Agenda 11/7/11 1)You – Draw and name major stages of early development on a piece of...

Agenda 11/7/111) You – Draw and name major stages of early development on a piece of

paper…initial cleavage, morula, blastula, gastrulaMe - (I will assume everyone has Lab 3 done – study it for quiz) and quick check Notes for Ch. 13 & 47 – need to confine this to 15 minutes

2) Finish Meiosis 15 min3) Start Development –watch video and start slides (25 minutes)http://www.youtube.com/watch?v=_22CFCxDUy0

Homework – Tonight- Study for quiz tomorrow – 11,12, 13, 47 all fair game (the more you

study this tonight, the better off you will be on unit test next week!)FOCUS- Cell signaling notes we took, lab 3, mitosis vs. meiosis (purpose and

phases), major events in development (cleavage, gastrulation, and organogenesis) and pictures of morula, blastula and gastrula

Ch. 14 Notes and self-quiz due Thursday

http://www.youtube.com/watch?v=_22CFCxDUy0

• Preformation: the egg or sperm contains an embryo that is a preformed miniature adult.

• Epigenesis: the form of an animal emerges from a relatively formless egg.

• An organism’s development is primarily determined by the genome of the zygote and the organization of the egg cytoplasm.

1. From egg to organism, an animal’s form develops gradually:

the concept of epigenesis

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Sea urchins are models for the study of the early development of deuterostomes.– Sea urchin eggs are fertilized externally.– Sea urchin eggs are surrounded by a jelly coat.

2. Fertilization activates the egg and brings together the nuclei of sperm

and egg


Fig. 47.2


Studied in sea urchins

Acrosomal and Cortical Reactions- what’s the point?

Fast block to polyspermy = brief membrane depolarization when sperm and egg membranes fuse

Slow block to polyspermy = formation of fertilization envelope

• Fertilization in Mammals.• Capacitation, a function of the female

reproductive system, enhances sperm function.– A capacitated

sperm migratesthrough a layerof follicle cellsbefore it reachesthe zona pellucida.

– Binding ofthe sperm cellinduces anacrosomalreaction similarto that seen in thesea urchin.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 47.5

• Enzymes from the acrosome enable the sperm cell to penetrate the zona pellucida and fuse with the egg’s plasma membrane.– The entire sperm enters the egg.– The egg membrane depolarizes: functions as a fast block to

polyspermy.

– A cortical reaction occurs Enzymes from cortical granules catalyze alterations to the zona pellucida: functions as a slow block to polyspermy

– The envelopes of both the egg and sperm nuclei disperse.• The chromosomes from the two gametes share a

common spindle apparatus during the first mitotic division of the zygote.

• .Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Cleavage follows fertilization.– The zygote is partitioned into blastomeres.

• Each blastomere contains different regions of the undivided cytoplasm and thus different cytoplasmic determinants.

3. Cleavage partitions the zygote into many smaller cells

Fig. 47.6Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• Continued cleavage produces the morula.


Fig. 47.8b

– Except for mammals, most animals have both eggs and zygotes with a definite polarity.• Thus, the planes of division follow a specific pattern

relative to the poles of the zygote.• Polarity is defined by the heterogeneous distribution

of substances such as mRNA, proteins, and yolk.– Yolk is most concentrated at the vegetal pole and least

concentrated at the animal pole.

• In some animals, the animal pole defines the anterior end of the animal.


• A blastocoel forms within the morula blastula


Fig. 47.8d

• In birds the yolk is so plentiful that it restricts cleavage to the animal pole: meroblastic cleavage.

• In animals with less yolk there is complete division of the egg: holoblastic cleavage.


Gastrulation rearranges the embryo into a triploblastic gastrula.– The embryonic germ layers are the ectoderm,

mesoderm, and endoderm.

4. Gastrulation rearranges the blastula to form a three-layered

embryo with a primitive gut


• Sea urchin gastrulation.– Begins at the vegetal pole where individual

cells enter the blastocoel as mesenchyme cells. • The remaining cells flatten and buckle inwards:

invagination.– Cells rearrange to form the archenteron.

• The open end, the blastopore, will become the anus.

• An opening at the other end of the archenteron will form the mouth of the digestive tube.



Fig. 47.9

– Frog gastrulation produces a triploblastic embryo with an archenteron.• Where the gray crescent was located, invagination

forms the dorsal lip of the blastopore.• Cells on the dorsal surface roll over the edge of the

dorsal lip and into the interior of the embryo: involution.

• As the process is completed the lip of the blastopore encircles a yolk plug.


