ChromosomalInheri Flashcards
What is the physical basis for Mendelian inheritance?
Mendelian inheritance has its physical basis in the behavior of chromosomes.
Chromosomes and genes are both present in pairs in diploid cells, and homologous chromosomes separate during meiosis.
What are sex-linked genes?
Sex-linked genes exhibit unique patterns of inheritance.
These patterns are often associated with specific sex chromosomes, such as X and Y.
Why do linked genes tend to be inherited together?
Linked genes tend to be inherited together because they are located near each other on the same chromosome.
This proximity reduces the likelihood of them being separated during meiosis.
What causes some genetic disorders?
Alterations of chromosome number or structure cause some genetic disorders.
Examples include Down syndrome, which is caused by an extra copy of chromosome 21.
What are exceptions to standard Mendelian inheritance?
Some inheritance patterns are exceptions to standard Mendelian inheritance.
These can include incomplete dominance, codominance, and polygenic inheritance.
How do chromosomes and genes relate?
Genes are located on chromosomes, and in diploid cells, chromosomes and genes are present in pairs.
What happens to chromosomes before cell division?
Chromosomes duplicate before cell division, resulting in two copies of each allele on sister chromatids.
During which phase of meiosis do homologous chromosomes separate?
Homologous chromosomes separate during meiosis I.
What is the result of fertilization after meiosis?
Fertilization restores the paired condition for both chromosomes and genes.
What did Walter S. Sutton and Theodor Boveri contribute to genetics?
They noted parallels between Mendel’s factors and chromosome behavior, leading to the chromosome theory of inheritance.
What was Thomas Hunt Morgan’s experimental organism?
Morgan used Drosophila melanogaster, a species of fruit fly, for his genetic studies.
What advantage does Drosophila melanogaster offer for genetic studies?
It has only four pairs of chromosomes, which are easily distinguishable with a light microscope.
What is the wild type phenotype in Drosophila?
The wild type phenotype is the most commonly observed trait, such as red eyes.
What are mutant phenotypes in Drosophila?
Mutant phenotypes are alternatives to the wild type, such as white eyes, due to alleles from mutations.
What does the notation for alleles in Drosophila signify?
The notation signifies the first mutant discovered for a character, e.g., w for white eyes and w+ for red eyes.
What ratio did Morgan observe in the F2 generation of his cross?
Morgan observed a 3:1 phenotypic ratio among the F2 offspring.
What conclusion did Morgan draw about the eye color gene in Drosophila?
Morgan concluded that the eye color gene was linked to sex and located on the X chromosome.
What is the significance of a female fly having two X chromosomes?
A female fly can only express a recessive trait if both X chromosomes carry the recessive allele.
What does the separation of homologs during anaphase I account for?
It accounts for the segregation of the two alleles of a gene into separate gametes.
What does the random arrangement of chromosome pairs at metaphase I account for?
It accounts for the independent assortment of alleles for two or more genes located on different homolog pairs.
How did Morgan’s findings support the chromosome theory of inheritance?
His findings demonstrated that a specific trait correlated with a specific sex chromosome.
What is the genotype of green wrinkled seeds in the given cross?
yyrr
What is produced by all F1 plants in the cross of green wrinkled seeds?
Yellow round seeds (YyRr)
During which phase do the R and r alleles segregate?
Anaphase I
What does each gamete receive in terms of alleles?
One long chromosome with either the R or r allele
What is the expected phenotypic ratio in the F2 generation from a dihybrid cross?
9:3:3:1
True or False: The F1 generation can produce gametes with four types of alleles.
False
What discovery did Morgan make that supported the chromosome theory of inheritance?
A trait (white eyes) correlated with the sex of flies
What are the two types of sex chromosomes in humans?
X and Y
What is the role of the SRY gene on the Y chromosome?
Required for the development of testes
What is the typical sex chromosome configuration for females in humans?
XX
What determines the sex of offspring in the X-Y system?
Whether the sperm cell contains an X or Y chromosome
In birds, what are the sex chromosomes and their typical configurations?
Z and W; females are ZW, males are ZZ
What happens to X chromosomes in female mammals during early embryonic development?
One X chromosome becomes inactivated
What is the term used for genes located on sex chromosomes?
