Chapter 15 (Chromosomal Theory) Flashcards
What are Mendel’s “factors”?
segments of DNA located along
chromosomes
What is the chromosomal theory of inheritance?
Mendelian genes have specific loci (positions) along
chromosomes, and it is the chromosomes that undergo segregation and independent assortment
Who is Thomas Hunt Morgan?
provided evidence that a specific gene with a specific chromosome existed
What did Thomas Hunt experiment on?
fruit flies (Drosophila melanogaster)
Why were fruit flies a good choice for Thomas Hunt to experiment on?
production of hundreds of offspring, new-generation forms every two weeks, easily distinguishable chromosomes
What is the wild type?
dominant (most abundant)
What is mutant type?
recessive (alt. form of wild type)
What change was significant in Hunt’s experiment and what did it explain?
only male had white eyes instead of the usual red, suggesting that mutation was sex-linked and it supported the theory of chromosomal inheritance
What is the notation for white eyes?
w
What is the notation for red eyes?
w+
What is a sex-linked gene?
gene located on sex chromosome
What are X-linked genes?
gene on X chromosome
What are Y-linked genes?
genes located on Y chromosome
What is a parental type?
looks like parent
What is a recombinant type?
looks like a mix of parents
What is the distance between genes if they are to be inherited together?
they have to be close together (unit wise)
What are serious x-linked diseases?
Duchenne muscular dystrophy and hemophilia (blood clotting gone)
What do dominant x genes affect?
physical
What do recessive genes affect?
enzymatic level
How can linked genes be inherited together?
they are located near each other on the same chromosome, they don’t sort independently and can affect the inheritance of two traits
Do linked genes deviate from Mendel?
yes
What is genetic recombination?
production of offspring with combinations of traits that differ from those found in either P generation parent
What does a 50% frequency of recombination suggest?
genes located on a different chromosomes or can be very far apart
What does a frequency of recombination lower than 50% suggest?
genes are located closely on chromosome
What is genetic recombination based on?
Based on crossing over of homologous chromosomes during prophase I of meiosis – exchange of DNA
What did Alfred Sturtevant do?
construct the first genetic map that has ordered list of loci along a particular chromosome
What is a linkage map?
A genetic map based on recombination frequencies
What are map units for a linkage map?
distance between genes for every 1% of genetic recombination frequency
When is the physical connection of genes contributing to the idea of unlinked genes?
Despite being on the same chromosome and thus being physically connected, the genes are genetically unlinked; alleles of such genes assort independently, as if they were on different chromosomes
What does a linkage map not portray?
physical location of a gene, only shows recombination frequencies
What can a large scale chromosomal alteration lead to?
miscarriage or developmental issues
What structure is supposed to distribute chromosomes to daughter cells without error?
mitotic spindle
What is nondisjunction?
members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis I (aka one gamete receives both pairs whereas the other game doesn’t receive anything)
What is aneuploidy?
zygote has an abnormal number of a chromosome (think a for abnormal)
What is monosomic?
the aneuploid zygote that is missing a chromosome (2n-1) (mono for one less)
What is trisomic?
aneuploid zygote that has one extra chromosome (2n+1) (tri for 3, 1 extra)
When does monosomic and trisomic occur?
in fertilization
What is polyploidy?
an organism has more than two complete sets of chromosomes
Which one has a more detrimental affect, aneuploidy or polyploidy?
aneuploidy
What are the different types of changes in chromosomes from errors in meiosis crossing over?
deletion, duplication, inversion, translocation
What is deletion?
the chromosomal fragment is lost
What is duplication?
“deleted” fragment may become attached as an extra segment to a sister or non-sister chromatid
What is an inversion?
A chromosomal fragment may also reattach to the original chromosome but in the reverse orientation
What is translocation?
fragment to join a nonhomologous chromosome
How are deletion and duplication related?
nonsister chromatids sometimes exchange unequal-sized segments of DNA, so that one partner
gives up more genes than it receives
products of such an unequal crossover are one chromosome with a deletion and one chromosome with a duplication
What is an aneuploid condition?
Down syndrome
What causes Down syndrome?
three copies of chromosome 21 (become trisomic)
What does Down Syndrome affect?
facial features, short stature, correctable heart defects, and developmental delays
In the mother, how does down syndrome frequency increase?
with age
What does nondisjunction in meiosis result in?
aneuploidy
What happens in the aneuploidy of sex chromosomes?
Y chromosome carries relatively few genes or extra copies of the X chromosome
What is Klinefelter syndrome?
an extra inactive X chromosome in a male (XXY) and it affect reproductive organs, Males can also display an extra Y chromosome (XYY)
Are females with XXX healthy or no?
healthy because the X is inactive
What is Turner syndrome?
only one X chromosome, are sterile because
their sex organs do not mature
How does a female and male have the same level of protein production?
female’s extra X is inactivated so one X in both male and female work
What is a Barr body?
inactive X chromosome in each cell of a female condenses into a compact object
When are Barr bodies reactivated?
to make eggs
Is the determination of which X chromosome get’s inactivated in females random or not?
it is random and independent (1 of the X in XX will get deactivated, but which one?)
What are mosaic cells and where are they found?
found in females, e with the active X derived
from the father and those with the active X derived from the mother, when a person has 2 or more genetically different sets of cells in his or her body.
If a female is heterozygous, what happens to her mosaic cells?
half of her cells will express one allele, while the others will express the alternate allele (ex: recessive mutation can lead to some patches of skin will have sweat glands while others will not)
