The Human Genome Chapter 14
14-1 Human Chromosomes Are pictured in karyotypes 46 human chromosomes pictures taken during metaphase Cut out photos and place in correct order 46 human chromosomes 2 sex chromosomes Females are XX Males are XY 44 autosomes
Karyotype
Human gametes All eggs have one X chromosome ½ of all sperm carry an X ½ of all sperm carry a Y *males determine gender of offspring*
Human traits Inherited by the laws of Mendelian genetics Most traits are NOT simple dominant/recessive inheritance Many traits influenced by environment *environmental effects are NOT inherited; only genes are inherited*
Human traits Can be traced through a family using a pedigree Individuals exhibiting the trait will be shaded Individuals without the trait are blank Males are square, females are round Mates are connected by horizontal line
Pedigree – autosomal dominant
Pedigree – autosomal recessive
Pedigree – sex (X) linked
Human genes for blood Rh factor is a single gene with 2 alleles; one + and one – + is dominant; - is recessive Rh stands for rhesus monkey; the animal in which it was discovered
Human recessive traits PKU (phenylketonuria)-inability to metabolize the amino acid phenylalanine Results in buildup in nervous system causing retardation Newborns are tested Controlled by diet
Human recessive traits Tay-sachs disease-nervous system break-down causing death before age 5 Found in Jewish families of European ancestry No cure Parents can be tested to determine risk
Recessive traits Cystic fibrosis (CF)-results in serious digestive problems and excess mucus in the lungs Found in people with ancestors from northern Europe
Human dominant traits Dwarfism (achondroplasia) Huntington’s disease-progressive loss of muscle control and mental function until death occurs No symptoms before age 30 No cure
Complex forms of inheritance Multiple alleles Codominance Incomplete dominance Polygenic traits
Human blood groups (multiple alleles) 3 alleles govern human blood types IA, IB, and i produce antigens on the surface of the red blood cells IAIA and IAi have A blood IBIB and IBi have B blood IAIB have AB blood (codominant) ii have O blood (recessive)
Codominance Black and white feather colors in chickens are equally dominant.
Codominance
14-2 Human chromosomes Linked genes are close together on the chromosomes; usually inherited together Linked genes can be separated during crossing over during meiosis
Incomplete dominance Two alleles governing a trait, but one does NOT completely dominate the other Produces a blending pattern in the heterozygote
Incomplete dominance
Incomplete dominance
Polygenic traits Traits determined by a combination of genes At least 3 genes are involved
Polygenic traits
Polygenic traits: epistasis Multiple genes involved with fur color in mice and other animals Some genes determine color Some genes determine the shade of the color Some genes determine spotting
Polygenic traits: epistasis
Sex-linked genes Genes located on the sex chromosomes Many on X chromosome Few on Y chromosome (Y is smaller)
Sex-linked traits Colorblindness Hemophilia Duchenne Muscular Dystrophy
Colorblindness Three genes on X chromosome Most common is red-green colorblindness 1 out of 10 males are affected 1 out of 100 females are affected *occurs in males more often because of only 1 X chromosome*
Hemophilia Two genes on X chromosome Affected individuals lack a blood-clotting protein 1 in 10,000 males are affected Can be treated with injections of normal blood-clotting agents
Duchenne Muscular Dystrophy Results in weakening and loss of skeletal muscle 1 in 3000 males affected in U.S. Caused by defective protein
X-chromosome Inactivation Males have 1 X chromosome Females have 2 X chromosomes (one is non-functional) Non-functional X becomes a Barr Body in the nucleus X chromosomes in females are randomly switched off; in males the X is always active
Chromosomal disorders Nondisjunction – chromosomes don’t separate properly in meiosis and some cells get abnormal numbers of chromosomes Down’s syndrome Turner’s syndrome Klinefelter’s syndrome
Down’s Syndrome Autosomal disorder of chrom. 21 (trisomy) 1 in 800 babies in U.S. Mild to severe learning disabilities Increased health problems Higher frequency of birth defects
Turner’s syndrome Females with only 1 X chromosome (45 chromosomes) Sterile Sex organs do not develop
Klinefelter’s syndrome Males with an extra X chromosome (47 chromosomes) sterile
14-3 Human molecular genetics DNA analysis Used to determine possibility of passing genetic disorders to children Use labeled DNA sequences to base pair to problematic complementary base sequences Can pinpoint exact genetic basis of some disorders
DNA fingerprinting Used to identify individuals Analyzes sections of DNA with little or no known function but vary widely between individuals
Human genome project Complete in 2000 Have determined entire DNA base sequences Using those sequences to determine genes and their locations
Gene therapy Replacing absent or faulty gene with the correct working gene Body can make correct proteins Still high-risk and experimental
Ethics in human genetics Curing diseases is essential Should we alter the outcomes of reproduction by altering natural genetics? All citizens are responsible for the WISE use of the information gained in research.