C HAPTER 14- H UMAN H EREDITY BIG IDEA: How can we use genetics to study human inheritance?

14.1 H UMAN C HROMOSOMES The study of any genome begins w/ chromosomes- found in nucleus of eukaryotes o Karyotype shows the complete diploid set of chromosomes grouped in pairs, from largest  smallest in size

Human karyotype contains (46 individual) / 23 pairs of chromosomes

The last pair of chromosomes (pair 23) are the sex chromosomes, which determine if you’re male or female Female= XX (contributes X always) Male= XY (50:50 chance of contributing X or Y) Autosomes are the remaining 44 chromosomes in the human karyotype

Many human traits follow simple patterns of dominance The alleles for many human genes display codominant inheritance

Sex-linked genes are genes located on either the X or Y chromosomes. Sex-liked genes on: Y: directly father  son X: given to daughter or son, but recessive diseases MUCH more common in males!!! -Males don’t have another X chromosome to mask diseases located on X chromosome Ex: color blindness, hemophilia, Duchnne muscular dystrophy

Females undergo “X-inactivation” =, where random genes in either chromosome are switched off (so it’s on in the other X) -Causes spots in calico cats A pedigree shows the presence or absence of a trait according to the relationships between parents, siblings, and offspring

14.2 HUMAN G ENETIC D ISORDERS Changes in a gene’s DNA sequence can change proteins by altering their amino acid sequences, which can directly affect phenotype

Disorders caused by Individual genes: o Sickle cell anemia: defect in beta-globin (carries oxygen), causing red blood cells to clump together o Cystic fibrosis: deletion of 3 bases, causing protein to missfold, problems w/ breathing and digestion o Huntington’s disease: “CAG” repeat x40, causing mental and physical deterioration

Genetic Advantage: 1/12 people w/ African descendent carry sickle cell. In Africa the heterozygous form of sickle cell makes them resistant to malaria, yet no symptoms of disease

Errors in meiosis Nondisjunction: failure of chromosomes to separate If nondisjunction occurs gametes w/ an abnormal # of chromosomes may result Down syndrome: trisomy 21 (mental retardation) Turner syndrome: female w/ 1 X (sterile) Klinfelter: XXY male (usually sterile)

14.3 S TUDYING THE H UMAN G ENOME By using tools that cut, separate, and then replicate DNA base by base, scientists can now read the base sequences in DNA from any cell Most DNA is too large to be analyzed, so it must be cut into smaller pieces by restriction enzymes.

After DNA is cut, gel electrophoresis is used to separate and analyze differently sized fragments. -Mix of DNA is put in top, voltage is applied, DNA is (-) charged, smaller DNA fragments move quickly to (+) end. Reading DNA: Dye-labeled nucleotides and DNA polymerase are inserted to produce a color banded complementary strand

Human Genome Project: The Human Genome Project was a 13-year international effort w/ the goal of sequencing all 3 billion base pairs of human DNA and identifying all human genes Sequencing and identifying genes: “shotgun sequencing”=rapid method cutting DNA into fragments and determining the sequence of those fragments. Linked together by overlapping frag.s and id-ing promoters

About 99.9% of genes in humans are the same, but bases that don’t match = single nucleotide polymorphism ( SNPs) Human Genome Project was completed in 2003, copies of certain human and other organisms genomes are in databases on the internet. Development from project: bioinformatics, which combines molecular biology w/ information science. Putting together human genome would’ve been impossible w/out computer databases Genomics- study of whole genomes, including genes and functions

Human Genome Project pinpointed genes and assocaited particular sequences w/ numerous diseases and disorders. Also id- ed 3 million diff. locations where single- base DNA differences occur in humans. -May help us understand, and eventually develop cure for certain diseases.

One day your genetic info. may be public to health insurance companies, doctors, employers, etc. Right now “Genetic Information Nondiscrimination Act” (2008) prohibits discrimination based off of genetic tests.