryotic cell? MFP

18. The zygote has two copies of each chromosome.

19.The reduction division that separates two haploid complements from each other is called meiosis.

20. The point of connection between the two sister chromatids before anaphase of mitosis separates them is called the centromere.

21. In one of the first steps in meiosis, the homologous pairs of chromosomes pair up along their length.

22. Between the two divisions of meiosis there is no S phase.

23.

A 39-year-old woman is in her sixth week of pregnancy. Due to her advanced maternal age, she is at high risk for having a baby with Down's syndrome. She would like to find out as early as possible whether or not her baby has Down's syndrome. Her doctor suggests chorionic villi sampling.

24. A cell biologist is conducting a karyotype procedure on alligator red blood cells. Exactly what does this mean?

It means that chromosomes from the red blood cells of the alligator will be examined with a microscope, photographed, counted,

lined up with their respective homologous partner, and displayed.

25. A diploid organism that has two identical alleles for the same trait is called _______ for that particular trait. homozygous

26. A gene for a particular trait that is only expressed in the presence of another gene of the same kind is called a(n) recessive gene

27.

A secretor is a person who secretes their blood type antigens into body fluids and secretions such as saliva. By comparison, a non-secretor does not. A person's status as a secretor or non-secretor is independent of blood type. Consider the following inheritance pattern of this trait: all offspring are secretorssecretor x secretor all offspring are non-secretorsnon-secretor x non-secretor all offspring are secretorssecretor x non-secretor F2 generation = 75% secretors, 25% non-secretorsF1 generation secretors The genotypic ratio produced in the F2 generation is

1:2:1.

28. A single gene has 3 or more alternative forms. These are called multiple alleles.

29. A test cross can be used to do all of the following except identify the chromosome on which a gene is located.

31. ABO blood group expression is an example of multiple alleles.32. All of the following animal cells are diploid except gametic.

33. All of the following are processes that promote new genetic combinations except mitosis.

34. Amniocentesis is a procedure that is normally used for diagnosis of genetic disorders.35. An allele that is present but unexpressed is recessive.

36. An individual possessing both kinds of alleles of two different traits is called dihybrid.

37. Animal cells typically achieve cytokinesis by forming a cleavage furrow that pinches the cell into two

38.As a genetic counselor, you are constructing a human pedigree for a particular disease. You note that every generation shows the trait, suggesting that it is

dominant.

39. Bacteria divide by binary _______, in which the cell divides into two nearly equal halves. fission

39a All of the following animal cells are diploid except Gametic

41. Before cell division of the body cells, each homologue replicates into two parts. These parts are connected by a centromere and are called

sister chromatids.

42.By the end of this phase of mitosis, the centromere joining each pair of sister chromatids is attached by microtubules to opposite poles of the spindle apparatus. This phase is called

prophase

43. Chromosomes exchange genetic information by crossing over44. Crossing over of chromosomes takes place in prophase I.45. Cytokinesis occurs right after telophase.

46.Difficult ****** Let P = purple flowers and p = white, and T = tall plants and t = dwarf. What combinations of gametes could be produced by a heterozygote for both the traits?

PT, Pt, pT, pt

47. Diploid organisms use meiosis for the development of gametes. Meiosis consists of how many rounds of nuclear division? two

48. DNA coiled around histone proteins forms a complex known as a _________. nucleosome

49. Each chromosome has a region called the _________ somewhere between the two ends where attachment of protein rays occurs. centromere

50. Eukaryotic chromosomes are composed of a complex of 60% protein and 40% DNA. The name of this chemical complex is chromatin

51. Genetic differences between individuals in a population are called polymorphisms.

52. Genetic exchange between two arms of a chromosome pair is more likely to occur if the distance between the genes is great. It is called crossing over.

53.

Height and eye colors are two examples of continuous variation in humans. Whereas in pea plants the tall allele is dominant over the short allele, there are no intermediate heights in peas. Which of the following is the best explanation for the differences described above?

Many genes, rather than one gene for a characteristic, control some variations in species.

54. Hemophilia is a recessive condition.

55. How many different types of gametes can be formed by plants with a genotype of PpYYrrTt? 4

56. Humans who have lost even one copy of an autosome are called monosomics.

56a What property distinguished Mendel’s investigation from previous studies? Mendel quantified his results

57.

Huntington's disease is caused by an autosomal dominant allele. It is a lethal disease, but it persists in the human population. Which of the following statements best describes why?

Huntington's disease presents symptoms in humans after many have already reproduced; therefore, they are unaware that they passed on Huntington's disease.

