Genetics

Multiples genes –
three or more forms of a gene for a trait. / Any of a set of three or more alleles, or alternative states of a gene, only two of which can be present in a diploid. That is the sequence of the bases is slightly different in the genes located on the same place of the chromosome.

1. Chinchilla
2. Himalyan (Russian)
3. Albino
4. Skin Colour in Mice
5. Eye Colour in Drosophila
6. ABO blood group system

Polygene -
polygenic inheritance occurs when one characteristic is controlled by two or more genes (usually by many different genes) at different loci on different chromosomes. there is more than one gene involved and their may be multiple alleles of the multiple genes.

1. Human height
2. Kernal color in wheat (5 phenotypic classes)
3. Skin color

Linked genes –
genes on the same chromosome pair. The phenotype ratio for this cross is 3:1.

1. flower color and pollen shape experiment
2. fruit flies eyes color
3. hemophilia
4. red-green colorblindness

Lethal Gene –
a gene that leads to the death of an individual; these can be either dominant or recessive in nature

1. Recessive yellow mouse coat color.
2. Dominant lethal gene - Huntington's disease in humans.

Pleiotropy –
a single gene controls several distinct, and seemingly unrelated, phenotypic effects.

1. human disease PKU (phenylketonuria)
2. sickle-cell anemia

Epitasis –
type of gene interaction in which a gene at one locus masks or suppresses the effects of a gene at a different locus.

1. combs in chicken
2. Flower Color in Peas

Codominance & I.dominance

What is Incomplete Dominance?

Incomplete dominance is when the two alleles inherited from the parents are neither dominant nor recessive, but blend together to give a physical trait that is somewhere between the two.

What is Codominance?

Codominance is quite similar to incomplete dominance in that neither parental trait is dominant nor recessive. However, with codominance, the two traits both appear in the offspring, often showing up in different parts of the plant or animal.

Examples of Incomplete Dominance and Codominance in Plants

In plants, snapdragons exhibit incomplete dominance for color traits. When a red snapdragon and a white snapdragon are crossed (mated), the color of the offspring is neither white nor red. Instead, the resulting snapdragon will be pink.

With codominance in flowers, on the other hand, the resulting offspring between red and white parents would not be pink. Instead, they would be red with white spots or white with red spots, the result of both colors being codominant.

Example of Incomplete Dominance and Codominance in Humans

The most well-studied example of incomplete dominance in humans occurs in the genes for curly hair. Inheriting a gene for curly hair from one parent and a gene for straight hair from the other parent will give a hair texture that is a blend of the two, wavy hair.

A codominant genetic trait in humans occurs with blood types. There are three different alleles for blood type: A, B and O. While the O type is actually the absence of either A or B proteins in the blood, the A and B blood types are codominant. If someone inherits one A allele and one B allele, they will not have a blood type that is in between those two, but will instead have a blood type AB, which expresses both A and B proteins in the blood.

C3 & C4 Plants

By looking at their anatomy,

in C3 plants,

- bundle sheath cells do not contain chloroplasts;
- carbon fixation and Calvin Cycle reactions occur in mesophyll cells
- (and in the presence of oxygen).
- more adapted to environments with more carbon dioxide.


In C4 plants,

- the bundle sheath cells contain chloroplasts;
- carbon is fixed in mesophyll cells too, then transported to bundle sheath cells where
- Calvin Cycle reactions occur in the absence of oxygen.
- more adapted to environments with more oxygen

In both, photosynthesized sugars then enter the plant's vascular system.

C4 have a concentric arrangement of the bundle sheath and mesophyll layer, the bundle sheath is also thicker.

Another difference is their intervenial distances, from one bundle sheath to another you have in C4 only around 4 mesophyll cells but on 3 they are separated by 12.

C3 Photosynthesis : C3 plants.

• Called C3 because the CO2 is first incorporated into a 3-carbon compound.

• Stomata are open during the day.

• RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of CO2.

• Photosynthesis takes place throughout the leaf.

• Adaptive Value: more efficient than C4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy)..

• Most plants are C3.

C4 Photosynthesis : C4 plants.

• Called C4 because the CO2 is first incorporated into a 4-carbon compound.

• Stomata are open during the day.

• Uses PEP Carboxylase for the enzyme involved in the uptake of CO2. This enzyme allows CO2 to be taken into the plant very quickly, and then it "delivers" the CO2 directly to RUBISCO for photsynthesis.

• Photosynthesis takes place in inner cells (requires special anatomy called Kranz Anatomy)

• Adaptive Value:
o Photosynthesizes faster than C3 plants under high light intensity and high temperatures because the CO2 is delivered directly to RUBISCO, not allowing it to grab oxygen and undergo photorespiration.

o Has better Water Use Efficiency because PEP Carboxylase brings in CO2 faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis.

• C4 plants include several thousand species in at least 19 plant families. Example: fourwing saltbush, corn, and many of our summer annual plants.

Examples:
C3----->wheat, barley, potatoes and sugar beet. (most of the plants are C3)
C4----->fourwing saltbush, corn ,many of summer annual plants.
CAM---> cactuses, aloe vera, some orchids and bromeliads (required less water)

Primary & Accessory Pigments

The most significant difference between primary and accessory pigments is that they absorb and give off light at different wavelengths.

When photons of light hit a leaf, they have a specific wavelength. Chlorophyll has a specific wavelength that it can absorb and give off light as. If chlorophyll was the only pigment a plant had, it could only use light that was of this particular wavelength. However, the presence of accessory pigments allows the plant to use light of all wavelengths.

Primary and accessory pigments also vary in color. Chlorophyll is green, while others are different. Carotenoids can be red, yellow or orange. Photosynthetic aquatic organisms like cyanobacteria also have phycobilins.

1. Primary pigments:

primary pigments In photosynthesis, pigments that emit electrons which directly drive the photosynthetic reactions.

In green plants there are two primary pigments,

both of which are forms of Chorophyll a: P680 and P700.

2. Accessory pigments:

a pigment in plants that can absorb light energy and pass the electrons along to the primary pigment which starts the process of photosynthesis.

In the flowering plants (angiosperms),

chlorophylls a and b provide the green color and absorb the light energy needed for photosynthesis.

However, other accessory pigments, such as yellow xanthophylls and orange carotenes are also present in the chloroplasts and collect additional light energy for photosynthesis.

All plants, algae, and cyanobacteria which photosynthesize contain chlorophyll "a".

A second kind of chlorophyll is chlorophyll "b", which occurs only in green algae and in the plant.

Carotenoids act as \"SHIELD PIGMENTS\" as they are located over the chlorophylls thus protecting them from photo-oxidation and photo-bleaching. (antioxidants)

Phycobilins are water-soluble pigments, and are therefore found in the cytoplasm, or in the stroma of the chloroplast. They occur only in Cyanobacteria and Rhodophyta.

Bonded to certain water-soluble proteins, ‘Phycobiliproteins’ then pass the light energy to chorophyll for photosynthesis.

The phycobilins are especially efficient at absorbing red, orange, yellow and green light, wavelengths which are not well absorbed by chlorophyll a. Organisms growing in shallow waters tend to contain phycobilins that can capture yellow/red light, while those at greater depth often contain more of the phycobilins that can capture green light, which is relatively more abundant there.