BSC1005, Chapter 9, Smartwork, Bio Exam 3, Biology, Chapter 8, Smartwork, Smartwork5- Chapter 7, Bio Exam 3
The outcome of meiosis is the
production of eggs and sperm.
If DNA polymerase did not have the ability to proofread, then DNA replication would
result in more mutations.
The typical number of chromosomes in a human is ______.
46 Humans typically have 46 chromosomes. Having more or fewer chromosomes than this leads to genetic disorders because of the extra or missing copies of genes. (Chromosomes, not homologous pairs)
How many chromosomes do humans have?
46 (23 pairs)
Below is a picture of a karyotype of a human's chromosomes. What information can you gain from the karyotype that can help explain why an individual having trisomy 13 (Patau's syndrome) has more health issues and a very limited life span compared to someone with trisomy 21 (Down syndrome)?
Chromosome 13 is larger than chromosome 21and has more genes that will be affected. Chromosome 13 has more genes than chromosome 21 because it is larger. The third copy of so many genes will cause more problems.
phenotypic ratio
the ratio of phenotypes produced by a cross
genotypic ratio
the ratio of the genotypes that appear in offspring
When a molecule of DNA replicates without error, each of the resulting molecules contains
the same amount of A as T.
Mendel's Law of Segregation
the two alleles of a gene found on each of a pair of chromosomes segregate independently of one another into sex cells. Remember: chromosome pairs are split into separate daughter cells during meiosis.
If two parents are heterozygous for an autosomal recessive disease,
they are both considered genetic carriers for the disease.
Down syndrome and cri du chat syndrome are both examples of chromosomal abnormalities in humans. Down syndrome results from having _____ while cri du chat syndrome results from ______.
three copies of chromosome 21; a deletion of part of chromosome 5
In a karyotype of a male, which of the following would indicate an abnormality
three copies of chromosome 22
The purpose of constructing a pedigree for a patient with a genetic disorder and their family is
to try to determine how the disorder may have been inherited. Looking at a pedigree for a genetic disoder can help a physician determine how the disorder was inherited by the patient.
genome size
total length of DNA in a single cell of an organism
complex traits
traits controlled by multiple genes, the interaction of genes with each other, and with environmental factors where the contributions of genes and environment are undefined. Cannot be predicted by Mendel's law of inheritance.
true/false; uracil is NOT a base found in DNA
true
On chromosomes within an individual, there are ________ alleles for a given gene found on ________ chromosomes.
two; homologous
What are the symptoms of Wiskott-Aldrich syndrome (WAS)?
uncontrollable bleeding, rashes, pneumonia, and recurring infections These are the symptoms of WAS. They can be treated with a bone marrow transplant, but most patients die in childhood from these symptoms.
the sequence of DNA differs among individuals within a species. This is the reason for
variations in phenotypes
hydrogen bonds
weak attraction between a hydrogen atom and another atom
deletion mutation
when a segment breaks off and is lost from the chromosome
translocation mutation
when a segment breaks off one chromosome and becomes attached to a different, nonhomologous chromosome
Gene therapy is most effective at treating disorders
where the patient lacks a necessary protein.
The successful union of one male and one female gamete forms a new single cell known as a
zygote.
Mendel's Law of Independent Assortment
genes found on different chromosomes are sorted into sex cells independently of one another
Rank the terms describing genetic material in descending order, from largest to smallest.
genome (largest) Homologous pair of chromosomes Single Dna molecule Gene for hair color (smallest)
DNA helicase is an enzyme responsible for unwinding DNA in the cell. What step of the polymerase chain reaction (PCR) does the job of this enzyme?
heating up the DNA
Mendel's laws of segregation and independent assortment both have their biological basis in events that take place during
meiosis.
Chromosomes are lined up at the middle of the cell during the ________ portion of cell division.
metaphase
A permanent change in the DNA base sequence due to an uncorrected mismatch error is called a(n)
mutation.
What part of a nucleotide accounts for the genetic variation between individuals?
nitrogenous base
A female carrier of the X-linked recessive gene for red-green color blindness will display a phenotype of
normal color vision.
The Y chromosome in humans is
normally found in a single copy The Y chromosome is normally found as a single copy in males. Human males are XY.
DNA replication
occurs before mitosis in the cell cycle.
Genetic carriers are individuals who carry
one copy of a recessive mutated allele and one normal copy.
Once replication in a DNA molecule is complete, each new DNA molecule contains
one old strand and one new strand.
DNA helicase is an enzyme responsible for unwinding DNA. What step of DNA replication is it involved in?
opening the two DNA strands
What are the three chemical groups that make up a nucleotide?
phosphate, deoxyribose, and a nitrogenous base
Phenotype
physical characteristics of an organism
A Punnett square is used to
predict the genotypes and phenotypes of a genetic cross.
The sex of a human child is determined by the
presence or absence of the Y chromosome.
Which is NOT a component of a nucleotide?
primer
Genotype
An organism's genetic makeup, or allele combinations.
Details of DNA replication
- occurs right before a cell enters mitosis - occurs when viruses hijack the cell machinery and copy of their own DNA
The outside of a DNA molecule (shown here in blue) is made of which of the following?
- phosphate - deoxyribose
Which of the following is the purpose of polymerase chain reaction (PCR) in the lab? Select all that apply.
- To produce millions of copies of a piece of DNA - To mimic the process of DNA replication outside of a cell
It was recently reported that George Church's group has created PERV-free piglets using CRISPR. They did so by editing the genome of pig embryos and then allowing them to develop into piglets. It is now possible to also edit human embryos with the CRISPR technique. What component(s) of the technique would change when editing a human embryo instead of a pig embryo?
- targeted DNA - guide RNA molecule
Which of the following are roles of DNA polymerase?
- to find errors during DNA replication - to fix errors during DNA replication - to build new strands of DNA
Why is it difficult to study the inheritance of genetic disorders in humans?