Fig. 47.10


Let’s watch videos of gastrulation

• Student textbook CD-ROM

• Ch. 47 Activities

• The derivatives of the ectoderm germ layer are:– Epidermis of skin, and its derivatives– Epithelial lining of the mouth and rectum.– Cornea and lens of the eyes.– The nervous system; adrenal medulla; tooth

enamel; epithelium of the pineal and pituitary glands.

5. In organogenesis, the organs of the animal body form from the three embryonic germ layers


• The endoderm germ layer contributes to:– The epithelial lining of the digestive tract

(except the mouth and rectum).– The epithelial lining of the respiratory system.– The pancreas; thyroid; parathyroids; thymus;

the lining of the urethra, urinary bladder, and reproductive systems.


• Derivatives of the mesoderm germ layer are:– The notochord.– The skeletal and muscular systems.– The circulatory and lymphatic systems.– The excretory system.– The reproductive system (except germ cells).– And the dermis of skin; lining of the body

cavity; and adrenal cortex.



Fig. 47.11

• The amniote embryo is the solution to reproduction in a dry environment.– Shelled eggs of reptiles and birds.– Uterus of placental mammals.

6. Amniote embryos develop in a fluid-filled sac within a shell or uterus


• The four extraembryonic membranes are the yolk sac, amnion, chorion, and allantois.– Cells of the yolk sac digest yolk providing

nutrients to the embryo.– The amnion encloses the embryo in a fluid-

filled amniotic sac which protects the embryo from drying out.

– The chorion cushions the embryo against mechanical shocks.

– The allantois functions as a disposal sac for uric acid.



Fig. 47.14

• Mammalian Development.– Recall:

• The egg and zygote do not exhibit any obvious polarity.

• Holoblastic cleavage occurs in the zygote.

– Gastrulation and organogenesis follows a pattern similar to that seen in birds and reptiles.


– Step 1: about 7 days after fertilization.• The blastocyst (mammalian version of blastula)

reaches the uterus.• The inner cell mass is surrounded by the

trophoblast.• The inner cell mass will become the embryo and

the trophoblast gives rise to the fetal placenta.

Fig. 47.15 (1)


• Changes in cellshape usuallyinvolvesreorganizationof thecytoskeleton.

1. Morphogenesis in animals involves specific changes in cell

shape, position, and adhesion


Fig. 47.16

• The cytoskeleton is also involved in cell movement.– Cell crawling is involved in convergent

extension.• The movements of convergent extension probably

involves the extracellular matrix (ECM).• ECM fibers may direct cell movement.• Some ECM substances, such a fibronectins, help

cells move by providing anchorage for crawling.• Other ECM substances may inhibit movement in

certain directions.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 47.17

• Holding cells together.– The role of the ECM in holding cells together.

• Glyocoproteins attach migrating cells to underlying ECM when the cells reach their destination.

• Cell adhesion molecules (CAMs): located on cell surfaces bind to CAMs on other cells.– Differences in CAMs regulate morphogenetic movement and

tissue binding.

• Cadherins are also involved in cell-to-cell adhesion.– Require the presence of calcium for proper function.


• In many animal species (mammals may be a major exception), the heterogeneous distribution of cytoplasmic determinants in the unfertilized egg leads to regional differences in the early embryo

• Cytoplasmic determinants are chemical signals like mRNA’s and transcription factors that may be parceled out unevenly in early cleavages.

2. The developmental fate of cells depends on cytoplasmic determinants

and cell-cell induction: a review


• Subsequently, in induction, interactions among the embryonic cells themselves induce changes in gene expression.– These interactions eventually bring about the

differentiation of the many specialized cell types making up a new animal.

NOTE – Mammalian embryonic cells remain totipotent (like stem cells/undifferentiated) until the 16 cell stage.


• Fate maps illustrate the developmental history of cells.

• “Founder cells” give rise to specific tissues in older embryos.

• As development proceeds a cell’s developmental potential becomes restricted.

3. Fate mapping can reveal cell genealogies in chordate embryos



Fig. 47.20

• Polarity and the Basic Body Plan.– In mammals, polarity may be established by the

entry of the sperm into the egg.– In frogs, the animal and vegetal pole determine

the anterior-posterior body axis.

4. The eggs of most vertebrates have cytoplasmic determinants that help

establish the body axes and differences among cells of the early embryo


• Restriction of Cellular Potency.– The fate of embryonic

cells is affected byboth the distributionof cytoplasmicdeterminants andby cleavage pattern.


