Variation in Chromosome Number and Structure Flashcards
Monoploidy
Only one set of chromosomes
Ants, bees, and wasps have monoploid males
Polyploidy
More than 2 sets of chromosomes
Autopolyploids
Mitosis stops before telophase (sister chromatids move to opposite polls, but cell doesn’t split-> 4N)
Chromosome sets are all identical
All chromosomes derived from same species
Bigger than diploid counterparts, more growth, less seed production
Allopolyploids
Fertile
Result of crosses between 2 or more species
plant doubles number of chromosome spontaneously to produce homologous pair
Aneuploidy
Diploid genome with lacks a chromosome or has an extra chromosome
Trisomies
2N +1 chromosomes (47 chromosomes)
Meiotic Nondisjunction: Meiosis I
Both chromosomes go to one cell in meiosis I (one cell has 2 chromosomes, the other has 0)
Results in 2 zygotes with 2 chromosomes each, 2 zygotes with no chromosomes
Meiotic Nondisjunction: Meiosis II
2 zygotes with 1 chromosomes each, 1 zygote with 2 chromosomes, 1 zygote with no chromosomes
Meiotic Nondisjunction in humans
Autosomal monosomes lost early in pregnancy
3 autosomal trisomies seen as live births
(trisomy 21- down syndrome)
(trisomy 13- pat syndrome)
(trisomy 18-edwards syndrome)
Correlation Between Incidence of Trisomies and Maternal Age
Trisomies increase in frequency with maternal age
Bivalents with crossovers near ends are fragile and increasingly unstable over time, dissociation of bivalent results in nonjsjunction (end up with 2 univalents instead of 1 bivalent)
Deletion/ Deficiency
Missing chromosome segment
Duplication
Extra chromosome segmetn
Hypoploidy
Less genetic material than you should have
Hyperploidy
More genetic material such as supplication of chromosome segment or gain of entire chromosomes
Pericentric Inversion
Segment of gene flips (includes centromere)
Paracentric Inversion
Segment of gene flips (excludes centromere)
Pairing Between Normal and Inverted Chromosomes
One homologue will loop so that genes can align, causes irregular segregation, more frequent non disjunctions
Tranlocations
Segment from one chromosome is detached and reattached to a different (non homologous) chromosome
Reciprocal Translocation
Pieces of 2 non homologous chromosomes are exchanged without any net loss of genetic material
Chromosome bend so genes line up
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Compound Chromosomes
Formed by fusion of homologous chromosomes, sister chromatids, or homologous chromosome segments
Robertsonian Translocations
Formed by fusion of 2 non homologous chromosomes at their centromeres
p arms are lost
Robertsonian Translocations: Down Syndrome
Chromosome 14 fuses with 21, p arms contain such little info that it is like inheriting a full chromosome 14 and a full chromosome 21 so parents are normal
Results in non disjunction because there are 3 chromosomes
XO
Turner Syndrome
XXY
Klinefelter Syndrome
XXX
Triple X Females
Monosomes
2N -1 chromosomes (45 chromosomes)
