BIO 139 Genetics and Genomics
Somatic cells in a human male contain which combination of sex chromosomes?
An X and a Y chromosome
When is sex determined?
At conception Explanation: Somatic cells in a male will contain an X and a Y chromosome, while female somatic cells will contain two X chromosomes. Consider when this chromosomal assortment is determined.
A woman wishes to have her unborn child tested for genetic disorders and see a full karyotype of her child's genome but does not want to have the amniotic sac punctured to retrieve samples. Which of the following tests will give the most accurate and thorough examination of the fetal genome without puncturing the amniotic sac to retrieve fetal DNA?
Chorionic villus sampling
If a mother is a carrier of an X-linked recessive disease and the father is not affected, what is the chance that a daughter born to the couple will have the trait?
0%
The approximate number of protein-encoding genes on the Y chromosome is
231
Consider a cross between a man and a woman who are both heterozygous for a particular genotype (Gg x Gg). For each of their offspring, indicate the chances (probability) of the different genotypes occurring.
25% chance of being homozygous dominant (GG); 50% chance of being heterozygous (Gg); 25% chance of being homozygous recessive (gg)
A couple is trying to calculate the chance of genetic traits in their potential offspring. From family history, the man presumes he is heterozygous for the height gene via the "tall" allele (T). His partner is short in stature, so she believes she is homozygous for the height gene via the "short" allele (t). Assuming the "tall" allele is completely dominant, what is the chance that their offspring would be tall in stature?
50%
In a simple dominant-recessive inheritance pattern, what is the chance of the offspring exhibiting the dominant trait if one parent is heterozygous and the other is homozygous recessive?
50%
Consider a cross between a man who is homozygous dominant for a trait (GG) and a woman who is heterozygous (Gg) (GG x Gg). For each of their offspring, indicate the chances (probability) of the different genotypes occurring.
50% chance of being homozygous dominant (GG); 50% chance of being heterzygous (Gg)
Complete the following sentences describing the inheritance of the cystic fibrosis allele.
Cystic fibrosis is an example of an autosomal recessive disorder. A person that is (homozygous recessive) for the gene will have the illness. A person who is (heterozygous) will be a carrier, but will be healthy. A person who is not a carrier and is healthy is (homozygous dominant) for the gene. Thus, these (three) (number) genotypes are associated with (two) (number) phenotypes for this disease (healthy and ill), because carriers of the gene are still healthy. If a mother who is a carrier conceives a child with a father who is not a carrier for the trait, there is (0%) chance the child will have cystic fibrosis. A homozygous recessive mother and a homozygous dominant father have a (100%) chance of conceiving a child that is a carrier of the trait.
What condition is the result of trisomy 21?
Down syndrome
Complete the sentences describing Duchenne muscular dystrophy and its inheritance.
Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder, in which the muscle protein called dystrophin is not produced. As an X-linked disorder, DMD is most commonly seen in (males). This is because (females) have two X chromosomes, and thus would have to inherit (two) recessive allele(s) to express the disease. Therefore, the disease is uncommon in this gender. If a woman who is a carrier for the DMD allele (heterozygous) marries and conceives children with a healthy man, her sons would have a (50%) chance of inheriting the disease. Her daughters would have a (0%) chance of inheriting the disease and a 50% chance of being carriers. A male with two healthy parents develops DMD. The abnormal allele would have been inherited from his (mother). Or it is possible that the abnormal allele resulted from a (de novo) mutation.
A heterozygote has identical alleles of a gene and a homozygote has different alleles.
False
A human male is hemizygous for genes on the X chromosome because he has two copies of that chromosome.
False
A pedigree is a chart that aligns chromosome pairs by size.
False
An inverted bell-shaped curve represents the distribution of phenotypes of a multifactorial trait in a population.
False
Beard growth is a sex-influenced trait.
False
Chromosomes carry genes and genes carry genomes.
False
Genes determine all of our characteristics.
False
Genetic information passes from protein to RNA to DNA.
False
Maternal serum marker tests detect metabolites in the fetus that may be associated with specific medical conditions.
False
Most of the DNA in the human genome encodes protein.
False
People with aneuploid sex chromosomes are more severely affected than people with aneuploid autosomes.
False
The expression of an inherited trait is the genotype and the DNA sequence is the phenotype.
False
The field of genetics deals only with disease.
False
The human genome contains millions of different genes.
False
A recessive allele will mask the expression of a dominant allele.
False Explanation: The designation of an allele as recessive means that its expression is "dominated" by a dominant allele.
Match each description with the correct type of prenatal test.
Fetal cells are collected from amniotic fluid at 14-16 weeks gestation; allows karyotyping of fetal chromosomes: Amniocentesis Imaging done via vagina or externally; allows measurement of head size and determination of growth rate: Ultrasound Sample of chorionic villi; allows karyotyping of chorionic cell: CVS Collection of fetal chromosomes from maternal blood; allows determination of fetal chromosome number: Cell-free fetal DNA
Which of the following best describes amniocentesis?
