* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Epigenetics of diabetes Type 2 wikipedia , lookup
Point mutation wikipedia , lookup
Long non-coding RNA wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Pathogenomics wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Gene desert wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Public health genomics wikipedia , lookup
Oncogenomics wikipedia , lookup
Essential gene wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
History of genetic engineering wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Genome evolution wikipedia , lookup
Ridge (biology) wikipedia , lookup
Minimal genome wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Gene expression programming wikipedia , lookup
Gene expression profiling wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Genomic imprinting wikipedia , lookup
Neocentromere wikipedia , lookup
Designer baby wikipedia , lookup
Microevolution wikipedia , lookup
Y chromosome wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Sex Chromosomes So far, what do you know about sex chromosomes? In addition to their role in determining sex, the sex chromosomes, especially X chromosomes, have genes for many characters unrelated to sex. We call these sex-linked alleles. Female cells can differ from male cells in two ways: 1. Female cells show dark spots of chromatin (called Barr Bodies) during interphase, male cells do not. 2. Female cells contain 2 X chromosomes and males contain only one X chromosome. The Y chromosome carries few genes. There are very few genes on the Y chromosome that are common on the X chromosome, and because of that, little crossing over may occur between an X and a Y. eg.) Calico cats Male cats tend to be black (XBY) or orange (X0Y). Female cats can be black (XBXB), orange (X0X0) or calico (XBX0) – a mixture between black and orange. Very few male cats can be calico, why? Those who do, carry a hidden X chromosome, and are likely sterile. • A male embryo does not differ from a female fetus until the 6th/7th week of pregnancy. • At this point, the “testes determining factor” (TDF) gene on the Y chromosome is activated. • The TDF gene initiates the production of a protein that stimulates the testes to begin secreting male hormones. Examples of sex linked traits. a. Hemophilia - lack or deformity of blood clotting factor VII or IX. b. Red Green colorblindness c. Pattern baldness - sex influenced not sexlinked. i. Humans carry two alleles for baldness. ii. In females the allele for baldness is recessive but in males, due to testosterone, it is dominant. We can also perform monohybrid crosses between sex chromosomes. For example: Brown eye color (B) is dominant to blue (b). Eye color is carried on the X chromosome. Homozygous dominant femaleXBXB (brown) Heterozygous female XBXb (brown) Homozygous recessive female XbXb (blue) Dominant male XBY (brown) Recessive male XbY (blue) Draw a Punnett square for a cross between a heterozygous female with a recessive male. Calculate the phenotypic & genotypic ratios. XB Xb Xb XBXb XbXb Y XBY In the F1 generation: XbY Phenotypic ratios: 1 brown eyed girl: 1 brown eyed boy: 1 blue eyed girl: 1 blue eyed boy Genotypic ratios: 1XBXb: 1XbXb: 1XBY: 1XbY Example #2 Is it possible to get a blue eyed female from crossing a blue eyed female with a brown eyed male? Explain. Xb Xb XB XBXb XBXb Y XbY XbY No it is not possible, all females would be browned eyed Chromosomal Theory The chromosomal theory is as follows: i) Chromosomes carry genes, the units of hereditary ii) Paired chromosomes segregate during meiosis. Each sex cell or gamete has half the number of chromosomes found in a somatic cell iii) Chromosomes sort independently during meiosis. Each gamete receives one of the pairs and that one chromosome has no influence on the movement of a member of another pair iv) Each chromosome contains many different genes Chromosome Mapping and Gene Linkage • A single chromosome contains many genes linked together and so does the other chromosome in the homologous pair. • The sequence of genes on each chromosome pair should match each other exactly. • Gene linkage reduces the chance for genetic recombination and variety among the offspring. • Parts of a chromosome holding many genes, may separate and switch places with the matching part of the other chromosome = crossing over. • The closer genes are to each other, the less likely they will separate during crossing over = linked genes. • Scientists use crossover frequencies on genes to determine their positions on chromosomes eg.) if the crossover frequency of a gene is 5%, then the two genes are 5 map units apart. • Crossover frequency is determined by the following formula: crossover % = number of recombinations x 100 total number of offspring • Gene markers are usually recessive genes that are easily observed in offspring and can be used to identify other genes found on the same chromosome. • By using crossover frequencies, we can determine gene maps. • Gene maps show the relative positions of genes on a chromosome (loci). • Gene maps are constructed by: - ordering fragments of DNA - studying chromosomal alterations - performing crosses to see how frequently crossing over occurs between fragments. Problem 1: 3 genes A, B, C AB – 12% CB – 7% A AC – 5% 12 mapB units C 5 map units 7 map units Problem 2: AB - 3% BC - 28% AC - 31% 31 map units A B 28 map units 3 map units C Problem 3: Genes X Y Z X 10 15 Y 10 5 Z 15 5 - X 15 map units 10 map units Z Y 5 map units Crossover Frequency of Some Genes on Chromosome #6 Genes Cross-over Frequency Diabetes(1) and Ovarian cancer (2) 21% Diabetes (1) and RH blood group(3) 12% Ragweed allergy (4) and RH blood group(3) RH blood group(3) and ovarian cancer (2) Ragweed allergy (4) and ovarian cancer (2) Hint: Start here 10.5 9% 19.5 Transposons (see handout) Gene Therapy: when defective genes are replaced with normal genes in order to cure genetic diseases Human Genome Project: to determine the complete sequence of the 3 billion DNA subunits (bases), identify all human genes, and make them accessible for further biological study.