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UNIT 3
ALL ORGANISMS NEED TO REPRODUCE, BUT WHY?
What is Involved in the Reproduction of Humans?
Types of Reproduction
________________________ reproduction
__________________________ are duplicated and cell divides
Each daughter cell is genetically ________________________ to the parent and the other daughter
_______________________ reproduction
Each offspring inherits a unique __________________________ of genes from both parents
Offspring can show great ____________________________
In order to get a good grasp of both sexual and asexual reproduction we must first begin with
understanding how cells reproduce.
Understanding of the _____________________________, which includes ___________________________,
will greatly increase your understanding if both sexual and asexual reproduction
The Cell Cycle
The cell cycle is defined as
There are two phases of the cell cycle
__________________________________ (cell growth and copying of chromosomes in
preparation for cell division)
______________________ (M) phase (_______________________) (mitosis and cytokinesis)
Interphase (about ____% of the cell cycle) can be divided into subphases
_________ phase (“first gap”)
_________ phase (“synthesis”)
_________ phase (“second gap”)
The cell grows during all three phases, but chromosomes are duplicated only during the S phase
The Key Roles of Cell Division
The ability of organisms to produce more of their own kind best distinguishes __________________
things from nonliving matter
The continuity of life is based on the reproduction of cells, or _______________________
In unicellular organisms, division of one cell reproduces the entire organism
Multicellular organisms depend on cell division for
Most Cell Division results in Genetically Identical Daughter Cells
Most cell division results in daughter cells with identical genetic information, ___________
_______________________ cells (nonreproductive cells) have two sets of chromosomes
The exception is ___________________, a special type of division that can produce sperm and egg cells
Gametes (reproductive cells: sperm and eggs)
Cellular Organization of the Genetic Material
All the DNA in a cell constitutes the cell’s ____________________
A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of
DNA molecules (common in eukaryotic cells)
There are several terms used to describe the genetic material in the cell
Chromatin and Chromosome
___________________________ is uncondensed complex of DNA and associated proteins
that is typical of the genetic material during interphase of the cell cycle
It eventually will condenses during cell division and become ________________________
Chromatids
___________________________ are similar to chromosomes in that they are condensed
DNA molecules but they are attached to their identical at a _______________________
In preparation for cell division, DNA is _______________
The entire structure is called a _________________________________ (one being the
original DNA and the other being the copy)
During cell division,
Once separate, the chromatids are called _______________________________
Eukaryotic cell division/mitotic phase consists of
_________________________, the division of the ____________________________ in the nucleus
_________________________, the division of the _______________________________
Mitosis is conventionally divided into five phases
Before we get to the stages of Mitosis lets quickly review Interphase
_______________________________: Duplication of the genetic material ends when
chromosomes begin to become visible
_______________________________ (the first stage of mitosis): The genetic material begins to
_______________________. The mitotic ______________________ is forming. ______________
migrate to opposite ends of the cell
______________________________: Chromatin completely coil into chromosomes and then
produce sister chromatids; nucleoli and nuclear membrane __________________
______________________________: The spindle is fully formed; sister chromatids are aligned
_____________________ file with centromeres on the metaphase plate
______________________________: Sister chromatids ___________________________ from
the centromere, dividing to arrive at opposite _________________
Genetic material is now called?
______________________________: Cell elongation continues, a nuclear envelope forms
around chromosomes, chromosomes uncoil, and nucleoli reappear
______________________________: The cytoplasm _________________________
Cytokinesis
In animal cells, cytokinesis occurs by a process known as ______________________,
forming a ___________________________________
In plant cells, a __________________________________ forms during cytokinesis
How is the Cell Cycle Regulated?
