Chapter 14 – The Human Genome Human Chromosome 3 Suzanna Macedo 2010 http://www.life.illinois.edu/ib/494/images/genome.jpg

Karyotype – a picture of all the human chromosomes

Sex chromosomes – determine gender males = XY females = XX

Autosomes – all other chromosome pairs (44) Huntington’s Disease is an autosomal-dominant disease.

A Family Tree To understand how traits are passed on from generation to generation, a pedigree, or a diagram that shows the relationships within a family, is used. In a pedigree, a circle represents a female, and a square represents a male. A filled-in circle or square shows that the individual has the trait being studied. The horizontal line that connects a circle and a square represents a marriage. The vertical line(s) and brackets below that line show the child(ren) of that couple.

1. This pedigree shows the inheritance of attached ear lobes 1. This pedigree shows the inheritance of attached ear lobes. Which parent has attached ear lobes? 2. How many children do the parents have? Which child has attached ear lobes? 3. Which child is married? Does this child’s spouse have attached ear lobes? Do any of this child’s children have attached ear lobes?

Dominance and Recessiveness in Humans Blood Groups – 3 alleles for blood type: IA, IB or i IA and IB are codominant i is recessive

Recessive Alleles a. some homozygous combinations of recessive alleles cause genetic diseases * PKU - phenylketonuria b. a person with one normal allele and one recessive is called a carrier

Dominant Alleles a. always expressed (only need one allele) i. achondroplasia

Codominant Alleles a. both alleles are expressed, can show as intermediate phenotype i. sickle cell anemia

Sex – Linked Genes – any gene on one or both of the sex chromosomes. Males have just one X chromosome, so any trait on the X chromosome is expressed (shows up), even if they are recessive.

Queen Victoria of England was a carrier of the gene for                                        Queen Victoria (1819-1901) Queen Victoria of England was a carrier of the gene for hemophilia.  She passed the harmful allele for this X-linked trait on to one of her four sons and at least two of her five daughters.  Her son Leopold had the disease and died at age 30, while her daughters were only carriers.  As a result of marrying into other European royal families, the princesses Alice and Beatrice spread hemophilia to Russia, Germany, and Spain.  By the early 20th century, ten of Victoria's descendents had hemophilia.  All of them were men, as expected.

caused by Autosomol Disorders Recessive alleles Dominant alleles Codominant alleles include include include Albinism Galactosemia Tay-Sachs disease Huntington’s disease Sickle cell disease Cystic fibrosis Phenylketonuria Achondroplasia Hypercholes- terolemia

Homologous chromosomes fail to separate Chromosomal Disorder Nondisjunction – failure of the chromosomes to properly divide into gametes. End result is missing or extra chromosomes. Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

Examples: Down Syndrome (Trisomy 21) or Klinefelter syndrome (XXY) in males

Detecting and Treating Genetic Disorders Sequencing Start signal Promoter Stop signal Gene

DNA Fingerprinting Restriction enzyme Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths. Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA varies from person to person. Here, one sample has 12 repeats between genes A and B, while the second sample has 9 repeats. The DNA fragments are separated according to size using gel electrophoresis. The fragments containing repeats are then labeled using radioactive probes. This produces a series of bands—the DNA fingerprint.

Gene Therapy Nucleus Bone marrow cell Normal hemoglobin gene Chromosomes Genetically engineered virus