-Humans usually have just a few offspring in their lifetime. -Ethical issues prevent researchers from doing many kinds of experiments on humans. -Humans pick their own mates with whom to have children. It is difficult to study the inheritance of genetic disorders in humans because it is not ethical to set up controlled matings between humans. And humans produce very few offspring in their lifetime compared to other species. As a result, genetics are frequently studied in model organisms like fruit flies or pea plants. The fact that humans pick their own mates would make it hard for researchers to control how genes were passed from parent to offspring. Furthermore, having a large sample size is better for calculating probabilities of inheritance. And finally, there are many ethical problems and concerns with experimenting on humans in general, and especially in regards to reproduction.
Wiskott-Aldrich syndrome is caused by a recessive allele, WAS, that is found on the female sex chromosome X. Why is it very rare to find females who have this disorder?
-If a male inherits an X chromosome with a WAS allele, there is no second non-WAS allele to mask its expression. -A woman must inherit two WAS alleles, one from each parent, to have the disorder. -Wiskott-Aldrich syndrome is a very severe and deadly disease; males with the disease do not live long enough to pass their X chromosome with the WAS allele to their daughters. All of these options are reasons why females rarely, if ever, exhibit Wiskott-Aldrich syndrome. Men inherit their X chromosome from their mothers, and if they inherit one with the WAS allele, they will have the disease. Women must have two copies, inherited from both parents. Males who suffer from the disease rarely survive to reproduce. However, with the possibility of curing WAS individuals with gene therapy, more males may live longer lives and pass the allele to their offspring.
This pedigree is, in fact, depicting members of a family that suffers from an autosomal recessive genetic disease, not WAS. What clues indicate that this is NOT the pedigree of an X-linked recessive disorder like WAS?
-In the pedigree, an affected mother (I-2) has an unaffected son. This could not happen with an X-linked recessive disorder. -In the pedigree, two unaffected parents (II-1 and II-2) have an affected daughter. This could not happen with an X-linked recessive disorder. You recognize that with two unaffected parents, X-linked recessive disorders, like Wiskott-Aldrich syndrome, cannot produce an affected daughter, and an affected mother cannot have an unaffected son. Females can exhibit X-linked recessive phenotypes if they inherit the recessive allele from both parents, in which case the father would exhibit the phenotype.
Marfan syndrome is caused by a defect in FBN1 gene located on chromosome 15. The gene normally encodes the fibrilllin-1, which is important for the elasticity and appropriate growth of connective tissue. The defect in the gene that causes Marfan syndrome results in a decrease in the amount of functional fibrillin-1 produced. One defective copy of the gene is sufficient to cause Marfan syndrome.
-It is an autosomal disorder. -It occurs because one healthy copy of the FBN1 gene does not produce enough fibrillin-1 to support normal connective tissue formation. Because Marfan syndrome can be caused by a single defective allele of a gene located on chromosome 15, it is an autosomal dominant disorder. Correct development of the connective tissue is dose dependent on the fibrillin-1 protein. The amount of protein produced from one healthy allele is too low of a dose to allow for correct development. The full dose from two healthy alleles is required. This dose dependence in Marfan syndrome is different from recessive disorders in which the defective allele does not produce its protein product, as is the case for cystic fibrosis and hemophilia. For both of those disorders, the amount of protein product made from one healthy allele is enough to result in the healthy phenotype.
There are no affected individuals in the first three generations shown in the pedigree. Affected individuals do not appear until generation IV. Identify the possible explanation(s) for the lack of affected individuals in generations I, II, and III.
-The allele was only present in unaffected female carriers in generations I, II, and III. -The allele was created by a mutation that occurred during the gamete production of either the mother or father in generation III. You chose the two possible explanations for why there are no affected individuals with the Wiskott-Aldrich syndrome in generations I, II, and III. Because the allele is recessive and X-linked, it could be carried by unaffected, heterozygous women in those generations, showing up only when a male in generation IV inherited the allele from his unaffected, carrier mother. Another possibility is that the allele was not present in the family until it was created by a spontaneous mutation in the gamete-producing tissue of the mother or father in generation III (meaning the trait would appear in generation IV). Such mutations do not affect the individuals in which they arise but can be passed to the next generation through the mutated gamete. Most cases of the autosomal dominant disease achondroplasia are due to such spontaneous mutations because the disease shortens the life span of affected individuals preventing them from having children.
Penny and Andrew are a young married couple with three children—two boys and one girl. Both parents have normal vision, and so does their daughter. However, both of their boys are red-green color blind. Penny and Andrew are confused as neither of their parents were color blind. In talking with her mother, Penny learns that her mother's maternal grandfather (Penny's great-grandfather) was red-green color blind as well. Penny does some research and learns that red-green color blindness is a genetic condition that can be passed on by normal-vision mothers to their sons and in rare instances to daughters if the father is also red-green color blind. Select all statements that correctly describe Penny and Andrew's family and the red-green color blindness gene.
-The sons inherited their X chromosome from their mother. -The father carries only a normal X chromosome. (He does not have the color blindness gene.) -The mother is a carrier of the gene for red-green color blindness. Red-green color blindness is due to a mutation on the X chromosome. Because women each have two X chromosomes, they can be carriers of this condition (carry the gene) but never display the phenotypic trait. Males on the other hand have only one X chromosome, which they inherit from their mother. If they inherit the mutation for red-green color blindness, they will not have another X chromosome to mask it, so they will display red-green color blindness. Daughters of a carrier mother have a 50% chance of also being carriers.
Cystic fibrosis is an autosomal recessive disease. Of the individuals in the pedigree above, which definitely carry the cystic fibrosis allele?
-individual II-1 -individual II-2 Individuals II-1 and II-2 are definitely heterozygous carriers of the cystic fibrosis allele. Neither individual has cystic fibrosis, but both passed the allele to two of their offspring (individuals III-2 and III-3).
Nondisjunction is an error that can occur during anaphase of mitosis and meiosis. In nondisjunction, homologous chromosomes (sister chromatids) do not separate and are pulled together to one pole of the dividing cell. Which of the chromosomal abnormalities shown in the figure above would be the most likely to result from nondisjunction during meiosis?
