Download Sex Chromosomes

Notes - The Chromosomal Basis of Inheritance
_________________________ was the first to associate a specific _____________ with a
specific ____________________ in the early 20th century

Like Mendel, Morgan made an insightful choice as an experimental animal,
______________________________________, a fruit fly species that eats fungi on fruit

Fruit flies have three pairs of _________________ and a pair of ________chromosomes
(________ in females, ________ in males)
He discovered a single __________ fly with ____________eyes instead of the usual red

The normal character phenotype is the ____________ type

Alternative traits are ______________ phenotypes
When Morgan crossed his white-eyed male with a red-eyed female, all the _______
offspring had __________ eyes

The red allele appeared _________________ to the white allele

Crosses between the _______offspring produced the classic ___________ phenotypic
ratio in the _________ offspring
Surprisingly, the _________________ trait appeared only in ____________

All the ______________ and half the ____________ had _________ eyes
Morgan concluded that a fly’s eye color was _____________ to its sex
Morgan deduced that the gene with the _________________ mutation is on the _______
chromosome alone, a ______________________ gene

Females (XX) may have two _________________ alleles and have red eyes or may
be ___________________ and have red eyes

Males (XY) have only a single allele and will be _________________ if they have a
red-eyed allele or ____________________ if they have a white-eyed allele
Each chromosome has __________________ or _____________________ of genes

Genes located on the same chromosome, ______________________, tend to be
inherited _______________ because the chromosome is passed along as a unit
Results of crosses with linked genes _______________ from those expected according to
_____________________________________

Morgan observed this linkage and its deviations when he followed the inheritance of
characters for __________________________ and _________________________
Morgan reasoned that body color and wing shape are usually inherited ________________
because their genes are on the same _____________________
Independent assortment of chromosomes and crossing over produce genetic
recombinants

The production of offspring with new ____________________ of traits inherited from two
parents is _______________________________________

Genetic recombination can result from independent assortment of genes located on
__________________ chromosomes or from ________________________ of genes
located on homologous chromosomes

A _________ frequency of recombination is observed for any two genes located on
different (____________________) chromosomes

The _________________________ of recombination between unlinked genes is the
random orientation of homologous chromosomes at __________________________

In contrast, linked genes tend to move together through _____________ and
______________________

Under normal Mendelian genetic rules, we would not expect ____________________ to
recombine into assortments of alleles not found in the ______________

The results of Morgan’s testcross for body color and wing shape
_____________________________ to either ______________________________ or
___________________ linkage

Under independent assortment the testcross should produce a ________________
____________________ ratio

If completely linked, we should expect to see a _________________ ratio with only
parental phenotypes among offspring
Morgan proposed that some mechanism occasionally exchanged ______________
between _____________________ chromosomes

This _________________ alleles between ___________________ chromosomes

The actual mechanism, ________________________ during prophase I, results in the
production of more _____________ of gametes than one would predict by Mendelian
rules alone
Sex Chromosomes

Although the _________________and ___________________ differences between
women and men are _________________, the chromosomal basis of sex is rather
_____________
In ______________ and other __________________, there are two varieties of sex
chromosomes, ______ and _____

This ___________ system of mammals is not the only chromosomal mechanism of
determining ___________

Other options include the __________ system, the __________ system, and the
______________________system

In the X-Y system, Y and X chromosomes behave as _________________
chromosomes during _______________

In reality, they are only _______________ homologous and ______________
undergo _________________________

In both ______________ (XY) and ______________ (XX), the two sex chromosomes
____________________ during meiosis and each gamete receives ___________
In humans, the ___________________ signs of sex first appear when the embryo is about
________ months old

In individuals with the __________gene (_______-determining ___________ of the
_____ chromosome), the generic embryonic gonads are modified into _____________

Activity of the SRY gene triggers a cascade of __________________,
____________________, and ___________________ features because it regulates
many other genes

In addition, other ___________ on the Y chromosome are necessary for the
production of functional ____________

