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Mendel’s Genetics [4]: examples of mutiple alleles

 

All the examples used in last classes have employed genes with only two alternative alleles. But the majority of genes exist in several different forms, multiple alleles. This is caused by the mutations of bases at different sites within the same gene, thus affecting different amino acids in the encoded protein.

examples of multiple-allele traits/diseases:

  • the human β-globin gene where a specific mutation at one site of the gene results in an allele responsible for the hereditary syndrome sickle cell (picture)anaemia, while mutations at several other sited sites in the gene cause a different syndrome, β-thalassemia(beta地中海贫血),

    genetics 4 SickleCell
    A SICKLE CELL,image from the Internet

Beta-thalassemia, inherited blood disorder caused by reduced or absent synthesis of     the beta chains of hemoglobin, resulting in variable phenotypes ranging from severe anemia to clinically asymptomatic individuals.

        Although they are alterations of the same gene, the changes are to different codons(a specific sequence of three consecutive nucleotides that is part of the genetic code and that specifies a particular amino acid in a protein or starts or stops protein synthesis). The resulting proteins have variant beta-globins with discrete differences in amino acid sequence and so behave differently.

—————————————————————————

  • In rabbits, multiple alleles of one gene are responsible for a number of different coat color phenotypes.

       Here we go, a little confusing but, interesting:

      There are four members of the allelic series: agouti, chinchilla,           Himalayan and albino. When homozygous, each series produces a distinct coat pattern. When heterozygous, there is a clear pattern of dominance. Agouti is dominant over all the alleles, chinchilla is dominant over Himalayan and albino, while Himalayan is dominant over albino, which fails to produce any pigment and hence is recessive to the others…Hope your mind is still clear!

1, Agouti rabbit:  the wild rabbit.

genetics 4 an agouti rabbit
AN AGOUTI RABBIT, image form the Internet

If you blow into the fur of an Agouti rabbit, you will see “bandings” of different colors along the shaft of the hair, being blue, black, tan, fawn. The Agouti also has light tan coloring around the nostrils and at the back of the neck. The belly is cream.(http://rabbit.wikia.com/wiki/Agouti)

2, Chinchilla rabbit: soft, grey fur.

genetics 4 A five-week-old Chinchilla rabbit
A FIVE-WEEK-OLD CHINCHILLA RABBIT, image from the Internet

Chinchilla Rabbits originated in France and were bred to standard by M. J. Dybowski. They were introduced to the United States in 1919. (wikipedia)

 

 

3. Himalayan rabbit:  white body with colored points, recognized colors are black, blue, chocolate and lilac.

A HIMALAYAN RABBIT, image from the Internet
A HIMALAYAN RABBIT, image from the Internet

red eyes; posed stretched out,  body to be 3.5 head lengths. They are the ancestors of Californians, one of the most common meat rabbits.(wikipedia: Himalayan_rabbit)

4. Albino rabbit: completely white since it’s  missing the melanin which determines the color of their skin, eyes, and fur.

genetics 4 albino rabbits
AN ALBINO RABBIT, image from the Internet

Not all white rabbits are albinos, so you’ll need to check their eyes. If their eyes are red or pink and their hair is totally white, they would be considered an albino. They are not rare. 

An albino rabbit may not have the greatest eyesight due to their lack of eye pigment. Since their eyesight is not the best, they should be caged or kept inside since they may not be able to see predators.(http://www.ask.com/question/albino-rabbits)

Having seen so much about rabbits, hope you haven’t forgotten what we were doing before those cute bunnies. We were learning about examples of multiple alleles of one gene.

  • the human ABO blood group system. 

(all form wikipedia: ABO blood group system:)

The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: i, IA, and IB. The gene encodes a glycosyltransferase— an enzyme that modifies the carbohydrate content of the red blood cell antigens. 

The IA allele gives type A, IB gives type B, and i gives type O.

Both IA and IB are dominant over i,  so only ii people have type O blood. Individuals with IAIA or IAi have type A blood, and individuals with IBIB or IBi have type B.

