Ch 10 GenesChromosomes Chromosome Theory of Heredity Genes

Ch. 10 Genes/Chromosomes Chromosome Theory of Heredity • Genes located on chromosomes (Sutton) • Genes can be linked (Morgan) • Genes can cross over (Morgan/Sturtevant) • Autosomes/Sex chromosomes (Stevens) • Sex Linked genes (Morgan) Mutations • Chromosomal mutations – genes • Mutation in genes – nucleotides Gene Expression • Incomplete dominance • Codominance • Polygenic inheritance

THOMAS MORGAN

Morgan’s DISCOVERY of LINKED GENES • Characteristics of linked genes 1. WHEN GENES ARE CLOSE TOGETHER ON A CHROMOSOME THEY TEND TO BE INHERITED TOGETHER 2. LINKED GENES tend to not SEPARATE from one another during Crossing Over Prophase I During Cross Over in Prophase, they tend to stay together instead of separating and switching

How Morgan Discovered Linked Genes • USED DROSOPHILA Genus name – common name Fruit flies WHY? • • They Mature in 2 weeks They Produce large numbers of offspring They only have 4 pair of chromosomes One pair are the Sex CHROMOSOMES

The Experiment for Linked Genes Part I • Thomas crossed PURE BRED fruit flies for two traits • Homozygous Dominant GRAY BODIES & NORMAL WING SIZE (GGWW) with Homozygous Recessive flies that had BLACK BODIES & SMALL WINGS (ggww) • GG WW X gg ww • WHAT Genotype DID HE EXPECT IN THE OFFSPRING? • Gg. Ww • WHICH IS WHAT HAPPENED • Okay Big deal! • What do you think he did next?

MORGAN’S Experiment Part II • He then crossed an F-1 of the Gg. Ww hybrid offspring w/a recessive ggww • What would you expect? • Fill out this punnett- • he did not get as expected… • ¼ GRAY NORMAL • ¼ GRAY SHORT • ¼ BLACK NORMAL • ¼ BLACK SHORT • INSTEAD, he got… Gg. Ww x ggww gw gw GW gw Gw g. W

Experiment’s Results for Part II Gg Ww alleles Expected Actual Results 2300 total offspring gg ww alleles

MORGAN’S RESULTS http: //nortonbooks. com/college/biology/animations/ch 11 a 01. htm • • • 41. 5% GRAY body/Normal wings 41. 5% BLACK body/small wings 8. 5% GRAY body/Small wings 8. 5% BLACK body/Normal wings MORGAN’s Conclusion The genes for wing size and body color were so commonly inherited as only two combinations either gray body/normal wing or black body/small wing that they had to be … • on the same chromosome! • This indicated that the genes for body color and wing size were… • LINKED onto one chromosome.

Crossing Over Explains the other 8. 5% combinations of either Black Body/Normal Wing or Gray body/Small Wing Homologous chromosomes Chromosome combinations for gametes

This means that even though genes can be linked, They can sometimes separate from one another during Crossing Over in Meiosis

Cross-over Used to Map Genes Short Arm Bands Represent Genes Long Arm

GENE MAP • If you know the frequency of how often genes cross over, you can use the percentage to estimate how far apart the genes are from on another on a chromosome • This is called a Gene Map • So if two genes have an 8% frequency of crossing then are they far apart or close on a chromosome? B c A

NETTIE STEVENS Discovered Sex Chromosomes • She worked with MEALWORMS • DISCOVERED they had 20 chromosomes. • MALES had 19 regular size & 1 small one. The Females all the same size chromosomes • SHE SAID “THE 19 that were the same are AUTOSOMES (body chromosomes), & the other set were SEX CHROMOSOMES” • FRUIT FLIES same for male/females • Males have XY • Females have XX

GENES ON SEX CHROMOSOMES http: //www. mhhe. com/biosci/esp/2001_gbio/folder_structur e/ge/m 3/s 2/index. htm • A gene located on a A SEX CHROMOSOME is called a SEX-LINKED GENE • MORGAN DISCOVERED the 1 ST SEX-LINKED gene in fruit flies • He crossed a PUREBRED Dominant RED-EYED FEMALE W+W+ with a PUREBRED recessive WHITE-EYED WW MALE • Let’s take a look at the 1 st cross.

Morgan’s 1 st Sex Linked Cross All offspring had red eyes

MORGAN’S 2 nd CROSS • HE crossed from the F-1 generation a heterozygous FEMALE, W+W RED-EYED with a RED-EYED W+ MALE (note only 1 allele! • Let’s do the cross • HE got a 3: 1 RATIO of Red eye to White eye, but only MALES had WHITE EYES! Why? • Since no FEMALES had WHITE EYES Morgan hypothesized that EYE COLOR must be a SEX-LINKED gene • IT must be on the X CHROMOSOME The Y chromosome does not carry a gene for EYE COLOR • The RECESSIVE TRAIT White eyes, is inherited more often in males that receive the r allele on their one and only X CHROMOSOME

MORGAN’S EXPERIMENTAL CROSS Red eyed female All females had red eyes 3: 1 ratio red eyes to white eyes White eyed male All males had red eyes Only males had white eyes

Mutations • Gene mutations – chemical change that affects the DNA molecule of a specific gene during DNA replication • Chromosomal mutation – change in the number or the structure of chromosomes during meiosis

Mutations http: //learn. genetics. utah. edu/content/begin/traits/predictdisorder/ Point mutation -single nucleotide is misplaced • A substitution may not be fatal, since there is redundancy in the amino acid codons • BUT it can code for the wrong amino acid which creates an incorrect or nonfunctional protein Frame shift mutation - the deletion/insertion of a single nucleotide causes a frame shift which often results in a nonfunctional protein

Chromosomal mutations

http: //en. wikipedia. org/wiki/Chromosomal_translocation http: //www. nature. com/scitable/topicpage/dna-deletion-and-duplication-and-theassociated-331 DUPLICATION, INVERSION, DELETION, TRANSLOCATION

Nondisjunction http: //www. mhhe. com/biosci/esp/2001_gbio/folder_structure/ge/m 3/s 3/i ndex. htm • Failure to separate chromosomes evenly during meiosis • Chromosomal mutations involving whole or complete pairs of chromosomes • 3 n-triploidy • 4 n-tetraploidy • Having more then one set of chromosomes-polyploidy • Fatal in humans, beneficial in plants

http: //www. pbs. org/wgbh/nova/genome/program. html 13: 08 time ONE WRONG LETTER

JOSEPH KOLREUTER • 1760 -Crossed white rr x red RR carnations • He got…Rr which were pink! • Phenotype was in between the parents • He crossed the Rr hybrid F 1 and got red, white and pink combos • This shows that R is incompletely dominant over the r gene • r does not code for a protein but R can not compensate for this so an intermediate hybrid is created

INCOMPLETE DOMINANCE • A PHENOTYPE THAT IS INTER MEDIATE OF EITHER GENE

CODOMINANCE Two genes are expressed equally • ONE gene is not DOMINANT over the other gene • Two dominant genes Are expressed • How does this happen?

POLYGENIC INHERITANCE • INHERITANCE OF SEVERAL GENES TO EXPRESS A SINGLE TRAIT LIKE SKIN COLOR

Concept map scientists in this chapter