Fluid is removed from the amniotic cavity; cells in the fluid are then cultured and studied.
Explain the term sex-influenced inheritance.
For some genes, sex hormones determine if an allele is dominant or recessive.
What is a complete set of genetic instructions for an organism called?
Genome
Match each description to the correct term.
Having the normal number of chromosomes.: Euploidy Having a number of chromosomes different from the normal amount.: Aneuploidy Having an entire extra set of chromosomes.: Polyploidy Missing one chromosome.: Monosomy Having an extra chromosome.: Trisomy
What term describes individuals who have two identical alleles for a particular trait?
Homozygous Explanation: Individuals have two copies of each gene. These copies are called alleles. Whether a person has two of the same allele, or two different alleles for any gene will influence the genetic expression of the trait.
Complete the sentences describing the different types of chromosomes.
A diploid cell contains (23) pairs of chromosomes. Pairs 1 to 22 are known as the (autosomes) and have thousands of genes, none of which determine sex. Segments of (DNA) making up the chromosomes form (genes) that code for traits, from eye color to the types of enzymes made by liver cells. The chromosomes of pair number 23 are the (sex) chromosomes. These chromosomes carry information determining male and female traits. The sex chromosomes within cells of (females) consist of two X chromosomes. Those of the (males) are an X and a Y chromosome.
Complete the statements describing different types of genotypes.
A person who is heterozygous for a gene with dominant and recessive alleles (will) (will/will not) express the trait. A person who carries two (identical) allelles for a gene is homozygous for that gene. Someone with the genotype of (Dd) for a gene would be considered heterozygous for the "D" trait. Someone with the genotype of (dd) for the gene would be considered homozygous recessive for the "D" trait. A genotype of DD occurs in someone who is (homozygous dominant) for the "D" trait.
What is pleiotropy?
A single gene effects several traits
What is the definition of a sex-limited trait?
A trait that affects a structure or function present in only males or only females.
Observing a karyotype for a fetus, an obstetrician notices that for the 16th chromosome, there are 3 structures shown. What sort of chromosomal abnormality does this fetus have?
A trisomy
Complete the sentences describing the inheritance of dominant and recessive traits.
A(n) (autosomal) illness or trait is equally likely to be inherited by offspring of either sex. In contrast, a(n) (X-linked) condition is more commonly expressed in males than in females. When a recessive illness or condition is inherited by a child of healthy parents, both parents are carriers, meaning they are (heterozygous) for the trait. A person who inherits a(n) (dominant) illness or trait would have at least one affected parent, meaning that the parent also expresses the trait.
An individual who is homozygous dominant for a trait can be symbolized
AA
An offspring of parents whose genotypes are Aa and Aa may be
AA, Aa, or aa.
Why are X-linked disorders more likely to occur in males than in females?
Males do not have the second X chromosome that can potentially mask a recessive allele. Explanation: X-linked disorders include conditions such as color blindness, hemophilia A, and several forms of muscular dystrophy.
Complete the sentences discussing polygenic and multifactorial traits.
Many traits are (polygenic), meaning that they involve several genes interacting together to determine a trait. An example is eye color. Factors within the (environment) such as nutrition, physical activity, and exposure to toxins can influence gene expression or traits. Traits that are the result of one or more genes plus environmental influences are called (multifactorial) traits. Examples are (height), skin color, and the tendency to develop heart disease — each of which are also polygenic.
Which of the following chromosomal abnormalities most severely affect a fetus?
Monosomy for a large autosome
Define the term euploidy.
Normal chromosome number
John exhibits a dominant phenotype for a trait. Which of the following statements is true?
One of his parents has the dominant trait.
Studies have indicated a genetic link between a chromosome abnormality and acute myeloid leukemia, a deadly cancer affecting white blood cell production. Many sufferers of the cancer also possess monosomy 7, which is passed along generations in their families and also corresponds with the incidence of cancer in its members. What would you notice on a karyotype taken from a family with a trend of genetic-linked acute myeloid leukemia?
Only one copy of the 7th chromosome
An individual has one extra complete set of chromosomes. What is this called?
Polyploidy Explanation: An abnormal number of chromosomes is associated with several genetic diseases.
Enzyme replacement therapy can be used to treat genetic conditions in which an enzyme is deficient or absent. How is this therapy classified?
Protein-based therapy Explanation: While protein-based therapies require a lifetime of treatments, DNA-based gene therapies can be successful using fewer treatments.
Match each statement with the correct term.
Sequence of DNA that codes for a particular protein.: Gene Complete set of genetic instructions.: Genome Threadlike strand of nucleic acid.: Chromosome
Complete the sentences describing the different types of genes and traits.
