Chapter 15: The Chromosomal Basis of Inheritance – Flashcards

Unlock all answers in this set

Unlock answers
question
What is the chromosome theory of inheritance?
answer
Mendelian genes have specific loci along chromosomes. Chromosomes undergo segregation and independent assortment.
question
Explain the law of segregation.
answer
The law of segregation states that chromosomes are equally separated between haploid gametes.
question
Explain the law of independent assortment.
answer
The inheritance of one trait has nothing to do, is independent from, the inheritance of another trait. Alleles/chromosomes are inherited and segregated independently from each other.
question
What did Thomas Hunt Morgan use for his genetic studies? Why were these excellent test subjects?
answer
He used fruit flies, aka drosophila melanogaster. These were good test subjects because they reproduce very quickly, they are relatively inexpensive to grow/obtain/feed, and they have only 4 chromosomes which makes them easy to study and observe.
question
Express the notation for a female fruit fly homozygous for red eyes, heterozygous for red eyes, and homozygous for white eyes.
answer
Xw+ Xw+, Xw+ Xw, Xw Xw
question
What unusual result suggested that the eye color trait is located on the X chromosome for fruit flies?
answer
There was a higher prevalence of males with white eyes than females with white eyes. More females had the wild type eye color, red, not the mutant type.
question
What are the many variations sex is determined for different species?
answer
X-Y system, mammals Z-W system, birds, fish, insects X-O system, grasshoppers, cockroaches, other insects Haplo-diploid system bees, ants
question
What is the SRY gene? Where is it found and what does it do?
answer
"Sex determining Region of Y". it is a gene on the Y chromosomes that codes for testes formation.
question
What is the definition of a sex-linked gene?
answer
A gene located on either sex chromosome
question
In humans, how has the term sex linked gene been historically modified?
answer
The term generally means that the disease is carried on the X chromosome.
question
Name three sex linked disorders
answer
Duchenne's muscular distrophy, hemophilia, and colorblindness
question
What is Duchenne's muscular dystrophy?
answer
progressive weakening of muscles and loss of coordination. rarely live past their early 20s. caused by the absence of a muscle protein called dystrophin. this disease is sex linked
question
What is hemophilia?
answer
an x linked recessive disorder caused by the absence of the proteins required for blood clotting. shows high prevalence in royal families
question
What is a barr body? Why do females show a barr body in their cells?
answer
A barr body is a compact object, an inactive X chromosome that has condensed. Females only use what is coded for from one x chromosome, the other x chromosome becomes a barr body.
question
What does x inactivation do?
answer
it maintains the proper gene dosage.
question
How is the X chromosome in females inactivated?
answer
Methyl groups (-CH3) are attactch to the nitrogenous bases of the DNA. A particular region of the X chromosome is involved. The two regions from each X chromosome associate briefly during embryonic development, and then one becomes inactive and the other becomes a barr body.
question
Why can you say that all calico cats are females?
answer
Color for cats is on the x chromosome. Calico/tortioseshell coloring is the result of a one black allele and one orange allele that come together in codominance. Males could never inherit this coloring since they only have one X chromosome, so can only be black or yellow.
question
What are linked genes? Do linked genes sort independently?
answer
Linked genes are genes that are close together on the same chromosome and tend to be inherited together unless recombination occurs. They do not sort independently since they are found close to each other on the same chromosome. The closer a gene is to another on the chromosome, the less likely it is to recombine and be inherited with a different gene.
question
If two genes are linked on the same chromosome, what is this combination called?
answer
the parental combination
question
What are the offspring called that display new combinations from crossing over?
answer
recombinants or recombinant types.
question
Review meiosis. When does crossing over occur?
answer
during prophase I
question
Who is Alfred H. Sturtevant?
answer
A student of Thomas Hunt Morgan. Used assumptions from observations of crossovers to map genes. Created a linkage map
question
What is a linkage map?