Sex-linked genes
What is the term for a male with an X-linked gene?
Hemizygous
What is Duchenne muscular dystrophy characterized by?
Progressive weakening of the muscles and loss of coordination
True or False: Females can express X-linked traits only if they are homozygous for that allele.
True
What does X inactivation result in for female mammals?
A mosaic of two types of cells
What is a Barr body?
The inactive X chromosome in a female cell
What is the inheritance pattern for X-linked traits?
Fathers pass X-linked alleles to daughters but not to sons
What condition is characterized by prolonged bleeding due to absence of clotting proteins?
Hemophilia
Fill in the blank: The gene for color blindness is typically inherited as an _______ trait.
X-linked recessive
How does X inactivation affect the gene dosage in female mammals?
Females have the same effective dose as males
What is X inactivation?
The process by which one of the X chromosomes in female mammals is inactivated, resulting in a mosaic of two cell types.
What type of cells do females consist of due to X inactivation?
Cells with the active X derived from the father and those with the active X derived from the mother.
What is the effect of X inactivation on a female that is heterozygous for a sex-linked trait?
About half of her cells will express one allele, while the others will express the alternate allele.
What phenomenon is illustrated by the patchy coloration of a tortoiseshell cat?
Mosaicism resulting from X inactivation.
In humans, what condition can mosaicism be observed in relation to?
A recessive X-linked mutation that prevents the development of sweat glands.
What is involved in the inactivation of an X chromosome?
Modification of DNA and histones, including attachment of methyl groups to DNA nucleotides.
What gene becomes active on the X chromosome that will become the Barr body?
XIST (X-inactive specific transcript).
What is the result of XIST gene activity?
It initiates X inactivation and regulates the process through interaction with the chromosome.
What is the probability that a second child will have Duchenne muscular dystrophy if the firstborn son has it?
Depends on the genotypes of the parents.
What are linked genes?
Genes that are located near each other on the same chromosome and tend to be inherited together.
What happens to inheritance patterns when genes are linked?
Results deviate from those expected from Mendel’s law of independent assortment.
What did Morgan’s Drosophila experiments reveal about body color and wing size?
These traits are genetically linked and tend to be inherited together.
What are parental types in genetics?
Offspring that have a phenotype matching either of the phenotypes of the P generation.
What are recombinant types?
Offspring with new combinations of traits that differ from those found in either P generation parent.
What is the significance of a 50% frequency of recombination?
It indicates that the genes are located on different chromosomes and are unlinked.
What is crossing over?
A process during prophase of meiosis I where segments of homologous chromosomes exchange genetic material.
How does crossing over affect linked genes?
It can break the physical connection between specific alleles of genes on the same chromosome.
What does a high proportion of parental phenotype offspring suggest?
That the genes are linked on the same chromosome.
What is the recombination frequency?
The percentage of recombinant offspring in the total pool of offspring.
True or False: Linked genes assort independently.
False.
Fill in the blank: Genes that are located on the same chromosome and tend to be inherited together are called _______.
linked genes.
What statistical test can be used to analyze whether two genes are linked or unlinked?
Chi-square (X²) test.
What does the presence of nonparental phenotypes indicate?
That some genetic recombination has occurred.
What is the expected phenotypic ratio of offspring from an unlinked genes testcross?
1:1:1:1
What statistical test is used to analyze phenotypes in genetic linkage studies?
Chi-square (X2) test
What does the chi-square (X2) statistic measure?
The discrepancy between observed values and expected values
What is the formula for calculating the chi-square (X2) value?
x2 = Σ((o - e)²/e)
What indicates statistically significant evidence against the hypothesis of unlinked genes?
A probability of 0.05 or less
What is a genetic map based on recombination frequencies called?
Linkage map
Who developed the method for constructing a genetic linkage map?
Alfred H. Sturtevant
What does one map unit equal in terms of recombination frequency?
1% recombination frequency
How do you calculate degrees of freedom (df) for chi-square tests in this context?
Number of categories minus 1
What is the maximum observed frequency of recombination for two genes on the same chromosome?
50%
What can cause genes that are physically linked to behave as if they are unlinked?
If they are far apart on the chromosome
What is the significance of crossing over during meiosis?
