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Chapter 12 . Human Genetics. 12.1 The nucleus contains an information rich genome. DNA can store vast amount of information in a tiny space. In one chromosome there are 3 billion base pairs! . DNA packaging in a single cell.
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Chapter 12 Human Genetics
12.1 The nucleus contains an information rich genome • DNA can store vast amount of information in a tiny space. In one chromosome there are 3 billion base pairs!
DNA packaging in a single cell • If you could straighten out all the DNA molecules in a cell’s 46 chromosomes and place them end to end, the DNA would stretch for 2 meters or 6 and a half feet! • Genome: • Complete set of an organism’s genetic material. • Histones: • Small protein balls
The genome can fit into the nucleus • DNA wraps around histones • DNA is wrapped into a tight helical fiber • Coil further into thick “supercoil” • Loops and compacts DNA in each chromosome
Human genome project • In 1990, DNA technology enabled scientists to completely sequence the human genome. • Government funded the Human Genome Project and a rough draft was completed in 2000. • Knowing the sequence of nucleotides helps us understand which regions of DNA is used for coding. • This can tell us the function of that polypeptide.
Why is this important to us? • Compare our human genome to other organisms. • Health and identifying genes can help diagnose, treat, or prevent diseases. • Ex. Cancer, allergies, diabetes.
12.2 Accidents affecting chromosomes can cause disorders • Meiosis occurs repeatedly in a person’s lifetime as males produce sperm or females produce eggs. Usually this happens without error but an accident can cause serious problems.
What is trisomy 21? • Trisomy 21: • Condition when an individual has three number 21 chromosomes, resulting in down syndrome. • Error happens in meiosis 1.
In most cases, human embryo with an abnormal number of chromosomes results in a miscarriage. Risk of having a child with down’ s syndrome increases with the age of the mother: • Women under age 23—1 in 2,000 births • Women at age 30—1 in 1,300 births • Women at age 35—1 in 400 births • Women at age 40—1 in 90 births • Women at age 45—1 in 32 births • Women at age 50—1 in 8 births
Turner’s Syndrome • When female has an X and the other chromosome is missing. (X,0) • Rare, swollen hands and feet, dry eyes, infertile
Klinefelter’s Syndrome • Condition when males have an extra X chromosome. (XXY) • Less testosterone, weaker muscles, less facial hair
Non disjunction: • Errors in chromosome number are usually caused by homologous chromosomes or sister chromatids failing to separate during meiosis.
Damaged chromosomes • Change in chromosome structure may also cause disorders. If a chromosome breaks it can affect genes. • Types of changes… • Duplication: • Part of a chromosome is repeated.
Deletion: • Fragment of a chromosome is lost. Sever problems! • Inversion: • Reversing a fragment of the original strand. • Translocation: • Fragment of one chromosome attaches to a nonhomologous chromosome.
Jumping genes • Transposons “jumping genes”: • Genetic element that moves from one location to another in a genome. • Barbara McClintock discovered that genes in corn cells could move around in a chromosome, which changed the corns color.
12.3 Mendel’s principles apply to humans • Would you like to know the probability of your children having specific traits? • Eye color? Hair color? Deaf? • Would you like to know the probability of your children having a disability?
We can! Knowing each member of your family's genetics can help predict offspring! • Pedigree: • Family tree that records and traces the occurrence of a trait in a family.
pedigree • Square = male • Circle = female • Colored shapes = affected individuals • Horizontal lines = parents
Disorders inherited as recessive traits • Some allele combination can be fatal. • Most human genetic disorders are recessive. • Recessive disorders could be albinism, to Tay-Sachs disease. • Tay-Sachs leads to major nerve damage.
Disorders recessive traits • What genotype does the parents have to be if a disorder is recessive? • They have to be heterozygous! • Carrier: • Individual who has one copy of the allele for recessive disorder but does not show trait.
Disorders inherited as dominant traits • Small number of human disorders are inherited as dominant traits. • Born with extra fingers and toes or achondroplasia. • Genotype for these disorders are heterozygous. • Having two copies of this allele is fatal.
Sex linked disorders • Sex-linked alleles are located on one sex chromosome but not on the other. • Example being colorblindness
Predicting and treating genetic disorders • Who would like to know what the odds are of your children having specific traits? • When two people are considering having children and have both family histories they can meet with a genetic counselor. • Genetic counselor: • Trained to collect and analyze data about inheritance patterns and explain results and their significance.
12.4 Genetic changes contribute to cancer • Recall cancer is uncontrollable cell growth. • We have genes that help function our cell cycle. • Growth factors: • Produce proteins that initiate cell division. • Tumor-suppressor genes: • Produce proteins that stop cell division.
If several mutations happen in our growth genes it is called oncogene. • Oncogene: • Cancer causing gene. • Cells with oncogene become over stimulated and divide more often.