59. If a eukaryotic cell has a single set of chromosomes, it is called haploid

60. If a human female has two Barr bodies, it is almost certain that she developed from a fertilized egg with 3 X chromosomes.

61. If a XY individual had a deletion of the SYR gene, they would develop as a female.

62.If an XY individual had a genetic disorder in which they were insensitive to androgens, their genotype and phenotype would be

XY, female.

63. If some alternative alleles with detrimental effects exist in significant proportions in populations, the condition is called a genetic disorder.

64.

If you needed to order genes on a chromosome, you would perform a three-point cross.

65.In 95% of cases of Down's syndrome, there is an entire extra chromosome 21 in every cell. This aneuploid condition is the result of

independent assortment.

66. In a heterozygous individual the allele being expressed is dominant.

67.

In a typical Mendel experiment on pea-seed color, if the dominant yellow seed-bearing plant was crossed with the recessive green seed-bearing plant, the F2 generation will show what ratio of each kind?

yellow: 1 green

68. In humans the diploid number of chromosomes is 46. The haploid The homologous chromosomes have

number is 23. Prior to mitosis in the cell cycle, the cell is in the G2 phase. Which of the statements is true?

all been copied through DNA replication and are now sister chromatids.

69. In humans, if a non-disjunction event led to an individual with a genotype of XXY, they would

be male because they have a Y chromosome.

70.

In humans, the male has an X and Y sex chromosome. The human female has two X chromosomes. In birds, the female has a Z and a W sex chromosome while the male has two Z chromosomes. Which of the following statements is accurate about which parent controls the gender of the offspring?

In humans the male controls the gender of the offspring, and in birds the female controls the gender.

71. In prophase, ribosomal RNA synthesis stops when the chromosomes condense, and this makes the nucleolus to disappear

72. In sickle cell anemia, the defective hemoglobin differs from the normal hemoglobin by a single amino acid substitution.

72a A true-breeding plant is one that produces offspring that are always the same as the parent

73. In the human, the body cells (non-sex cells) contain two sets of chromosomes totaling 46

74. Individuals carrying two "factors" for most traits are diploid.

75.

Irene and William are having their first child. Irene knows her blood type is A, but William does not know his blood type. However, William knows that his mother and father were B. Their first child is a boy named Gregory. Gregory has type O blood. Of course, Irene and William do not understand how this happened. You could explain this to them using which of the following choices?

Irene's genotype is AO, and William's genotype is BO; thus, Gregory expresses the phenotype of O.

76.Let P = purple flowers and p = white, and T = tall plants and t = dwarf. Of the 16 possible gamete combinations in the dihybrid cross, how many would be the phenotype white, tall?

3

77.Let P = purple flowers and p = white, and T = tall plants and t = dwarf. What would be the appearance of a plant with the genotype PpTt?

purple flowers, tall

78.

Let R = red pigment and r = no pigment. In carnations, RR offspring make a lot of red pigment, rr offspring make no pigment and Rr offspring make a small amount of red pigment, thus appearing pink. Pink carnations are therefore an example of

incomplete dominance.

79. Located in the nucleus are Chromosomes

80. Meiosis also has been called reduction division because

there is a reduction in the chromosome number during two separate nuclear and cell divisions to produce gametes.

81.Meiosis and mitosis are both processes that involve nuclear division. What is the difference between the two?

Mitosis is nuclear division, which ultimately leads to diploid somatic cells. Meiosis is nuclear division, which ultimately leads to haploid gametes.

82. Mendel referred to the trait that was expressed in the hybrid, F1 or first filial generation as dominant.

83. Mendel's first law encompasses all of the following except all genes found in an individual are

not separable into gametes.

84. Mendel's understanding of the inheritance of traits in peas, expressed in modern language, included all of the following except

if a given allele is present, its effects will be seen in the individual

85. Microtubules become shorter, pulling chromatids to the ends of the spindle, during anaphase.

86. Most eukaryotic cells go through a repeating process of growth and division referred to as the cell ______. cycle

87. Nondisjunction of autosomes can lead to all of the following except euploidy.

88. Nuclear division in eukaryotic cells is called mitosis.

89.Occasionally, chromosomes fail to separate during meiosis, leading to a condition in which the diploid number is not normal. This phenomenon is called

nondisjunction.

90. One of the general principles of biology that was accepted before much was known about genetics was that

heredity occurs within species, and species "breed true."

91.One of the main reasons genes assort independent of one another is that

they are on different chromosomes.