IAIB people have both phenotypes, because A and B express a special dominance relationship: codominance(we talked about it last class), which means that type A and B parents can have an AB child.

A type A and a type B couple can also have a type O child if they are both heterozygous (IBi,IAi)

Hope your mind is still clear!

NOTE: the concept of multiple alleles of one gene is totally different from multiple-gene inheritance. 

A polygene, multiple factor, multiple gene inheritance, or quantitative gene is a group of,  non-allelic, genes that together influence a phenotypic trait.

The blueprint of life [3] secondary and some special structures of DNA

Let’s pick up where we dropped, the secondary structure of DNA.

IN FACT, a number of different forms of nucleic acid double-helix have been observed and studied, all having the basic pettern of two helically-wound antiparallel strands.
Polymorphism （多样性）of DNA  Secondary Structure
―due to conformational changes of sugar-ring on the nucleotide chain.
1. B-form:
  • right-handed
  • the structure identified by Watson and Crick,
  • the most common form,
  • believed to be the idealized form of the structure adopted by virtually all DNAin vivo (in the living body of a plant or animal), or,  at physiological (characteristic of or appropriate to an organism’s healthy or normal functioning) pH and salt concentration.

characterized by:

  • a helical repeat of 10bp/turn (although now it is known that ‘real’ B-DNA has a repeat closer to 10.5bp/turn);
  • the presence of base pairs lying on the helix axis and almost perpendicular to it;
  • having well-defined, deep major and minor grooves.
2. A-form: 
  • right handed
  • adopted by DNA in vivo under unusual circumstances, (conversed from B-form in low moisture (<75%))
  • presents in certain DNA-protein complexes

characterized by:

  • a helical repeat of 11 bp/turn.
  • the presence of base pairs tilted with respect to the helix axis, and actually lying off the axis.
  • being the helix formed by RNA and DNA-RNA hybrids. (Similar to some RNA-DNA duplex or RNA-RNA duplex.)
3. Z-form:
  • left-handed
  • formed by stretches of alternating pyrimidine-purine sequence, e.g. GCGCGC, especially in negatively supercoiled DNA in high saline (盐) solution.
  • not easily form even in DNA regions of repeating GCGCGC, since the boundaries between the left-handed Z-form and the surrounding B-form would be very unstale

characterized by:

  • a zigzag (锯齿型) pattern where its name comes from
  • 12 bp/turn

(1)

A. B, Z-DNA
slide shown by prof.Dong,COMPARISON AMONG A-,B-,Z-DNA
(2)
A.B.Z-DNA instant notes
picture from Instant Notes in Molecular Biology (3rd Edtion)
====================================================
Some special structures of DNA 
1. Inverted repeats and direct repeats
Inverted Repeat is functionally important as recognition sites on the DNA for the binding of a variety of proteins (e.g. restriction and modification enzymes)
Inverted Repeat is either discontinuous or continuous,
Continuous → palindromic structure (回文结构:inverted repetitions of base sequence over the two strands form a symmetric structure )
Discontinuous→ hairpin & cruciform (发卡、十字结构:self complementary within each of the strands )
palindromic structure
palindromic structure
hairpin structure & cruciform structure
hairpin structure & cruciform structur
2. DNA triplex (The intramolecular triplex (H-DNA) as an example)
shown by prof.Dong, DNA TRIPLEX
shown by prof.Dong, DNA TRIPLEX
• AG-rich strand vs. CT-rich strand with Hoogsten hydrogen bond
(a quick glance at Hoodsten hydrogen bond:
image from wikipedia/hoogsten base pair
image from wikipedia/hoogsten base pair
• Mirror inverted repeat
• a barrier for different DNA and RNA polymerases, and so it is a negative regulator for gene expression.
3. G-quadruplex structure
G-rich sequence(s) to form 4-stranded structure by unusual G-G
H-bonds
shown by prof.Dong, G-AUADRUPLEX
shown by prof.Dong, G-AUADRUPLEX

Mendel’s Genetics[3]: Variations of the 3:1ratio

 

Variations of the 3:1 ratio

The simple 3-to-1 monohybrid ratio is not always observed in instances where only one gene is responsible for a particular phenotype.

