Chromosome Flashcards
what did mendel call the things that were passed down between generations?
factors
what parallel did scientists find between mendel’s factors and what they knew?
parallel between genes and chromosomes
chromosomal theory of inheritance
who was the first to associate genes with chromosomes in fruit flies?
TH Morgan
scientific name of fruit flies
Drosophila melanogaster
how many offspring does a single mating of fruit flies have?
hundreds
a new generation of fruit flies can be bred?
every 2 weeks
how many chromosomes do fruit flies have?
3 pairs of autosomes and 1 pair of sex chromosomes
what mutation did Morgan discover?
white eyes instead of red eyes
wild type
normal phenotype for a character/the most common in natural populations
mutant
alternate to wild type
genotype of homozygous red eyed fly in morgans way
w+w+
genotype of white eyed male mutant
x^wy
homozygous red female
x^w+x^w+
F1 phenotype when mating homozygous red female with white eyes male?
all had red eyes
what did Morgan observe when he bred the F1 flies?
3:1 phenotypic ratio with F2s
when did the white eye trait show up?
only in males
1/2 males had red, 1/2 males had white
all females had red
what did Morgan conclude when he noticed only the males had white eyes?
the gene affecting white eyes is located on the X chromosome
what are gene located on the sex chromosomes or x chromosomes called?
sex-linked genes
x-linked genes
what needs to be mated to get a white eyed female?
heterozygous red eyed female X^w+X^w
white eyes male X^wY
why are genes on the same chromosomes inherited together?
chromosome is passed along as a unit
linked genes
genes on the same chromosome
if linked genes are followed across generations, what law do they disobey?
Law of Independent Assortment
wild type for body color? mutant?
gray; black
wild type for wings? mutant?
long; vestigial
if the body color and wing genes were on different chromosomes, what would the phenotypic ratio be?
1:1:1:1
indication of linked genes
offspring look like parentals
what are recombinants?
phenotypes that occur due to crossing over in prophase I
how to find map units?
[(# of recombinant)/total] x 100%
what are map units
distance between genes on the same chromosome
who constructed the genetic map?
Sturtevant
what is a genetic map?
an ordered list of loci along a chromosome
how do you get a linkage map?
by associating frequencies of recombinants along the chromosome
diff between linkage map and genetic map?
linkage map is a genetic map with distances
what did recombinant frequencies correspond with?
distance between genes on a chromosome
what happens the probability of a crossover and recombinant frequency the further apart 2 genes are on a chromosome?
higher probability and higher frequency
one map unit=
1% chance of recombination
how far do genes have to be to not be considered as linked? why?
50 map units apart
their results are indistinguishable from genes located on different chromosomes
what two characteristics that mendel studies are on the same chromosomes? why didnt they show up in his work?
flower and seed color
they were >50 mu apart
who determines the gender of the offspring in humans? why?
males
females only carry X
X-Y system
humans
male - XY (
female - XX
50/50
X-O system
crickets, roaches
only one X, no Y
male - X
female - XX
Z-W system
birds, some fish
opposite of humans, mom determines sex
male - ZZ
female - ZW
the haplo-diploid system
social insects: bees and ants
only females are fertilized eggs
male - haploid (16)
female - diploid (32)
how do x-linked work in heredity?
fathers pass x linked genes to all daughters and none to sons
mothers pass x linked genes to both sons and daughters
what must a female be to express a recessive sex-linked allele?
homozygous recessive
X^aX^a
since males only have one locus, what do we call them?
hemizygous
why do more males have sex-linked recessive disorders?
any male receiving recessive allele from mother gets the trait
what are parents from a female to get a sex-linked recessive disorder?
mom - carrier X^AX^a
dad - must have recessive disorder X^aY
Red-green colorblindess
mild recessive sex-linked disorder
Duchenne Muscular Dystrophy
X-linked recessive
1 in 3500
leads to weakening f muscles and loss of coordination because a key muscle protein (dystrophin) in missing
Hemophilia
X-linked recessive trait
absence of a protein for clotting
hemophiliacs bleed excessively when injured even with minor cuts or bruises
what happens to the 2 X chromosomes in females mammals during embryonic development?
one of them becomes almost completely inactive
Barr body
inactive X condenses into a compact object
where is the barr body located?
lies along the inside of the nuclear envelpoe
are genes expressed in barr bodies?
most of then are not- some remain active
where are Barr bodies reactivated?
ovaries
how is it determined which X chromosome becomes inactivated?
completely random and differs from one cell to the next
females consist of a mosaic of what two types of cell due to randomization of inactivation?
