Resumen

1900’s Thomas Hunt Morgan started studying Drosophila Melanogaster. (fruit fly)
He discovered fruit flies have 4 pairs of chromosomes:
3 pairs – autosomes
1 pair – sexchromosomes (x/y)

Sex Linked Genes: traits carried by sex chromosomes
X-Linked Traits: carried in the x chromosome
Males only have ONE X-chromosome, for females to express the traitboth xx must carry the trait.

Mutations: mistake or change in the normal DNA sequence.
Types of Mutations:
1. Germ Cell Mutation: occur in gametes & affects offspring, NOTindividual
2. Somatic Cell Mutation: occur in body cells (somatic cells) & affect individual, NOT offspring.
EX- skin cells, blood cells, muscle cells.

Chromosome Mutations:affect entire chromosome
1. Deletion: loss of a piece of chromosome
2. Invertion: piece of chromosome breaks off and attaches in the opp. Direction
3. Translocation: piece ofchromosome breaks off and attaches to another homonolongous pair.
4. Non-disjunction: homonolongous pair of chromosome fail to separate during Anaphase of Meiosis, as a result one cellhas an additional chromosome and the other has a missing one.
** Most Popular: Down Syndrome. 1 Monosomy, 1 Trisomy

Gene Mutations: affect nucleotide only
1. Deletion: onenucleotide is missing from the DNA sequence.
2. Insertion: one nucleotide is inserted in the DNA sequence.
3. Substitution: one nucleotide is replaced by the wrong one.

• Lesson2
Pedigree: diagram that shows how a trait is inherited over generations.

Patterns of Inheritance for Several Human Traits:
SIMPLE ALLELE (Dominant)
1. Huntington Disease:affects during 30’s-40’s. Causes: loss of muscle control & even death
2. Achondroplasia: dwarfism
3. Cataracts: tissue growth in eye
4. Polydactyly: extra fingers and toes