Biology TodayThird Edition

Chapter 3

Human Genetics

Copyright © 2004 by Garland Science

Eli Minkoff • Pam Baker

What Do Genes Do?

• Direct the production of a protein– Two steps:

1. transcription of DNA to RNA2. translation of RNA to protein• together, are called gene expression

• Just because you have a gene for a trait doesn’t mean it will be expressed (show up)

RNA: the other nucleic acid

• Ribonucleic Acid

• How is it similar to DNA?– Made of nucleotides

• A sugar• A phosphate• Nitrogenous bases

RNA: the other nucleic acid

• Ribonucleic Acid

• How is it different from DNA?– Made of nucleotides

• A sugar: ribose instead of deoxyribose

• A phosphate: the same PO4

• Nitrogenous bases: Adenine, Cytosine, Guanine, and URACIL (no Thymine)

– Single stranded

RNA: the other nucleic acid

• Three types….three different jobs– mRNA = messenger RNA– tRNA = transfer RNA– rRNA = ribosomal RNA

Figure 3.2

Figure 3.2a

Figure 3.2b

Figure 3.3 (1)

Figure 3.3 (2)

Figure 3.3 (3)

Figure 3.3 (4)

Figure 3.4

Figure 3.5

Figure 3.5 (1)

Figure 3.5 (2)

Figure 3.5 (3)

Figure 3.6

Figure 3.6a

Figure 3.6b

Figure 3.7a

Figure 3.7b

Figure 3.7c

Identifying genetic causes for traits/diseases

• Is the trait/disease environmental or genetic?– Lifestyle-can still be influenced by family– Studies of twins

• Pp. 72 to 75-discuss how a particular trait/disease might be linked to a particular gene; not testworthy

Figure 3.8

Figure 3.9a

Figure 3.9b

Linkages found 1980-1990

• Huntington’s-chromosome 4

• Cystic fibrosis-chromosome 7

• Alzheimerj’s disease-chromosome 21

• One colon cancer-chromosome 2

• Two forms of manic depression-chromosome 11 and X

Figure 3.10

Only a few follow simple Mendelian genetic processes:

• Alkaptonuria

• Phenylketonuria

• Duchenne’s muscular dystrophy

• Cystic fibrosis-chromosome 7

• Huntington’s disease/chorea-chromosome 4

Some genes increase risk or susceptibility

• Alcoholism

• Obesity

Some traits are governed by several to many genes

• Height

• Skin color

How can this info be used?

• Gather/share info through genetic testing and counseling

• Change individual genotype (gene therapy)

• Change gene pool at populational level

• Change balance between environmental and genetic factors

Figure 3.11a

Figure 3.11b

Figure 3.12Polymerase Chain Reaction (PCR)-Nobel-worthy discovery

Figure 3.13

Figure 3.13a

Figure 3.13b