Chapter 8 Flashcards
What is genetic variation
The difference between members of the same species or different species
How can chromosomes vary in structure and number
Very in structure by segments of the chromosome being deleted, duplicated, or rearranged
They vary in number of individual chromosomes or number of chromosome sets
What is cytogenetics
Involves microscopic examination of chromosomes
What does cytogenetics allow for
Examining of chromosomal composition of a particular cell
Detection of individual with abnormal chromosomes
Allows a way to distinguish species
What three ways is cytogenetics used to classify chromosomes
Location of centromere
Size
Banding patterns
What is a karyotype
Micrograph that shows all chromosomes within a single cell arranged in standard fashion
What is G banding and what does it means when you have light or dark bands
When chromosomes are exposed to the giemsa stain
Dark bands are regions that heavily bind to dye
Light bands are regions that don’t bind to dye heavily
What is a deletion
Removes dna
Loss of chromosomal segment
What is a duplication
Adds dna
Repetition of chromosomal segment
What is an inversion
Flipped dna segments or change in direction
What is Translocation
Movement of DNA
Segment of one chromosome becomes attached to another chromosome
What is a simple translocation
Piece of chromosome attached to another chromosome
What is Reciprocal translocation
Two different types of Chromosomes exchange pieces and produce two abnormal chromosomes
When a chromosome is broken into pieces what happens
The part without the centromere is eventually lost
The remaining chromosome has a terminal deletion
What happens when a chromosome breaks in two places
The central fragment is lost and the two outer pieces reattach
This chromosome has an interstitial deletion
What do phenotypes depend on when it comes to deletions
The size of the deletion and the material deleted
What can repetitive sequences often cause
Misalignment between homologous chromosomes
If crossover occurs a nonallelic homo,goys recombination results
If you have a segment of dna with equal sizing, does a deletion of this segment or a duplication cause a more harmful affect
Deletion
What do small chromosomal duplications lead to
Formation of gene families
What is a gene family
Two or more genes in a single species derived from the same ancestral gene
What is a paralog
Homologous genes within a single species
What are globin genes
Encode subunits of proteins that bind oxygen
Different globulins are expressed in red blood cells during different developmental stages
What is copy number variation
Segment of dna that varies in copy number among members of the same species
Could be missing a gene of it could be a duplication
What are three possible reasons for copy number variations
Nonallelic homologous recombinations
Proliferation of transposable elements
Errors in dna replication
What is break points affect
Occurs within vital gene which separates it into two nonfunctional parts
What is position affect
Gene is repositioned in a way that alters gene expression
What are inversion heterozygotes
Individuals with one copy of a Normal chromosome and one inverted chromosome
In regards to inversion heterozygotes what happens during meiosis I
Normal and inversion chromosomes synapse and form an inversion loop
What happens if crossing over occurs in the inversion loop
Highly abnormal chromosomes are produced
What happens if crossing over occurs in the inversion loop of a pericentric inversion chromosome
You create two parental types but both pairs have a deletion and a duplication
What happens if crossing over occurs in the inversion loop of a paracentric inversion chromosome
One chromosome is missing a centromere and one has two centromeres
What is reciprocal translocation
Two non homologous chromosomes exchange genetic material
Occur because of chromosomal breakage or dna repair and abnormal crossovers
What is a balanced translocation
Rearrangement of genetic material
No change in amount of material
What are unbalanced translocations
Genetic material is duplicated or deleted
What is robertsonian translocation
When breaks occur near the centromeres of two non homologous Acrocentric chromosomes
Small acentric fragments lost
Larger fragments fuse at centromeric regions to form single chromosome which is metacentric or submetacentric
Do individuals with balanced or unbalanced translocations have greater risk of producing gametes with unbalanced combinations
Balanced
What must form for a translocated chromosome to synapse correctly
Translocation cross
What is alternate segregation
Viable gametes
Chromosomes diagonal to each other within the translocation cross segregate into the same cell following meiosis
One cell receives 2 normal chromosomes and the other receives 2 translocated chromosomes
What is adjacent 1 segregation
4 genetically unbalanced gametes
Adjacent non homologous chromosomes segregated into the same cell after meiosis 1
All four cells have one normal and one translocated chromosome
What is adjacent 2 segregation
4 genetically unbalanced gametes
Centromeres don’t segregate properly during meiosis 1
One cell receives both copies of the centromere on chromosome 1 and other copies of the centromere in chromosome 2
All 4 cells have one normal and one translocated chromosome
What are the two most likely outcomes when an individual carriers a reciprocal translocation
Alternate and adjacent 1 segregation
What is semisterility
An individuals fertility is lowered when they have less viable gametes
What is euploidy
A variation of complete sets of chromosomes
If you have three or more sets of chromosomes you are considered polyploid
What is aneuploidy
Variation in the number of particular chromosomes within a set of
Trisomic is having three copies of a chromosome instead of 2
Monosomic is having one copy of a chromosome instead of 2
Why can aneuploidy cause abnormal phenotypes
It leads to imbalanced amounts of gene products
3 copies of a gene leads to 150 percent production
Do trisomic and monosomic individuals have a better chance of survival than euploid individuals
No because they are an imbalance of gene products which is detrimental to
On what chromosomes does aneuploidy occur (not a number)
Autosomal
What might cause phenotypic effects in aneuploidy
Expression of X linked genes prior to embryonic X linked chromosome inactivation
Imbalance in expression of pseudoautosomal genes
What causes Down syndrome
Failure of chromosome 21 to segregate properly
Non disjunction
Why might Down syndrome be connected to maternal age
A females oocytesare arrested in prophase of meiosis 1 so as she ages her primary oocytes have been arrested for a significantly longer time which contributes to increased frequency of nondisjunction
What is endopolyploidy
Diploid animals produce tissues that are polyploid
What are polytene chromosomes
When doubling of pairs of chromosomes produce a bundle of chromosomes that lie together in parallel fashion
Also considered repeated chromosome replication
What is a chromocenter
Where polytene chromosome’s central point aggregate
Polyploids with an odd number of chromosomes are usually what
Sterile which is a detrimental trait
What are three ways chromosome number may vary
Meiotic nondisjunction
Mitotic nondisjunction
Interspecies crosses
What is nondisjunction
Failure of chromosomes to segregate properly during anaphase
Can occur in meiosis I or II
What does meiotic nondisjunction produce
Haploid cells that have too many or too few chromosomes
If this gamete is fertilized the resulting individual will have abnormal chromosomal composition in all of its cells
If non disjunction occurs in meiosis II what is the probability of abnormal and normal gametes
50% normal 50% abnormal
What is complete nondisjunction
When all chromosomes that undergo nondisjunction migrate to one daughter cell which results in one diploid cell and one without chromosomes
What is mitotic nondisjunction
When sister chromatids separate improperly which leads to trisomic and monosomic daughter cells
What is chromosome loss
One of the sister Chromatids doesn’t migrate to a pole which leads to normal and monosomic daughter cells
What is mosaicism
Genetic abnormalities that occur after fertilization lead to this
Size and location of the mosaic region depends on the timing and location of the original abnormality
What is autopolyploidy
Increase in the number of sets of a single species
Alloploidy
Combing of chromosome sets from different species
Allopolyploidy
When the number of chromosome sets increase in an alloploid
What is an allotetraploid
Contains two complete sets of chromosomes from two different species
