Download Fertilization and meiosis alternate in sexual life cycles

Notes on Meiosis and Sexual Life Cycles
A ____________________ is the generation-to-generation sequence of stages in the
___________________ history of an organism

It starts at the __________________ of an organism and continues until it
produces its own ________________
Fertilization and meiosis alternate in sexual life cycles:
In humans, each ______________ cell (all cells other than _________ or __________) has
_____ chromosomes

A _________________ display of the 46 chromosomes shows 23 pairs of
chromosomes, each pair with the same ____________, _______________
position, and _______________ pattern

These _________________ chromosome pairs carry genes that control the same
__________________ characters

An exception to the rule of homologous chromosomes is found in the _________
chromosomes, the _____ and the _____

The pattern of inheritance of these chromosomes determines an individual’s
________

Human females have a _________________ pair of _____ chromosomes
(_______)

Human males have an _____ and a _____ chromosome (_________)

Because only small parts of these have the same ___________, most of their
genes have no _________________ on the other chromosome
The other 22 pairs are called ____________________
The occurrence of homologous pairs of chromosomes is a consequence of sexual
reproduction

We inherit _______ chromosome of each __________________ pair from each
______________

The _________ chromosomes in a somatic cell can be viewed as two sets of 23,
a __________________ set and a ___________________ set

___________________ or _________ (gametes) have only one set of
chromosomes — _________ autosomes and an ______ or a ______

A cell with a single chromosome set is ______________

For humans, the haploid number of chromosomes is __________
(______________)
By means of ________________________________, a haploid ____________ reaches
and fuses with a haploid ____________

These cells fuse (________________) resulting in __________________

The fertilized egg (______________) now has two _______________ sets of
chromosomes bearing genes from the ____________ and ____________ family
lines
The zygote and all cells with two sets of chromosomes are _____________ cells

For humans, the diploid number of chromosomes is ________
(_______________)
As an organism develops from a _____________ to a sexually mature ___________, the
zygote’s genes are passed on to all ______________ cells by ________________
_____________, which develop in the gonads, are not produced by _____________

Instead, gametes undergo the process of _______________ in which the
chromosome number is _____________

Human ____________ or __________ have a ________________ set of 23
different chromosomes, one from each _______________ pair

_____________________ restores the ______________ condition by combining
two ______________ sets of chromosomes
Fertilization and meiosis alternate in sexual life cycles

The _____________ of meiosis and fertilization does __________ among
species
The life cycle of ______________ and other _____________ is typical of one major type

_____________, produced by meiosis, are the only _____________ cells

Gametes undergo no divisions themselves, but fuse to form a ____________
zygote that divides by ______________ to produce a multicellular organism
Steps of Meiosis:

Similar to ____________________

However, in meiosis, there are two consecutive cell divisions,
__________________ and ___________________, that result in _______
daughter cells

Each final daughter cell has only __________ as many chromosomes as the
parent cell
Meiosis reduces chromosome number by copying the chromosomes ____________, but
dividing ______________

The first division, meiosis I, separates
____________________________________

The second, meiosis II, separates
_______________________________________

Division in meiosis I occurs in four phases: _________________,
________________, _________________, and ___________________
During the preceding __________________ the chromosomes are ________________ to
form _____________________________

These are genetically _________________ and joined at the
__________________

The single __________________ is replicated
In prophase I, the chromosomes ___________________ and homologous chromosomes
_________________ to form ________________

In a process called __________________, special proteins attach homologous
chromosomes ______________ together

At several sites the chromatids of homologous chromosomes are
_______________ (chiasmata) and segments of the chromosomes are
_______________

A _______________ forms from each centrosome and spindle fibers attached to
____________________ on the chromosomes begin to move the _________
around
At metaphase I, the ________________ are all arranged at the ______________________

_____________________ from one pole are attached to the kinetochore of one
___________________ of each tetrad, while those from the other pole are
attached to the other
In anaphase I, the homologous chromosomes ________________ and are pulled toward
___________________________
In telophase I, movement of ______________________________________ continues until
there is a _______________ set at each pole