It generates variation in offspring
What does a linkage map show?
The relative locations of genes along a chromosome
What is the role of random fertilization in genetic variation?
It increases the number of variant allele combinations
True or False: The frequency of crossing over is uniform across a chromosome.
False
Fill in the blank: The physical behavior of chromosomes during meiosis contributes to the generation of ______ in offspring.
variation
What are the two types of maps that geneticists use to locate genes?
- Linkage maps
- Cytogenetic maps
What do cytogenetic maps locate genes with respect to?
Chromosomal features visible under a microscope
What is the primary method used today to map the locations of genes?
DNA sequencing
What does the interplay between environment and phenotype determine?
Which genetic combinations persist over time
What must scientists do to determine if the observed data are consistent with the hypothesis of unlinked genes?
Compare observed and expected values using the chi-square test
What happens if the observed data deviate significantly from expected values?
The hypothesis that the genes are unlinked may be rejected
What kind of traits are expected to thrive in a given environment according to natural selection?
Traits conferred by advantageous combinations of alleles
How are genes arranged on a linkage map?
In the order that best fits the recombination data
What are cytogenetic maps used for?
To locate genes with respect to chromosomal features visible under a microscope.
What has increased the rate and affordability of DNA sequencing in recent decades?
Technical advances.
What is the ultimate physical map of a chromosome?
The entire nucleotide sequence.
When comparing a linkage map with a physical map, what is identical?
The linear order of genes.
What can cause recombinant offspring in a testcross?
Two genes located on the same chromosome.
What is nondisjunction?
When homologous chromosomes do not separate properly during meiosis.
What is the result of nondisjunction in terms of gametes?
One gamete receives two of the same type of chromosome, another receives none.
What condition results from a gamete with no copy of a particular chromosome?
Aneuploidy.
What is the term for when a zygote has one less chromosome than normal?
Monosomic.
What is the term for a zygote with an extra chromosome?
Trisomic.
What percentage of human conceptions are estimated to involve monosomy and trisomy?
10-25%.
What is polyploidy?
The condition of having more than two complete chromosome sets.
What is the term for three complete chromosome sets?
Triploidy (3n).
What is the term for four complete chromosome sets?
Tetraploidy (4n).
What can cause chromosomal alterations?
Errors in meiosis or damaging agents like radiation.
What happens during a deletion in chromosome structure?
A chromosomal fragment is lost.
What occurs during a duplication in chromosome structure?
A chromosomal segment is repeated.
What occurs during an inversion in chromosome structure?
A segment is reversed within a chromosome.
What is a translocation in chromosome structure?
A segment moves from one chromosome to a nonhomologous chromosome.
What is the most common aneuploid condition in humans?
Down syndrome (trisomy 21).
What is the average frequency of Down syndrome births in the U.S.?
1 in 830.
What increases the frequency of Down syndrome?
The age of the mother.
What condition does Klinefelter syndrome describe?
Males with an extra X chromosome (XXY).
What is the occurrence rate of males with Klinefelter syndrome?
Approximately 1 in every 650 live male births.
What is a common trait of females with trisomy X?
Generally healthy.
How does aneuploidy of sex chromosomes differ from that of autosomes?
It appears to upset the genetic balance less.
Fill in the blank: Down syndrome is often called _______.
trisomy 21.
True or False: Individuals with Down syndrome have a higher rate of high blood pressure.
False.
What are common signs and symptoms of individuals with an extra Y chromosome (XYY)?
Taller than average height, less muscle mass, enlarged breast tissue, and potential learning disabilities.
What therapy helps stimulate typical puberty changes in males with an extra Y chromosome?
Testosterone replacement therapy.
What is trisomy X and how common is it?
A condition where females have an extra X chromosome (XXX), occurring in approximately 1 in 1,000 female births.
What is Turner syndrome and its occurrence rate?
A condition caused by monosomy X (XO), occurring in about 1 in every 2,500 female births.
What is the primary characteristic of individuals with Turner syndrome?
Phenotypically female but usually sterile due to immature sex organs.
What syndrome results from a deletion in chromosome 5?
Cri du chat syndrome.
What are the symptoms associated with cri du chat syndrome?