-monosomy -trisomy Trisomy and monosomy are the chromosomal abnormalities caused by nondisjunction. Changes in chromosome number are usually lethal in humans, resulting in death of the embryo or in death soon after birth. Trisomy 21 and monosomy of the X chromosome are two of the few examples of nonlethal changes in chromosome number.
Chromosomes that are NOT involved in determining gender are known as
. autosomes.
Some daughter cells are described as clones. For this description to be appropriate, the daughter cells must
. contain a set of DNA that is identical to that of the parent cell.
During meiosis I, the chromosome number is reduced to haploid by separating
. one of each homologous chromosome pair into two different daughter cells.
A ________ is a chart that shows genetic relationships within a family over several generations.
. pedigree
Most inherited human genetic disorders are inherited as ________ alleles
. recessive
The difference between the alleles of a single gene is
. their DNA base sequences.
Red-green color blindness is caused by a recessive mutation on the X chromosome (b). If a mother is not color blind and not a carrier but her husband is color blind, what is the chance they will have a child that is color blind?
0 percent
Consider an X-linked recessive disorder as described in the video. A man who has the X-linked recessive disorder has children with a noncarrier, nonaffected woman. What are the chances that the couple will have a son with the X-linked recessive disorder?
0 percent All of the couple's sons would inherit the dominant, healthy allele from the woman and the Y chromosome from the man. As a result, 100 percent of the sons would be unaffected and zero percent would have the disorder.
If a segment of double-stranded DNA has 20 percent adenine (A), how much of it is cytosine (C)?
30 percent
Using the information from the infographic and from the table below, what is the frequency of inheritance for the recessive disorder?
1,140 births per 4 million births Cystic fibrosis is a recessive disorder. The table indicates that two copies of the defective allele are required to cause the disorder. It does occur with a rate of 1,140 births per 4 million births in the United States. Individuals with cystic fibrosis have respiratory and digestive issues and usually die of lung infections. Replacing the defective CFTR gene through gene therapy might someday cure cystic fibrosis patients.
Steps of DNA replication
1. Initiation (proteins bint the origins of replication, unwind the DNA helix and break down the hydrogen bonds connecting the bases of the two strands) 2. Elongation (The DNA polymerase enzyme uses each strand as a template to build another new strand starting from primers.) 3. Termination (replication occurs, so there are now two new DNA helixes)
Now that he is cured, what are the chances of Felix passing the Wiskott-Aldrich syndrome allele to his children?
100 percent chance of passing it to his daughters The defect on Felix's X chromosome was corrected only in a subset of his cells. The germ line cells that will produce his sperm still contain the defective allele; thus, he can pass the allele to his future children. The defective allele is on his X chromosome, so he will pass it to all of his daughters but to none of his sons.
Colorblindness is X-linked and recessive. A colorblind female and a male with color vision have a child. If the child is a boy, what is the chance that he will be colorblind?
100%
An actively dividing cell has six chromosomes. How many sister chromatids are present within this cell at the end of G2 phase?
12
A replicated chromosome consists of ________ sister chromatid(s).
2
Humans have ________ pairs of homologous chromosomes
23
Duchenne muscular dystrophy (DMD) causes deterioration of the muscles over time. This disorder is caused by a recessive, X-linked allele. P and her husband J both had brothers with the disorder but they themselves do not have it. P has been tested for the allele and knows she is a carrier. What is the chance they will have a child with DMD?
25%
Hemophilia is a sex-linked disorder that is caused by a recessive allele. If the mom is a carrier of hemophilia and the dad doesn't have hemophilia, what is the chance that they will have a child with hemophilia?
25% chance
Carnations exhibit incomplete dominance in their flower color. The red (R) allele is incompletely dominant to the white allele (W). When red carnations are crossed with white carnations, all the F1 offspring are pink (RW). What would be the probable offspring in the F2 generation if the pink carnations were allowed to self-fertilize? Choose one: A. 100% pink B. 75% red, 25% white C. 25% red, 25% white, 50% pink D. 50% red, 50% white
25% red, 25% white, 50% pink
Assume a certain molecule of DNA is composed of exactly 22 percent adenine. How much cytosine would you expect to find in this molecule?
28 percent
If a female who carries the X-linked recessive gene for hemophilia mates with a male who does not have hemophilia, what is the chance that their daughter will be a carrier of the gene
50 percent
Sickle-cell disease is an inherited chronic blood disease caused by an autosomal recessive allele. Suppose a man with sickle-cell disease fathers a child by a woman who is a carrier for sickle-cell disease. What are the chances their children will exhibit the disease?
50 percent
Among children with parents who are both carriers of Tay-Sachs, an autosomal recessive disorder, chances are that
50 percent will be carriers
Among children with parents who are both carriers of Tay-Sachs, an autosomal recessive disorder, chances are that
50 percent will be carriers.
Hemophilia is a disorder in which the blood does not form clots. It is caused by an X-linked, recessive allele (h). If the father has hemophilia and the mother is a carrier, what percentage of their children will NOT have hemophilia?
50%
R is a carrier for Tay-Sachs disease which is caused by an autosomal recessive allele. The disease causes severe brain damage, and children with it usually die by age four. Her husband E is not a carrier. What is the chance they will have a child who is a carrier for Tay-Sachs?
50%
M has Huntington disease, a progressive brain disorder caused by a mutation in the HTT gene located on chromosome 4. This allele is dominant and M is heterozygous for the allele. M and his wife S, who does not have the Huntington allele, have had one child. What is the chance that their child will be diagnosed with Huntington disease?
50% M is heterozygous for Huntington disease so his genotype is Hh. Therefore, his child has a 50% chance of inheriting the dominant Huntington allele and a 50% chance off inheriting the recessive healthy allele. Huntington disease causes uncontrolled movements and loss of intellectual faculties later in life. When individuals are diagnosed, they have likely already had children and may have passed the allele to their children.
If a plant has a total of 18 chromosomes, how many chromosomes would be present in each of its gametes?
9
Pedigree
A "family tree" showing genetic relationships among family members over two or more generations based off of a family's medical history. Helps analyze information to learn about inheritance of genetic traits/disorders.
