Chapter 14 The Human Heredity

2. Fertilized egg = zygote 14-1 Human Chromosomes I. Genome = fell set of genetic info that an organism carries in its DNA II. Karyotype Picture of complete diploid set of chromosomes arranged in pairs from largest to smallest III. Human Chromosomes A. 46 individual or 23 pairs 23 from egg & 23 from sperm 2. Fertilized egg = zygote Page 392

- Eggs only contain X’s (23,X) - Female = XX B. Sex chromosomes = Pair 23 - Male = XY 1. Female:Male Ratio = 50:50 Page 393 - Eggs only contain X’s (23,X) - Sperm contain an X or a Y (23,X or 23,Y) 2. X Chromosome is larger more than 1200 genes 3. Y Chromosome is smaller contains about 140 genes Page 393

C. Autosomes = Pairs 1-22 D. Total number of chromosomes are written as: 46,XX or 46, XY III. Transmission of Human Traits A. Simple Dominance 1. Dominant Traits = ONE dominant allele = disorder (HH or Hh) Examples: Huntington’s, Dwarfism

2. Recessive Traits  TWO recessive alleles = disorder (aa) *Carriers = do not have disorder but carry the allele for it (Aa) Examples: Phenylketonuria (PKU), Albinism, Cystic Fibrosis, Tay-Sachs

B. Codominant and Multiple Alleles 1. Blood Groups - Known as ABO blood groups - Three Alleles (Multiple Allele): IA, IB, i - IA and IB are Codominant - Four Blood Types: A, B, AB, and O - Produce antigens on the surface of Red Blood Cells (RBC’s) - Allele Combinations: (GENOTYPES) A IAIA, IAi B IBIB, IBi (Universal Recipient) AB IAIB O ii (Universal Donor)

* Rh blood group: - determined by a single gene with two alleles - Named after the Rhesus Monkey - Positive allele (Rh+) is dominant (Rh+ Rh+ or Rh+ Rh-) - Negative allele (Rh-) alleles are recessive (Rh- Rh-) - Rh- can give to Rh+ but Rh+ cannot give to Rh-

Page 350 C. Sex-Linked Traits 1. Located on sex chromosomes (Pair 23) 2. More than 100 sex-linked disorders on X chromosome WHY? because X is larger than Y 3. Genetic disorders: colorblindness, hemophilia, Duchenne Muscular Dystrophy Page 350

4. Recessive sex-linked traits more common in males than females because: a. To be expressed in females, there must be two recessive alleles, one on each of the two X chromosomes. XdXd b. Males have just one X chromosome. Thus, all recessive X-linked alleles are expressed in males. XdY

IV. Chromosome Inactivation A. One X is randomly switched off and forms a Barr Body (dense region in the nucleus ) B. Barr bodies are generally not found in males because their single X chromosome is still active. C. Responsible for different color spots in female cats (Page 352) 1. In parts of the female cat one X is switched off resulting in black spots and in other parts of the cat the other X is switched off resulting in orange spots; therefore, orange and black spots 2. Good way to tell male from female: males only have one color spots

V. Pedigree A. Chart showing the relationship of traits within a family B. Uses Symbols = female Shaded in = expresses the trait = male Not shaded in = does not express the trait Page 397

14-2 Human Genetic Disorders VI. Molecule to Phenotype A. Changes in gene’s DNA can change proteins by altering their amino acid sequences, which may affect one’s phenotype B. Disorders caused by individual genes Sickle Cell Anemia -defective allele for beta-globin that makes hemoglobin less soluble causing hemoglobin to stick together when O2 levels decrease -Advantage  If heterozygous (RS), then produce both round & sickle shaped RBC’s = resistant to malaria

2. Cystic Fibrosis -Loss of 3 DNA bases in a gene for the protein that transports Cl- ions so salt balance is upset -Cause a build up of thick mucous in lungs & digestive tract -Advantage  If heterozygous for CF, then do not have CF & the protein produced by the CF allele blocks the entry of the bacterium that causesTyphoid

VII. Chromosomal Disorders A. The most common error in meiosis occurs when homologous chromosomes fail to separate = NONDISJUNCTION B. If nondisjunction occurs, abnormal numbers of chromosomes enter the gametes, and a disorder may result. Nondisjunction Page 401

C. If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with three copies of a chromosome. 1. Example: Down Syndrome a. Also called Trisomy 21 b. Has three #21 chromosomes c. produces mild to severe mental disability

D. Sex Chromosome Disorders 1. Disorders that occur on the sex chromosomes a. In females, nondisjunction can lead to Turner’s syndrome. - usually inherit only one X chromosome (karyotype 45,X). - Usually are sterile b. In males, nondisjunction causes Klinefelter’s syndrome (karyotype 47,XXY). - The extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing.

14-3 Studying the Human Genome VIII. Manipulating DNA A. Cutting DNA 1. DNA too long to analyze so must be cut into smaller segments 2. Restriction enzymes – highly specific & cut DNA into smaller pieces at a specific nucleotide sequence Recognition sequences Page 404

Gel Electrophoresis B. Separating DNA: 1. Gel electrophoresis – used to separate and analyze the different sized fragments Page 404 Gel Electrophoresis

C. Reading sequence through gel http://www.dnalc.org/resources/3d/29-sanger-sequencing.html

IX. The Human Genome Project A. 13 year project to sequence all human DNA and identify all human genes B. Has pinpointed genes & associated certain sequences with numerous diseases & disorders.