Transcript Sexual reproduction

Introduction to
Plant Biotechnology
Chapter 10
Learning Outcomes
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Describe mechanisms of plant pollination and differentiate between
haploid and diploid cells and their role in sexual reproduction
Identify various natural and artificial ways to propagate plants to
increase genetic variety or maintain the genetic composition
Discuss the function and composition of different plant structures,
tissues, and organelles and give examples of foods that are derived
from various plant organs
Describe the processes of germination and plant growth
Perform the calculations to predict expected plant phenotypes for
specific genetic genotypes, using Punnett Square analysis
Perform statistical calculations and analysis of data for a plant
breeding experiment
10.1 Introduction to Plant Propagation
There are several methods of modifying or improving plants or plant parts.
One of the first advances occurred when farmers discovered they could
control pollination and the resulting seed crop.
Plant breeding involves sexual reproduction.
Plant breeding involves asexual reproduction (cloning).
Flower Structure. Most flowers are “complete” with both male (stamen) and female
(pistil) sex organs. A seed develops when pollen reaches and fertilizes an ovule.
New Gene Combinations. Crossing-over and gene shuffling during meiosis (sex cell division)
created new combinations of genetic information on chromosomes. The new combination of genes
is carried in sex cells to the zygote of the next generation. What genetic information would a sex
cell be carrying if it got one or another of the final chromosomes?
Vocabulary
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Pollination – the transfer of pollen (male gametes) to the pistil (the female part of the
flower)
Breeding – the process of propagating plants or animals through sexual reproduction of
specific parents
Sexual reproduction – a process by which two parent cells give rise to offspring of the next
generation by each contributing a set of chromosomes carried in gametes
Zygote – a cell that results from the fusion of a sperm nucleus and an egg nucleus
Embryo – a plant or animal in its initial stage of development
Gametes – sex cells (ie, sperm or eggs)
Meiosis – a special kind of cell division that results in four gametes (N) from a single diploid
(2N) cell
Selective breeding – parent selection and controlled breeding for a particular characteristic
Cuttings – pieces of stems, leaves, or roots for use in asexual plant propagation
Tissue culture – the process of growing plant or animal cells in or on a sterile medium
containing all the nutrients necessary for growth
Callus – a mass of undifferentiated plant cells developed during plant tissue culture
10.1 Review Questions
1.
How many parents are necessary for an offspring to be produced by
sexual reproduction? How many parents are necessary for an offspring
to be produced by asexual reproduction?
2.
Which two cells fuse to make a zygote? From where do the
chromosomes of a zygote come?
3.
How does a cutting become a functioning, independent organism?
4.
What is the smallest number of cells required to clone a plant through
tissue culture?
10.2 Basic Plant Anatomy
Plants are multicellular organisms composed of organs and tissues.
Plants have a wide variety of organ structures.
Plant organs are grown as food or commercial crops.
Plant Tissue
Plant tissues are groups of similar cells with a specific function.
Plant Cells
Plant cells have all the organelles found in other cells, plus special organelles.
Vocabulary
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Meristematic tissue – tissue found in shoot buds, leaf buds, and root tips
that is actively dividing and responsible for growth
10.2 Review Questions
1.
List some foods that are examples of the following plant organs: stems,
roots, leaves, flowers (ovaries), and seeds (fertilized ovules).
2.
Which plant tissue type is the source of cells for tissue culture?
3.
Give an example of a plant that has been modified by genetic engineering.
10.3 Plant Growth, Structure, and Function
Plants have specific regions where cell division can occur.
Meristems are found at
each growing tip.
During mitosis,
cells make exact
copies of
themselves. The
tightly wound
mitotic
chromosomes
are visible using
a microscope.
Dicot See Germination. The diagram shows a
germinating bean seed with an enlarged radicle growing
down. The epicotyl will grow up into the leaves and stem.
The two cotyledons emerge from the seed as a food
source, but they wither after a short while.
Monocot Seed Germination. Four
germinated corn seedlings. The coleoptile
protects the emerging leaves. Corn plants
are monocots since they have only one
section to the seed.
Vocabulary
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Meristems – regions of a plant where cell division occurs, generally found in the growing
tips of plants
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Radicle – an embryonic root-tip
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Differentiation – the development of a cell toward a more defined or specialized function
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Plant hormones – signaling molecules that, in certain concentrations, regulate growth and
development, often by altering the expression of genes that trigger certain cell specialization
and organ function
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Herbaceous plants – plants that do not add woody tissues; most herbaceous plants have a
short generation time of less than one year from seed to flower
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Woody plants – plants that add woody tissue; most woody plants have a long generation
time of more than one year from seed to flower; most woody plants grow to be tall, thick,
and hard
10.3 Review Questions
1.
Name the parts of the plants that contain actively dividing cells.
2.
After mitotic division, how many chromosomes do daughter cells
have, compared with the parent?