Punnett Square
A chart that shows all the possible combinations of alleles that can result from a genetic cross
What is the correct definition of a chromosomal duplication?
A chromosome acquires extra copies of a segment and becomes longer.
The disease cystic fibrosis (CF) is caused by a mutation to the CFTR gene which affects the respiratory, endocrine, reproductive, and digestive systems. The most common cystic fibrosis allele is missing three bases compared to the normal allele, resulting in the loss of one amino acid in the CFTR protein. What kind of mutation caused the cystic fibrosis allele?
A deletion mutation
Which of the following chromosome pairs would contain all of the same genes (not necessarily at the same loci)?
A homologous pair of chromosomes after an inversion in one chromosome in the pair Deletions and translocation change the length of a chromosome and the resulting chromosome would not contain all of the genes found in the homologous chromosome. An inversion involves a rearrangement of a chromosome but does not eliminate material. The sex chromosomes in a male human, X and Y, are not homologous.
Carrier
A person whose genotype includes a gene that is not expressed in the phenotype.
What is the correct definition of a chromosomal translocation?
A segment of a chromosome breaks off and attaches to a nonhomologous chromosome.
What is the correct definition of a chromosomal inversion?
A segment of a chromosome breaks off and is reattached in reverse order.
What is the correct definition of a chromosomal deletion?
A segment of the chromosome breaks off and doesn't reattach to the originating chromosome.
Pleiotropy
A single gene controls a dog's head shape and limb shape.
Mendel wanted to trace the inheritance of two traits in pea plants. He decided to look at height, which is controlled by two alleles. The dominant allele T produces a tall plant, while the recessive allele t produces a short plant. Flower color is controlled by one gene with two alleles as well. The dominant allele P produces purple flowers, and the recessive p produces white flowers. If the female parent has the genotype TtPp, which allele combinations can be found in her gametes? Choose one or more: A. Tp B. tP C. Tt D. Pp E. tt F. tp G. TP H. pp
A. Tp B. tP F. tp G. TP
If a genetic disorder is caused by a dominant allele, individuals with which of the following genotypes would be affected by the disorder?
AA and Aa
Nucleotide bases
Adenine, Thymine, Guanine, Cytosine
Some dominant genetic disorders cause debilitating effects in the people that have them and some are even lethal. How is it possible that these dominant genetic disorders that are so harmful continue to exist in the human population?
All of these are possible explanations of the persistence of genetic disorders in human populations.
Why are autosomal dominant disorders rarer than autosomal recessive disorders?
An allele for an autosomal dominant disorder cannot "hide" in someone who is heterozygous, so it is less likely to be passed down.
DNA replication is called "semiconservative." What does this mean?
At the end of replication, each molecule has one strand that is original and one strand that is new.
Sort the following descriptions of autosomal and sex chromosome inheritance by dragging them into the "Autosomal" box or into the "Sex-linked" box. Some descriptions may apply to both types of inheritance and should be dragged into the "Both" box.
Autosomal: Chromosome pair(s) is(are) always homologous; The same pattern of inheritance is exhibited by both males and females; Involves 22 pairs of choromosomes Sex-linked: The two chromosomes may be homologous or nonhomologous; Revessive disorders are more common in males than in females; Involves only two chromosomes Both: In each pair, one chromosome is inherited from the individual's mother and on from the individual's father. You recognize that sex-linked inheritance involves only one chromosome pair. In females, that chromosome pair, XX, is homologous. In males, that chromosome pair, XY, is nonhomologous. X-linked disorders like hemophilia and color blindness are more common in males, whereas autosomal disorders like cystic fibrosis exhibit the same inheritance pattern in males and females.
Two important genetic technologies are CRISPR and PCR. Sort the descriptions of these technologies by dragging each one to the appropriate box. The descriptions may apply to CRISPR only, to PCR only, or to both technologies.
CRISPR: - Requires the Cas9 protein - Involves the cutting of DNA - Requires a guide RNA PCR: - Requires DNA polymerase - Involves cycles of different temperatures - Produces copies of a targeted DNA sequence Both: - Requires the base-pairing of targeted DNA and a short nucleotide sequence -
Mendel's experimental design
Controlled the mating of plants with differing physical traits Mendel hand pollinated plants selectively Ex. Pollen from a tall plant used to fertilize a short plant Resulting seeds grown Physical characteristics of progeny observed and noted
The hereditary genetic material present in all living cells is
DNA
Cancer is caused by mutations that result in uncontrolled cell division. Tumor suppressor genes prevent cancer. The gene for which of the following is most likely to be a tumor suppressor?
DNA repair proteins
A chromosome consists of
DNA wound tightly around proteins.
Below are pictures of four different types of abnormalities in chromosome structure. Match each picture with the correct name of the chromosome structure problem.
Deletion, Inversion, Translocation, Duplication
According to the infographic, which autosomal disorder occurs at the highest rate?
Down syndrome The disorders shown in the top portion of the infographic are autosomal. They show the same inheritance pattern in both males and females, so their frequencies are given as a number per 4 million U.S. births. As the infographic shows, Down syndrome is the autosomal disorder that occurs with the highest frequency. Down syndrome occurs when an individual inherits three copies of chromosome 21. As a woman ages, her chances of having a child with Down syndrome increases.
How mutations affect phenotype
The mutation affects the phenotype by changing the physical appearance of the organism
Gene therapy is a technique for correcting defective genes responsible for disease development. Scientists are investigating gene therapy treatments for hemophilia. Although it affects more people, Down syndrome is not a good candidate for gene therapy. Use the information in the following table to determine why Down syndrome would be more difficult to treat with gene therapy than hemophilia.
Down syndrome is caused by an extra chromosomal copy, whereas hemophilia is caused by a single defective gene. Down syndrome is caused by the presence of an extra chromosome 21, which is a more difficult defect to correct than replacing a single defective gene, as is the case with hemophilia. As a result, a cure for hemophilia using gene therapy is much closer than a cure for Down syndrome. Wiskott-Aldrich syndrome, another X-linked recessive disease like hemophilia, has been cured in a few children using gene therapy. Hemophilia and Wiskott-Aldrich syndrome are both X-linked, but autosomal recessive disorders can also be treated by gene therapy. An example is lipoprotein lipase deficiency, which affects an individual's ability to break down fat and whose locus is on chromosome 8. It has received the first commercially approved gene therapy treatment.
