Presentation on theme: "Chromosomal Basis of Inheritance Chapter 15. Most genetics work done on fruit flies (little time to observe many generations) Thomas Morgan - fruit fly."— Presentation transcript:
Chromosomes have hundreds or thousands of genes. Genes located on same chromosome, linked genes, inherited together - chromosome passed as unit.
"A" and "B" are linked due to their occurrence in the same chromosome. Similarly, "a" and "b" are linked in the other chromosome. http://anthro.palomar.edu/biobasis/images/linked_genes.gif
Production of offspring with new combinations of traits inherited from 2 parents - genetic recombination. Can occur during crossing over - sections of homologous chromosomes exchanged during meiosis I.
Sex chromosomes 2 sex chromosomes - X and Y. Males – XY, females - XX. Other species - X-0 system, Z-W system, haplo-diploid system. Humans - X-Y system like normal chromosomes - 50/50 chance of having male or female.
Sex chromosomes, have genes for traits other than sex. Trait recessive - female will only inherit it if both parents pass it on. Males - 50% chance of inheriting it (only have 1 X chromosome) Males have higher rate of sex- linked diseases than females.
Only 1 X in females turned on. Other - Barr body - reactivated in ovaries during egg production (to pass genes on). Females exhibit characteristics from mother, some from father (sex chromosomes only).
http://www.columbia.edu/cu/biology/courses/c2005/images/barr_body.19.gif Barr body replicated, not transcribed
Pattern responsible for mosaic of effects (tortoiseshell cats) Due to patches of cells expressing orange allele, others have nonorange allele.
Errors Errors can occur both in DNA and in chromosomes. Nondisjunction - homologous chromosomes fail to separate during meiosis I, or chromatids - during meiosis II. Some gametes receive 2 of same type of chromosome; another gamete receives no copy.
Abnormal # of chromosomes - aneuploidy. Trisomy - gamete receives 3 of same chromosomes (2n + 1). Monosomy - gamete receives 1 of same chromosome (2n – 1). Earlier in development - more profound effect - those cells go through mitosis.
A rodent species that is the result of polyploidy
Deletion - piece of chromosome broken off during cell division. Duplication - fragment becomes attached as extra segment to sister chromatid. Inversion - piece breaks off, turns around, reattaches (backwards). Translocation - chromosomal fragment joins nonhomologous chromosome.
Some traits dependent on who passes alleles (mother or father) Prader-Willi syndrome caused by deletion on chromosome 15 (father) Deletion from mother - Angelman syndrome. Due to genomic imprinting - gene on 1 homologous chromosome silenced, allele on homologous chromosome expressed.