A number of factors:

  • Partial or incomplete dominance

Complete dominance means the phenotype of first filial generation(heterozygous) is exactly identical to that of one of the parents(both homozygous). Partial or incomplete dominance means the first filial has phenotype somewhere between that of both parents.

For example, When two pure-bred snapdragons, with white and red petals respectively, cross, their first filial generation has pink petal rather than red or white.

In this case, the homozygous phenotypes are red, or white petals while heterozygous one is between white and red: pink petal.

Thus, it is conceivable that when it comes to the second filial generation, which was produced by the self fertilization of the heterozygous F1, F2 should have three different phenotypes, white, pink, and red. And we can also deduce the ratio of them is 1:2:1.

  • Codominance

Codominance is similar to incomplete dominance, but here the heterozygote displays both alleles(两种等位基因均被表达).

For example, in humans the MN blood group is controlled by a single gene.

In humans the main blood group systems are the ABO system, the Rh system and theMN system.

Only two alleles exist, M and N. Children whose father is an NN homozygote with N blood and whose mother is a MM homozygote with group M blood are MN heterozygotes and have group MN blood.Both phenotypes are identifiable in the hybrid. And the ratio also switches from 3:1 to 1:2:1.

  • Lethal alleles

Some alleles affect the viability of individuals that carry them.

In most cases the homozygous recessive does not survive but the heterozygotes may have a normal lifespan.

The best-known example of lethal alleles is the inheritance of yellow coat color in mice.

Yellow fur can arise in strain of mice with different colors, or instance, black. Yellow coat color is dominant to black coat. Mice with BB alleles are back, with BBy are yellow, with ByBy alleles are supposed to be yellow as well, but ByBy alleles are lethal and any mice with this genotype die in utero(in the uterus : before birth).

SO it is conceivable that when two yellow mices are mated ratio of the different phenotypes of their first generation is 2 : 1,  rather than 3 : 1 or 1 : 2 :1.

NOTE: The  allele By is recessive in its relation to its effect on viability (only homozygous ByBy s die, while the heterozygotes survive ), but dominant in relation to coat color(heterozygotes present in yellow fur in stead of black fur.). 

Other examples where alleles are lethal when homozygous but have a dominant effect when heterozygous, include :

  • tailless Manx cats
genetics
a manx cat, image from the Internet

a breed of domestic cat(Felis catus) originating on the Isle of Man, with a naturally occurring mutation that shortens the tail.

The Manx taillessness gene is dominant and highly penetrant; kittens from two Manx parents are generally born without any tail. Being homozygous for the taillessnees gene is lethal in utero.Thus, tailless cats can only be heterzygous. Because of the danger of having homozygous taillessness gene, breeders avoid breeding two entirely tailless Manx cats together.(wikipedia: Manx (cat))

  • short-legged Creeper chickens.

====================================================

(Annie: If none of the homozygous yellow mice can survive before birth, then where did all the heterozygous yellow mice come from in the first place???????)

Answer: Through mutation. The presence of one mutant allele alters development so as to produce characteristic changes to the animal, but when two of the mutant alleles are present, development is so aberrant as to cause death.

This may occur in utero as described above or resulted in shortened life expectancy as found in several examples in humans, such as Tay-Sachs disease, Huntington’s syndrome（亨丁顿舞蹈症） or sickle-cell anemia（镰刀形红血球病）. (from Instant Notes)

the blueprint of life [2]: primary and secondary structure of DNA

Molecular structure of DNA:

professor Dong first showed us where DNA is:

molecular structure of DNA
slide shown by Prof.Dong,WHERE IS DNA?

Then he introduced the molecular structure of DNA with 4 parts:

1. Primary structure of DNA:

Arrangement of nucleotides along a DNA chain.

Annie: So…the primary structure of DNA is a line.

Conventionally, the repeating monomers of DNA are represented by their single letters A, T, G, C.

Professor: There’s a convention to write the DNA sequence with 5′ at the left, that is, in a 5′ to 3′ orientation from left to right.