In individuals lacking the ____________ gene, the generic embryonic gonads develop
into _________________
In addition to their role in ______________________________, the sex chromosomes,
especially the ________ chromosome, have genes for many _________________
unrelated to __________

If a _______________________ trait is due to a _________________ allele, a female
will have this phenotype only if _____________________

Heterozygous females will be __________________

Because males have only __________ _____ chromosome (__________________),
any male receiving the _________________allele from his mother will express the trait
The chance of a female inheriting a _________________________ of the mutant allele is
much ____________ than the chance of a male inheriting a ____________________

Therefore, _____________ are far more likely to inherit _____________________
recessive disorders than are __________________
Several serious human disorders are sex-linked
1. ____________________________________ affects one in ____________ males born
in the United States

Affected individuals rarely live past their early ___________

This disorder is due to the _______________ of an X-linked gene for a key muscle
protein, called __________________

The disease is characterized by a progressive ______________________ of the
muscles and a loss of _____________________
2. ________________________ is a sex-linked recessive trait defined by the absence of
one or more ___________________________

These proteins normally ____________ and then _____________ bleeding

Individuals with hemophilia have _________________ bleeding because a firm clot
forms _______________

Bleeding in ______________ and _______________ can be painful and lead to serious
____________________

Individuals can be treated with _____________________________ of the missing
________________
Although female mammals inherit __________ X chromosomes, only ___________ X
chromosome is ________________

Therefore, males and females have the same _______________________ (one copy)
of genes on the ______ chromosome
During female development, one X chromosome per cell _______________ into a compact
object, a ____________body

This _________________ most of its _______________

The condensed Barr body chromosome is _________________ in _______________
cells that produce _________
As a consequence, females consist of a mosaic of cells, some with an active
_____________________, others with an active ________________________

After Barr body formation, all ____________________ cells have the same
____________________

If a female is ____________________ for a sex-linked trait, approximately _________
her cells will express one allele and the other half will express the other allele
_______________________ occurs when problems with the _____________spindle cause
errors in ____________________________

This may occur if ____________ chromosomes do not separate properly during
_____________________

Alternatively, ______________________________ may fail to separate during
_______________________
As a consequence of nondisjunction, some gametes receive _________ of the same type of
chromosome and another gamete receives _________ copy

Offspring results from fertilization of a ______________ gamete with one after
____________________will have an abnormal chromosome number or
____________________
________________ cells have three copies of a particular chromosome type and have
____________________ total chromosomes
________________ cells have only one copy of a particular chromosome type and have
____________________ chromosomes

If the organism survives, __________________ typically leads to a distinct __________
If aneuploidy happens ___________ in development, this condition will be passed along by
________________ to a large number of ____________

This is likely to have a __________________ effect on the organism
Organisms with ______________ than two complete sets of chromosomes, have
undergone _______________________

This may occur when a ________________ gamete fertilizes another gamete in which
there has been _____________________ of all its chromosomes

The resulting zygote would be _____________________
If a _________ zygote failed to divide after replicating its chromosomes, a
____________________ embryo would result from subsequent successful cycles of mitosis
___________________ is relatively common among ______________ and much less
common among __________________
____________________ are more nearly normal in phenotype than __________________

One ______________ or _______________ chromosome apparently upsets the genetic
balance during development more than does an _________________________ set of
chromosomes
____________________ of a chromosome can lead to four types of changes in
chromosome structure
1. _____________________ - occurs when a chromosome fragment lacking a centromere
is lost during cell division

This chromosome will be missing certain _____________
2. ____________________ - occurs when a fragment becomes attached as an extra
segment to a _______________________________
3. ____________________ - occurs when a chromosomal fragment reattaches to the
________________ chromosome but in the ____________ orientation
4. ____________________ - a chromosomal fragment joins a ____________________
chromosome

Some ____________________ are ____________________, others are not
_________________ and _____________________ are common in _______________

Homologous chromatids may break and rejoin at _________________________,
such that one chromatid will ____________ more genes than it receives
A diploid embryo that is _________________ for a large _______________ or __________
with a large deletion to its ____________________ chromosome is usually missing
many __________________ genes and this leads to a _____________ outcome