Fig. 47.21

• Induction: the influence of one set of cells on a neighboring group of cells.

– Functions by affecting gene expression.• Results in the differentiation of cells into a

specific type of tissue.

5. Inductive signals drive differentiation and pattern formation in invertebrates


• The “Organizer” of Spemann and Mangold.• Grafting the dorsal lip

of one embryo onto the ventral surface ofanother embryoresults in the develop-ment of a secondnotochord and neuraltube at the siteof the graft.– Spemann referred

to the dorsal lip as a primary organizer. It influences surrounding cells by induction.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 47.22

Agenda 11/8/11

• Finish Development• Quiz• Gregor Mendel – online cd activity – 4-2-2

• Homework – • Ch. 14 Notes and self-quiz due Thursday, Ch.

15 Notes and self-quiz due Monday 11/14 but suggest you get done during the week

• Next Unit Test (Ch. 11-15, 47) Tues. 11/15, be working on review manuals (will be checked day of test)

Agenda 11/9/11

• Gregor Mendel – online cd activity – 4-2-2 (15 minutes)• Slides on Inheritance• Punnett Square practice

• Homework – Ch. 14 Notes and self-quiz and Punnett square practice due tomorrow, Ch. 15 Notes and self-quiz due Monday 11/14 but suggest you get done sooner

• Next Unit Test (Ch. 11-15, 47) Tues. 11/15, be working on review manuals each night (will be checked day of test)

• Genetics has some unique, useful vocabulary.• An organism with two identical alleles for a

character is homozygous for that character.• Organisms with two different alleles for a character

is heterozygous for that character.• A description of an organism’s traits is its

phenotype.• A description of its genetic makeup is its

genotype.– Two organisms can have the same phenotype but have

different genotypes if one is homozygous dominant and the other is heterozygous.


Mendel’s Experiments

Law of Segregation and Hybrids

Dihybrid Crosses

Crosses of two traits

Illustrates the Principle of Independent Assortment.

Alleles for one trait segregate independently of alleles from other traits during gamete formation.

Traits are inherited separately. Inheritance of one trait does not affect the inheritance of another trait.

If the traits are on different chromosomes.

Dihybrid Crosses – Using Probability – Rules of Multiplication and Addition

Different patterns of Inheritance

• Incomplete Dominance

• Codominance

• Multiple Alleles

• Epistasis

• Polygenic Inheritance

• A clear example of incomplete dominance is seen in flower color of snapdragons.– A cross between a

white-flowered plant and a red-flowered plant will produce all pink F1 offspring.

– Self-pollination of the F1 offspring produces

25% white, 25% red, and 50% pink offspring.


Fig. 14.9

Codominance and Multiple Alleles – Blood Types

• The dominance/recessiveness relationships depend on the level at which we examine the phenotype.– For example, humans with Tay-Sachs disease lack a

functioning enzyme to metabolize gangliosides (a lipid) which accumulate in the brain, harming brain cells, and ultimately leading to death.

– Children with two Tay-Sachs alleles have the disease.– Heterozygotes with one working allele and homozygotes

with two working alleles are “normal” at the organismal level, but heterozygotes produce less functional enzyme.

– However, both the Tay-Sachs and functional alleles produce equal numbers of enzyme molecules, codominant at the molecular level.


• Dominant alleles do not somehow subdue a recessive allele.

• It is in the pathway from genotype to phenotype that dominance and recessiveness come into play.– For example, wrinkled seeds in pea plants with two

copies of the recessive allele are due to the accumulation of monosaccharides and excess water in seeds because of the lack of a key enzyme.• The seeds wrinkle when they dry.

– Both homozygous dominants and heterozygotes produce enough enzyme to convert all the monosaccharides into starch and form smooth seeds when they dry.


• Because an allele is dominant does not necessarily mean that it is more common in a population than the recessive allele.– For example, polydactyly, in which individuals

are born with extra fingers or toes, is due to an allele dominant to the recessive allele for five digits per appendage.

– However, the recessive allele is far more prevalent than the dominant allele in the population.• 399 individuals out of 400 have five digits per

appendage.


• Dominance/recessiveness relationships have three important points.

1. They range from complete dominance, though various degrees of incomplete dominance, to codominance.

2. They reflect the mechanisms by which specific alleles are expressed in the phenotype and do not involve the ability of one allele to subdue another at the level of DNA.

3. They do not determine or correlate with the relative abundance of alleles in a population.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

• The genes that we have covered so far affect only one phenotypic character.