Polygenic Inheritance
Eye color in humans is controlled by more than one gene.
If one strand of DNA has the sequence CGATT, the sequence of the other strand of the same molecule will be
GCTAA.
Mendel's experiment
Gregor Mendel cross-pollinated plants that had different traits, and found that they were heritable.
If a father is unaffected by an X-linked condition and the mother is a carrier, what is the probability of their children being affected?
Half of the sons will be affected. The cross between an unaffected male (XAY) and a female carrier (XAXa) of an X-linked condition is as follows: 50 percent of females will be carriers (XAXa), 50 percent of females will be normal, 50 percent of males will be affected (XaY), and 50 percent of males will be unaffected (XAY).
Which of the following genotypes represents a human male?
XY
Zoe is a child with cystic fibrosis, a genetically inherited disease caused by the CFTR gene. Neither of her parents nor any of her grandparents have this disease. She also has several siblings who do not have cystic fibrosis. Which statement is incorrect concerning the inheritance of cystic fibrosis?
If a child inherits the CFTR gene from just one parent, that child has a 50% chance of developing cystic fibrosis. Because cystic fibrosis is a recessive disease, a child must inherit two copies of the CFTR gene, one copy from each parent. If they do inherit two copies, they will absolutely develop cystic fibrosis. If they only inherit one copy they will be a carrier but otherwise have normal health.
The color of peas is controlled by a gene called Y. The dominant allele Y produces yellow peas, and the recessive allele y produces green peas. How do you think it's possible that all the peas in the grocery store are green if the dominant allele is yellow? Choose one: A. There was a mutation that changed the colors of the peas from yellow to green. B. Insect pests are attracted to yellow peas, so those plants are often destroyed. C. There are yellow peas, but the farmers just pull out all the yellow ones before sending them to be sold. D. If you breed green peas (yy) with other green peas (yy), you will always get green peas.
If you breed green peas (yy) with other green peas (yy), you will always get green peas.
Most genetic disorders caused by dominant alleles are rarer than those caused by recessive alleles. Why?
Individuals with dominant genetic disorders often die before they can reproduce and pass on their allele to their children. Many dominant disorders are so severely debilitating that people born with them don't live long enough to have children.
Epistasis
Labrador coat color depends on a pigment color gene and an expression gene.
How do the chromosomes in a male human differ from those in a female human?
Males have a Y chromosome, which females lack.
Why are males more likely than females to inherit X-linked disorders?
Males will have the disorder if they inherit one copy of the recessive allele. Remember that a males inherit one X chromosome from the mother and a Y chromosome from the father. Because they only have one copy of the X chromosome, inheritance of the one recessive X-linked allele will result in the recessive phenotype. Wiskott-Aldrich syndrome is an example of an X-linked recessive disorder. Males suffer from the disorder, which affects the formation of blood cells and the immune system, more than females because females can inherit a healthy dominant allele on their second X chromosome which will save them from the disorder.
According to the infographic, which autosomal disorder occurs at the lowest rate?
Marfan syndrome The disorders shown in the top portion of the infographic are autosomal.They show the same inheritance pattern in both males and females, so their frequencies are given as a number per 4 million U.S. births. As the infographic shows, Marfan syndrome is the autosomal disorder that occurs with the lowest frequency. Marfan syndrome occurs when an individual inherits one or two copies of the defective FBN1 gene.
Dr. Klein first tested his gene therapy treatment on mice before he used it on patients like Felix. If he was sure the procedure was going to work, why didn't he just run the tests on patients first? Select all that apply.
Mice are often used for medical testing because they have similar genes to humans, and they allow researchers to see if there are side effects of their experiments.
What information in a pedigree would indicate that a condition is likely sex-linked?
Most of the affected individuals are males.
The polymerase chain reaction, or PCR, is a tool used frequently in biotechnology. Because PCR mimics the natural DNA replication that occurs in the cell, the two processes share many characteristics. Sort the descriptions of these processes by dragging them to the appropriate boxes. The descriptions may apply to natural replication only, to PCR only, or to both processes.
Natural Replication: - Produces a copy of the whole genome - Begins at origins of replication - Occurs before mitosis and meiosis PCR: - Produces millions of copies of a segment of DNA - Requires cycles of temperatures Both: - Requires DNA polymerase - Requires primers - Results in semiconservative replication
Because an individual with an XX genotype is a female, is an individual with an XO (no second sex chromosome) a male
No, because the Y chromosome contains the gene that makes an embryo male.
In cats, the length of fur is determined by a pair of alleles. The dominant allele L codes for short fur, and the recessive allele l codes for long fur. If a cat had short fur, could you tell by looking at it what its genotype would be? Choose one: A. No, if it is showing the dominant phenotype, then there must be other alleles that are influencing the phenotype. B. Yes, if it is showing the dominant phenotype, then its genotype must be LL. C. Yes, if it is showing the dominant phenotype, then its genotype must be Ll. D. No, if it is showing the dominant phenotype, then its genotype could be LL or Ll.
No, if it is showing the dominant phenotype, then its genotype could be LL or Ll.
Dominant Inheritance
Occurs when an abnormal gene from one parent causes disease, even though the matching gene from the other parent is normal. Abnormal gene dominates.
Assume that you chemically label both strands within a molecule of DNA. You then allow this DNA to replicate using unlabeled nucleotides. Which of the following statements about the two resulting DNA molecules would be FALSE?
One molecule would contain the chemical label and the other would not.
sex linked diseases
Passed down through families through one of the X or Y chromosomes
What accurately describes crossing over?
Paternal chromosome 7 exchanges segments of DNA with maternal chromosome 7.
intermediate phenotype
Phenotype that combines the phenotypes of a dominant and a recessive allele; product of incomplete dominance
In humans, the "master sex switch" that determines whether an embryo will become a male is the
SRY gene.
