Download ch 13 test-patterns of inheritance

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Sexual Reproduction in Plants
Chapter 12.5
(sorry no pictures of mosses or flowers this time…it would take wayyy to long…so just use your lab for that part.)
-plants generally reproduce sexually
-however, many plants can also reproduce asexually and some have lost the ability to reproduce
sexually
Mosses
-simple plants, like mosses, spend most of their lives in the haploid stage
-these plants require a moist environment to reproduce
-their sperm swim through wet soil to reach the plant’s female reproductive structures
-spores fall to the ground and grow into tiny haploid plants that produce male and female gametes
-after fertilization, the zygote grows into a new diploid fern
-mosses are bryophytes which never get taller
-they get water through osmosis because they don’t have a transport system like xylem or phloem
tubes
-the sporophyte grows out of the gametophyte
-the sporophyte is temporary and has the capsule at the top of it which opens and releases spores
-the gametophyte produces gametes (egg and sperm cells)
Complex Plants
-more complex plants, like flowers, are large diploid structures
-their haploid stage is just a small tissue in their reproductive organs – the ova are protected inside
-unlike fern sperm, the sperm of seed plant’s don’t need to swim through wet soil
-wind of symbiotic animals like bees, bass, and butterflies carry the sperm that has been packages inside
tough protective pollen grains to the female organs
Self-fertilization in Pea Plants
-the petals of the pea flower completely enclose the reproductive organs
-as a result, the pollen from the anthers falls on the stigma of the same flower
-pollen tubes grow down through the female reproductive organ to the ovules in the ovary
-the ovules develop into seeds, and the ovary wall develops into the pea pod
-if you plant a bean or pea seed and water them, they will produce
Flowers
-the most successful plants are the flowering plants
-haploid cells in the flowers form gametes
-each flower may produce sperm, ova, or both
-at the center of an ovum-producing flower, one or more modified leaves called carpels fuse edge to
edge, forming a hollow structure
-the base of this carpel is the ovary which contains one or more small structures called ovules
-the ova develop in the ovules
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-within each ovule, a specialized cell undergoes meiosis—4 haploid cells result, three of which
disintegrate; the fourth cells divides by mitosis to produce 7 cells—one of these cells becomes the
ovum
-cells in the anther undergo meiosis, producing four haploid cells
-each haploid cell divides mitotically to produce a pollen grain containing two cells—a tube cell and
a second cell that divides to produce two haploid sperm nuclei
-sexual reproduction begins as the anthers shed pollen
-in nonflowering plants like pine trees, wind carries the pollen to the carpel of the same or other flowers
-insects, bats, and other animals that eat flower parts carry the pollen of flowering plants
-pollination: the transfer of pollen from anther to carpel
-cross pollination: pollination between two different plants of the same species
-it increases genetic variation by combining chromosomes from two parents
-many intricate mechanisms for pollination have evolved
-some insects and flowering plants have became so completely dependent of each other that
neither can reproduce without the other
The Fertilization Process
-when pollen lands on the tip of the carpel tunnel, or the stigma, the pollen grain germinates and forms
a pollen tube that grows toward the ovule, carrying the sperm nuclei
-fertilization occurs when one sperm nucleus fuses with the egg
-the resulting diploid zygote divides mitotically and eventually develops into an embryo
-the second sperm nucleus fuses with the two polar nuclei, forming a triploid cell that develops into the
endosperm
-fertilization ends the short haploid stage in the life cycle of a flowering plant
-the ovule then becomes the seed, forming a protective coat around the embryo and endosperm
-auzin produced by the seeds stimulates the ovary to enlarge and develop into a fruit
How seeds spread
-seeds spread in various ways
-many fruits are carried by the wind
-some are adapted to stick to animal fur
-many seeds remain inside fruits, which may be eaten by animals and transported great distances in
their digestive systems until they eventually deposit the undigested seeds along which other organic
wastes which actually help nourish the seeds in their new location
-flowering plants are found in widely different environments
Several adaptations contribute to this:
-the dominance of the diploid stage in the life cycle, which allows development of complex structures
-the evolution of pollen, which allows the transfer of sperm from plant to plant without the need for
water
-the evolution of the seed and endosperm, which protects the dormant embryo and provides food and
protection for the young plant
-a variety of adaptations that promote pollen and seed dispersal
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Mosses and Flowers Lab
Mosses
-mosses are bryophytes which means they will never get taller
-structurally, they don’t have a transport system, like xylem and phloem tubes  they get water
through osmosis instead
-this means that the water can’t rise up through the moss using cohesion and adhesion
-moss spores are produced in the capsule of the sporophyte through meiosis
-spores are dispersed through the wind or through animals that carry the spores to other places
Flowers
-the petals attract animals to the flower so they will pollinate with it; the bright colors of the petals lure
the animals in
-the anthers shed pollen—insects, bats, and other animals that eat flower parts carry the pollen of
flowering plants to the carpel
-pollen as tiny grain that looks like a fine powder
-pollen is adapted through the evolution of pollen, which allows the sperm to disperse from plant to
plant without needing water
-the stigma is sticky, so it traps the pollen grains
-nutrients and other substances in the stigma stimulate the pollen grain to grow
-the ovule contains developing ova, or egg cells. There are two egg cells per ovule. They are produced
through meiosis and mitosis.
