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Chapter 15 - Coggle Diagram

- - - - For a recessive X-linked trait to be expressed,
      - a female needs two copies of the allele (homozygous)
      - a male needs only one copy of the allele (hemizygous)
      - Disorders
        
        Some disorders caused by recessive alleles on the X chromosome in humans:
        
        Color blindness (mostly X-linked)
        
        Duchenne muscular dystrophy
        
        Hemophilia
        
        X inactivation
        
        In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development
        
        The inactive X condenses into a Barr body
- - - - Morgan’s discovery of a trait that correlated with the sex of flies was key to the development of the chromosome theory of inheritance
- - - - Offspring with nonparental phenotypes are called recombinant types, or recombinants
        
        some process must occasionally break the physical connection between genes on the same chromosome is crossing over
        
        genetic map, an ordered list of the genetic loci along a particular chromosome
        
        linkage map is a genetic map of a chromosome based on recombination frequencies
        
        Distances between genes can be expressed as map units
- - - - trisomic zygote has three copies of a particular chromosome
        
        Polyploidy is a condition in which an organism has more than two complete sets of chromosomes
        
        Alterations
        
        Breakage of a chromosome can lead to four types of changes in chromosome structure:
        
        –Deletion removes a chromosomal fragment
        
        –Duplication repeats a segment
        
        –Inversion reverses orientation of a segment within a chromosome
        
        –Translocation moves a segment from one chromosome to another
        
        Down syndrome is an aneuploid condition that results from three copies of chromosome 21
        
        the phenotype depends on which parent passed along the alleles for those traits
        •Such variation in phenotype is called genomic imprinting