15. The Chromosomal Basis of Inheritance

The Connection Between Mendel and Chormosomes

• In the early 1990 scientist showed that Mendels laws were proven by meiosis or during the sexual life cycles.

Thomas Hunt Morgan's Discovery

• Morgan discovered that specific genes had specific chromosomes
• Discovery proved that Mendel was right about the location of heritable factors
• Found that the X-link in the fly Drosophila melanogaster carries the gene for eye color
• Genes located on a sex chromosomes are called sex linked genes.
• Phenotypes most common in a population are called the Wild type.

Linked Genes

• Linked Genes are genes that are on the same chromosome and are inherited together.
• They usually do not mix themselves independently.

Genetic Recombination

• The production of offspirng with combinations of their parents genes is Genetic Recombination.
• Recombinant offspring show new combinations of their parents' genes.

Recombinant Data Map a Chromosomes Genetic Loci

• You can map genes by looking at there crossover data. The further the genes the are on a chromosome the more likely the will be seperated.
• A Linkage Map is a map based on recombinant frequency's.
• Cytological Maps are maps of genes based on chromosomal features.

Sex Chromosomes

• Our sex is most noticable phenotypic feature.
• In males the sex chromosoms are XY in females XX.
• The sex of an offspring depends on the chromosome that the sperm is carring during conception.

Sex Linked Genes are Unique

• Certain genes carry certain traits. What determines which offspring will inherit the trait is determined by type of chromosome carries the trait.
• Barr Body is the inactive X chromosome in a females' cell. When an organism has more than two complete sets of chromosomes it's called Polypoidy.

Error and Exceptions in Inheritance

The additon or deletion of a chromosome can cause genetic disorders. Some organisms' phenotypes depend on whether they got thier gene from their mother or father.