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 WHEN GENES ARE CLOSE TOGETHER ON A CHROMOSOME THEY TEND TO BE INHERITED TOGETHER 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? GgWw WHICH IS WHAT HAPPENED Okay Big deal! What do you think he did next?

MORGAN’S Experiment Part II GgWw x ggww GW gw Gw gW   He then crossed an F-1 of the GgWw 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…

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

MORGAN’S RESULTS http://nortonbooks 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 Crossing Over Explains the other 8.5% combinations of either Black Body/Normal Wing or Gray body/Small Wing Chromosome combinations for gametes Homologous chromosomes

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 A gene located on a A SEX CHROMOSOME is called a SEX-LINKED GENE MORGAN DISCOVERED the 1ST 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 1st cross.

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

MORGAN’S 2nd 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 White eyed male Red eyed female All females had red eyes All males had red eyes 3:1 ratio red eyes to white 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 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 http://en.wikipedia.org/wiki/Chromosomal_translocation http://www.nature.com/scitable/topicpage/dna-deletion-and-duplication-and-the-associated-331 DUPLICATION, INVERSION, DELETION, TRANSLOCATION

Nondisjunction http://www. mhhe Failure to separate chromosomes evenly during meiosis Chromosomal mutations involving whole or complete pairs of chromosomes 3n-triploidy 4n-tetraploidy Having more then one set of chromosomes-polyploidy Fatal in humans, beneficial in plants

http://www. pbs. org/wgbh/nova/genome/program 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 OF SEVERAL GENES TO EXPRESS A SINGLE TRAIT LIKE SKIN COLOR

Concept map scientists in this chapter