Extending Mendelian Genetics Chapter 7 Mr Scott Human

Extending Mendelian Genetics Chapter 7 Mr. Scott

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

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

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

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

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

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

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

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

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

Human Chromosomes

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Human Molecular Genetics Ø Gene therapy l Changing the gene that causes a genetic disorder • Use viruses to infect cells with good gene • 1999 - First person cured of genetic disorder

Human Heredity Ø Human chromosomes l Karyotype – a picture of chromosomes arranged in pairs

Human Heredity

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