The frequency of cell division _______________ with the _______________ of cell
These differences result from regulation at the molecular level
Cancer cells manage to escape the usual _________________________ on the cell cycle
The Cell Cycle Control System
The sequential events of the cell cycle are directed by a distinct ______________________________,
which is similar to a clock
The clock has specific ___________________________ where the cell cycle stops until a goahead signal is received
For many cells, the _____ checkpoint seems to be the most important
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually _____________________
the S, G2, and M phases and divide
If the cell does not receive the go-ahead signal, it will exit the cycle, switching into a
nondividing state called the ______________ phase
The Cell Cycle Clock: Cyclins and Cyclin-Dedpendent Kinases
Two types of regulatory proteins are involved in cell cycle control:
Cdks activity fluctuates during the cell cycle because it is ______________________ by cyclins,
so named because their concentrations vary with the cell cycle
Stop and Go Signs: Internal and External Signals at the Checkpoints
An example of an internal signal is that _______________________________ not attached to
spindle microtubules send a molecular signal that delays anaphase
Some external signals are ___________________________, proteins released by certain cells
that stimulate other cells to ________________________
For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast
cells in culture
A clear example of external signals is _____________________________________________,
in which crowded cells stop dividing
Most animal cells also exhibit _______________________________, in which they must be
attached to a substratum in order to divide
Cancer cells exhibit ________________ density-dependent inhibition nor anchorage dependence
Loss of Cell Cycle Controls in Cancer Cells
_____________________ cells do not respond normally to the body’s control mechanisms
Cancer cells may not need growth factors to grow and divide
They may make their own __________________________
They may convey a growth factor’s signal ______________ the presence of the growth factor
They may have an ________________________ cell cycle control system
A normal cell is converted to a cancerous cell by a process called ________________________
Cancer cells that are not eliminated by the immune system, form tumors, masses of abnormal
cells within otherwise normal tissue
If abnormal cells remain at the original site, the lump is called a ____________________ tumor
_____________________________ tumors invade surrounding tissues and can
________________________, exporting cancer cells to other parts of the body, where they
may form additional tumors
Why does sexual reproduction require 2 parents and how does it promote genetic diversity?
Variations on a Theme
Living organisms are distinguished by their ability to reproduce their own kind
Genetics is the scientific study of
Heredity is the
Variation is demonstrated by the differences in appearance that offspring
Offspring Acquire Genes From Parents by Inheriting Chromosomes
In a literal sense, children do not inherit particular ____________________ traits from their parents
It is __________________ that are actually inherited
What are Genes?
Inheritance of Genes
Genes are
Genes are passed to the next generation via reproductive cells called _____________________
(sperm and eggs)
Gametes are considered ____________________________________ cells because they
only have one complete set of chromosomes
Each gene has a specific location called a __________________ on a certain chromosome
Sets of Chromosomes in Human Cells
Human ______________________ cells (any cell other than a gamete) have 23 pairs of chromosomes
How many total chromosomes?
We refer these cells as being __________________________ cells
Cell with ________________ sets of chromosomes
A ________________________ is an ordered display of the pairs of chromosomes from a cell
The two chromosomes in each pair are called ____________________________ chromosomes,
or __________________________
Chromosomes in a homologous pair are the same ________________ and __________________
and carry __________________ controlling the same inherited characters
The __________ chromosomes, which determine the sex of the individual, are called X and Y
What are female’s sex chromosome combination?
What are male’s sex chromosome combination?
The remaining 22 pairs of chromosomes are called _____________________________
Now lets talk about sexual reproduction in Humans
Behavior of Chromosome Sets in the Human Life Cycle
At sexual maturity, the ________________ and __________________ produce haploid gametes
Gametes are the only types of human cells produced by __________________, rather than mitosis
Meiosis results in __________________ set of chromosomes in each ____________________
Why do the gametes have to be haploid?
_____________________________ is the union of gametes
The fertilized egg is called a ________________________ and has one set of chromosomes
from each ________________________________
The zygote produces somatic cells by _________________ and develops into an _____________
How do we make haploid gametes?
Meiosis Reduces the Number of Chromosome Sets From __________________ to _________________
Meiosis
Like mitosis, is preceded by chromosome __________________________
Unlike mitosis, cell divides _______________ to form __________ haploid daughter cells
The Stages of Meiosis
After chromosomes duplicate, two divisions follow
Meiosis I (reductional division):
Meiosis II (equational division)
The result is _____________ haploid daughter cells with ___________________ chromosomes
Meiosis I
In __________________________, homologous chromosomes are ______________
In ______________________________, homologous chromosomes __________________
corresponding segments
Each homologous pair divides into ______ daughter cells, each with one set of chromosomes
consisting of two ____________________________
Meiosis II
Essentially the same as ____________________
Sister chromatids of each chromosome ___________________________
Result is _________ cells, each with ____________ as many chromosomes as the parent
A Comparison of Mitosis and Meiosis
Mitosis produces cells that are ______________________ identical to the parent cell
Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid),
producing cells that differ ____________________ from each other and from the parent cell
Three events are unique to meiosis, and all three occur in meiosis l
__________________________ and ____________________________ in prophase I:
Homologous chromosomes physically __________________ and __________________
genetic information
At the metaphase plate, there are paired homologous chromosomes (________________),
instead of individual replicated chromosomes
At anaphase I, it is _________________________ chromosomes, instead of sister
chromatids, that separate
How do we get genetic diversity?
