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
Trisomic
Zygote has three copies of particular chromsome
Polyploidy
Condition in which an organism had more than two complete sets of chromosomes
Ex: Triploidy and tetreploidy
Polyploids are common in plants
More normal in appearance than aneuploidy
Deletion
Removes a chromosomal segment
Duplication
Repeats a segment
Inversion
Reverses orientation of a segment within a chromosome
Translocation
Moves a segment from one chromosome to another
Syndrome
a specific set of symptoms
Down syndrome
An aneuploid condition that results from three chromsome 21s
XXX females
Aneuploids
Completely healthy
Klinefelter syndrome
XXY extra chromosome in males
XO females
Turner syndrome (monosomy x)
Females are sterile
What is the only viable monosomy?
X0
45-X
Turner syndrome
Translocations of chromsomes…
can cause certian cancers
Two execptions to normal Mendelian genetics
- Chromosomes located in the nucleus
2. Genes located outside the nucleus
Genomic imprinting
Silencing of certain genes depending on which parent passes them on
Result of methylation (CH3)
Result of methylation
Genomic imprinting
What is important about genomic imprinting?
Has to be reversible so you dont have individuals with completely silenced genes after meiosis
Extranuclear genes
Found in organelles
Ex: mitochondria and chloroplasts
How are extranuclear genes inherited?
Maternally
Zygote’s cytoplasm comes from the egg
First evidence of extranuclear genes
Patches of color on leaves
Chloroplast genes
Defects in mitochondrial genes
Can prevent cells from making enough ATP
Affects muscular and nervous systems
Autosomal genes
Regular chromosomes
Not sex linked or anything
What do crossovers cause?
Recombination
Why can’t we use map units for physical distances?
Frequency of crossing over varies
Philadelphia
Chromosome 22
Where does down syndrome come from?
Nondisjunction in either parent in gamete cell production
Theory of inheritance
Genes are at specific loci on the chromosome and in turn segregate during meiosis
Non-reciprocal crossover
Deletion and duplication
XIST gene
Activated only one x chromosome on females
Inversion on chromsome
abnormal gametes may be found