92.One of the main reasons genes assort independently of one another is that

they are on different chromosomes

93.

Over time, natural selection eliminates individuals with detrimental phenotypes from a population. However, there are several examples in the human population in which harmful genetic polymorphisms are maintained. Why?

Heterozygous individuals have some other advantage over individuals with two wild type alleles

94.

Plant cells typically achieve cytokinesis by—forming a cell plate across the middle of the cell

95.Recent studies on cell cycle controls have revealed that animal cells can employ certain factors to override the inhibitory controls of cell division. These belong to a class of proteins called

Growth factors.

96. Sexual reproduction increases genetic variability through all of the following except mitosis.

97. Sickle cell anemia is caused by a defect in the oxygen carrying pigment hemoglobin.

98.Some of the portions of the chromatin are permanently condensed so that their DNA is never expressed. All of these portions stain very intensely and are given a common name of

heterochromatin.

99. Sometimes one gene pair will interact so as to control the expression of a second gene pair in an interaction called epistasis.

100. The accommodation of the very long DNA fiber into a limited space of the nucleus is achieved by coiling around beads of histones into repeating subunits. These subunits of chromosomes are given

nucleosomes

the name __________.101. The actual process of cell division in prokaryotic cells is called binary fission.

102. The bacterial genome exist as a

single, circular, uncoated, double stranded DNA molecule.

103. The bacterial genome exist as asingle, circular, uncoated, double stranded DNA molecule

104. The cell organelles replicate prior to genomic separation in __phase G2105. The cell produced by the fusion of an egg and a sperm is the zygote.106. The chromosomes line up at the equator of the spindle during metaphase

107. The division of a bacterial cell occurs as the

plasma membrane pinches inward constricting the cell.

108. The division of a bacterial cell occurs as theplasma membrane pinches inward constricting the cell

109. The first stage of mitosis, when the chromosomes become visibly shorter and thicker is prophase

110. The four haploid cells resulting from meiosis may further divide by mitosis in all of the following organisms except? animals

111. The fusion of male gamete cells with female gamete cells is called syngamy

112.

The majority of the meiosis I is spent in prophase I and metaphase I. After metaphase I is completed, anaphase I and telophase I quickly proceed, thus ending meiosis I. What immediately follows meiosis I?

prophase II

113.The most common condition of trisomy, in which three copies of a chromosome are present instead of the normal two, is of chromosome

21.

114. The number of chromosomes characteristic of eukaryotes, in general, histones

115.The observable outward manifestation of the genes of an individual is referred to as its phenotype

116. The pairing of chromosomes along their lengths which is essential for crossing over is referred to as Synapsis

117. The phase of the cell cycle during which the cytoplasm divides to form two cells is

C

119. The physical distribution of cytoplasmic material into the two daughter cells is called

cytokinesis

120. The physical map of the array of chromosomes is called karyotype122. The primary growth phase of a cell is G1123. The proteins that participate in the functioning of the cyclins and cyclin-dependent

checkpoints for cell cycle control are kinases

124. The synaptonemal complex develops early in meiosis. It is a lattice of proteins that holds homologues together

126. The two copies of each chromosome in body cells are called homologous chromosomes

127. The white eye mutation in Drosophila was shown to be sex-linked and caused by a gene residing on chromosome X

128.What is the name of the cross that involves the mating of a hybrid F1 plant with a homozygous recessive plant for the same trait?

test cross

129.What is the relationship between recombination frequency and true genetic distance on a chromosome?

As genetic distance increases, the recombination frequency first increases in a linear fashion, but then levels off to a frequency of 0.5

130.

When Mendel crossed two purple-flowered pea plants with each other, he obtained a phenotypic ratio of 3:1 (purple-flowered pea plants to white-flowered pea plants). His results are consistent with which of the following sets of parents?

heterozygous purple pea plant and heterozygous purple pea plant

131. When the two haploid gametes contain two different alleles of a given gene, the resulting offspring is called heterozygous

132. Which of the following cell functions are maintained by cell division? growth, reproduction

133.Which of the following is an explanation for independent assortment, a factor in producing genetic variability?

In anaphase I, where how one pair separates does not affect how any other pair separates.

134. Which of the following is essentially the reverse of prophase? telophase

134aHow do sister chromatids differ from homologous chromosomes?