answer
A creation of Alfred H. Sturtevant. A linkage map uses recombination frequencies to estimate locations of genes on a chromosome in relation to one another. The lower the recombination frequency, the closer the two genes are to each other on the chromosome. Units of distance on a chromosome are measured in map units, a rather arbitrary unit that arises from the recombination frequencies (percentage).
question
What is a map unit?
answer
1 map unit= 1% recombination frequency. Used in linkage maps of a chromosome
question
What occurs in nondisjunction?
answer
Homolgous chromosomes or sister chromatids fail to separate in cell division. The result is gametes with incorrect chromosome counts.
question
Explain aneuploidy
answer
An incorrect number of chromosomes in a fertilized zygote. Result of nondisjunction
question
What is monosomy?
answer
When a cell is missing a chromosome (normal chromosome count is 2 of each). has 1 chromosome
question
What is trisomy?
answer
When a cell has an extra chromosome (normal chromosome count is 2 of each) . has 3 chromosomes
question
What is polyploidy?
answer
Having three or four chromosomal sets. more common in plants than in animals
question
What is Down Syndrome? Symptoms? Inheritance?
answer
A disease caused by a third 21st chromosome (trisomy 21). causes intellectual deficits and physical changes. symptoms include flattened facial features, poor muscle tone, a small head, small height, short neck, and upward slanting eyes
question
What is Kleinfelter? Symptoms? Inheritance?
answer
A boy is born with an extra X chromosome. this disease may go undetected until adulthood based on severity. symptoms include small testicles, taller than average, absent/delayed/incomplete puberty, enlarged breast tissue, shyness, intellectual delays, and attention difficulties.
question
What is Turner Syndrome? Symptoms? Inheritance?
answer
When a woman only has one X chromosome. signs and symptoms for this disease vary extremely. Some examples of symptoms include a receeding or small jaw, short fingers or toes, unable to conceive a child, learning and social disabilities.
question
What is Cri du Chat? Symptoms? Inheritance?
answer
a disease that occurs when a portion of the 5th chromosome is missing. causes abnormal larynx development, small size at birth, cry like a cat, small head, wide set eyes
question
What is Chronic Myelogenous Leukemia? Symptoms? Inheritance?
answer
mutation of chromosome 9 and 22, allows blood cells to grow out of control, causes too many white blood cells. symptoms include easy bleeding, fever, fatigue, night sweats
question
What results from the genotype "XXY" ?
answer
A male with Kleinfelter syndrome. Symptoms include small testes, sterility, breast enlargement, female characteristics, and subnormal intelligence.
question
What results from the genotype "XXX" ?
answer
A female with trisomy x. Symptoms include being slightly taller than average and being at risk for learning disabilities.
question
What results from the genotype "XO" ?
answer
A female with turner syndrome. Symptoms include being sterile and having sex organs that do not mature (not going through puberty)
question
What results from the genotype "XYY" ?
answer
A male that does not undergo normal sexual development and is taller than average.
question
What happens in a deletion?
answer
A chromosomal fragment is lost
question
What happens in a duplication?
answer
Extra gene is added
question
What happens in an inversion?
answer
Order of genes is reversed
question
What happens in a translocation?
answer
A portion of the lost fragment joins a non-homologous chromosome.
question
What is genomic imprinting?
answer
a zygote expresses only one allele of an imprinted gene depending on which parent passed the allele along. ex. igf2 gene in mouse that codes for insulin.
question
What group of genes have you inherited only from your mother?
answer
Mitochondrial DNA, "extranuclear genes", or "cytoplasmic genes"
question
What are some diseases carried through mitochondrial DNA?
answer
defects in atp synthase proteins, mitochondrial myopathy which causes weakness, an intolerance to exercise, and muscle deterioration. also levers hereditary opt neuropathy, causes sudden blindness in people in young 20s or 30s. mitochondrial dna might also contribute to diabetes, heart disease, and alzheimers
question
Why are extranuclear genes inherited maternally?
answer
The zygote's cytoplasm comes from the egg (female)
Get an explanation on any task
Get unstuck with the help of our AI assistant in seconds
New