PKU is a genetic disorder which results in brain damage unless a special diet is followed. It is caused by a recessive allele found on chromosome 12. Alfredo and Lisa have a child with PKU. Alfredo has the disorder, but Lisa does not. What is Lisa's genotype for PKU? Use P to represent the normal allele and p to represent the PKU allele.
She must be Pp because she doesn't have PKU, but she did pass on a recessive allele to her child. Lisa must have one dominant normal allele because she doesn't have PKU. Since she has a child with PKU, she must have passed on her recessive allele to her child.
The DNA polymerase used in the polymerase chain reaction (PCR) was initially isolated from the bacterium Thermophilus aquaticus that lives in hot springs like Old Faithful in Yellowstone Park. Now called Taq polymerase, this enzyme can be produced synthetically and ordered from a catalog. What best explains why Taq polymerase must be used in PCR rather than human DNA polymerase?
Taq polymerase can withstand the high temperature needed to separate the DNA strands.
How mutations affect genotype
The mutation affects the genotype by changing whether the organism carries the allele for that mutation
The CRISPR system has two parts: a protein component called Cas9 and an RNA component. How were these two components used by Church's group to inactivate the viral pol gene in the pig embryos?
The RNA component base-paired with 2 specific pol sequences. The Cas9 protein then clipped the DNA, resulting in a deletion mutation in the pol gene.
Which of the following genetic changes would be passed from parent to child?
The addition of a chromosome in an egg cell The only chromosomal abnormalities that will be passed from parent to child are those that affect eggs and sperm.
mismatch repair
The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.
A man and his wife are both carriers for a recessive disease allele. If the couple has a child, which of the following statements is true?
The child has a 25 percent chance of being affected by the disease. Carriers have one copy of the recessive disease allele and one copy of the dominant allele. The chance of a child receiving a recessive allele from one parent is 1/2 or 50 percent. The chance of a child inheriting recessive disease alleles from both parents is 1/2 multiplied by 1/2 or 1/4 (25 percent).
Using the information from the infographic and from the following table, determine which of the three diseases occurs with the greatest frequency.
The disease caused by a chromosomal abnormality occurs with the greatest frequency. Of the three diseases illustrated in the infographic, Down syndrome occurs with the greatest frequency. You recognize that because Down syndrome is caused by a trisomy of chromosome 21, it is a disease that is caused by a chromosomal abnormality and not a dominant or recessive allele. Chromosomal abnormalities include an increase or decrease in normal chromosome number or changes to chromosome structure. Turner syndrome is another condition caused by a chromosomal abnormality. Individuals with Turner syndrome have one sex chromosome, an X, instead of the normal two sex chromosomes. These individuals suffer from mild to moderate reproductive issues.
How do most autosomal recessive alleles that lead to lethal diseases persist in human populations?
The disease-causing allele can "hide" in the heterozygous condition. Autosomal recessive alleles are found as single copies in unaffected heterozygous carriers. Two healthy parents can each pass on a recessive allele, and the disease, to their child. Only individuals with two copies of the recessive allele are affected by the disease.
Robert is the infant son of Aimee and Brian. He has Tay-Sachs disease, which is an inherited disorder that destroys the nerve cells (neurons) of the brain. Neither Aimee nor Brian have Tay-Sachs disease, but they each had several male and female cousins that had it. How is it possible that neither parent has the disease but their child does?
The disorder is caused by a recessive allele, and both parents are heterozygous. Robert has inherited one of each of his parent's recessive Tay-Sachs alleles.
The disease discussed in the animation is caused by a recessive allele. Recessive alleles frequently do not produce a protein product. Dominant alleles, on the other hand, may produce a harmful protein. How might treating a dominant disorder with gene therapy differ from treating a recessive disorder with gene therapy, as discussed in the video?
The dominant disease allele needs to be inactivated so that it does not produce the harmful protein. Recessive alleles only need to be replaced whereas dominant alleles need to be inactivated and replaced by gene therapy. In Chapter 9 you will learn about a new genetic engineering technique called CRISPR that can be used to specifically remove sequences, like dominant alleles, from the genome.
Siamese cats have pale, cream-colored bodies with dark brown fur on their extremities (their ears, face, legs, and tail). Siamese cats that live outside in warm climates tend to have lighter fur, and those that live outside in cooler climates tend to have darker fur. What is the best explanation for this pattern? Choose one: A. The gene that controls fur color in Siamese cats is affected by the environment. B. Fur color in Siamese cats is controlled by multiple genes that interact with each other. C. Heterozygous Siamese cats display an intermediate phenotype. D. The alleles that control fur color in Siamese cats are equally visible in the phenotype.
The gene that controls fur color in Siamese cats is affected by the environment.
What would promote a cell to move through the G2 checkpoint?
The genetic information has been duplicated.
Which of the following is true for an individual who is homozygous for a gene?
The individual has two copies of the same allele for the gene.
What would you expect for an individual with the genotype XXY?
The individual would develop as a male.
Why did Mendel analyze thousands of plants while conducting his research?
The likelihood of seeing a clear pattern is higher with a larger data set.
Look at the family pedigree below. Why do you think that only males have the genetic disorder when it says that a female introduced the gene into the family?
The mutation where the gene is located must be on the X chromosome. Because the pedigree indicates that a female introduced the mutation into the family and only males were affected, the gene must be on the X chromosome.
Autosomal Chromosomes (Autosomes)
The other 44 chromosomes that are not sex chromosomes
Why did Dr. Wiskott suspect his young male patients had a genetic disease rather than one caused by an infectious, environmental, or toxic agent?
The other children in the family were healthy. If the sickness had been caused by an infectious, environmental, or toxic agent, Dr. Wiskott was sure that all the children in the family would have been exposed. If they had all been exposed, they should have all developed the illness.
What is the significance of crossing over?
The resulting gametes will have novel gene combinations compared to their parent cells' gene combinations.
In humans, does the egg or the sperm determine the sex of the child?
The sperm determines the sex because it contains either an X or a Y chromosome.
It is said that the double-helical structure of DNA resembles a spiral staircase. If so, which part of the structure makes up the steps of the staircase, and which part makes up the handrail?
