Extending Mendelian Genetics Chapter 7 Mr. Scott

Human Heredity Human body 46 chromosomes Haploid sperm cell with 23 chromosomes Haploid egg cell with 23 chromosomes They form a diploid zygote or fertilized egg cell with 46 chromosomes

Human Heredity Sex chromosomes 2 of the 46 chromosomes Determine the sex of that person Females have X and X or XX chromosomes Males have X and Y or XY chromosomes

Human Heredity Autosomes (Autosomal Chromosomes) The other 44 chromosomes found in all body cells These are the chromosomes separate from the sex cells Typically numbered on a karyotype

Human Heredity  Human traits Pedigree chart – Shows the relationship within a family Shows how traits may be passed through generations

Human Heredity  Human genes Blood group genes Rh blood groups Positive and negative Rh+ is dominant ABO blood groups IA, I B, and i IA and I B are codominant

Human Heredity Recessive alleles Genetic disorders usually are not discovered until seen in the environment Dominant alleles Anyone carrying an allele will have the disorder Epistasis – one of the polygenic genes turns all the others off

Human Heredity  From gene to molecule Cystic fibrosis Common in people from northern Europe Serious digestive and breathing problems Caused by the deletion of just one amino acid

Human Heredity Sickle cell disease Blood cells doughnut or comma shaped Heterozygous people don’t contract malaria Humans with all sickle celled blood can die Why do so many African Americans have sickle celled blood?

Human Chromosomes  Human genes and chromosomes One cell has 6 billion base pairs or A,C,T,& G 46 Chromosomes are found in every diploid human cell

Human Chromosomes Only 2% of all DNA is used for genes or transcribed into RNA Average genes are 3,000 base pairs Largest gene is 2 million base pairs

Human Chromosomes Chromosomes 21 and 22 are the smallest 22 has 545 genes (43 million base pairs) 21 has 225 genes (21 million base pairs) Lou Gehrig’s Disease or Amyotrophic Lateral Sclerosis(ALS)

Human Chromosomes

 Sex-linked genes – genes located on the sex chromosomes Colorblindness Red-green colorblindness 1 in 10 males 1 in 100 females Why do more males have colorblindness?

Human Chromosomes Hemophilia Blood does not clot properly Is determined by two genes on the X-chromosome 1 in 10,000 males Ryan White

Human Chromosomes Duchenne Muscular Dystrophy Progressive weakening and loss of skeletal muscle 1 in 3,000 males Caused by a defective gene that codes for a protein in muscles

Human Chromosomes  X-chromosome inactivation Barr body – dense area in a nucleus where the inactivated X chromosome is located Each cell controls which X chromosome is turned off Calico cat

Human Chromosomes  Chromosomal Disorders Nondisjunction – error in which homologous chromosomes fail to separate

Human Chromosomes Down syndrome Caused by trisomy or three copies of chromosome 21(Trisomy 21) 1 in 800 babies This is a nondisjunction condition

Human Chromosomes  Sex chromosome disorders Turner’s syndrome Females (45,X) Sterile No sex organs Klinefelter’s syndrome Males (47, XXY) Sterile

Linkage and Gene Maps  Gene linkage Chromosomes assort independently, not individual genes

Linkage and Gene Maps  Gene linkage was explained through fruit flies. Morgan found that linked traits are on the same chromosome. Morgan found that linked traits are on the same chromosome. Chromosomes, not genes, assort independently during meiosis. Chromosomes, not genes, assort independently during meiosis.

Linkage and Gene Maps  Gene maps Shows the exact location of each known gene on one chromosome

Linkage and Gene Maps  The frequency of crossing over is related to the distance between two genes Gene A-B 8%, Gene B-C 10%, Gene A-C 2%Gene A-B 8%, Gene B-C 10%, Gene A-C 2% How many units apart? How many units apart? What is the order of the genes? What is the order of the genes?

Linkage and Gene Maps  Linkage maps estimate distances between genes. The closer together two genes are, the more likely they will be inherited together. The closer together two genes are, the more likely they will be inherited together. Cross-over frequencies are related to distances between genes. Cross-over frequencies are related to distances between genes.

Human Molecular Genetics  Human DNA analysis Search the human genome using sequences of DNA bases

Human Molecular Genetics DNA fingerprinting No two humans are exactly alike Analyze and compare low function DNA segments

Human Molecular Genetics  The Human Genome Project An ongoing effort to analyze the human sequence Finished in 2000

Human Molecular Genetics A breakthrough for everyone Public access to Human genome project

Human Molecular Genetics  Gene therapy Changing the gene that causes a genetic disorder Use viruses to infect cells with good gene First person cured of genetic disorder

Human Heredity  Human chromosomes Karyotype – a picture of chromosomes arranged in pairs

Human Heredity

Human Molecular Genetics  Ethical issues in human genetics  Should we use genetics to make people better?