====================================================

2. Secondary structure of DNA—stabilized partial structure formed by polymers of nucleotide

Professor Dong: First, please familiarize yourselves with Chargaff’s Rule:

A+G=T+C & G+T=A+C

↓↓

A=T & G=C

(Chargaff’s Rule)

(Based on analysis of the chemical composition of duplex DNA in the early 1950s, E. Chargaff deduced these rules about the amounts of different nucleotides in DNA.)

Professor: The secondary structure of DNA is a partial structure formed by polymers of nucleotide. The structure is referred to as the double-helix structure.

Two separate chains of DNA are wound around each other, each following a helical (coiling) path, resulting in a right-handed double helix structure.

In 1953, Watson and Click proposed the DNA double-helix structure based on Chargaff’s Rule and DNA Crystallography and X-ray diffraction images of DNA structure by Wilkins and Franklin.  (Rosalind Franklin, who was not that well-known as Watson, Click and Wilkins but apparently played a equally significant role in the discovery of the structure.The whole was later nominated Nobel Prize but her, is that even fair?)

—————————————————————————

The backbone of duplex DNA is a serious of phosphodiester group (the covalent linkage of a phosphate group between the 5′-hydroxyl of one sugar and the 3′-hydroxyl of the next, that is , repeats of P-sugar unit) linked by phosphodiester bond.

—————————————————————————
The strands are joined noncovalently by hydrogen bonding between the bases on opposite strands, to form base pairs.
There are around 10 base pairs per turn in the DNA double-helix. The two strands are oriented in opposite directions in terms of their 5’to3′ direction(the nucleotides in one strand is opposite to their direction in the other strand).
stand direction
More crucially, the two strands are complementary in terms of sequence. The bases hydrogen-bond to each other as purine-pyrimidine pairs which have very similar geometry and dimensions.
         A–T:  2 H-bonds ;    C–G:  3 H-bonds
   5’- A   T   G    T   C -3’
   ¦¦    ¦¦  ¦¦¦   ¦¦   ¦¦¦
   3’- T   A   C   A   G -5’

 Thus, the sequence of one strand uniquely specifies the sequence of the other, with all that which implies for the mechanism of replication of DNA and its transcription to RNA.

——————————————————————————-
Professor Dong added:
Between the backbone stands run the major and minor grooves.

In a detailed analysis of DNA structure, there are two types of grooves that can be seen; the major groove has the nitrogen and oxygen atoms of the base pairs pointing inward toward the helical axis, while in the minor groove,the nitrogen and oxygen atoms point outwards;

major groove A_T
Shown by prof.Dong, MAJOR GROOVE A-T
major groove GC
Shown by prof.Dong, MAJOR GROOVE G-C
—Major Groove                        —Minor Groove
—Depth: 8.5 Å                             —Depth: 7.5 Å
—Width: 11.7 Å                          —Width: 5.7 Å
Å
Definition: Symbol for Ångström, a unit equal to 0.1 nanometer, mainly used in expressing sizes of atoms, lengths of chemical bonds, and wavelengths of electromagnetic radiation.
Supplement: The unit is named after the Swedish physicist, Ångström, Anders Jonas.
instant notes

picture from Instant Notes in Molecular Biology

Professor: The major groove is more dependent on base composition. and major grooves and minor grooves are also recognition and binding sites for certain  protein factors, and are involved in the regulation of gene expression.

——————————————————————————
grooves
slide shown by Prof.Dong

Professor: Summary of “Double Helix” Model (B-DNA):

  • —Right Handed Double Helix
  • —Outside: P-Sugar backbone
  • Inside: Base pairing linked by H-bonds
  • —Minor and Major grooves
 （note: bp=base pair(s)）

Illustrations of wild animals [insect 4 Praying Mantids]

螳螂目 MANTODEA

Mantodea (Mantids / Praying Mantids)

The name Mantodea is derived from “mantis”, the Greek word for these insects.

  • Classification & Distribution

Hemimetabola

  • incomplete development (egg, nymph, adult)

Orthopteroid

  • closely related to Orthoptera and Blattodea

Distribution: Common in tropical and subtropical climates.

