17: Inheritance of Genetic Information II Flashcards
Module 3, Lesson 6
The chromosomal theory of inheritance was first proposed by…
Walter Sutton
The chromosomal theory of inheritance states that…
Chromosomes are the carriers of genetic information and the basis for genetic inheritance.
The first evidence that genes resided on chromosomes was provided by…
T.H. Morgan
In Morgan’s F1 generation, all the fruit flies had…
Red eyes
What was unusual about Morgan’s F2 generation?
Only male fruit flies had white eyes
How is sex determined in fruit flies?
The number of X chromosomes
During meiosis, females can produce…
X gametes only
During meiosis, males can produce…
Either X or Y gametes
The sex of a zygote is determine by the…
Father
In humans, sex is determined by…
The presence or absence of the Y chromosome
True or false:
The human Y chromosome is very similar to the X chromsome.
False
The Y chromosome is highly condensed and has few expressed genes.
The “default” sex for humans is…
Female
In order for a zygote to develop as male…
The SRY gene (on the Y chromsome) must be present
Humans have ____ pair(s) of sex chromsomes.
1
Chromosome pairs that do not influence the individual’s sex are called…
Autosomes
Humans have ____ pair(s) of autosomes.
22
The human genome contains a total of ____ chromosome pairs.
23
A trait controlled by a gene located on the X chromosome is considered…
Sex-linked or X-linked
True or false:
A male who expresses an abnormal X-linked trait can pass that trait onto his sons.
False
He will pass the trait onto his daughters, but cannot pass it on to his sons.
For X-linked traits, the male phenotype is dependent on the X chromosome inherited from his…
Mother
Females will only express an X-linked recessive trait if…
They are homozygous for that trait
(actually this isn’t entirely true but not relevant to a basic biology course)
True or false:
The daughters of a male who is affected by an X-linked trait and a female who is a carrier for the trait may be affected.
True
True or false:
All X-linked traits are recessive.
False
Regulators of gene expression that do not change the DNA sequence are called…
Epigenetic mechanisms
List two examples of epigenetic mechanisms.
- Dosage compensation
- Genomic imprinting
____ ensures that an equal number of genes are expressed from sex chromosomes.
Dosage compensation
True or false:
Because human females have twice as many X-linked genes as males, they have twice as much gene expression for these traits.
False
How does dosage compensation occur in humans?
In females, one X chromosome is inactivated and condenses into a Barr body
True or false:
The X chromosome that is inactivated varies randomly from cell to cell.
True
Females that are heterozygous for an X-linked trait are sometimes called…
“Genetic mosaics”
The unique coloration of calico cats is due to…
X-chromosome inactivation
In which two groups of organisms does genomic imprinting occur?
- Flowering plants
- Mammals (incl. humans)
Genes that are “imprinted” are…
Inactivated
Cells determine which genes to imprint based on…
Which parent they were inherited from
____ occurs when one allele is inactivated while the other is expressed.
Genomic imprinting
True or false:
Traits associated with organelle genomes (mitochondria and chloroplasts) follow Mendelian inheritance patterns.
False
The organelle genome is usually inherited solely from the…
Mother
Organelle genes are passed from parent to offspring via…
Maternal inheritance
The first human disease shown to result from a mutation in a protein was…
Sickle-cell anemia
What causes sickle-cell anemia?
A single base substitution in the gene that codes for hemoglobin
A person who is homozygous for sickle-cell anemia will…
Exhibit intermittent illness and have a reduced lifespan
An individual who is heterozygous for sickle-cell anemia will…
Appear normal under normal oxygen conditions
Sickle-cell anemia is particularly prevalent in people of ____ descent.
African
Why is the proportion of people heterozygous for sickle-cell anemia abnormally high in African populations?
Having one mutated copy of the gene confers higher resistance to malaria
The failure of homologues or sister chromatids to separate properly during meiosis is called…
Nondisjunction
____ is the gain or loss of a chromosome.
Aneuploidy
____ refers to the loss of a chromosome.
Monosomy
(because there is now only one chromsome from that pair present in the cell)
____ refers to the gain of a chromosome.
Trisomy
(because there are now three chromosomes from that pair in the cell
In humans, individuals with trisomy can only survive if the trisomy occurs on one of ____ autosome pairs.
