Module 4—The Chromosomal Basis of Inheritance Flashcards
mendel’s 3rd law
law of dominance
does not reflect most traits
Schleiden & Schwann
cell theory
Walter Flemming
discovered chromosomes via microscopy
saw they were separated during mitosis
Sutton & Boveri
connected events of meiosis with Mendel’s laws
Thomas Hunt Morgan
fly lab
mapped first genes to specific chromosomes
found by Morgan not to exhibit Mendelian inheritance
sex-linked traits
hemizygous
describes males’ Y chromosome paired with X chromosome
reciprocal cross
cross of mutant father + wild type mother, AND cross of mutant mother + wild type father
homogametic
2 copies of same sex chromosome
female
heterogametic
sex chromosomes differ
male
__________ X chromosome has no effect on sons
paternal
in mammals, sex is determined by….
presence of Y chromosome
gene for testes development
SRY
how mammals deal with double dose of X chromosomes in females
___ bodies
X inactivation
Barr bodies - bound up X chromosome in heterochromatin
can become ovary or testis based on…
bipotential gonad
presence or absence of SRY gene
X-O system
XX is female
X0 is male
Z-W system
ZW is female
ZZ is male
haplo-diploid system
diploids are female
haploids are male
males have no fathers; develop from unfertilized eggs
genic sex determination
genes, not chromosomes, determine sex
environmental sex determination example
temperature determines ratio of males in all the eggs
(reptiles)
linked genes
located close together on same chromosome
gave evidence for recombination that separated linked genes
production of nonparental alleles in small numbers
recombination frequency
degree to which 2 linked genes assort independently due to crossing over
= 100 (total recombinants / total offspring)
the closer two genes are, the _____ likely they will be separated
less
Alfred Sturtevant
used recombination frequencies to map genes on particular chromosomes
Sturtevart used __________ to calculate rates of recombination
3-factor crosses
3 linked genes together
smaller recombination frequency = _______ distance between genes
shorter
recombination frequency cannot exceed…
0.5
(normal independent assortment)
map of chromosomes based on recombination frequency
linkage map
first whole-genome analysis
Alfred Sturtevant’s linkage map
chromosome scale variation
large scale chromosomal alterations
tolerated better by plants
chromosome scale variation
aneuploidy
removal of chromosome segment
example
deletion
crit du chat syndrome
repetiton of a segment
cause?
duplication
unequal crossing over
reversal of a segment
inversion
movement of a segment from one chromosome to a nonhomolog
2 types
translocation
reciprocal (trading)
nonreciprocal (no trading)
duplications can lead to…
new functions
subfunctionalization
one copy of a duplicated gene expressed in some tissue, the other in some other tissue
neofunctionalization
significance
duplicated gene takes on a new function
potentially origin of more complex genes
most common fate of duplications
degeneration / gene loss
translocations can form…
ex. chronic myeloid leukemia
gene fusions
gene fusions can occur during _____
mitosis
normal amount of chromosomes
euploidy
aneuploidy
fewer or extra chromosomes
other trisomies (besides Downs)
Edward
Patau
less disruptive aneuploidies located on…
sex chromosomes
Klinefelter syndrome
male traits
XXY
XXYY
XXXY
Turner syndrome
female traits
XO
only viable monosomy
Turner syndrome
XO
aneuploidy results from…
nondisjunction events
2 forms of nondisjunction
homologs fail to separate in meiosis I
sisters fail to separate in meiosis II
common carriers of whole genome duplications
crop plants
autopolyploids
genome is duplicated; meiotic error leads to failure to separate
gametes fuse to form polyploid zygote
allopolyploids
chromosome sets combine from different species
amphibians
allowed for the evolution of vertebrates
2 genome duplication events