The Chromosomal Basis of Inheritance. Chapter 15

Transcription

1 The Chomosomal Basis of Inheitance Chapte 15

2 The Chomosomal Theo of Inheitance Mendelian genes have specific loci (positions) along chomosomes. It is the chomsomes that undego segegation and independent assotment.

3 Fig P Geneation ellow-ound seeds () Geen-winkled seeds ( ) Meiosis Gametes Fetilization All F 1 plants poduce ellow-ound seeds () F 1 Geneation LAW OF SEGEGATION The two alleles fo each gene sepaate duing gamete fomation. Meiosis Metaphase I LAW OF INDEPENDENT ASSOTMENT Alleles of genes on nonhomologous chomosomes assot independentl duing gamete fomation. 1 1 Anaphase I Metaphase II 2 2 Gametes 1 / 1 / 1 / / 4 F 2 Geneation 3 An F 1 F 1 coss-fetilization 9 : 3 : 3 : 1 3

4 Thomas Hunt Mogan Dosophila melanogaste Wild Tpe- the phenotpe fo a chaacte most commonl obseved in natual populations. Mutant Phenotpes- taits that altenatives to the wild tpe. A student at UK

5 Fig. 15-4b EXPEIMENT P Geneation F 1 Geneation All offsping had ed ees ESULTS F 2 Geneation

6 The Chomosomal Basis of Sex Detemination S- Sex detemining egion of -The pesence of this gene on the chomosome codes fo the development of testes. In the absence of this gene, the gonads develop into ovaies

7 Sex Linked Genes A gene located on eithe sex chomosome is called a sex-linked gene In humans, sex-linked usuall efes to a gene on the lage X chomosome Fo a ecessive sex-linked tait to be expessed -A female needs two copies of the allele -A male needs onl one cop of the allele Sex-linked ecessive disodes ae much moe common in males than in females

8 Fig N= nomal colo vision X N X N X n X N X n X N X N X n X n

9 Fig X N X N X n X N X n X N X N X n X n Spem X n Spem X N Spem X n Eggs X N X N X n X N Eggs X N X N X N X N Eggs X N X N X n X N X N X N X n X N X n X n X N X n X n X n X n X n (a) (b) (c)

10 Mogan s Expeiments Linked Genes- genes located on the same chomosome that tend to be inheited togethe in genetic cosses.

11 What tpe of atios would ou expect to see in the testcoss offsping if the genes wee located on diffeent chomosomes? What if the wee located on the same chomosome and paental alleles ae alwas inheited togethe?

12 Mogan s Expeiments Linked Genes- genes located on the same chomosome that tend to be inheited togethe in genetic cosses. Genetic ecombination- the poduction of offsping with combinations of taits that diffe fom those found in eithe paent.

13 Paental Tpes- offsping that inheit a phenotpe that matches one of the paental phenotpes. Gametes fom ellow-ound heteozgous paent () Gametes fom geenwinkled homozgous ecessive paent ( ) Paentaltpe offsping ecombinant offsping ecombinant Tpes o ecombinants- offsping that have new combinations of phenotpes.

14 ecombination Cossing Ove- accounts fo the ecombination of linked genes. Genetic Map- an odeed list of the genetic loci along a paticula chomosome. Linkage Map- a genetic map based on ecombination fequencies. Displas ode but not pecise location. Distances ae expessed in map units- equivalent to 1% ecombination fequenc. (Centimogans)

15 Exit Slip In humans, pseudohpetophic muscula dstoph is a condition in which the muscles gaduall waste awa, ending in death in the eal teens. This tpe of muscula dstoph is dependent upon a sex-linked ecessive gene that occus onl in bos and has neve been epoted in gils. Hpothesize wh it does not appea in gils? Wh does the sex-linked gene fo pseudohpetophic muscula dstoph not become eliminated fom the human ace since all bos showing the tait die befoe eaching matuit?

16 Alteation of Chomosome Numbe Nondisjunction- pais of homologous chomosomes do not sepaate nomall duing meiosis As a esult, one gamete eceives two of the same tpe of chomosome and the othe gamete doesn t eceive a cop. Aneuploid- a chomosomal abeation in which one o moe chomosomes ae pesent in exta copies o deficient in numbe Polploid- a chomosomal alteation in which the oganism possesses moe than two complete chomosome sets.

17 Fig Meiosis I Nondisjunction Meiosis II Nondisjunction Gametes n + 1 n + 1 n 1 n 1 n + 1 n 1 n n Numbe of chomosomes (a) Nondisjunction of homologous chomosomes in meiosis I (b) Nondisjunction of siste chomatids in meiosis II

18 Alteation of Chomosome Stuctue Deletion- emoves a chomosomal segment Duplication- epeats a segment Invesion- eveses a segment within a chomosome Tanslocation- moves a segment fom one chomosome to anothe

19 Exceptions to the Standad Chomosome Theo Genomic Impinting- a vaiation in phenotpe depending on whethe an allele is inheited fom the male o female paent. Extanuclea Genes- genes outside of the nucleus. Some ae located in oganelles in the ctoplasm.