All organisms: are composed of different proteins have DNA made up of the same 4 nucleotides. So… how can organisms be different if their genetic material is made of the same 4 nucleotides?????
By the way the nucleotides are sequenced in DNA Example: A-C-C-T-T-G vs. G-G-C-T-A-T. (Like the words STREAM and MASTER – both have same letters, BUT different arrangement and meaning) If one tiny mistake occurs in one pair-- > a particular protein will not be made
Organisms with very similar sequences are very closely related Example: the chimpanzee and gorilla
Long strands of DNA Each one contains many genes Homologous pairs 2 chromosomes that look similar & have the same genes Humans = 46 chromosomes (23 pairs) 22 homologous pairs 2 sex chromosomes (Male =XY, Female = XX)
A cell sample is taken & chromosomes are photographed Homologous pairs are matched up Normal Karyotype: 46 chromosomes (22 homologous, 2 sex chromosomes) Can detect chromosomal abnormalities in fetus by amniocentesis Missing, extra, or broken chromosomes
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.
Chromosome: made of many genes Gene: DNA sequence that codes for a trait Allele: alternate form of a gene Examples: eye color gene has blue, brown, green alleles