Genetic Variation Produced in Sexual Life Cycles Contributes to Evolution
____________________________ (changes in an organism’s DNA) are the original source of
genetic diversity
Mutations create different versions of genes called _________________
_____________________________ of alleles during sexual reproduction produces genetic variation
Origins of Genetic Variation Among Offspring
The behavior of chromosomes during meiosis and fertilization is responsible for most of the
variation that arises in each generation
Three mechanisms contribute to genetic variation
Independent Assortment of Chromosomes
Homologous pairs of chromosomes orient _______________________ at metaphase I of meiosis
In ________________________ assortment, each pair of chromosomes sorts maternal and paternal
homologues into daughter cells independently of the other pairs
The number of combinations possible when chromosomes assort independently into gametes
is 2n, where n is the ___________________ number
For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes
Crossing Over
Crossing over produces _______________________ chromosomes, which combine DNA
inherited from each parent
In crossing over, homologous portions of two ____________________ chromatids trade places
Crossing over contributes to genetic variation by __________________ DNA from two
parents into a ______________________ chromosome
Random Fertilization
Random fertilization ________ to genetic variation because any sperm can fuse with any ovum
(unfertilized egg)
The fusion of two gametes (each with 8.4 million possible chromosome combinations from
independent assortment) produces a zygote with any of about 70 trillion diploid combinations
Crossing over adds even more variation
Each zygote has a unique genetic identity
Alterations of Chromosome Number or Structure Cause Some Genetic Disorders
Large-scale chromosomal alterations in humans and other mammals often lead to spontaneous
_____________________ (miscarriages) or cause a variety of developmental disorders
Plants tolerate such genetic changes better than animals do
Abnormal Chromosome Number
In ________________________, pairs of homologous chromosomes do not separate normally
during meiosis
As a result, one gamete receives two of the same type of chromosome, and another gamete
receives _____ copy
_____________________________ results from the fertilization of gametes in which
nondisjunction occurred
Offspring with this condition have an abnormal _______________ of a particular chromosome
A ________________________ zygote has only one copy of a particular chromosome
A ________________________ zygote has three copies of a particular chromosome
Down Syndrome (Trisomy 21)
Down syndrome is an _____________________ condition that results from three copies of
chromosome ______
It affects about one out of every 700 children born in the United States
The frequency of Down syndrome increases with the ______ of the mother, a correlation that has
not been explained
Aneuploidy of Sex Chromosomes
_________________________ of sex chromosomes produces a variety of aneuploid conditions
_____________________________ syndrome is the result of an extra chromosome in a male,
producing ______________ individuals
Monosomy X, called _________________ syndrome, produces ______ females, who are
sterile; it is the only known viable monosomy in humans
__________________________ is a condition in which an organism has more than two complete sets
of chromosomes
_______________________ (3n) is three sets of chromosomes
_______________________ (4n) is four sets of chromosomes
Polyploidy is common in ________________, but not ____________________
Polyploids are more normal in appearance than _________________________
Alterations of Chromosome Structure
Breakage of a chromosome can lead to four types of changes in chromosome structure
_________________________ removes a chromosomal segment
_________________________ repeats a segment
_________________________ reverses orientation of a segment within a chromosome
_________________________ moves a segment from one chromosome to another
How are traits/characteristics passed on to future generations?