3.
When a seed germinates, what is the first plant part to emerge
from the sprouting seed?
4.
There is a vast diversity among plant cells and plant tissues.
What are the chemicals called that trigger much of the cell and
tissue specializations in plants?
10.4 Introduction to Plant Breeding
Alternation of generations. Each
sex cell gets one copy (1N) of each
chromosome and, therefore, one
copy of each gene. Most genes exist
in one of two or more forms (alleles).
When the zygote (2N) forms, it
receives both sets of chromosomes
(and genes) for the two sex cells.
Depending on what was carried in
the sex cells, the zygote could receive
two matching alleles or two different
alleles for a particular trait. The
alleles of an organism are its
genotype and, ultimately, determine
the traits expressed (phenotype).
Genotypes and Phenotypes
The alleles an organism possesses are called its genotype.
They determine the plant’s characteristics.
Breeding Plants for Desired Phenotypes
Plant breeders try to study, predict, and manipulate crosses between flowers
in an attempt to produce plants of desired phenotypes.
Using Punnett Square Analysis
Shows the possible gene combinations that could result when crossing
specific genotypes.
Vocabulary
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Diploid – having two sets (2N) of homologous (matching) chromosomes
Haploid – having only one set (1N) of chromosomes
Alleles – alternative forms of a gene
Dominant – referring to how an allele for a gene is more strongly expressed than an alternate
form (allele) of the gene
Recessive – referring to how an allele for a gene is less strongly expressed than an alternate form
(allele) of the gene; a gene must be homozygous recessive (ie, hh or rr) for an organism to
demonstrate a recessive phenotype
Homozygous – having two identical forms or alleles of a particular gene (ie, hh or RR)
Homozygous dominant – having two of the same alleles for the dominant version of the gene
(ie, HH or RR)
Heterozygous recessive – have two different forms or alleles of a particular gene (ie, Hh or Rr)
Polygenic – traits that result from the expression of several different genes
Punnett Square Analysis – a chart that shows the possible gene combinations that could result
when crossing specific genotypes
Monohybrid cross – a breeding experiment in which the inheritance of only one trait is studied
Dihybrid cross – a breeding experiment in which the inheritance of two traits is studied at the
same time
10.4 Review Questions
1.
Which of the following are diploid (2N) and which are haploid? egg,
zygote, embryo, parent plant, sperm, and seed?
2.
A plant has purple flowers and hairy stems. Is this description its
genotype or phenotype? Propose some allelic symbols for purple
flowers and hairy stems.
3.
Consider a cross between two Brassica rapa parent plants known to
be heterozygous tall. Using the same allelic symbols as in the text,
show the entire cross (problem), including the chances of this
breeding resulting in short plants.
10.5 Statistical Analysis of Data
Using Numerical Data to Ensure Accuracy
Instead of using words to describe data,
scientists try to make all observations of
experiments in numerical form.
Using Multiple Replications to Determine Averages
Experiments must be repeated enough to
ensure that results reflect what really happens.
Evaluating Validity of Data
The 10% Rule
Standard Deviation
Standard Deviation.
If the SD is twice as
large (right graph) as
another (left graph),
then we know that the
data for the right graph
are very dissimilar, and
we would have less
confidence in the data
collection.
Using Goodness of Fit (Chi Square Analysis) to Test the Hypothesis
How To Calculate the Chi Square Value (c2)
C2 = S[(O-E)2/E]
The terms represent the following:
O = observed number for a phenotype group
E = expected number for a phenotype group
S = the Greek letter Sigma, which represents “sum of”
Vocabulary
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Average – a statistical measure of the central tendency, that is calculated by dividing the
sum of the values collected by the number of values being considered
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Mean – the average value for a set of numbers
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Standard deviation – a statistical measure of how much a dataset varies
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Chi Square – a statistical measure of how well a dataset supports the hypothesis or the
expected results of an experiment
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Degrees of freedom – a value used in Chi Square analysis that represents the number of
independent observations (eg, phenotypic groups) minus one
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Null hypothesis – a hypothesis that assumes there is no difference between the
observed and expected results
10.5 Review Questions
1.
A set of plant DNA extractions is measured on the UV spec. There are 13
samples and the average concentration is 18.8 mg/mL. One sample has a
value of 17.2 mg/mL. Using the 10% rule, is the sample’s value valid and
acceptable?
2.
An experiment is conducted to determine the number of kindergarten children
with attention deficit disorder (ADD) in the United States. The result shows
that 80 out of 1000 students, on average, with a standard deviation of 5,
exhibit ADD. A town near a nuclear plant has an average of 84 students per
1000 with ADD. Should the citizens be concerned? Why or why not?
3.
A family had 22 children; 14 boys and 8 girls. Calculate the Chi Square value
for such a cross and determine whether the results are due to a random
mating or an environmental or genetic disorder.
Questions and Comments?