Small head, unusual facial features, severe intellectual disabilities, and a distinctive cry.
What chromosomal alteration is associated with chronic myelogenous leukemia (CML)?
Reciprocal translocation involving chromosome 22 and a fragment from chromosome 9, resulting in the Philadelphia chromosome.
True or False: The Philadelphia chromosome is a normal chromosome.
False.
What is genomic imprinting?
A phenomenon where the phenotype of a gene depends on whether it is inherited from the mother or the father.
How many imprinted genes have been identified in humans?
About 100 imprinted genes.
What is an example of an imprinted gene in mice?
Insulin-like growth factor 2 (Igf2).
What role does methylation play in genomic imprinting?
It can silence an allele in one type of gamete or activate it in another.
What are extranuclear genes?
Genes located outside the nucleus, often found in organelles like mitochondria and plastids.
How are mitochondrial genes inherited?
Maternal inheritance.
What is a common effect of defects in mitochondrial genes?
Reduced ATP production, affecting the nervous system and muscles.
What is mitochondrial myopathy?
A disorder causing weakness, intolerance of exercise, and muscle deterioration.
What is Leber’s hereditary optic neuropathy?
A mitochondrial disorder that can cause sudden blindness in young adults.
Fill in the blank: The Philadelphia chromosome results from a reciprocal translocation between chromosome 22 and chromosome _____.
9.
What is the significance of gene dosage in development?
It is crucial for proper development by ensuring the right number of gene copies are expressed.
True or False: Most mitochondrial diseases are lethal.
False.
What did Morgan’s work with a gene in Drosophila demonstrate?
Mendelian inheritance has its physical basis in the behavior of chromosomes
This led to the chromosome theory of inheritance.
What does the chromosome theory of inheritance state?
Genes are located on chromosomes and the behavior of chromosomes during meiosis accounts for Mendel’s laws.
What distinguishes parental types from recombinant types in a dihybrid testcross?
Parental types have the same combination of traits as those in the P generation, while recombinant types have new combinations of traits.
What is the frequency of recombination for unlinked genes?
50% frequency of recombination in the gametes.
How are genetic distances between genes determined?
From recombination frequencies observed in genetic crosses.
What is a linkage map?
A type of genetic map constructed from recombination frequencies.
What are sex-linked genes primarily located on?
Virtually all are on the X chromosome.
Why are males more affected by X-linked disorders than females?
Males have only one X chromosome, so a recessive X-linked allele will be expressed.
What does aneuploidy result from?
Nondisjunction during meiosis.
What are the outcomes of aneuploidy?
Trisomy (extra chromosome) or monosomy (missing chromosome).
What can chromosome breakage lead to?
Alterations in chromosome structure: deletions, duplications, inversions, translocations.
What genetic disorder is commonly caused by trisomy of chromosome 21?
Down syndrome.
Why are inversions and reciprocal translocations less likely to be lethal?
They do not typically result in a loss of genetic material.
What is genomic imprinting?
A phenomenon where one allele is not expressed in offspring depending on the parent it is inherited from.
How is mitochondrial inheritance characterized?
It depends solely on the maternal parent.
What is the significance of the cytoplasm in zygote inheritance?
It contains mitochondria and plastids inherited from the egg.
What is the effect of mitochondrial gene defects?
They can prevent cells from making enough ATP.
What is the inheritance pattern of traits controlled by mitochondrial genes?
Maternal inheritance.
What are the four phenotypes of flower genes mentioned?
Blue petals, white petals, round stamens, oval stamens.
What is the expected outcome when crossing homozygous plants with linked genes?
Four phenotypes based on the linkage and recombination frequencies.
What does a recombination frequency of 50 map units indicate?
Genes are unlinked and assort independently.
What phenomenon does crossing over in meiosis promote?
Genetic diversity through the shuffling of alleles.
What is the implication of Y-linked genes having homologous regions?
It allows for some crossing over, which may prevent degeneration.
What can scientists deduce from recombination frequencies between genes?
The relative order of genes on a chromosome.
What is the result of a testcross involving heterozygotes?
It helps determine the genotypes and recombination frequencies.
What is the effect of nondisjunction during the first mitosis in a gynandromorph butterfly?
It may result in half male and half female characteristics.