Each chromosome consists of linked ________________________________
______________________ by the same mechanisms as mitosis usually occurs
__________________________
________________________ is very similar to _________________

During prophase II a ________________ apparatus forms, attaches to
______________________ of each sister chromatid, and _____________ them
around

At metaphase II, the sister chromatids are arranged at the
_______________________

At anaphase II, the ___________________ of sister chromatids ________________
and the now separate sisters travel toward ____________________________

In telophase II, separated sister chromatids arrive at
__________________________

______________ form around the _________________

___________________ separates the _________________

At the end of ________________, there are _________haploid daughter cells
Mitosis and meiosis have several key differences
1. The chromosome number is _____________ by half in ____________, but not in
_______________
2. Mitosis produces daughter cells that are ______________________________ to the
________________ and to ____________________________
3. Meiosis produces cells that ______________ from the ______________ and
____________________________
4. ____________ events, unique to ______________, occur during the ___________
division cycle
a. During prophase I, homologous chromosomes pair up in a process called
_________________

Later in prophase I, the joined homologous chromosomes are visible as a
_______________

At X-shaped regions called chiasmata, sections of _________________
chromatids are ____________________

Chiasmata is the physical manifestation of _______________________, a form of
genetic ______________________
b. At metaphase I _____________________________ of chromosomes, not individual
chromosomes are _________________ along the metaphase plate

In humans, you would see _________ tetrads
c. At anaphase I, it is ____________________ chromosomes, not ______________
chromatids, that ________________ and are ____________ to opposite poles of
the cell

________________ chromatids remain attached at the _________________ until
________________________
The processes during the _______________ meiotic division are virtually identical to
those of _______________
Mitosis produces _____________________________________ daughter cells, but
meiosis produces ________________________________ cells
Origins of Genetic Variation:

The behavior of chromosomes during __________________ and
__________________ is responsible for most of the ___________________ that
arises each generation during _______________ reproduction
Three mechanisms contribute to genetic variation:
1. _______________________________
2. _______________________________
3. _______________________________
Independent assortment of chromosomes contributes to genetic variability due to the
__________________ orientation of __________________ at the metaphase plate
There is a _____________________ chance that a particular daughter cell of meiosis I will
get the ____________________ chromosome of a certain homologous pair and a
fifty-fifty chance that it will receive the ________________ chromosome

Each homologous pair of chromosomes is __________________ independently
of the other pairs at ______________________

Therefore, the first meiotic division results in independent assortment of
_____________ and __________________ chromosomes into daughter cells
The number of combinations possible when chromosomes assort independently into
gametes is ____________, where ______ is the haploid number of the organism

If ___________, there are ______________ possible combinations

For humans with n = 23, there are ____________ or about
___________________ possible combinations of chromosomes

Independent assortment alone would find each _____________________
chromosome in a _______________ that would be exclusively maternal or
paternal in origin
__________________________ produces recombinant chromosomes, which
__________________ genes inherited from each parent

Crossing over begins very early in _____________________ as homologous
chromosomes ___________________ gene by gene

In crossing over, homologous portions of two __________________ chromatids
trade places
(For humans, this occurs ________ to _____________ times per chromosome
pair)

One sister chromatid may undergo ______________ patterns of crossing over
than its _________________

Independent assortment of these ______________________ sister chromatids
during _____________________ increases still more the number of genetic types
of _________________that can result from meiosis

The _____________________ nature of ________________________ adds to
the genetic _____________________ arising from meiosis

Any __________________ can fuse with any ____________
An ________________ is one of approximately 8 million possible chromosome
combinations (actually __________)
The successful ________________ represents one of 8 million different possibilities
(actually ____________)
The resulting _______________ is composed of 1 in ___________________
(______________________) possible combinations of chromosomes

____________________________ adds even more __________________ to
this
All three mechanisms __________________ the various genes carried by individual
members of a ______________________
_____________ and ______________________ are two sources of the continual
generation of new genetic ______________________