WORLDWIDE
Number of Families
8
Number of Species
~1800
  • Life History & Ecology

Mantids have elongate bodies that are specialized for a predatory lifestyle:  long front legs with spines for catching and holding prey, a head that can turn from side to side, and cryptic coloration for hiding in foliage or flowers.

Mantids are most abundant and most diverse in the tropics; there are only 5 species commonly collected in the United States and 3 of these have been imported from abroad.

  • Physical Features
mantid image

Adults:

  • Filiform antennae
  • Head triangular with well-developed compound eyes
  • Mouthparts mandibulate, hypognathous
  • Prothorax elongate with large, spiny front legs adapted for catching prey
  • Front wings thickened, more slender than hind wings
  • Tarsi 5-segmented
  • Cerci short, multi-segmented

Immatures:

  • Structurally similar to adults
  • Developing wingpads often visible on thorax
  • Major Families 
      • Mantidae — this family includes all of the common North American mantids.

The name mantid refers only to members of the family Mantidae.

  • Bug Bytes
    • Mantids are the only insects that can turn their head from side to side without moving any other part of the body. Many humans mistakenly interpret this behavior as a sign of intelligence.
    • A female mantid may eat her mate while he is still linked with her in copulo.  This behavior is probably more common in captivity than in the wild.
    • Most mantids are cryptically colored to blend with their environment.  A pink Malaysian species spends most of its time hunting for prey on pink orchids.
    • Although mantids usually feed on insect prey, they have been known to catch and eat small frogs, lizards, and even birds

====================================================

↑Quoted from the General Entomology course
at North Carolina State University >Resource Library > Compendium > Mantodea (© 2009 by John R. Meyer; Last Updated: 8 April 2009)

>Learn more about pray mantids (mantodearesearch.com)

====================================================

螳科 Mantidae
  1. 大刀螳螂Tenodera aridifolia

2.  中华刀螳Tenodera sinensis

3. 短胸大刀螳Tenodera brevicollis

  1. 棕静螳 Statilia maculata
  1. 广斧螳 Hieroduia patellifera
长颈螳科  Vatidae

中华屏顶螳Kishinouyeum sinensae

the blueprint of life[1]

Of course the blueprint of life is DNA.

DNA is important because it is the genetic material ←contain all the info for the synthesis and functioning of a living form duplicate and passes through to the next generation.

Hearing this Annie questioned herself: DNA is not the genetic for ALL viruses. RNA “blueprints” for the rest of the viruses. Virus, though not even having a cell structure, is a form of life. So why not be fair, and say the blueprint of life are DNA and RNA?

Professor Dong continued,

Proofs:

  1. Bacterial Transformation Experiment

—Griffith, 1928

Professor: So what is the transforming principle? 

Annie: It could be a cool type of enzyme that moved the toxic part of S strain onto R strain…

Professor: Well, Enzyme did help a lot in the experiment we’ll talk about later, but it is not the hero of the story.

Annie: So what’s the story?

Professor:

—Avery et al., 1944

slide shown by Prof. Dong ,AVERY REPEATED GRIFFITH’S EXPERIMENT WITH MODIFICATION

Only DNA is responsible for the transformation.

Annie thought: Well, there still existed possibilities that DNA and some other things that were not sugar, lipid or protein cooperated to complete the transformation… The “other things” also contributed to the transformation but could not complete it without DNA?  In this case DNA is not the only one that is responsible,  

  1. T2 Bacteriophage Infection (Blender Experiment)

—Hershey &Chase, 1952

Experiment 1

Experiment 2

Radioactive labeling of proteins and DNA

The professor continued. So now let’s go deeper and see the chemical composition of DNA.

A 5-carbon sugar , hand in hand with base group and phosphorous group, thought Annie.

It’s not that simple as you learned in high school, said the professor. We need to know the chemical composition of the base group, deoxyribon and phosphorous group as well.

sugar group
slide shown by Prof. Dong,SUGAR GROUP

 Professor:

Base
slide shown by Prof. Dong,BASE GROUPS

Annie thought: Pyrimid-ine, Could it have anything to do with the Pyramid in Egypt?