Homologous chromosomes are similar, but sister chromatids are exact copies

134b What is the role of cohesin proteins in cell division? They hold the DNA of the sister chromatids together

134c Replication of the organelles of the eukaryotic cell occurs during

G2

135. Which of the following produces identical cells? mitosis

136. Which of the following sequence of cell-cycle phases is characteristic of eukaryotes? G1 to S to G2 to M to C

137. Which of the following statements about crossing over is false? Crossing over takes place between sister chromatids

138. Which one of the following represents interphase? G1 + G2 + S

139. Why can't you use mitochondrial DNA to distinguish between these two suspects?

The brothers share the same mitochondrial DNA

140. Yellow-seeded plants might be homozygous or heterozygous. We could find out which by crossing these plants with true breeding greenseeded plants

141. You are a forensic technician working on a DNA sample obtained from a crime scene. Your job is to compare the unknown DNA sample with known DNA samples collected from five different

single nucleotide polymorphisms (SNPs)

suspects. Preliminary analysis using only a few DNA markers revealed that the unknown sample could possibly match two of the suspects. After consulting the case file, you find out that these two suspects are brothers (but not twins). You realize that you will have to do a more detailed analysis on the samples so that you can distinguish between the brothers and determine which brothers' DNA matches the unknown sample.120. Which of the following will help you distinguish between the two final suspects?

142.You are studying mitosis in an organism that has 28 chromosomes as its diploid number. How many chromosomes will the cell have after mitosis, but before cytokinesis?

56

143. You can use a Punnet square to do all of the following except establish a pedigree

144 Nucleosomes are located in the Nucleus and are composed of DNA and histones

145 The attachment of which molecules is critical for the proper separation of sister chromatids?

microtubules

146 A scientist wants to study histones. Histones areproteins that are tightly bound to the double strands of DNA

147

As a doctor, you are examining a patient who recently experienced some liver damage as a side effect of the medication that she was taking for an unrelated medical condition. You explain to her that the liver problem may take some time to resolve as certain liver cells have a cell cycle of about

1 year.

148 If you wanted to convert a proto-oncogene to an oncogene, which of the following methods would you choose?

genetic damage

149 Which of the following is NOT involved in binary fission in prokaryotes? Assembly of the nuclear envelope

150 Chromatin is composed of DNA and protein

151 What is a Nucleosome?Is is a region of DNA wound around a collection of histone proteins

152 Replicated copies of each chromosome are called_______ and are connected at the _________. sister chromatids; centromere

153 Kinetochores are associated with which of the following on a sister chromatid? Centromere

154 Separation of the sister chromatids and elongation of the cell occurs during Anaphase

155 Why is cytokinesis an important part of cell division?It is responsible for the proper separation of the cytoplasmic contents

156 At which stage in the cell cycle does a cell make a commitment to undergo cell division? At the G1/S checkpoint

157 How is the activity of cyclin-dependent kinases (Cdk’s) regulated All of the above158 Why is the function of the protein p53 important for preventing

cancer?It checks for DNA damage before allowing replication during S

phase

159 What is a protooncogene? A normal gene that can result in cancer if it becomes mutated

160 Gametes contain _________the number of chromosomes found in somatic cells. Half

161 Somatic cells are __________, whereas gametes are _____________. diploid; haploid

162 An organism is said to be diploid if it contains genetic information from two parents

163 What are homologous chromosomes?Two genetically similar chromosomes, one from each parent

164 When homologous chromosomes form chiasmata, they are- Exchanging genetic information

165 Crossing over involves each of the following with the exception of the transfer of DNA between two sister chromatids

166 Terminal chiasmata are seen during which phase of meiosis Metaphase I

167

Which of the following occurs during anaphase I?Homologous chromosomes move to opposite poles.

168 Telophase 1 results in the production oftwo cells containing one homologue of each homologous pair

169 Which of the following does NOT contribute to genetic diversity? Metaphase of meiosis II

170 How does S phase following meiosis I differ from S phase in mitosis? DNA does not replicate during S phase following meiosis I

171 What occurs during anaphase of meiosis II? Sister chromatids are pulled to opposite poles

172 What is an aneuploid gamete? A gamete cell with the wrong number of chromosomes

173 Which of the following is NOT a distinct feature of meiosis? Attachment of sister kinetochores to spindle microtubules

174 Which phase of meiosis I is most similar to the comparable phase in mitosis Telophase I

175 In animals, the cells that will eventually undergo meiosis to produce gametes are set aside early in the development. These are

germline cells

176 At the end of telophase II of meiosis, each of the four resulting cells contains

one full set of chromosomes, each a single chromatid

177 The homologous chromosomes (homologues) pair up during meiosis I. Each homologue pairs along its entire length. This process is called

Synapsis

178 A monohybrid cross-- examines two variants of a single trait

179 At the end of telophase II of meiosis, each of the four resulting cells contains

one full set of chromosomes, each a single chromatid

180 What was the appearance of the F1 generation of a monohybrid cross of purple (PP) and white (pp) flower pea plants?

All the F1 plants had purple flowers

181 The F1 plants from the previous question are allowed to self-fertilize. 3 Purple: 1 White.

What will the phenotypic ratio be for this F2?

