Chapter 14 The Human Genome 14 1 Human

Chapter 14: The Human Genome

14 -1 Human Heredity n How many chromosomes does an adult human cell contain? n Autosomes – any chromosomes that are not sex chromosomes. n Sex Chromosomes – X and Y – determine sex of individual.

14 -1 Human Heredity n Notations used to describe individuals n Normal Individuals represented as n Males 46, XY n Females 46, XX

Human Cell 22 pairs of homologous chromosomes – called autosomes n 1 pair of sex chromosomes – 23 rd pair n Gametes What sex chromosomes are carried by egg and sperm cells? – N chromosomes – egg only carries an X – sperm carries an X or Y

ID-ing Chromosomes n Chromosomes are identified by n 1. SIZE n 2. CENTROMERE LOCATION n 3. BANDING PATTERNS

n a picture of chromosomes n homologous chromosomes paired together. n What are they? Numbered 1 -22 in order of size n What is the 23 rd pair? n n What does the size of the chromosome indicate? Karyotype

Which of the karyotypes represent Normal Individuals?

CONCEPT CHECK n 1. Apr 28 What is an autosome? n 2. Explain the significance of the size of different chromosomes. n 3. Interpret the following notation. 45, XX

CONCEPT CHECK 1. Any one of the numbered chromosomes (1 -44) that are not sex chromosomes n 2. Chromosome size determines the numbers of genes within a chromosome. Larger chromosomes contain more genes and are most necessary for normal growth and development. n 3. 45, XX identifies the individual as a female having 45 n chromosomes. Missing an autosome Presence of a genetic disorder

Question of the DAY n Which statement is not true regarding homologous chromosomes? n A. Specific genes are found at the same loci n B. They have the same size n C. Genes will express identical traits n D. They are joined at the same centromere locations

Factors Affecting Phenotypes n Traits n Do are determined by our genes. other factors have an impact on our characteristics?

Genes and the Environment n All of our inherited characteristics are governed by our genes. – Many traits are polygenic. n Other factors influence our phenotypes. – Nutrition and Exercise n Average height has increased 10 cm in the last 200 years 3. 93 inches – U. S. and Europe

Alleles Figure 14 -6 n Dominant – Some genetic disorders are expressed through these alleles – Only requires one allele n Recessive – Most genetic disorders are transmitted through these alleles n Codominant – Sickle Cell Disease

Pedigree Analysis n rely on family histories and medical records to study humans n pedigree: diagram that follows the inheritance of a single trait through several generations

Pedigrees record and trace the occurrences of traits within a family.

British Royal Family

The Story of Anastasia

Concept Check May 3 n Explain why males cannot be carriers for sex-linked disorders. n Support your explanation with evidence.

14 -2: Sex-linked Inheritance sex determination – XX female – XY male n sex-linked genes: genes located on the sex chromosomes – almost always on the X chromosome – Y chromosome contains a few genes for male development n

Sex-linked Inheritance males inherit these disorder much more often gets passed from father to daughters, then daughters to their sons n examples are hemophilia, colorblindness, Duchenne’s muscular dystrophy n n

Human Genetic Disorders n autosomal genetic disorders – albinism § recessive allele on chromosome 11 § can’t produce melanin – cystic fibrosis § recessive allele on chromosome 7 § heavy mucus clogs lungs and breathing passageways

n tay sachs – recessive allele on chromosome 15 – suffer from breakdown of the nervous system n sickle cell disease – recessive allele on chromosome 11 – produces an alternate form of hemoglobin that causes the red blood cells to become a sickle shape – one DNA base changed – Glutamic acid for Valine

Sickle Cell Disease n Allele very prominent in African Americans – Carried by many individuals n Connected to malaria – a parasitic disease that affects red blood cells n Individuals who are heterozygous for sickle cell are resistant to malaria n When body destroys sickled cells, parasite causing malaria also destroyed. – Low oxygen = sickle shape = cells clump together

n PKU: phenylketonuria – recessive allele on chromosome 12 – causes mental retardation n Huntington’s disease – dominant allele on chromosome 4 – lose muscle control and nervous system breaks down

Chromosome Number Disorders n occurs by nondisjunction: when abnormal number of chromosomes are produced in the sex cells due to them not separating correctly

Turner’s Syndrome either a sperm or an egg is produced without a sex chromosome n XO genotype – O means sex chromosome is missing n sex organs are not fully developed n can not have children n only in females n

Klinefelter Syndrome n have an extra X chromosome – XXY genotype causes mental retardation n can not reproduce n only in males n

Down Syndrome n trisomy 21 – means 3 copies of chromosome #21 n causes heart and circulatory problems, mental retardation, and a weakened immune system

Other Causes of Disorders deletions: can occur from pieces of chromosomes breaking off and getting lost in meiosis n translocation: when pieces of chromosomes break off and become reattached to another n

Prenatal Diagnosis want to detect if unborn child will have a disorder n two ways – amniocentesis: withdraw fluid from sac around fetus – chorionic villus sampling: tissue surrounding fetus is removed and examined n

Special Topics in Human Genetics n n barr body: dense region in the nucleus of most cells in human females condensed turned-off X chromosome not found in males because their one X chromosome is active happens in some tissues and in some cells

14 -3 Testing for Alleles n DNA probes – specific DNA base sequences that detect the complementary base sequences found in disease causing alleles n Cystic Fibrosis and Tay Sachs are examples that use DNA probes.

DNA Fingerprinting n Repeats are specific sequences of DNA unique to every individual – Do not code for proteins n Repeats cut with restriction enzymes n Gel electrophoresis separates fragments n Labeled with radioactive probes n Forensics, detection of inherited diseases, and paternity cases

Human Genome Project n Sequencing of all of the genes within an organism. n Human genome sequencing completed in 2003. n Included sequencing of other organisms including E. coli, multiple strains of yeast, the fruit fly, the mosquito, the honey bee, the cow, the dog, the horse, and the rat.