Chapter 15: Chromosomal Inheritance Flashcards
Why did Morgan study Drosophila melanogaster?
- They produce many offspring
- A generation can be bred every two weeks
- They only have four pairs of chromosomes
Wild type
Normal phenotype
More common
What was the key to the development of the chromosome theory of inheritance?
Morgan’s discovery of a trait that correlated with the sex of flies
Only males had white eyes
SRY
Sex determining region on the Y
Responsible for development of the testes in an embryo
Common x-linked recessive disorders
Color blindless
Muscular dystrophy
Hemophilia
Barr body
Only one of two x chromosomes is used
The inactivated x chromsome condenses into a Barr body
Linked genes
Genes located on the same chromsome that tend to be inherited together
What did morgan find about linked genes?
Body color and wing size are usually inherited together
Genetic recombination
The production of offspring with combinations of traits differing from either parent
When is a 50% frequency of recombination observed?
Any two genes on different chromosomes
Variation factors
Recombinant chromosomes (caused by crossing over)
Random fertilization
All increases genetic variation with natural selection works upon
Genetic map
Ordered list of the genetic loci along a particular chromosome
What did Sturtevant predict?
The farther apart two genes are, the higher the probability that crossing over will occur and therefore have a higher recombination frequency
Map units
Distance between genes
Centimorgan or map unit=1% recomonbination frequency
How did Sturtevant find linkage groups?
Saw that genes clustered into four groups of linked genes
Provided additional evidence that genes are on chromosomes
Plants and genetic changes
They tolerate them much better than animals
Nondisjunction
Pairs of homologous chromosomes do not separate normally during meiosis
Aneuploidy
Results from the fertilization of gametes in which nondisjunction occurred
All offspring do not have the correct number of a particular chromsome
Monosomic
Zygote has only one copy of a particular chromosome