Five
Infants born with trisomy 13, 15, or 18…
Die within a few months of birth
People born with trisomy 21 or 22…
Can survive to adulthood, albeit with physical and mental disabilities
“Trisomy 21” is more commonly known as…
Down Syndrome
Down Syndrome can also occur if a small, critical portion of chromosome 21 is…
Translocated
The consequences of nondisjunction in sex chromosomes is generally ____ severe than in autosomes.
Less
Nondisjunction of sex chromosomes often results in…
Abnormal features, mental disabilities, and sterility
True or false:
Some individuals with sex chromosome nondisjunction can still be fertile.
True
The fertilization of an XX egg with an X sperm results in…
Triple X syndrome
A zygote with Triple X syndrome will…
Develop female, just with two Barr bodies
The fertilization of an XX egg with a Y sperm results in…
Klinefelter syndrome
A zygote with Klinefelter syndrome will…
Develop male, with female characteristics and mental disability
The fertilization of an O egg with an X sperm results in…
(an O egg is one that has no sex chromosome)
Turner syndrome
A zygote with Turner syndrome will…
Develop into a sterile female with immature sex organs and diminished mental abilities
A zygote fertilized by an O egg and a Y sperm is…
Nonviable
The fertilization of an X egg with a YY sperm results in…
Jacobs syndrome
A zygote with Jacobs syndrome will…
Develop into a fertile male with larger stature and some mental disability
True or false:
Many genetic disorders can be predicted and detected in utero.
True
____ provides risk assessment and guidance to parents about how genetic conditions may affect phenotype.
Genetic counseling
A mutation in the BRCA1 or BRCA2 results in…
A greatly elevated risk of breast cancer in women
Genetic counselors can predict the likelihood of genetic disorders using…
A pedigree analysis of the parents
List two methods of collecting fetal cells for genetic testing.
- Amniocentesis
- Chorionic villi sampling
During ____, fetal cells are collected from the amniotic cavity.
Amniocentesis
During ____, fetal cells are collected from the fetal portion of the placenta.
Chorionic villi sampling
Both amniocentesis and chorionic villi sampling carry a risk of…
Miscarriage
____ is the independent assortment of genes on the same chromosome as a result of crossing over.
Genetic recombination
When crossing over occurs, parental alleles are…
Recombined
Crossing over occurs during ____ of meiosis.
Prophase 1
Recombination allows us to measure…
The distance between genes on a chromosome
T.H. Morgan suggested that the frequency of recombinant offspring reflected…
The location of relevant genes on the chromosome
As physical distance increases, the probably of recombination…
Increases
We use ____ to measure recombinant frequency.
Test crosses
If a significant number of offspring display a recombinant phenotype, then…
The genes must be far apart
If few offspring display the recombinant phenotype, then…
The genes must be close together
Two genes that are close together are called…
“Linked traits”
A test cross that examines two gene loci is called a…
Two-point cross
During a two-point cross…
Doubly heterozygous offspring are crossed with the homozygous recessive parent.
Offspring with ____ are not recombinant.
Parental phenotypes
Offspring with a mixture of parental traits are…
Recombinant
Dividing the number of recombinant offspring by the total number of offspring yields the…
Recombination frequency
Each 1% of the recombination frequency represents a unit of measure called the…
Map unit or centimorgan
List four methods that can be used to map the human genome.
- Test crosses and linkage analysis
- Disruption of genes of unknown functions
- Inducing mutant phenotypes
- Analysis of historical pedigrees
Why was it originally difficult to map the human genome?
There were limited useful genetic markers and limited historical data
Human genome mapping was made significantly easier with the discovery of…
Large numbers of genetic markers that do not alter phenotype
What are the two “landmarks” that aid in mapping the human genome?
- Short Tandem Repeats (STRs)
- Single Nucleotide Polymorphisms (SNPs)
____ are a sequence of 2-4 repeated bases that differ in number between individuals.
Short tandem repeats
(STRs)
____ are differences that affect a single base of a gene locus, with a low frequency in the general population.
Single nucleotide polymorphisms
(SNPs)