-the diploid stage of the moss life cycle is comparable to the ovule
-the pollen grain is deposited on the stigma. It then grows on the stigma.
-after it grows, the pollen grain forms a pollen tube that grows toward the ovule, and carries the sperm
nuclei
-fertilization occurs when one sperm nucleus fuses with the egg
-the ovary wall develops into the pod of a bean or pea
-the origin of the seed is the ovule. After fertilization ends, the ovule becomes a seed and forms a
protective coat around the embryo and endosperm
-if you plant a bean or pea seed and water them, they will produce a pea flower or pea or bean plant
-the embryo and endosperm are the two structures that are present in a seed as a result of fertilization
-the endosperm has the nutrients that provide food and energy for the embryo and also protects the
embryo
-the ovary becomes the pod or fruit of the plant
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Heredity and Environment
-organisms are products of their heredity and of their environment
-ex: Siamese cats inherit genes for enzymes that produce a dark pigment in their fur
-if you apply an ice pack to the cat’s belly after shaving him, the fur will turn dark
-if you apple a warm cloth to the cat’s tail, the fur will turn light
-this is only a temporary change
-identical twins develop when a zygote forms two complete embryos which have the exact same genetic
information
-fraternal twins come from separate eggs and sperm cells and are no more genetically similar than other
siblings
-if identical twins exhibit the same trait more than fraternal twins, then the trait is probably heavily
influenced by genetic factors
-if the trait differs in identical twins, then the environment must have a strong influence on the trait
-the theory of “blending” was once a popular explanation of heredity
-according to this theory, an individual’s genetic makeup was formed when the parent’s genes mixed at
fertilization and resulted in an average of the parents’ genes,
-but once the parents’ genes were blended, they couldn’t be passed on separately to future
generations
-genetics no longer includes the theory of “blending”
-there were some events that blending couldn’t explain:
-why some individuals resemble their grandparents, healthy parents have sick kids, etc.
Mendelian Genetics
-Gregor Mendel was a monk, gardener, high school science teacher, mathematician, and scientist
-he is called the “father of genetics”
Mendel’s Experiment
-he used garden peas to study heredity
-peas are very easy to grow and he could study many generations during his 8 years of experimenting
and are also self-fertilizing
-mendel decided to study traits that didn’t fit the blending theory
-seed shape
-embryo color
-flower and seed coat color
-pod shape
-pod color
-flower position
-stem length
-mendel worked with his plants for several years to be sure he had true-breeding varieties for each of
the traits he selected
-true-breeding plants produce offspring identical to themselves generation after generation
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-mendel then crossbred his plants and classified all the offspring
-he mated a plant with round seeds and a plant with wrinkled seeds
-he found that the next generation only produced round seeds
-when those plants self-fertilized, the next generation was wrinkled and round
-mendel demonstrated with these pea plants that both parents pass on to their offspring genetic factors
that remain separate generation after generation
Alleles
-the concept of alleles has replaced mendel’s genetic factors
-an allele is one of two or more possible forms of a gene
-each allele of a particular gene has a different base sequence
-for example: the allele for round seeds encodes an enzyme that produces round seeds, and the allele
for wrinkled seeds is a different form of the same gene
-a different allele can code for a different color
-one allele can code for a yellow pod and the other allele can code for a green pod
-all organisms have genes that exist as different alleles
-many traits like hair color, skin color, nose shape, and handedness result from the complex interaction
of several genes with each other and the environment
Genes and Chromosomes
-the arrangement of genes in chromosomes differs in eukaryotes and prokaryotes
-in eukaryotes:
-chromosomes are long molecules of DNA wrapped around protein
-but only part of this DNA codes for proteins
-the other part, noncoding DNA or introns, isn’t translated
-about 1.5% of their DNA is translated as proteins
-in prokaryotes:
-bacteria have a single circular chromosome with little associated protein
-their genes generally don’t have introns
-about 90% of their DNA is translated
-many bacteria also have plasmids- small circles of DNA that contain additional genes
-plasmids may move from one bacterium to another and can carry genes that provide resistance to
antibiotics
-homologous chromosomes carry the same genes, but their genes may be present as different alleles
-to distinguish homologous chromosomes from each other:
-staining: the stains bind to specific regions of the chromosomes, creating banding patterns specific
to each chromosome
-chromosome painting: fluorescent dyes of different colors are chemically bonded to short pieces of
DNA (probes) that bind to genes on different chromosomes – this process stains each homologous
pair a different color
-chromosomes are easiest to study in the condensed form they have during cell division
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-for this reason, white blood cells are used most to study human chromosomes
-chemicals are added to stop cell division during metaphase and the cells are looked at under a
microscope