The professor was explaining the structure and Annie didn’t interrupt him with her question.

After class, Annie searched the Internet for an answer, and this is what she found.

 The professor continued.

Bonds

P group——phosphester bond–—Sugar—–glycosidic bond—–B group

Mendel’s Genetics[2]: The monohybrid cross

Keywords:

  • Phenotype

Any character (trait) which can be shown to be inherited, such as eye color, leaf shape or an inherited disease, such a cystic fibrosis, is referred to as a phenotype.

Description: A fly may be described as having a red-eyed phenotype. A child may be described as displaying the cystic fibrosis phenotype.

  •  Genotype

The pattern of genes that are responsible for a particular phenotype in a individual is referred to as genotype.

  • Dominance

In hybrids between two individuals displaying different phenotypes, only one phenotype may be observed. This phenotype is referred to as the dominant trait and the un-shown one the recessive.

For instance, if the wife has wide eyes while the husband has small eyes, and their little girl has wide eyes, then the wide eyes are dominant to small eyes.

  •  Pure-breeding lines

Organisms which have been inbred for many generations in which a certain phenotype remain the same.Pedigree breeds of dogs or cats are commonplace examples of pure-breeding lines.

A puppy from two purebred dogs of the same breed, for example, will exhibit the traits of its parents, and not the traits of all breeds in the subject breed’s ancestry.

  • Homozygous: Individuals with two identical copies of a gene.

“True breeding (pure-breedind) organisms are always homozygous for the traits that are to be held constant.”

  • Heterozygous: Individuals with two different copies of the gene.
  • Alleles: The different variants of a gene.

====================================================

Mendel made a cross between two pure-breeding lines of pea plants, one of which had violet petals and the other white petals. The hybrids produced in this cross were referred to as the F1 (first filial) generation.

In Mendel’s experiment, the ratio of violet pedals and white ones in the second filial were very close to 3 to 1, which applied to the theoretic reasoning shown above.

He did many other experiments focusing on different types of genotypes of the pea plants and the results were shockingly similar. The hidden phenotype in the first filial reappeared in the second filial and the ratio of the dominant to the recessive phenotype were all close to 3 to 1.

The 3:1 ratio is referred to as the monohybrid ratio and is the basis for all patterns of inheritance in higher organisms.

One simple extension of the 3:1 phenotype ratio is a 1:1 ratio, produced when a heterozygous F1 individual is crossed to the homozygous-recessive parent. The process is known as testcross.

Testcross is useful in any condition when it is necessary to determine whether an individual is heterozygous or homozygous. Conceivable that if F2 all have dominant phenotype, then the tested parent is homozygous-dominant; if F2 have a 1:1 ratio of dominant and recessive phenotype, then the tested parent is heterozygous.

 

IIllustrations of wild animals [insect 3 Odonata]

Before this section, make sure you have read the page introducing classification of insects.(Illustrations of wild animals [insect 1])

====================================================

蜻蜓目 ODONATA

Odonata means “toothed jaws,” and indeed the larger species of dragonflies and damseflies may give you a startling but harmless bite.Despite what your mother told you about dragonflies sewing up your lips, they cannot stitch or sting you in any way.

The order Odonata is subdivided into three suborders: Anisoptera, the dragonflies; Zygoptera, the damselflies; and Anisozygoptera, mostly fossilized species with only two known living members.

  • physical features

extremely large eyes (in proportion to its head)

a long, slender abdomen

Large mandibles(jaw), chewing prey quickly and easily, an important feature since these insects tend to eat on the move.

Thorax tilted, positioning the legs just below the mandibles where they function as a prey-catching basket.

“Primitive winged,” ( wings that cannot be folded).  giving Odonates the interesting abilities to hover, fly backward, and take off vertically, similar to a helicopter.

Being able to rotate their heads nearly 360 degrees, giving them an almost limitless field of view.

Dragonflies and damselflies have tiny antennae, so vision is their primary means of navigating and capturing prey.

