Chapter 9.7 Flashcards
Two possible outcomes of error in meiosis
- extra chromosomes
2. missing chromosomes
POLYPLOID
“many sets”
one or more complete sets of chromosomes
human vs plant polyploid tolerance
human : cease as embryos or fetus
plant : 30% of flowering plants and many crop plants tolerate well ( e.g. durum wheat is tetraploid =4 sets)
NONDISJUNCTION
gametes have just ONE extra or missing chromosome
why does NONDISJUNCTION occur
When chromosomes fail to separate at either the first or the second meiotic division
the result an egg or sperm cell with 2 copies or non at all, rather than the normal one copy
When a gamete with Non disjunction fuses with another in fertilization the result in number of chromosomes
1 too little: 45
1 too many 47
too many is better than too few
TRISOMY
An example of 1 extra chromosome resulting from 1 extra
3 different types of autosomal trisomy
extra autosomes : 21, 18 13
Trisomy 21
the most common cause of Down syndrome that has 3 copies of 21 instead of 2
4 possibilities of sex chromosomes abnormalities
Resulting from aa gamete having 2X OR 2Y
XXX TRIPLO-X (FEMALE)
XXY KLINEFELTER (MALE)
XYY JACOBS (MALE)
Resulting from a gamete have no X nor Y
XO TURNER SYNDROME ( FEMALE)
Why hasn’t a OY been reported
since a x chromosome carries so much genetic information an embryo would not survive many cell divisions
XXX TRIPLO-X (FEMALE)
1.tallness
2. menstrual irregularities
3. normal range IQ
4.
XXY KLINEFELTER (MALE)
- sexually underveloped
- rudimentary testes
3 no pubic or facial hair - slow to learn
- large hands long limbs
XYY JACOBS (MALE)
- apparently normal
- very tall
- acne
4, problems with speech and reading
XO TURNER SYNDROME ( FEMALE)
- female with missing x chromosome has only one
- short
3 sexually underdeveloped - infertile
4 smaller scale chromo abnormalities
Normal: ABCDEFG
- deteltion: ABCD
- duplication ABCEEFGEFGEFG
- inversion adcefg
- translocation
DELETION
LOSS OF ONE Of one or more genes
eg cri du chat -gene deletion of some of chromo 5
DULPICATION
PRODUCES MULTIPLE COIES OF PART OF A CHROMO
eg Fragile X syndrome= duplication of genes on the X chromosome
INVERSION
part of the chromosome flips and reinserts, changing the gene sequence
less harmful than deletion
TRANSLOCATION
a non homologous pair exchange parts
It often breaks gens and sometimes result in leukemia
If no genes are broken then they have a normal amount of genes just rearranged
What is polyploidy?
Polyploidy means having extra sets of chromosomes, for instance 3n (triploid), 4n (tetraploid), or 6n (hexaploid).
How can nondisjunction during meiosis lead to gametes with extra or missing chromosomes?
If the chromosomes don’t separate properly at anaphase I or II, chromatids are unequally portioned into cells during meiosis I or II. Some gametes will have too few chromosomes, whereas others will have too many.
How can deletions, duplications, inversions, and translocations cause illness?
Deletions, duplications, inversions, and translocations can delete, duplicate, or damage genes, which may affect the normal production of proteins. Chromosome duplication may be the least harmful, because the spare genes can mutate while the working genes continue their normal functions. Chromosome deletions may mean that an individual cannot make some proteins. Inversion produces symptoms because chromosomes may not align properly, causing fertility problems, miscarriage, or birth defects. In translocation, chromosomes may be missing parts, or genes can be broken. Affected individuals may lack proteins, produce harmful proteins, or have fertility problems
How do inversions and translocations cause fertility problems?
Both inversions and translocations result in faulty chromosomes that are missing segments or have segments in which genes are out of order. Because an abnormal chromosome may not successfully match with its homolog during meiosis, an affected person may be infertile. Even if gametes are produced, embryonic development may be abnormal, and the pregnancy often will end in a miscarriage.
