Chapter 8 Genetic Variation Flashcards
Genetic Variation
genetic differences among SAME or DIFFERENT species
Allele Variation
difference in species genes
Chromosome Identified 3 ways:
Location of Centromere
Size
Banding Pattern
Metacentic
Centromere located in center of chromosome
Submetacentric
Centromere slightly off center
acrocentric
Centromere way off center
Telocentric
Centromere at one end (so short arm does not exist)
Short arm represented by letter?
P
Long arm represented by letter?
Q
In a Karyotype chromosomes are organized based on what?
- numbered according to size
- short arm on top
- largest have smallest number
Deletion
change in total number of chromosomes resulting from a deletion a segment of genetic material (also referred to as deficiency)
Duplication
Change in total number of chromosomes resulting from section of chromosome being repeated
Inversion
chromosomal rearrangements- changes direction of genetic material
Translocation
chromosomal rearrangement-one segment of chromosome becomes attached to another chromosome OR another part of same chromosome
Simple Translocation
One segment of a chromosome moves to another segment
Reciprocal Translocation
Two chromosomes EXCHANGE pieces
Terminal Deletion
A chromosome breaks in two pieces and the end of a chromosome is lost
Interstitial Deletion
A chromosome breaks in to three pieces and the center piece is lost
Cri-Du Chat Syndrome
Deletion in short arm of chromosome 5 resulting in mental deficiency, facial abnormality, and catlike cry at birth
Prader Willi Syndrome and Angelman Syndrome
Deletion in chromosome 15
Repetitive Sequence
homologous chromosome carrying identical or similar fragments of genetic material
Nonallelic homologous recombination
two repetitive sequences align causing a duplication in one chromosome and a deletion in the other due to the misalignment
Gene Duplication
number of genes at specific location duplicates
Charchat Marie-Tooth
Small duplication in chromosome 15 causing abnormality in development of hands and feet
Gene Family
Two or more genes similar to each other that were created from the same ancestral gene
Paralogs
Homologous genes from SAME species
Orthologs
Homologous genes from DIFFERENT species
Pericentric inversion
Inversion occurs within region of centromere
Paracentric Inversion
Inversion occurs outside region of the centromere
Position Effect
location a gene changes (due to translocation or inversion) sometimes causing abnormal phenotypic expression Ex: Hemophilia Type A
Inversion Heterozygote
One chromosome has inverted fragment and one is normal (will possibly produce abnormal zygote)
Inversion Loop
Loop created during meiosis I so that the inverted region of the chromosome does not separate incorrectly causing abnormalities. Larger inversion region=larger potential for abnormality
Pericentric Crossing Over
Results in two abnormal chromosomes
1 with deletion 1 with duplication
Paracentric Crossing Over
One dicentric chromosome and one acentric fragment
Dicentric Chromosome
Chromosome with two centromere–created from paracentric crossing over
Acentric Fragment
Fragment with no centromere–created from paracentric crossing over (usually degrades and is lost)
Telomere
Region at end of linear chromosome that keeps chromosomes from unnecessarily attaching to each other
Mechanisms that cause translocation
1) Chromosomal breakage (multiple chromosomes break and then reattach to each other in mismatched forms)
2) Abnormal Crossing Over (results in rearrangement of genetic material)
Unbalanced Translocation
Different amount of chromosomes duplicate/delete (usually occurs in offsprings of carriers with reciprocal translocation)
Robertsonian Translocation
fusion of two chromosomes (sometimes causing down syndrome)
Down Syndrome
can be a result of unbalanced translocation creating three fragments of chromosome 21
Translocation Cross
Two Possible Methods:
abnormal pairing of homologous chromosomes
1) Diagonal Cross: results in two normal and two reciprocal translocation chromosomes
2) Adjacent 1 Segregation: results in 4 haploid abnormal cells (half deleted/half duplicated chromosomes)
Semi Sterility
not all gametes viable sometimes in reciprocal transolcation women because half of gametes will not be viable)
Why is aneuploidy detremental to phenotype?
Being trisomic or monosomic is bad because genes are over or under expressed
Trisomy 21
Causes down syndrome. Has an extra chromosome 21
*chromosomes do not seperate correctly during anaphase
XXY
Klinefelter
XYY
Jacobs Syndrome
Trisomy X
Females with an extra X chromosome
XO
Turner Syndrome
Haplodiploidy
One gender is haploid and one is diploid like in insects
What is polyploid and what are some expamples?
Polyploid is three or more sets of chromosomes. Examples are some amphibians and reptiles
When is variation in euploidy common?
In plants
What is chromosome nondisjunction and what is result?
instances in which chromosomes do not segregate properly
What is meitoic Nondisjunction and what does it produce?
produces haploid cells with too many or too few chromosome.
What is mitotic nondisjunction?
Leads to patch of tissue in organisms with altered chromosome number
What does nondisjunction during meiosis 1 lead to?
2 monosomic and 2 trisomic cells
What does nondisjuction during meiosis 2 lead to?
1 mono 1 trisomic, and 2 normal cells
What does complete nondisjunction lead to?
diploid cells or cells without any chromosomes
What is mosaicism
Genetic abnormality that occurs after fertilization resulting in a small patch of cells with a different chromsome number .
What is bilateral gynadromorphy?
An insect that is half male and half female as a result of mitotic nondisjunction. Produces and XX and an XO individual
What is autopolyploidy?
increase in number of chromosome sets in an individual species as a result of complete nondisjunction
What is alloploidy?
An organism with one set of chromosomes from two DIFFERENT SPECIES. results from interspecies cross
What is allopolyploid?
Contains two sets of chomosomes from two or more species
What is allodiploid?
An alloploid that has one set of chromosomes from two different species. Usually sterile