The science of genetics has ancient roots
Early attempts to explain heredity have been rejected by later science
Hippocrates' theory of _____________________________
Particles from each part of the body travel to eggs or sperm and are passed on
Early 19th-century biologists' _________________ hypothesis
Traits from both parents __________ in the offspring
Ex. If you cross a black and a brown lab you will get all black but then the next
generation they will get a mixture of brown and black
Experimental genetics began in an abbey garden
____________________________________ hypothesized that there are alternative forms of
genes, the units that determine heritable traits
Mendel crossed _____________________ plants that differed in certain characteristics
Terminology of Mendelian genetics
______________________________: fertilization of eggs by sperm-carrying pollen of the same
flower
______________________________: (cross): fertilization of one plant by pollen from a
different plant
______________________________:: identical offspring from self-fertilizing parents
______________________________:: offspring of two different varieties
______________________________:: true-breeding parents
______________________________:: hybrid offspring of true-breeding parents
______________________________:: offspring of self-fertilizing F1 parents
The ____________ characteristic Mendel followed in his studies
Mendel's law of _________________________ describes the inheritance of a single characteristic
From his experimental data, Mendel developed several hypotheses
There are alternative forms (_________________) of genes that account for variation in inherited
characteristics
If the two alleles of an inherited pair differ
The ______________________ allele determines the organism's appearance
Ex. Purple flower (___)
The ______________________ allele has no noticeable effect on the organism's appearance
Ex. White flower (___)
For each characteristic, an organism inherits two alleles, one from each parent
__________________________: two __________________ alleles
Homozygous dominant (____)
Homozygouse recessive (____)
__________________________: two ____________________ alleles
Pp
The law of segregation:
The best way to understand the law of segregation is to know how to complete a ___________________
If you know an individuals phenotype do you automatically know it’s genotype?
An organism's appearance does not always reveal its genetic composition
__________________________: Genetic makeup
__________________________: Expressed (physical) traits
How do we figure out an unknown genotype?
The ___________________
How can we tell the genotype of an individual with the dominant phenotype?
Such an individual could be either ___________________ dominant or __________________
The answer is to carry out a _________________: breeding the mystery individual with a
homozygous _______________________ individual
If any offspring display the recessive phenotype, the mystery parent must be heterozygous
The law of independent assortment is revealed by tracking two characteristics at once
Mendel's law of independent assortment:
The Laws of Probability Govern Mendelian Inheritance
Mendel’s laws of ____________________ and ________________________________ reflect
the rules of probability
When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss
In the same way, the alleles of one gene segregate into gametes independently of another gene’s
alleles
How do you calculate probabilities when dealing with just one gene?
How do you calculate probabilities when dealing with multiple genes?
Variations of Mendel’s Laws
Incomplete dominance results in intermediate phenotypes
Complete dominance
Incomplete dominance
Many genes have more than two alleles in the population
In a population, _____________________ alleles often exist for a single characteristic
Example: human _____________ blood group
Involves three alleles of a single gene
AB blood group is an example of ________________________________-both alleles are
expressed in heterozygotes
A single gene may affect many phenotypic characteristics
Pleiotropy:
Example: sickle cell disease
Why is sickle cell disease common among people of African descent?
Epistasis
In epistasis,
For example, in Labrador retrievers and many other mammals, coat color depends on two genes
One gene determines the pigment color (with alleles B for black and b for brown)
The other gene (with alleles C for color and c for no color) determines whether the pigment
will be deposited in the hair
A single characteristic may be influenced by many genes
Polygenic inheritance is
Example: human skin color
Controlled by at least __________________ genes
The environment affects many characteristics
Many characteristics result from a combination of genetic and environmental factors
_______________ vs. ____________________ is an old and hotly contested debate
Only genetic influences are inherited
Ex. Heart disease, intellegence, body weight hydrangea flowers of the same genotype
range from blue-violet to pink, depending on soil acidity
Genes on the same chromosome tend to be inherited together
________________________ genes
Lie ___________________ together on the same ___________________________
Tend to be _____________________________ together
Generally do ____________ follow Mendel's law of independent assortment
How Linkage Affects Inheritance
Morgan did other experiments with __________________ to see how linkage affects
inheritance of two characters
Morgan crossed flies that differed in traits of body color and wing size
Morgan found that body color and wing size are usually inherited together in specific
___________________________ (parental phenotypes)
He noted that these genes do not ___________________ independently, and reasoned
that they were on the same chromosome
However, nonparental phenotypes were also produced when you had linked genes
Understanding this result involves exploring ___________________________________
(crossing over), the production of offspring with combinations of traits differing from
either parent
For example
Genetic Recombination and Linkage
The genetic findings of Mendel and Morgan relate to the chromosomal basis of
recombination and the chromosomal basis of inheritance
Recombination of Unlinked Gene: Independent Assortment of Chromosomes
Mendel observed that combinations of traits in some offspring differ from either parent
Offspring with a phenotype matching one of the parental phenotypes are called
Offspring with nonparental phenotypes (new combinations of traits) are called
What is a Genetic Disorder?
