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The Human GenomeThe Human GenomeChapter 14
Human HeredityHuman Heredity14-1
NOVA: Cracking the Code of NOVA: Cracking the Code of LifeLifeChapter 1: Instructions for
Making a Human Being
Human ChromosomesHuman Chromosomes
A karyotype is a picture of chromosomes from a cell arranged in homologous pairs.
Human ChromosomesHuman ChromosomesHumans have 46 chromosomes.
◦44 autosomes◦2 sex chromosomes
Normal female: 46 XX Normal male: 46 XY
Sperm: 23 X or 23 Y Egg: 23 X
Human ChromosomesHuman Chromosomes
Human ChromosomesHuman ChromosomesWhat determines the sex of a
child? The sperm……
Human TraitsHuman TraitsTo study the inheritance of
human traits genetic counselors use a pedigree chart.
From this, geneticists can infer genotypes of family members.
Human TraitsHuman TraitsDraw a pedigree chart.
Human TraitsHuman TraitsAssociating an observed human
trait with a gene is difficult. Many human traits are polygenic. The environment influences the
expression of a trait.
Human GenesHuman GenesHumans have 4 blood types
caused by 3 alleles.◦A & B – codominant◦O – recessive
Types: A, B, AB, O
Blood types must be matched for a safe transfusion.
Draw blood type chart…………………..
Human GenesHuman GenesRh factors represent another
group of antigens found on some red blood cells.◦Rh+ = present.◦Rh- = absent.
Human GenesHuman GenesMost genetic disorders are
caused by recessive alleles. To have the disorder an individual must
inherit two recessive alleles. Ex: PKU, Tay-Sachs, Cystic Fibrosis, Albinism
Chromosome # 7
CFTR gene
The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein.
Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane.
The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.
Figure 14-8 The Cause of Cystic Fibrosis
Cystic Fibrosis
Human GenesHuman GenesA few are caused by dominant
alleles. Only one allele needs to be inherited to
be expressed. Ex: Huntington’s disease, Dwarfism
Human GenesHuman GenesSickle cell anemia is caused by a
codominant allele. One normal allele and one abnormal
allele are inherited for making the protein hemoglobin. The sickle cell allele is inherited among many
African Americans. Carrying this allele produces resistance to the
Malaria parasite.
Sickle Cell Anemia
NOVA: Cracking the Code of NOVA: Cracking the Code of LifeLifeChapter 2: Getting the Letters
Out
Human ChromosomesHuman Chromosomes14-2
Human Genes and Human Genes and ChromosomesChromosomes
Only 2% of your DNA functions as genes.
Human Genes and Human Genes and ChromosomesChromosomes
Genes located on the same chromosome are linked.◦They tend to be inherited together.◦They can be separated by crossing-
over during meiosis.
Crossing-OverCrossing-Over
Sex-Linked GenesSex-Linked Genes
Sex-linked genes are located on the sex chromosomes.
More genes are on the X than the Y.
Sex-Linked GenesSex-Linked GenesGenes on the X chromosome are always expressed in males even if recessive.◦Males get sex-linked disorders more
often than females. Colorblindness, hemophilia, muscular
dystrophy
X-Chromosome X-Chromosome InactivationInactivationIn females, one X chromosome is
randomly switched off.◦Calico cats are always female.
X-Chromosome X-Chromosome InactivationInactivationThe switched off X chromosome
becomes a dense region in the nucleus known as a Barr body.
Barr bodies aren’t found in males.
Olympics and Barr BodiesOlympics and Barr BodiesSex testing was introduced in
competitive sports in the mid-1960s, amid rumor that some competitors in women's events were not truly female - especially two Soviet sisters who won gold medals at the 1960 and 1964 Olympics, and who abruptly retired when gender verification testing began.
Olympics and Barr BodiesOlympics and Barr BodiesThe first tests, at the European
Championships in 1966 and the Pan-American Games in 1967, required female competitors to undress before a panel of doctors. Other methods used during this period included manual examination or close-up scrutiny of the athlete's genital region.
Olympics and Barr BodiesOlympics and Barr BodiesWhen athletes complained that these
tests were degrading, the IOC at the Mexico City Olympics in 1968 introduced genetic testing in the form of a sex chromatin (Barr body) analysis of cells from a buccal smear. The procedure was further modified at the Barcelona games, using the polymerase chain reaction to amplify the DNA extracted from a specimen to allow detection of a Y chromosome gene, SRY, that codes for male determination.
Journal of the American Medical Association, July 17, 1996, vol. 276, no. 3, pp. 177-178
Chromosomal DisordersChromosomal DisordersCaused by nondisjunction
during meiosis.◦Homologous chromosomes fail to
separate resulting in sex cells with one too many or one too few chromosomes.
Homologous chromosomes fail to separate
Meiosis I:Nondisjunction
Meiosis II
Section 14-2
Nondisjunction
Non disjunction
Chromosomal DisordersChromosomal DisordersDown’s syndrome = 47,XX or
47,XYTurner’s syndrome = 45,XKlinefelter’s syndrome = 47,XXY
Down’s SyndromeDown’s Syndrome
Turner’s SyndromeTurner’s Syndrome
Kleinefelter’s SyndromeKleinefelter’s Syndrome
Human Molecular Human Molecular GeneticsGenetics14-3
Human DNA AnalysisHuman DNA AnalysisEven though the human genome is
over 6 billion bases long, genetic tests exist for detecting the presence of defective recessive genes.
Prospective parents can now be tested to determine if they carry recessive alleles for hundreds of disorders.
Is this a good idea?
DNA FingerprintingDNA FingerprintingAll humans share the same
genes.The 98% of DNA that is not
encoded in genes is what makes us different from each other.
DNA fingerprinting makes use of this difference to identify individuals.
Restriction enzyme
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.
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.
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.
DNA Fingerprinting4-18 DNA Fingerprinting
The Human Genome The Human Genome ProjectProjectIn 2000, the entire human
genome was sequenced.◦Dr. Francis Collins, Dr. Eric Lander
and Dr. Craig Venter (NOVA – Cracking the Code of Life)
Advances in technology allowed this to happen in several years rather than the predicted 20.
Promoter Start signal
Gene Stop signal
Gene Sequence
Rapid Sequencing
Gene TherapyGene TherapyThe process of changing a gene
that causes a disorder.◦An absent or defective gene is
replaced by a normal functioning gene.
Viruses are often used to deliver functional genes to affected cells.
Normal hemoglobin gene
Bone marrow
cellChromosomes
Genetically engineered virus
Nucleus
Bone marrow
Gene Therapy
Ethical Issues…Ethical Issues…Genetic curesDesigner babiesMedical costsResearch costs
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