Sequences of DNA that encode for particular proteins are called (genes). They exist in variant forms called (alleles). A person who has two identical alleles of a particular gene is (homozygous) for that gene. In contrast, a person with two different alleles for a particular gene is (heterozygous) for the gene. If one of the alleles masks the expression of the other allele, it is considered a (dominant) allele. The allele which is not expressed is considered (recessive). The combination of different alleles in a person's genome is called their (genotype), while the expression that develops from the genes is their (phenotype).
After receiving a karyotype of a fetus, it is discovered that it has Klinefelter's syndrome. What does this designation indicate?
The fetus is male and the result of a Y-bearing sperm fertilizing an XX egg.
Which of the following is true of autosomal dominant trait inheritance?
The trait is expressed in either homozygous or heterozygous genotypes.
A disorder that skips generations, affects both sexes, and is transmitted by parents who either have the condition or carry it is autosomal recessive.
True
A trait determined by more than one gene is polygenic.
True
Absence of the SRY gene and expression of the Wnt4 gene are necessary for female reproductive structures to develop in an embryo and fetus.
True
An autosomal dominant condition in a family will disappear if in any generation no one inherits the disease.
True
Chorionic villus sampling can be performed earlier in pregnancy than amniocentesis.
True
Chromosome abnormalities include having a number other than 46, a chromosome that has an inverted sequence, and different chromosome types that exchange parts.
True
Freckles are a phenotype and the allele combination that causes a clotting disorder is a genotype.
True
Gametes pass genetic information from generation to generation.
True
Genes have multiple alleles that differ in DNA sequence because a gene consists of many nucleotides, each of which can be any of four types.
True
Genetics is the study of the inheritance of traits and their variability.
True
In genomic imprinting, the sex of a parent transmitting an allele is important in the phenotype of the offspring.
True
In incomplete dominance, the phenotype of a heterozygote is in between that of either homozygote.
True
Janet is homozygous dominant for the wild type allele of the gene that when mutant causes cystic fibrosis. Her brother Henry is a heterozygote. They both do not have the disease cystic fibrosis.
True
Variable expressivity and pleiotropy can account for a disease that produces different intensities of symptoms or different symptoms among individuals.
True
Multiple alleles occur because of variations in DNA base sequence within the gene.
True Explanation: A gene typically has a variety of alleles, each producing a slightly different product.
Which of the following prenatal tests is non-invasive?
Ultrasound
Complete the sentences that describe the function of the genome.
Within the genome, segments called (genes) code for the production of proteins. These segments, in their entirety, constitute the (exome). The exome accounts for less than (2) percent of the genome. Other regions of the genome control genetic expression. The cell is able to produce (more) (more/fewer) proteins than the number of genes. Entire genes can be transcribed. In addition, only parts of genes might be transcribed, producing different proteins. This feature of genetic expression (increases) (increases/decreases) the number of proteins that a cell can make.
Virtually all sex-linked traits are associated with the __________ chromosome.
X
Your family has a strong genetic predisposition to abnormal blood clotting and deep vein thrombosis. How does this affect or determine your chances of suffering from the same conditions?
You have a higher risk of suffering from these conditions, but you can still take preventative steps to reduce the risk if you know about the genetic predisposition. You are not absolutely guaranteed to suffer deep vein thrombosis because environmental factors can be changed.
A gene typically has many alleles because
a DNA sequence can vary in many ways
A gene is
a DNA sequence that contains the information for producing one type of protein.
Hemophilia A is
a defect in the clotting mechanism.
A karyotype is
a size-ordered chart of chromosomes.
Whole genome sequencing generates a list of __________.
all base pairs in a person's DNA
Antonio is colorblind. His partner Emilia is not colorblind nor is she a carrier (heterozygote) for colorblindness. The offspring of this couple would
all have normal color vision.
Two or more versions of a gene are called __________.
alleles Explanation: The fact that genes have multiple forms allows for variation in phenotypes throughout a population.
A trait that is inherited on one of the 22 nonsex chromosomes is a(n) __________ trait.
autosomal
Huntington disease is an __________ condition in which both the heterozygous genotype and the homozygous dominant genotype will exhibit the disease.
autosomal dominant Explanation: For an autosomal dominant disorder to be expressed, only one dominant allele is needed. For an autosomal recessive disorder to be expressed, both alleles must be the recessive allele.
An example of a sex-influenced trait is
baldness
In humans, the allele for cleft chin (C) is dominant to the allele for uncleft chin (c). The combination of alleles, or the genotype, for an uncleft chin would be __________.
cc
If everyone that inherits a particular genotype for a genetic disorder exhibits the characteristic phenotype (expression of symptoms), the genotype is said to be __________. However, if the phenotype (symptoms) are NOT expressed by everyone with the genotype, the genotype is __________.
completely penetrant; incompletely penetrant
An allele that masks the effect of another is
dominant
A human cell with 46 chromosomes is
euploid
Y-linked genes can only be transmitted from __________.
father to son Explanation: Somatic cells in a male will contain an X and a Y chromosome, while female somatic cells will contain two X chromosomes.