Genetic traits in humans can be tracked through family __________________________
The inheritance of many human traits follows ______________________ laws
What would the genotype be or an individual if they exhibited a dominant disorder?
What would the genotype be or an individual if they exhibited a recessive disorder?
Pedigree Analysis
A _________________________ is a family tree that describes the interrelationships of parents
and children across generations
Inheritance patterns of particular traits can be ____________ and __________________ using pedigrees
Many inherited disorders in humans are controlled by a ________________ gene
Thousands of human genetic disorders follow simple Mendelian patterns of inheritance
__________________________ disorders
_________________________ genetic disorders
Can be carried unnoticed by __________________________
?
The Behavior of Recessive Alleles
Recessively inherited disorders show up only in individuals ______________________ for the allele
__________________________ are heterozygous individuals who carry the recessive allele but
are phenotypically normal; most individuals with recessive disorders are born to carrier parents
_____________________ is a recessive condition characterized by a lack of pigmentation in
skin and hair
If a recessive allele that causes a disease is __________, then the chance of two carriers meeting and
mating is _________________
____________________________ matings (i.e., matings between close relatives) _________________
the chance of mating between two carriers of the same rare allele
Most societies and cultures have laws or taboos against marriages between close relatives
________________________ disorders
Some serious, but ____________________, disorders (achondroplasia)
Lethal conditions ____________________ common than in recessive disorders
Cannot be carried by _________________________ without affecting the
?
Multifactorial Disorders
Many diseases, such as heart disease, diabetes, alcoholism, mental illnesses, and cancer have
both genetic and environmental components
Little is understood about the genetic contribution to most multifactorial diseases
Genetic Testing and Counseling
Genetic __________________ can provide information to prospective parents concerned about a
family history for a specific disease
Counseling Based on Mendelian Genetics and Probability Rules
Using family histories, genetic counselors help couples determine the _______ that their children
will have genetic disorders
Probabilities are predicted on the most accurate information at the time; predicted probabilities
may change as new information is available
Tests for Identifying Carriers
For a growing number of diseases, tests are available that identify carriers and help define the
odds more accurately
Fetal Testing
In ___________________________, the liquid that bathes the fetus is removed and tested
In ______________________________ (CVS), a sample of the placenta is removed and tested
Other techniques, such as __________________ and __________________, allow fetal
health to be assessed visually in __________
Newborn Screening
Some genetic disorders can be detected at _____________ by simple tests that are now routinely
performed in most hospitals in the United States
The Chromosomal Basis of Inheritance
Mendelian Inheritance has its Physical Basis in the Behavior of Chromosomes
Mitosis and meiosis were first described in the late 1800s
The _________________________________________________ states:
Mendelian genes have specific ___________ (positions) on chromosomes
Chromosomes undergo ___________________ and independent _____________________
The behavior of chromosomes during _______________________ can account for Mendel’s
laws of segregation and independent assortment
Sex-Linked Genes Exhibit Unique Patterns of Inheritance
In humans and some other animals, there is a chromosomal basis of ________ determination
Many animals have a pair of chromosomes that determine sex
Humans: ___________ system
Male is ______; the ___ chromosome has genes for the development of testes
Female is _____; absence of a ___ chromosome allows ovaries to develop
A gene that is located on either sex chromosome is called a ________________________ gene
Genes on the Y chromosome are called __________________ genes; there are few of these
Genes on the X chromosome are called __________________ genes
Most sex-linked disorder are _____________________ disorders
Inheritance of X-Linked Disorders
X-linked disorders are typically ___________________________ disorders
For a recessive X-linked trait to be expressed
A female needs two copies of the allele (___________________________)
A male needs only one copy of the allele (_____________________________)
X-linked recessive disorders are much more common in ___________________ than in females
Some disorders caused by recessive alleles on the X chromosome in humans
___________________________ (mostly X-linked)
___________________________
X Inactivation in Female Mammals
In mammalian females, one of the two ____ chromosomes in each cell is randomly ________________
during embryonic development
The inactive X condenses into a ____________________________
If a female is heterozygous for a particular gene located on the X chromosome, she will be a
_________________________ for that character