——————————————————————————-

Odonate eggs are laid in water, where they hatch into wingless naiads. The naiads have gills, and will molt up to 15 times, depending on the species. Some naiads remain in their aquatic environment for as long as two years before reaching adulthood. The final molt produces functioning wings, and the adult dragonfly or damselfly can hunt over water or land.

  • Habitat and Distribution:

Odonates inhabit every continent except Antarctica, in habitats where fresh water is present. Most species in the order are tropical.

  • Major Families and Superfamilies in the Order:
  1.  Aeshnidae – darners
  2. Gomphidae – clubtails
  3. Libellulidae – common skimmers and chasers
  4. Coenagrionidae – narrow-winged damselflies
  5. Corduliidae – emeralds

====================================================

↑Quoted from Order Odonata – Characteristics of Dragonflies and Damselflies By Debbie Hadley

>Learn more about Odonata 

====================================================

蜓科  Aeshnidae  (darners)
  1. 黑纹伟蜓 Anax nigrofasciatus
  1. 碧伟蜓 Anax parthenope
春蜓科  Gomphidae (clubtails)

1. 弗鲁戴春蜓 Davidius fruhstorferi

  1. 联纹小叶春蜓 Gomphidia confluens

4. 小团扇春蜓 Ictinogomphus rapax

蜻科  Libellulidae (common skimmers and chasers)

1.  六斑曲缘蜻 Palpopleura sexmaculata

  1. 半黄赤蜻Sympetrum croceolum

3. 夏赤蜻 Sympetrum darwinianum

4. 大黄赤蜻 Sympetrum uniforme

5. 小黄赤蜻Sympetrum kunckeli

6.竖眉赤蜻 Symprtrum eroticum ardens

7. 红蜻 Crocothemis servilia

9. 晓褐蜻 Trithemis aurora

蟌科 Coenagriidae  (narrow-winged damselflies)
  1.  截尾黄蟌 Ceriagrion erubescens

2. 矛斑蟌 Coenagrion lanceolatum

3. 杯斑小蟌 Agriocnemis femina

 

Review of Mendel’s Genetics

Here I found a great page story-telling  Mendel’s Genetics.Can’t be more suitable as a revision of what we learned about genetics and inheritance in high school.  >>Mendel’s Genetics

I believe by reading the link page you have remembered the principles of Mendel’s Genetics. We’ll  summarize these principles again in next posts.

While Mendel’s research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms.”

It must be a cliche to summarize the success factors of Mendel’s experiments, but it has to be done, for many of the factors are still important for today’s experimentalists.

Firstly, before the experiment,Mendel spent a long time observing different traits of the peas and decided which traits he was going to focus on in the after experiments. He was prepared, had anticipation and, perhaps already held some hypothesis of what was going to happen.

Then it was the choice of his “lab-rats”. As the link page says,”Mendel picked common garden pea plants for the focus of his research because they can be grown easily in large numbers and their reproduction can be manipulated. ” Based on a large number of offspring, the resulting statistics can be assumed as very close to theoretic  statistics.  In this case, it’s  way more convenient to study the traits of these peas than those of some fragile and rare pole plants. 

More important, “pea plants have both male and female reproductive organs.  As a result, they can either self-pollinate themselves or cross-pollinate with another plant.  In his experiments, Mendel was able to selectively cross-pollinate purebred plants with particular traits and observe the outcome over many generations.  This was the basis for his conclusions about the nature of genetic inheritance.”

Reproductive
structures of
flowers

drawing of a flower cross-section showing both male and female sexual structures
the picture is from http://anthro.palomar.edu

Last but not least, Mendel was a pioneer in applying Math(Statistics) to experiment analysis. He rounded the ratio of numbers of different traits to a whole number and discovered the astonishing similarity of all the results.

In high school that’s all the factors, but actually there’s more. For one, Mendel succeeded because all the genes that controlled traits he picked to observe happened to be on different chromosomes. Otherwise, the  phenomena of “linkage” would have appeared (which we’ll talk about later)and he should never have had such a groundbreaking discovery.