182 Which of the following is NOT a part of Mendel’s five-element model?

If an allele is present it will be expressed

183 A heterozygous individual is one that carriestwo different alleles for a given gene

184 An organism’s ___________ is determined by its _____________. phenotype; genotype

185 Which of the following represent the phenotype for the recessive human trait, albinism?

Both a and c

186

A dihybrid cross between a plant with long smooth leaves and a plant with short hairy leaves produces a long smooth F1. If this F1 is allowed to self-cross to produce an F2, what would you predict for the ratio of F2 phenotypes?

9 long smooth:3 long hairy:3 short smooth:1 short hairy

187A testcross is used to determine if an individual is— homozygous dominant or

heterozygous

188 What is a polygenic trait?A single phenotypic trait determined by more than one gene.

189 When a single gene influences multiple phenotypic traits the effect is called—

Pleiotropy

190 What is the probability of obtaining an individual with the genotype bb from a cross between two individuals with the genotype Bb?

¼

191What is the probability of obtaining an individual with the genotype CC from a cross between two individuals with the genotypes CC and Cc?

½

192When Mendel crossed dark purple-flowered pea plants with white-flowered pea plants, he never got any pea plants with light purple flowers. This was counter to the

theory of blending inheritance

193 Mendel's observations that different pairs of genes assort independently of each other is known as Mendel's

Second Law of Heredity

194

Let Cy = curly wings and Cy+ = wild type. In Drosophila, the Cy allele behaves as a dominant mutation that produces curly wings in the heterozygous condition (Cy/Cy+), but also behaves as a recessive lethal mutation. Flies homozygous for the Cy allele die before reaching adulthood. If you crossed flies heterozygous for the Cy allele, what surviving genotypes would you find in the F2 generation?

Cy+/Cy+ and Cy/Cy+

195 Early geneticists demonstrated all of the following about inherited traits except

all traits breed true

196

Knight followed up on attempts of English farmers to improve varieties of agriculture with his studies on garden peas. When he crossed two true breeding varieties, he found out a number of things about an inherited trait. Which of the following about inherited traits is false?

An inherited trait is always present in every generation

197 The theory of chromosomal inheritance was first proposed by Sutton

198 Morgan's student Sturtevant demonstrated that the recombination Ywvm

frequencies between a series of linked genes is additive. Examine the following recombination data from Sturtevant, and determine the proper order of the genes on the Drosophila X chromosome. Assume y is in the 0.0 position.

199The geneticist who discovered the white eye mutation in Drosophila and helped establish that genes are carried on chromosomes was Morgan

200 Which of the following statements about calico cats is false? Calico cats can be male of female

201In Drosophila, the sex of an individual is influenced by the number of copies of which chromosome? X

202Why is the white-eye phenotype always observed in males carrying the white-eye allele?

Because the allele is located on the X chromosome and males only have one X

203 An autosome is a chromosome that— determines all other traits of an organism other than sex

204 Sex linkage in humans occurs when— all allele is located on the X chromosome

205 What are Barr bodies?

Barr bodies are X chromosomes inactivated to prevent overexpression of the alleles found on the X chromosome in females

206How does maternal inheritance of mitochondrial genes differ from sex linkage?

Since mitochondria are inherited from the mother, females and males are equally affected.

207 What cellular process is responsible for genetic recombination? Crossing over

208 The number of map units between two genes is determined by— the recombination frequency

209How many map units separate two alleles if the recombination frequency is 0.07? 7 cM

210 Multiple crossovers lead to— restoration of the paternal combination of genes

211 The disease sickle cell anemia is a caused by— Both b and c

212 What determines whether an individual is a genetic mosaic?The inactivation of an allele on the X chromosome of a heterozygous female

213 Down syndrome is the result of—nondisjunction of chromosome 21 during meiosis

214 Which of the following examples of nondisjunction of sex chromosomes is lethal?

OY

215 What is imprinting? The expression of different phenotypes dependent upon the

parent from which the allele was inherited

216 Which of the following is NOT a method used in genetic counseling? Ultrasound