Genes and Chromosomes

Gene

• Segment of DNA whose sequence codes for a specific product– Examples: physical trait, RNA, enzymes etc.

• Genes are located on chromosomes

Alleles

• Alternate forms of a gene• Cause variations and diversity

Chromosomes

• Homologous chromosomes contain same genes but can have different alleles

• Humans have 44 autosomes and 2 sex chromosomes

• Female = XX; Male = XY• Which parent determines

the sex of the child?

Identifying and Studying Chromosomes

• Chromosome samples obtained (by amniocentesis for fetus)

• Chromosomes stained, photographed, cut out, matched up by size, shape, and banding patterns and arranged in order to form a karyotype

• Allows for determination of sex and chromosomal abnormalities

Karyotyping:

• Picture of an individual’s chromosome

• Can you see the extra chromosome?....... This one shows an extra chromosome #21 – called trisomy 21.

• A person with this karyotype has Down’s Syndrome.