-this technique helped determine that human cells (except gametes) have 46 chromosomes
-stained chromosomes can be photographed under the microscope
-a karyotype is a display of individual chromosomes cut out of an enlarged photograph and arranged by
size and shape
-karyotypes of fetal cells can be used to check for suspected chromosomal abnormalities in developing
fetuses
Probability and Genetics
-diploid organisms usually carry different alleles of many genes
-the distribution of those alleles among games in meiosis and the combination of alleles that come
together in fertilization are a matter of chance
-probability predicts the chances that a certain event will occur
-can be expressed as a fraction or percent
-geneticists use probability to predict the alleles of the offspring of various crosses, or matings
-mathematical tests can help show whether the difference between the observed and expected results
is significant (in other words: if the difference is due to change or to some other factor)
-genetic counselors use probability to help parents assess the risk of passing on a genetic disorder to
their children
-expected genotypes are the genotype that has been predicted through probability calculations and are
arrived at mathematically
-observed genotypes are the genotypes of individuals from actual fertilization experiments and are due
to chance
-the larger the sample size, the wider range of results you have, and the outcome will be more correct
Inheritance of Alleles
-monohybrid cross: a genetic cross between individuals that only differ in one trait
-ex: mendel crossed plants that differed in only seed shape
-parental (P) generation: the parental organisms involved in the first genetic cross
-first filial or F1 generation: the first generation of hybrid offspring in a genetic cross
-ex: the plants that grew from the parental seeds produced all round seeds for the F1 generation
-second filial or F2 generation: offspring resulting from interbreeding of the hybrid F1 generation
-ex: mendel allowed the F1 generation plants to self-fertilize, and had a 3:1 ratio of round to
wrinkled seeds for the F2 generation
-for each of the seven traits mendel studied, only one trait of each pair was visible in the F1 generation
-dominant: an allele that masks the presence of a recessive allele of the same gene in a heterozygous
organism
-recessive: an allele that’s masked and not expressed in a heterozygous organism
-(still using the ex from above): the round seeds are dominant and wrinkled seeds are recessive
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-the recessive trait reappeared unchanged in the F2 generation
-mendel used the ratio 3:1 to describe the ratio of traits, dominant to recessive
-he used mathematics to conclude that each true-breeding plant has two identical copies of the
factor for a particular trait
-the allele for a dominant trait is represent by a capital letter and the allele for a recessive trait is
represented by a lowercase letter
-most multicellular organisms are diploid, so they have two alleles for every gene
-genotype: genetic make up of an organism
-ex: purebred round seeded plant = RR; wrinkled seeded plant = rr
-homozygous: the genotype where both alleles are the same; having 2 identical alleles for a given trait
-ex: RR or rr
-heterozygous: the genotype where the 2 alleles are different; having 2 different alleles for a given trait
-ex: Rr
-the genotype of each individual is responsible for its phenotype
-phenotype: an individual’s appearance or observable characteristics
-because the round-seeded phenotype is dominant, both the homozygous RR and heterozygous Rr
will produce plants with round seeds
-a punnett square can be used to calculate ratios of genotypes and phenotypes
-to follow the inheritance of 2 traits at once, mendel made dihybrid crosses
-dihybrid cross: a genetic cross between individuals that differ in 2 traits
Mendel’s 3 Laws of Inheritance
1. law of segregation
Bb
B
or
b
-the alleles of each gene segregate during meiosis when homologous chromosomes are divided
among gametes
-when gametes formed during meiosis, only one copy of the factor went into each pollen or egg cell
-at fertilization, the F1 generation received a round seed factor from one parent and a wrinkled seed
factor from the other parent  only one of these factors, either round or wrinkled, went into each
gamete formed by the F1 plants
2. law of independent assortment
BB
Bb
Bb x Bb
Bb
bb
-alleles for one trait assort, or divide up, among the gametes during meiosis, independently of
alleles for other traits
3. law of dominance
-the presence of dominant traits masks recessive traits (except during incomplete and codominance)
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Landsteiner Blood Types
phenotypes
genotypes
A
AA, AO
IAIA or IAi
B
BB, BO
IBIB or IBi
AB
AB
IAIB
O
OO
Ii
Alleles without Dominance
-mendel worked with traits that were either dominant or recessive; however, some genes don’t follow
this pattern
incomplete dominance
-occurs when the dominant trait isn’t fully expressed
-the heterozygote appears as a “dilute” form of the dominant trait
-ex: when red snapdragons are crossed with white-flowered snapdragons, all the F1 plants are pink
codominance
-occurs when both dominant and recessive traits are equally expressed in the heterozygote
-when both phenotypes appear in heterozygous individuals
-ex: roan- when there’s both red and white in an individual although red is dominant and white is
recessive
*THERE WILL ALSO BE PUNNETT SQUARES, PEDIGREES, MONOHYBRID, DIHYBRID,
INCOMPLETE DOMINANCE, AND CODOMINANCE PROBLEMS TO WORK OUT!!
(but i can’t really make a study guide for that….)
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