During amniocentesis
fetal fibroblasts in amniotic fluid are cultured and a karyotype constructed.
In order for __________ to work, the correct DNA sequence must be delivered to cells, taken up by the cells, and used to produce mRNA that can be translated into the protein needed to halt progression of a disease.
gene therapy
A person's _________ is determined by the combination of alleles found within their DNA. Their ________ is the appearance or characteristics that results from their combination of alleles.
genotype; phenotype
The origin of the 46 chromosomes in a human zygote is
half from the sperm and half from the egg.
Which of the following traits is multifactorial?
height
Different alleles of the same gene are said to be
heterozygous
Identical alleles are said to be
homozygous
An individual with two identical alleles for a gene is ___________ for that gene. In contrast, an individual with two different alleles is __________ for that gene.
homozygous; heterozygous
In a certain species of fly, eye color is designated by the W+ and w alleles, with the W+ allele being dominant. Typical eye color is red for these flies, while a rarer white color variant exists. There is also a pink eye color that occurs when flies inherit both the W+ and w alleles. The pink phenotype is an example of __________.
incomplete dominance
When the phenotype of a heterzygous genotype is intermediate between that of either homozygote, the gene is said to exhibit __________.
incomplete dominance Explanation: Phenotype (the expression of the genotype) depends on the relationship between the alleles of the gene.
Polydactyly is an example of a trait that is both ___________ and variably expressive.
incompletely penetrant
In von Willebrand disease, which is either autosomal recessive or autosomal dominant, clotting time slows and the person bruises and bleeds easily. Not everyone who inherits the disease genotype actually develops the phenotype. Affected individuals have differing degrees of difficulty in blood clotting. This condition is
incompletely penetrant, variably expressive, and genetically heterogeneic.
Genetics is the study of
inheritance of characteristics
Images of paired chromosomes are arranged according to size when using a technique called __________.
karyotyping Explanation: The technique of charting one's chromosomes can be helpful in determining chromosomal abnormalities.
The processes that pass genetic information from generation to generation are
meiosis and fertilization.
The chemical groups that binds to DNA causing genomic imprinting are
methyl groups.
How alike are our genomes?
nearly 100%
Down syndrome is caused by
nondisjunction or a translocation.
A person normally has two alleles of a gene because
one allele of a gene is carried on each of two homologous chromosomes.
A multifactorial trait is determined by
one or more genes and the environment.
Cells from a woman with Turner syndrome have
only one X chromosome
The phenotypes and genotypes that result from a cross of Aa and aa (A = normal pigmentation and a = albinism) are
phenotypes:50% normal and 50% albino; genotypes:50% heterozygous and 50% homozygous recessive.
The genotypes and phenotypes that result from the cross of Aa and Aa (A = normal pigmentation and a = albinism) are
phenotypes:75% normal and 25% albino; genotypes:25% homozygous dominant and 50% heterozygous and 25% homozygous recessive.
Phenylketonuria (PKU) is a genetic disease caused by mutation of the PAH gene, which normally produces the enzyme phenylalanine hydroxase. This enzyme is essential for the conversion of the amino acid phenylalanine into tyrosine. Without the enzyme, phenylalanine builds up in the blood and tissues of various body regions. It can produce severe skin discolorations and foul odor, but also intellectual disabilities and behavioral problems. Some people may experience only one type of PKU symptoms and not the others. PKU is an example of
pleiotropy.
A trait determined by more than one gene is classified as __________.
polygenic
A baby has three copies of each chromosome in every cell. She is
polyploid
An allele that is not expressed in the heterozygous condition is
recessive
The two general types of chromosomes are
sex chromosomes and autosomes.
Gender determination for males reflects expression of
the SRY gene but not the Wnt4 gene.
In incomplete dominance,
the heterozygous phenotype is intermediate between that of either homozygote.
A bell curve is characteristic of the distribution of phenotypes of a multifactorial trait because
the phenotypes at the ends of the curve correspond to fewer genotypes than the phenotypes at the middle of the distribution.
The term "exome" refers to
the protein-encoding parts of the genome.
In genomic imprinting
the same allele has a different effect if inherited from the mother or father.
The two types of information needed to predict the inheritance pattern of a trait are
the way genes are distributed in meiosis and the way that they come together when sperm joins egg.
A human cell that has 47 chromosomes is
trisomic
The condition in which cells have one extra copy of a particular chromosome is called __________.
trisomy Explanation: Deviations from the normal human chromosome number of 46 produces syndromes. A common syndrome involving an extra chromosome is Down syndrome.