1) active X derived from the mother
2) active X derived from the father
what happens to the resulting cells after a mitotic division of a cell with an inactive X?
they all have the same inactive X
how do Barr bodies come about?
because methyl groups inactivate one of the X
how does X-inactivation explain why calico cats are almost always female?
one X - black color
other X - orange color
codominance/sex - linked
female can inherit both alleles, while males only get one
so when barr bodies form randomly in different cells of a female cat heterozygous for coat color, the typical calico pattern forms
where are chromosomes not separated as expected? what is this called?
anaphase I - homologous pairs
anaphase II - sister chromatids
nondisjunction
abnormal chromosome number
aneuploidy
three chromosomes in a cell
trisomy
one chromosome in cell
monosomy
what happens to the zygote in most cases of aneuploidy?
it dies
can nondisjunction occur in mitosis? what happens?
yes- if it happens during the development of the embryo, it will affect a large number of ells
what is it called when an organism inherits an entire set of chromosomes?
polyploidy
one extra set of chromosomes
triploidy
where is polyploidy common in?
plant kingdom
5 types of changes in chromosomes structures
1) deletion
2) duplication
3) inversion
4) reciprocal translation
5) nonreciprocal translation
nonreciprocal translation
a chromosome segment is given to a nonhomologous chromosome without receiving a segment in return
Trisomy 21
Downs Syndrome
how is trisomy 21 caused?
result of extra chromosome 21
each body cell has a total of 47 chromosomes
symptoms of trisomy 21 (6)
characteristic facial features
short stature
heart defects
respiratory infections
mental retardation
some sterile
what are people with trisomy 21 prone to?
leukemia and Alzheimer’s - both located on Chromosome 21
what affects the frequency of down’s?
higher the age the mother- more perceptible especially 35+
XXY
Klinefelter’s syndrome
characteristic of XXY males
male sex organs but small testes and sterile
breast development
normal intelligence
XYY
“Super Male” Jacobs Syndrome
characteristics of XYY male
taller than average
XXX
trisomy X
characteristic of XXX female
healthy and cannot be distinguished from XX except via a karyotype
XO
Monosomy X/ Turners syndrome
characteristic of XO female
phenotypically female with underdeveloped sex organs, sterile, short, and of normal intelligence
Cri du Chat cause and symptoms
deletion in chromosome 5
mental retardation, small head, unusual facial features, and a cry that ensembles a distressed cat
Leukemia cause and symptoms
reciprocal translocation between chromosome 22 and 9
affects cells that give rise to WBC/ leukocytes
what is imprinting in terms of genetics?
some inherited disorders depend upon whether they are inherited from mom or dad
2 different disorders that come from imprinting
Prader Willi syndrome and Angelman syndrome
deletion in chromosome 15
Prader Willi syndrome cause and symptoms
inherits abnormal chromosome from dad
insatiable appetite
obese
short
retardation
Angelman syndrome
inherits abnormal chromosome from mom
“happy puppets”
uncontrollable laughter
jerky movements
can’t talk
seizures
genomic Imprinting
parental origin of the chromosomes is printed on the chromosomes
these imprints are erased between offspring produces its own gametes
Fragile X
tip of an X chromosome is hanging by a thin thread of DNA
mental retardation
how does genomic imprinting explain fragile x syndrome?
abnormal X is inherited from mothers, so male offspring are most affected
how is DNA transferred from mitochondria and plastids own DNA?
reproduce themselves and transmit their genes to daughter organelles
what do male humans contribute to the zygote?
DNA
what do female humans contribute to zygote?
DNA
cytoplasm and al the organelles including mitochondria
what do disorders associated with mitochondrial DNA affect?
ATP
what happens when there is a reduction in the amount of ATP?
energy deprivation especially to the nervous system and muscles
how are yellow and white patched in plants determined?
DNA determined in chloroplasts, even though they have mitochondrial DNA
where do the genes that determine whether a leaf is spotted or striped come from?
ovule - maternal
not pollen