__________________ and _____________________ are typically harmful

_______________________________ or __________________ can alter
__________________ because a gene’s expression is influenced by its location
Several serious human disorders are due to alterations of chromosome number and
structure

Although the frequency of _________________ zygotes may be quite high in humans,
most of these alterations are so _________________ that the embryos are
spontaneously ______________ long before birth

These developmental problems result from an _________________ among gene
products

Certain aneuploid conditions upset the balance ____________, leading to
____________________ to birth and beyond
These individuals have a set of _____________________ — a ____________________ —
characteristic of the type of aneuploidy
One aneuploid condition, _____________________________, is due to three copies of
chromosome ________


It affects one in __________ children born in the United States.
Although chromosome 21 is the _______________ human chromosome, it
_______________ alters an individual’s __________________ in specific ways

Most cases of Down syndrome result from ____________________ during
____________ production in one parent

The frequency of Down syndrome correlates with the __________ of the ____________

This may be linked to some ________________________ abnormality in the
______________checkpoint during ____________________, leading to nondisjunction
_____________________ of other chromosomes also increase in incidence with
___________________ age, but it is rare for infants with these autosomal trisomies
to ________________ for long
_________________________ of sex chromosomes produces a variety of
______________ conditions in humans

Unlike autosomes, this aneuploidy upsets the genetic balance ____________________

This may be because the ________ chromosome contains relatively few ___________

Also, extra copies of the ______ chromosome become inactivated as ___________
bodies in _______________ cells
1. ______________________ syndrome - an _________________, occurs once in every
_____________ live births

These individuals have male _______________________, but are ______________

There may be ___________________ characteristics

Their intelligence is _______________
2. Males with an extra ______ chromosome (____________) tend to somewhat
___________ than average

Associated with ___________________________
3. ___________________ - (_________), which occurs once in every _________ live
births, produces _______________ females
4. ___________________ or ______________________ (_________) - , which occurs
once in every 5000 births, produces _________________, but _______________
females
___________________________________ of chromosomes can also cause human
________________

__________________, even in a heterozygous state, cause severe ______________
and _________________ problems
One syndrome, _______________________, results from a specific deletion in
chromosome _______

These individuals are ___________________________, have a small __________ with
unusual facial features, and a cry like the ___________ of a distressed _________

This syndrome is ____________ in infancy or early childhood
The phenotypic effects of some mammalian genes depend on whether they were
inherited from the mother or the father (imprinting)

For most ______________ it is a reasonable assumption that a specific allele will have
the same effect regardless of whether it was ________________ from the
______________ or _______________

However, for some _____________ in ____________________, it does depend on
which _________________ passed along the alleles for those traits

The genes involved are not _____________________ and may or may not lie on the
________ chromosome
Two disorders with different phenotypic effects, __________________________ syndrome
and _____________________ syndrome, are due to the same cause, a
__________________ of a specific segment of chromosome _________
__________________________ syndrome is characterized by ______________________,
_______________, _____________ stature, and unusually small _________ and
_______________

These individuals inherit the abnormal chromosome from their _______________
Individuals with ____________________ syndrome exhibit spontaneous ______________,
_______________ movements, and other _____________ and _______________
symptoms

This is inherited from the __________________
The difference between the disorders is due to _______________________________

In this process, a gene on one homologous chromosome is _________________, while
its allele on the homologous chromosome is ______________________

The ___________________ status of a given gene depends on whether the gene
resides in a ______________ or a _____________

The same alleles may have different effects on offspring, depending on whether they
arrive in the _______________ via the ____________ or via the _____________

In the new generation, both maternal and paternal imprints are apparently
“_________________” in ______________-producing cells

Then, all chromosomes are __________________ according to the ____________ of
the ______________________ in which they reside
Several hundred mammalian genes, many critical for ________________________, may
be subject to ________________________

______________________ is critical for _____________________ development