GENETICS

4. The Chromosome theory of heredity

Seven pairs of identical twins. Although the twins were given no instructions regarding how to pose for the photograph, note the similar posture, hand placement, and facial expressions of bother members of each pair of twins.

1. DNA replication is a precursor to asexual and sexual cell division.

2. DNA replicates by unwinding and using the exposed strands as alignment guides for new synthesis; hence, each daughter molecule is half old and half new. = "semiconservative replication"





3. DNA polymrase adds nucleotides at 3' growing.



- replication starts at the origin site:


- proofreading by the DNA polymerase


- DNA polymerase requires 'PRIMER':




- DNA topoisomerases (I & II) prevent DNA from becoming tangled ahead of the replication fork:
DNA topoisomerase II: cuts both strand of DNA and rejoin the ends to produce one negative superturn.


4. Telomerase: replication of linear chromosome termini


- DNA polymerase can't synthesize DNA at the terminus of the lagging strand.


5. Phenotypic ratios in progeny are determined by the movements of chromosome pairs at meiosis.

- Mendel's laws of segregation and independent assortment.


- chi square test : test of fitness of a hypothesis
The distribution of chi-square values shows how often chi-square will exceed a particular value solely by chance. If the hypothesis is correct, the chi-square statistic will exceed this critical value only 5 percent of time.




6. Chromosome theory: 1910, Thomas Morgan

genes are situated on chromosomes


- Genes for eye color are linked to the X chromosome:







7. sex chromosome-linked genes

Hemophilia

male determining genes

male determining gene: SRY

male determining genes

8. X-inactivation





9. Organelle genes (mitochondria, chloroplast) are inherited maternally.