The Molecular Basis of inheritance_Chapter 16

The structure of DNA.

The structure of DNA is double helix, with about 10 nucleotide pairs per helical turn. Each spiral strand, composed of a sugar phosphate backbone and attached bases, is connected to a complementary strand by hydrogen bonding (non- covalent) between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C). Adenine and thymine are connected by two hydrogen bonds (non-covalent) while guanine and cytosine are connected by three. This structure was first described by James Watson and Francis Crick in 1953.

Replication of DNA, and the enzymes.

the video link below describes the replication of dna very well.

http://www.johnkyrk.com/DNAreplication.html

Nucleoid, chromatin, and telomerase.

Telomerase is an enzyme that catalyzes the lenghthening of telomeres in eukaryotic germ cells, so it restores their original lenght abd compensating for the shortening that occurs during the replication. Nucleoid is the dense region of DNA in a bacterium, but is is not bounded by membrane. Eukaryotic DNA is precisely combined with a large amount of protein. Together, this complex of dna and protein, called chromatin, fits into the nucleus through an elaborate, multilevel system of DNA packing.

5 facts on this chapter:

. Nucleic acid strands are always antiparallel, whether it is DNA/DNA or DNA/RNA or R NA/RNA interactions.

. DNA replication is semiconservative.

. The strand that alongs 5' to 3' is called leading strand, and the strand that goes along 3' to 5' is called lagging strand.

. The lagging strand is synthesized in separate pieces called Okazagi Fragments, which are then sealed together by DNA Ligase.

. As DNA becomes more highly packaged, it becomes less accessible to transcription enzymes. This reduces the gene expression.

The Chromosomal Basis of Inheritance_Chapter 15

1. What are the genetic symbols, and their meanings?

Mendel used upper and lower cases.T tall, t short. + means that its wild. (mutant phenotype)

dominant-recessive, dominant is upper case, recessive is lower case. F1 is the first generation, F2 is the second generation from F1 generation.

2. Mutations;

.deletion

.duplication

.inversion

.translocation

3. Human disorders, their results.. (caused by chromosome alterations)

down syndrome: an aneuploid condition that's the result of having an extra chromosome 21. Characteristic facial features, short stature, heart defects, mental retardation.

klinefelter syndrome: an aneuploid condition in which a male possesses he sex chromosomes XXY. males have male sex organs but are sterile.

turner syndrome: a monosomic condition in which the female has just one sex chromosome, an X. sterile female organ.

Video on Chromosome Mutations:

http://www.youtube.com/watch?v=OrXRSqa_3lU

A good website about human disorders due to chromosome alterations:

http://www.biology.iupui.edu/biocourses/n100/2k2humancsomaldisorders.html

Patterns of Inheritance with Sex-Linked Traits

5 main facts on this chapter:

. In humans, there are two types of sex chromosomes. X is for females, Y is for males. Males have one X and one Y.

. Sex linked genes are usually located in X chromosome. So if a boy is hemophilia, that means that his mom has a recessive/dominant hemophilia gene.

. While genes that are on the same chromosome tend to be inherited together, the process of crossing over enables "linked" genes to sort independently. Those that are linked but located farther apart on the chromosome will undergo crossing over more frequently than those located very close together on a chromosome simply because there are more sites between the two genes at which crossing over can take place.

. Turner syndrome is the only known viable monosomy in humans.

. Fertilization restores the diploid number in a sexually reproducing organism. The two major events in the life cycle of sexually reproducing organism are meiosis and fertilization.