The Secret of Life Walter Sutton 1902 Chromosome theory: Genes are located on chromosomes, each gene occupies a specific place (locus) on a chromosome. A gene may exist in several forms (alleles) but each chromosome has just one allele for each gene. Mendel says traits controlled by genes, said they come in contrasting forms - differences in genetic sequence difference. Differences Genes: Mendel - Genes come in contrasting forms Theory - Simply minor changes in nitrogenous bases Dominance & Recessiveness Mendel: Some alleles are or are not expressed. Theory: Dominant Allele codes for function of protein, recessive doesn’t. Segregation Mendel: All plants have two alleles for every trait. Theory: Plants had two chromosomes, which come in pairs. Independent Assortment: Mendel: Segregation of one allele has nothing to do with segregation for other genes. Theory: Separation of chromosomes and chromatids is independent of others in meiosis. Genes on the same chromosome are said to be linked Linked genes are inherited together. They do not undergo independent assortment. Mendel was lucky he had chosen traits from different chromosomes. Thomas Hunt Morgan Fruit flies are ideal for genetic studies. He found that the gray body is dominant to black. Normal wings are dominant to small. Morgan’s Experiment: Crossed purebred gray normal wing flies (GGWW) with purebred black small wing flies (ggww) In F1, all are gray with normal wings (GgWw) He does not go to F2, but he takes F1 and does a test cross. He crossed something with a homozygous recessive. Results: 25% of each, 41.5 GW, 41.5 gw, 8.5 gW, 8.5 Gw X^2 is 43.56 at 3 df Conclusion: The two genes are linked/connected. They do not assort independently. They are on the same chromosome. Linkage Groups Groups of genes that tend to be inherited together. Fruit flies have 4 linkage groups. Fruit flies have 4 pairs of chromosomes. Corn has 10 linkage groups. Corn has 10 pairs of chromosomes. What about the 17% that did assort independently? Crossing over - most have blonde hair blue eyes, but crossing over can create blonde hair brown eyes. Produces individuals with rearranged linkage groups - “Recombinants” Frequency of crossing-over can be used to “map” genes. Sex Determination Autosomes - homologous pairs of chromosomes. Sex chromosomes Not necessarily homologous - X or Y Determines the sex of an individual XX = female XY = male Cannot live without X Sex-linkage Genes on the sex chromosome are “sex-linked” Usually on the X chromosome. Recessive X-linked traits are more often expressed in males. Morgan’s Experiment The gene for eye color is located on the X chromosome. Red eye color is dominant to white. Crossed white eyed male (XrY) with homozygous red eye female (XrXr) Conclusion: All F1 had red eyes - XRXr or XRY Gene Interactions Incomplete Dominance Active allele does not completely compensate for an inactive allele Carnations Red x White → Pink Pink X Pink → 1 Red, 2 Pinks, 1 White Codominance Both alleles are expressed. Cattle White X Red → Roan Roan X Roan → 1 Red, 2 Roan, 1 White Polygenic Inheritance Trait is controlled by many genes Tends to follow a gradient, not either/or Ex

What was the primary purpose of the Silk Road?

To establish a vast network of trade routes connecting the East to the West.

During which dynasty was the Silk Road established?

The Han Dynasty of China.

What was the most valuable commodity traded on the Silk Road?

Silk.

Name three other goods traded along the Silk Road.

Spices, tea, porcelain, and precious metals.

What period did the Han Dynasty span?

206 BCE – 220 CE.

What types of exchanges did the Silk Road facilitate?

Cultural, economic, and political exchanges between diverse civilizations.

What is the Silk Road?

A vast network of trade routes established during the Han Dynasty of China that connected the East to the West.

Which civilization primarily developed the Silk Road?

The Han Dynasty in China.