• However, most genes are pleiotropic, affecting more than one phenotypic character.– For example, the wide-ranging symptoms of

sickle-cell disease are due to a single gene.

• Considering the intricate molecular and cellular interactions responsible for an organism’s development, it is not surprising that a gene can affect a number of an organism’s characteristics.


• In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus.– For example, in mice and many other

mammals, coat color depends on two genes.– One, the epistatic gene, determines whether

pigment will be deposited in hair or not.• Presence (C) is dominant to absence (c).

– The second determines whether the pigment to be deposited is black (B) or brown (b).• The black allele is dominant to the brown allele.

– An individual that is cc has a white (albino) coat regardless of the genotype of the second gene.


• A cross between two black mice that are heterozygous (BbCc) will follow the law of independent assortment.

• However, unlike the 9:3:3:1 offspring ratio of an normal Mendelian experiment, the ratio is nine black, three brown, and four white.


Fig. 14.11

• Some characters do not fit the either-or basis that Mendel studied.

• Quantitative characters vary in a population along a continuum

• These are usually due to polygenic inheritance, the additive effects of two or more genes on a single phenotypic character.– For example, skin color in humans is controlled

by at least three different genes.– Imagine that each gene has two alleles, one

light and one dark, that demonstrate incomplete dominance.

– An AABBCC individual is dark and aabbcc is light.


• A cross between two AaBbCc individuals (intermediate skin shade) would produce offspring covering a wide range of shades.– Individuals with

intermediate skin shades would be the most likely offspring, but very light and very dark individuals are possible as well.

– The range of phenotypes forms a normal distribution.


Fig. 14.12

X-linked (Sex-linked) Diseases

• Phenotype depends on environment and genes.– A single tree has leaves that vary in size,

shape, and greenness, depending on exposure to wind and sun.

– For humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence tests.

– Even identical twins, genetic equals, accumulate phenotypic differences as a result of their unique experiences.

• The relative importance of genes and the environment in influencing human characteristics is a very old and hotly contested debate.


• The product of a genotype is generally not a rigidly defined phenotype, but a range of phenotypic possibilities, the norm of reaction, that are determined by the environment.– In some cases the norm of reaction has no

breadth (for example, blood type).

• Norms of reactions are broadest for polygenic characters.– For these multifactorial

characters, environment contributes to their quantitative nature.


Fig. 14.13

• Rather than manipulate mating patterns of people, geneticists analyze the results of matings that have already occurred.

• In a pedigree analysis, information about the presence/absence of a particular phenotypic trait is collected from as many individuals in a family as possible and across generations.

• The distribution of these characters is then mapped on the family tree.

1. Pedigree analysis reveals Mendelian patterns in human inheritance


Agenda 11/10/11

• Hand back quizzes• Finish Inheritance/Pedigrees• Genetics Practice Problems Key – while you

look I will check Ch. 14 notes• Disease Chart • Probably Monday - Watch Online CD – 4-3-2

(Overview of Ch. 15)

Homework – Finish Disease chart, Ch. 15 Notes and self-quiz due Monday, get studying for Unit Test on Tuesday!!!!

• Thousands of genetic disorders, including disabling or deadly hereditary diseases, are inherited as simple recessive traits.– These range from the relatively mild (albinism) to

life-threatening (cystic fibrosis).

• The recessive behavior of the alleles occurs because the allele codes for either a malfunctioning protein or no protein at all.– Homozygous recessive disease– Heterozygotes carrier with normal phenotype

-one “normal” allele produces enough of the required protein.

2. Many human disorders follow Mendelian patterns of inheritance


• Tay-Sachs disease is another lethal recessive disorder.– It is caused by a dysfunctional enzyme that

fails to break down specific brain lipids.– The symptoms begin with seizures, blindness,

and degeneration of motor and mental performance a few months after birth.

– Inevitably, the child dies after a few years.– Among Ashkenazic Jews (those from central

Europe) this disease occurs in one of 3,600 births, about 100 times greater than the incidence among non-Jews or Mediterranean (Sephardic) Jews.


• The most common inherited disease among blacks is sickle-cell disease.– It affects one of 400 African Americans.– It is caused by the substitution of a single

amino acid in hemoglobin.– When oxygen levels in the blood of an affected

individual are low, sickle-cell hemoglobin crystallizes into long rods.

– This deforms red blood cells into a sickle shape.


• This sickling creates a cascade of symptoms, demonstrating the pleiotropic effects of this allele.

• Doctors can use regular blood transfusions to prevent brain damage and new drugs to prevent or treat other problems.