The steps would be the complementary base pairs, and the handrail would be the sugar-phosphate backbone.
When identifying the 62 copies of PERVs, how did the investigators differentiate between viral DNA and the pig genome?
The viral sequence of nucleotides differs from the pig sequence.
Which of the following statements about autosomes is true?
There are 44 autosomes in humans. Autosomes are all of the chromosomes other than the sex chromosomes. They are found as 22 homologous pairs. Within a homologous pair, autosomes have the same length, shape, and genes.
Does is ALL genetic material for life?
There are certain genes that all living organisms contain. These genes must be found in all genomes, whether large or small. Therefore, the extra genetic material is probably not material required for life (although it could be important for the organism that contains it).
Carla has Huntington's disease (HD), which is a genetic disorder caused by an autosomal dominant allele. Like most people with HD, Carla is heterozygous. Her husband Ricardo does not have Huntington's disease. What is the chance they will have a child with the disorder?
There is a 50% chance.
In Labrador retrievers, coat color is controlled by two different genes. The B gene has two alleles. The dominant allele B produces a black coat while the recessive allele b produces a brown coat. The second gene E can block the expression of the B allele. If two copies of the recessive allele e are present, the coat of the dog will be yellow. If at least one copy of the E allele is present, the coat will be whatever color is determined by the B/b alleles. Imagine a cross between the two Labrador retrievers pictured. If the black dog is heterozygous for both genes and the brown dog is heterozygous for the E gene, what is the chance they will have a yellow puppy? Choose one: A. There will be 3/8 chance. B. There will be 1/4 chance. C. There will be a 1/2 chance. D. There will be no chance.
There will be 1/4 chance.
Polycystic kidney disease type 1 (PKD1) causes cysts (fluid-filled sacs) to develop in the kidneys, reducing their ability to filter the blood and produce urine. The most common type of PKD1 is inherited and caused by an autosomal dominant allele of the PKD1 gene. R has an aggressive form of PKD1 where both his alleles are dominant. His wife J does not have PKD1. What is the chance that they will have a child with PKD1?
They have a 100% chance of having a child with PKD1.
Phenylketonuria, or PKU, is a disease where a missing enzyme leads to a buildup of lipids in the brain, damaging it. In the United States, all babies are tested for this disorder since the symptoms can be managed by following a special diet. A couple, neither of whom have PKU, are expecting their third child. Their first two children were born with PKU. What is the chance they will have another child with PKU?
They have a 25% chance of having another child with PKU.
If a point mutation occurs in a gene, is it possible for there to be no effect on the phenotype of the organism?
Yes, occasionally gene mutations result in little or no change to the protein coded by the gene, leading to no change in phenotype.
A female who is a carrier for an autosomal recessive disorder has the genotype
Tt Carriers of an autosomal recessive disorder are heterozygous for alleles that are not on the sex chromosomes.
In a karyotype of a human female, which of the following would indicate a normal karyotype?
Two X chromosomes A normal karyotype of a human female will show 22 homologous pairs of autosomes. In addition, a female would have two X chromosomes (a male would have one X chromosome and one Y chromosome).
Which of the following is true for autosomal recessive alleles associated with a disease?
Two copies of the allele are required for the individual to be affected. Autosomal recessive alleles are equally likely to be found in males and females. Two copies of the recessive allele are required for the disease to be seen.
Some genetic traits are invariant in a species, which means they don't change from individual to individual. Other genetic traits in a species are highly variable from individual to individual. Think about what you know about dogs, and determine whether the traits below are variable or invariable.
Variable : Coat color, ear shape, fur texture Invariable: having two eyes, having four legs
duplication mutation
When a chromosome becomes longer after acquiring an extra copy of one of its chromosome segments
inversion mutation
When a segment breaks off and is reattached in reverse order.
The infographic refers only to male births and not to female births because it is illustrating the frequencies of which of the following? The infographic gives the frequencies of three disorders in males. Which of the following statements is true about the incidence of these diseases in females?
X-linked disorders Duchenne muscular dystrophy, hemophilia, and fragile X syndrome are all X-linked disorders whose genes are found on the X chromosome. Because males only have one X chromosome, they exhibit the disease significantly more frequently than females. Because females have two X chromosomes, they have a second chance to inherit the healthy allele. Females can exhibit the disease phenotype if it is caused by either a dominant or a recessive allele. Females do exhibit X-linked disease phenotypes if they inherit only one copy of an allele that causes a dominant disorder. This occurs in the fragile X syndrome. If the X-linked disease is recessive, females can exhibit the disease phenotype if they inherit two copies of the recessive allele. Duchenne muscular dystrophy and hemophilia are recessive X-linked disorders that can affect females if they inherit two recessive alleles. Because males will exhibit the disease if they inherit only one copy of the recessive allele, they are affected more frequently by recessive X-linked traits. But under the right circumstances, females can also inherit the disease phenotype. Page 143
There is a misconception that girls cannot inherit recessive X-linked disorders. Girls can in fact inherit these disorders, but at a lower rate than boys. The following choices give the genotypes for pairs of mothers and fathers. Which pair of parents could have a daughter with the recessive disorder a?
XAXa × XaY You chose the only pair of parents, XAXa × XaY , that could have a daughter with the disease phenotype. If a girl inherits the recessive allele on the X chromosome from her mother and on the X chromosome from her father, then she will exhibit the recessive phenotype of an X-linked disorder. Hemophilia, Duchenne muscular dystrophy, Wiskott-Aldrich syndrome, and adrenoleukodystrophy are all examples of recessive X-linked diseases that can be inherited by girls but are more frequently inherited by boys. Page 143
Genetic disorders
a mutation in a person's genes. caused by an abnormality in the genome. *Several thousand human genetic disorders are inherited as recessive traits on autosomes*
Which best describes a gene? A. the expression of a particular trait in an organism B. the total amount of RNA in an organism C. a segment of DNA that codes for at least one trait D. all the genetic information in an organism
a segment of DNA that codes for at least one trait
gene therapy
a technique that places a gene into a cell to correct a hereditary disease or to improve the genome
An allele is
a version of a gene.
