Genetic and heredity

 

Punnett squares/inheritance

 

            Character traits inherited by humans are dictated in the form of genes. A gene is a sequence of DNA found on a chromosome. Each gene has a set of alleles, which are the different forms of that trait. For example if the trait were eye color, the alleles would be the different colors that your eye may be.

            The way that traits are passed on to offspring by parents is that each parents gene is crossed, creating a certain amount of combinations. One of these combinations is what is expressed by the offspring. A visualization of the crossing of two genes and the combinations that they can produce may be expressed in the form of a punnett square.

            Let us examine the trait for eye color in mice. If the two possible eye colors are brown and red, and the color red is dominant to brown, then the gene would be expressed as Rr. A dominant allele is more likely to be expressed. It is expressed if it is present on the gene, even if it is paired with a recessive trait, for example, Rr. A recessive trait is only expressed if paired with another recessive trait, for example, rr. If the alleles of a pair are both dominant or both recessive, this is called a homozygous pair. If there is one dominant, and one recessive, this is called a heterozygous pair.

 

Here is what the punnett square would look like for eye color in mice if the male was heterozygous (Rr) and the female was homozygous recessive (rr):

 

(Punnett Square)

 

What this means is that there is a 2/4 chance the offspring are going to have red eyes (Rr), and a 2/4 chance that the offspring are going to have brown eyes (rr).

 

 

DNA

 

A set of 4 amino acids arranged in a double helix pattern. DNA passes on genetic information to offspring. DNA is arranged in a double helix pattern of base pairs. The four amino acids of DNA that form these pairs are adenine, thymine, guanine, and cytosine.

            When DNA is synthesized, each base is matched to its complementary base. Guanine and cytosine are complementary, and adenine and thymine are complementary. A double helix of DNA is split into two single strands. Base pairs are created and matched in a process called transcription.

A sequence of DNA forms a gene. Gene’s occupy chromosomes, on which there are millions of genes. A gene determines a particular trait for an organism.

 

Cell cycle

 

http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/01a.html

G1, S-Phase, G2, M

Gap 1

DNA Synthesis – DNA replication occurs

Gap2

Mitosis

 

Interphase – DNA replicates, centrioles divide, proteins are actively produced

Prophase – The nucleolus fades. Chromatin condenses into chromosomes. Microtubules, which are responsible for shape, become visible.

Metaphase – Tension applied by spindle fibers align chromosomes to the center of the cell.

Anaphase – Spindle fibers shorten. Daughter chromosomes begin to move to the poles of the cell, and the cell stretches.

Telophase – Daughter chromosomes arrive at the poles and spindle fibers disappear. The nucleolus reappears.

Cytokinesis – In animals, a fibrous ring composed of protein punches the cell into two daughter cells, each now with their own nucleus. In plants, a cell plate is synthesized between two daughter cells.