Fig. 14.15

• At the organismal level, the non-sickle allele is incompletely dominant to the sickle-cell allele.– Carriers are said to have the sickle-cell trait.– These individuals are usually healthy, although

some suffer some symptoms of sickle-cell disease under blood oxygen stress.

• At the molecule level, the two alleles are codominant as both normal and abnormal hemoglobins are synthesized.


• The high frequency of heterozygotes with the sickle-cell trait is unusual for an allele with severe detrimental effects in homozygotes.– Interestingly, individuals with one sickle-cell

allele have increased resistance to malaria, a parasite that spends part of its life cycle in red blood cells.

– In tropical Africa, where malaria is common, the sickle-cell allele is both a boon and a bane.• Homozygous normal individuals die of malaria,

homozygous recessive individuals die of sickle-cell disease, and carriers are relatively free of both.

• Its relatively high frequency in African Americans is a vestige of their African roots.


• Normally it is relatively unlikely that two carriers of the same rare harmful allele will meet and mate.

• However, consanguineous matings, those between close relatives, increase the risk.– These individuals who share a recent common

ancestor are more likely to carry the same recessive alleles.

• Most societies and cultures have laws or taboos forbidding marriages between close relatives.


• Although most harmful alleles are recessive, many human disorders are due to dominant alleles.

• For example, achondroplasia, a form of dwarfism, has an incidence of one case in 10,000 people.– Heterozygous individuals have the dwarf phenotype.– Those who are not achodroplastic dwarfs, 99.99% of the

population are homozygous recessive for this trait.

• Lethal dominant alleles are much less common than lethal recessives because if a lethal dominant kills an offspring before it can mature and reproduce, the allele will not be passed on to future generations.


• A lethal dominant allele can escape elimination if it causes death at a relatively advanced age, after the individual has already passed on the lethal allele to his or her children.

• One example is Huntington’s disease, a degenerative disease of the nervous system.– The dominant lethal allele has no obvious

phenotypic effect until an individuals is about 35 to 45 years old.

– The deterioration of the nervous system is irreversible and inevitably fatal.


• While some diseases are inherited in a simple Mendelian fashion due to alleles at a single locus, many other disorders have a multifactorial basis.– These have a genetic component plus a significant

environmental influence.– Multifactorial disorders include heart disease, diabetes,

cancer, alcoholism, and certain mental illnesses, such a schizophrenia and manic-depressive disorder.

– The genetic component is typically polygenic.

• At present, little is understood about the genetic contribution to most multifactorial diseases– The best public health strategy is education about the

environmental factors and healthy behavior.


• A preventative approach to simple Mendelian disorders is sometimes possible.

• The risk that a particular genetic disorder will occur can sometimes be assessed before a child is conceived or early in pregnancy.

• Many hospitals have genetic counselors to provide information to prospective parents who are concerned about a family history of a specific disease.

3. Technology is providing new tools for genetic testing and counseling


• Tests are also available to determine in utero if a child has a particular disorder.

• One technique, amniocentesis, can be used beginning at the 14th to 16th week of pregnancy to assess the presence of a specific disease.– Fetal cells extracted from amniotic fluid are

cultured and karyotyped to identify some disorders.

– Other disorders can be identified from chemicals in the amniotic fluids.


Fig. 14.17a

• A second technique, chorionic villus sampling (CVS) can allow faster karyotyping and can be performed as early as the eighth to tenth week of pregnancy.– This technique extracts a sample of fetal tissue

from the chrionic villi of the placenta.– This technique is not suitable for tests requiring

amniotic fluid.


Fig. 14.17b

• Other techniques, ultrasound and fetoscopy, allow fetal health to be assessed visually in utero.

• Both fetoscopy and amniocentesis cause complications in about 1% of cases.– These include maternal bleeding or fetal death.– Therefore, these techniques are usually reserved for

cases in which the risk of a genetic disorder or other type of birth defect is relatively great.

• If fetal tests reveal a serious disorder, the parents face the difficult choice of terminating the pregnancy or preparing to care for a child with a genetic disorder.


• Some genetic tests can be detected at birth by simple tests that are now routinely performed in hospitals.

• One test can detect the presence of a recessively inherited disorder, phenyketonuria (PKU).– This disorder occurs in one in 10,000 to 15,000 births.– Individuals with this disorder accumulate the amino

acid phenylalanine and its derivative phenypyruvate in the blood to toxic levels.

– This leads to mental retardation.– If the disorder is detected, a special diet low in

phenyalalanine usually promotes normal development.


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