Genes and Chromosomes III: Alterations of Chromosomes Flashcards
What did Thomas Hunt Morgan notice when he breeded his wild type (red eyed) flies with the mutant (white eyed) flies?
He noticed that 25% of the offspring had white eyes which was normal. However, ALL of the offspring that contained the mutant phenotype were male.
He concluded that fly’es eye color is linked to its sex/X chromosome.
Gene Linkage
This is solely for autosomes.
Genes located on the same chromosome that tend to be inherited together in genetic crosses are “linked” genes.
What did Morgan notice in terms of the ratio of offspring for his testcross involving body color and wing type of drosophila?
He noticed that there was a very small amount of offspring with nonparental phenotypes. This indicated that some mechansim occasionally breaks the linkage between genes on the same chromosome (CROSSING OVER).
What mechanism breaks the linkage between genes on the same chromosome?
Crossing Over
Recombination Frequency
What accounts for the occurence of recombinant phenotypes?
Percentage of recombinant offspring, the recombinant frequency, is related to the distance between linked genes.
The occasional production of recombinant gametes during prophase I accounts for the occurrence of recombinant phenotypes in Morgan’s testcross.
What is a linkage map?
Linkage maps show the relative locations of genes along a chromosome
How is only one X chromosome active in females even though they inherit two X chromosomes?
During female development, one X chromosome condenses into a Barr body, inactivating about 90% of its genes.
Hypohidrotic ectodermal dysplasia
A heterzygous woman will have patches of normal skin and skin patches lacking sweat glands. This is because approximately half her cells wil express one allele and the other half iwll express the other allele.
Aneuploidy of sex chromosome. What are the 4 cases in humans?
XXY: in males, Klinefelter syndrome
XYY: in males, Jacob’s syndrome
XXX: in females, Triple X syndrome
X0: in females, Turner syndrome
Genomic Imprinting
related to autosomes
What is it? When does it occur?
Genomic imprinting occurs during formation of the gametes and results in the silencing of one allele of certain genes.
What are the four types of alterations of chromsome structure?
Deletion: a deletion removes a chromosomal segment
Duplication: a duplication repeats a segment
Inversion: a segment is inverted, put back in backwards
Translocation: a segment is moved from one chromosome to another nonhomologous chromosome
