Unit 5 - Ch 16 - Genetic Disorders Flashcards
Genetic Disorders. Three major types:
- Mendelian Inheritance - dominant or recessive allele that is autosomal or sex-linked
- Variations in Chromosome Number
- Variations in Chromosome Structure
Two major types of Variations in Chromosome Number:
- Polyploidy - exact multiples of the haploid condition
2. Aneuploidy - the absence or addition of individual chromosome(s)
Triploid
A polyploidy organism with homologous triplets.
3n
3 of every chromosome
=> in humans 3n=69 (66 autosomes and 3 heterosomes)
- lethal, found in miscariages
Tetraploid
A polyploidy organism with homologous quads.
4n
4 of every chromosome
=> humans 4n=92 (88 auto and 4 hetero)
Pentaploid
5n organism
5 of every chromosome
=> dog rose 5n=35
Hexaploid
6n organism
6 of every chromosome
=> wheat 6n=42
What causes polyploid organisms?
When 2n tissue acts as a gamete (2n + n = 3n or 2n + 2n = 4n)
What results occur in polyploid plants and animals?
Plants tolerate well. They produce larger fruits, leaves, seeds and flowers, desirable in agriculture.
Usually lethal to animals.
Reproductive viability of polyploid organisms
Even multiples are fertile. Odd multiples are sterile.
What causes aneuploidy?
Nondisjunction - chromosomes fail to separate during meiosis I or II
Nullisomic
An aneuploid (2n-2) Missing a homologous pair
Both parents have nondisjunction for the same chromosome (rare)
=> humans 44 chromosomes
- lethal (miscariages)
Monosomic
An aneuploid (2n-1) Missing one chromosome of a homologous pair
One parent has nondisjunction
=> humans 45 chromosomes, 22 homologous pairs
Trisomic
An aneuploid (2n+1) One homologous triplet
Abnormal gamete from one parent
humans => 47 chromosomes
Tetrasomic
An aneuploid (2n+2) Abnormal gametes from both parents (n+1); rare.
humans => 48 chromosomes
Turners Syndrome (XO)
Monosomic condition
- no barr bodies (suggests male)
- actually sterile female
- webbed neck
Kleinfelter’s Syndrome (XXY)
Trisomic condition
- one barr body (appear female)
- actually male with small testes
- sterile
Superfemale (XXX or XXXX)
Trisomic or tetrasomic
- tri X comes from one parent
- tetra X from both parents
- usually fertile
XYY
Trisomic condition
- from father
- used to think this led to anti-social behavior (discredited)
YO
Monosomic condition
- from mother
- egg cell missing the sex chromosome; lethal in utero
What are four variations in chromosome structure?
Deletion
Duplication
Inversion
Translocation
What is a deletion in chromosome structure? Homozygous and heterozygous?
The chromosome is missing segments
Homozygous - impacts both homologs (rare) - usually lethal
Heterozygous - only one homolog impacted
a. Cri-Du-Chat Syndrome - part of #5 missing
Duplication in chromosome structure
Gene segment present more than once in a homologous chromosome
Inversion in chromosome structure. Homozygous and heterozygous
Chromosome segment “rotates” within a chromosome
Homozygous - both homologs are inverted
- often no impact
Heterozygous - impacts one homolog
- problem if crossing over occurs
- results in duplication and deletion
Translocation in chromosome structure
Gene segments exchanged between non-homologous chromosomes.