Cystic fibrosis is caused by an autosomal recessive allele. Below is a Punnett square showing a genetic cross between two individuals that are carriers for cystic fibrosis. Select the genotype that represents a child with cystic fibrosis.
aa
incomplete dominance
alleles that do not exert their full effect when found together in a heterozygote. Usually displays intermediate phenotype.
What is meant by the term "genetic carrier"?
an individual who is heterozygous and carries the recessive allele for a disorder
chromosomal abnormalities
any change in the chromosome number or structure, compared to what is typical for a species.
Autosomal disorders occur on
any chromosome other than the X or Y chromsome.
The processes of mitosis, meiosis, and binary fission all
are used to produce daughter cells.
Human chromosomes 1 through 22 do not determine sex; instead, they are present as homologous pairs in both males and females. What are these chromosomes?
autosomes Humans have 22 pairs of autosomes that each contain thousands of genes. The autosomes do not determine the sex of the individual but are instead present as homologous pairs in males and females.
codominant traits
both genes being expressed; traits are both expressed in the organism
Recessive Inheritance
both matching genes must be abnormal to cause disease. If only one gene in the pair is abnormal, the disease does not occur.
A certain enzyme is known to be responsible for separating the two strands of a DNA molecule to facilitate the process of DNA replication. This enzyme most likely
breaks hydrogen bonds between bases.
What is the role of DNA polymerase?
build new DNA strands
A genetic disorder is a disorder
caused by a genetic mutation that can be inherited by offspring from their parents.
If two different alleles for the same trait have an equal effect on the phenotype, the alleles are
codominant
In humans, the presence of an SRY gene
commits a developing embryo to the male sex.
CRISPR/Cas9
composed of Cas9 proteins and the RNA that guides the Cas9 proteins. The RNA guides Cas9 to targets in a genome where Cas9 cuts both strands of the DNA.
Homologous chromosomes
consist of a maternal and paternal copy of each chromosome.
homologous chromosomes
contain the same genes in the same locations.
DNA
contains genetic information
Most human genetic characters are
controlled by more than one gene
The structure of DNA has a spiral ladder shape made of two twisted strands of nucleotides. The nucleotides in each strand are bonded together by what type of bond?
covalent bonds
Along one side of a DNA molecule, the nucleotides are connected to each other by ________ bounds between ________
covalent; phosphate groups and sugar molecules
In genetics, a pedigree is a
diagram that shows how a particular genetic condition was passed down through the generations of a family.
Allele
different versions of a gene
Two copies of the same gene on a single chromosome would indicate a(n) ________ had occurred.
duplication
Which of the following foods is MOST likely to contain haploid cells?
egg
Mendel's laws
explain how genes are inherited.
The X chromosome in humans is
found as a pair in females.
Mendel used ________ as his research organism to study patterns of genetic inheritance.
garden peas
If two alleles at a locus on homologous chromosomes are the same, the cell is ______; if the two alleles are different, the cell is _____.
homozygous; heterozygous
The two strands of a DNA molecule are held together by ________ bonds between their base pairs.
hydrogen
The two strands of DNA in the double helix are held together by bonds between the bases of the two strands. What kind of bond holds these base pairs together?
hydrogen bonds
Use the following figure to help answer this question. The chemical bonds that hold the two complementary strands of the DNA double helix close to each other are
hydrogen bonds
Replication of DNA cannot begin until ________ bonds between ________ are broken.
hydrogen; complementary bases
A chestnut-colored (red-colored) horse is mated with a cremello (cream-colored) horse. Over a 10-year period, all of their offspring are palominos (gold-colored). This pattern of inheritance is best explained by
incomplete dominance.
The possible combinations of alleles in gametes ________ due to independent assortment and crossing over.
increases
A pool of cells is treated with a chemical that halts progress through the cell cycle. In which stage of the cell cycle would most cells be found?
interphase
Even though you and your brothers or sisters are all humans, odds are that each of you has a somewhat different genetic makeup. The molecular basis for this inherited genetic variation
is related to the difference in the DNA nucleotide sequence of your genes.
PCR (polymerase chain reaction)
is used to copy and amplify minute quantities of DNA (extremely hard to make work)
Inheritance of the SRY gene is considered sex-linked because
it is located on the Y chromosome. The SRY gene is located on the Y chromosome, which is a sex chromosome. Genes located there are considered to be sex-linked.
The significance of specific base pairing in DNA is that
it provides a method for making exact copies of DNA.
When Mendel proposed the law of segregation, which of the following pieces of information did he NOT have
knowledge of the location of the alleles for flower color
DNA polymerase is used by the cell to
make copies of a DNA sequence.
Gametes are produced by meiosis rather than mitosis because
meiosis reduces the chromosome number so that zygotes produced will have one full genome
Gametes are produced by meiosis rather than mitosis because
meiosis reduces the chromosome number so that zygotes produced will have one full genome.
When DNA replicates, DNA polymerase utilizes one strand as a template and builds a new strand using base-pairing rules. The end result is two molecules, each with one template strand and one new strand. This type of replication is called
semi conservative replication
SRY gene
sex-determining region of the Y chromosome/ "master sex switch"
Would it be easier to study an organism with a large genome size, or small? why?
small, because this has less material to sort through.
Consider the three-dimensional structure of DNA. Which of the following has a structure analogous to a molecule of DNA?
spiral staircase
Covalent bonds
strongest bond between atoms.
When examining the rapidly dividing cells of a fish embryo, a researcher notices a cell that seems to contain two nuclei. The middle of the cell is pinched inward. This cell must be in ________ of mitosis.
telophase
In humans, X-linked genetic diseases
tend to be expressed more in males than in females.
In Mendel's controlled mating experiments, the individuals produced by crossing two true-breeding parents are referred to as
the F1 generation.
DNA replication
the duplication of a DNA molecule/cells genetic material
What is the locus of a gene?
the position of the gene on a particular chromosome
Karyotyping
the process of sorting chromosomes into their matched pairs. An important technique for investigating chromosomal disorders
