1
Q
chromosome theory of inheritance
A
A basic principle in biology stating that genes are located at specific positions (loci) on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.
2
Q
wild type
A
The phenotype most commonly observed in natural populations
3
Q
mutant phenotypes
A
alternatives to the wild type
4
Q
SRY
A
- in humans, the anatomical signs of sex begin to emerge when the embryo is about 2mo old
- sex-determining region of Y chromosome
- required for development of testes; in its absence, gonads develop into ovaries
- codes for a protein that regulates other genes
5
Q
X vs Y chromosome
A
- Y: (identified) 78 genes that code for 25 proteins; most help determine sex
- X: ~1,100 genes; have genes for many characters unrelated to sex
6
Q
Duchenne muscular dystrophy
A
- X-linked
- affects 1/3,500 males born in US
- progressive muscular weakening, loss of coordination
- affected individuals rarely live past early 20s
- absence of a key muscle protein called DYSTROPHIN
7
Q
hemophilia
A
- X-linked
- absnece of 1 or more of the proteins required for blood clotting
- treated w/ intravenous injections of the missing protein
8
Q
Barr body
A
- most of 1 X in each cell in female mammals becomes inactive during early embryonic development
- it condenses into a compact object called a Barr body, which lies along the inside of the nuclear envelope
- in the ovaries, Barr-body chromosomes are reactivated in the cells that give rise to eggs, so every female gamete has an active X
9
Q
mosaic
A
- females consist of a mosaic of 2 types of cells: those w/ the active X from the dad and those w/ the active X from the mom
- if a female is heterozygous for a sex-linked trait, about half her cells will express one allele, while the others will express the alternate allele
10
Q
X inactivation process
A
- involves modification of the DNA and the histone proteins bound to it, including attachment of METHYL groups to one of the nitrogenous bases of DNA nucleotides
- a particular region of X chromosome contains several genes involved in the inactivation process. the 2 regions, one on each X chromosome, associate briefly w/ e/o in each cell at an early stage of embryonic development
- then one of the genes, called XIST (X-inactive specific transcript) becomes active only on the chromosome that will become the Barr body
- multiple copies of the RNA product of XIST attach to the X chromosome on which they’re made, eventually almost covering it
- interaction of this RNA w/ the chromosome initiates X inactivation, and the RNA products of other genes nearby on the X chromosome help to regulate the process
11
Q
linked genes
A
- Genes located close enough together on a chromosome that they tend to be inherited together.
- a 50 percent frequency of recombination is observed for genes that AREN’T linked
12
Q
cinnabar
A
in Drosophila, a mutant phenotype; brighter red than the wild type
13
Q
cytogenic maps
A
A map of a chromosome that locates genes with respect to chromosomal features distinguishable in a microscope.
14
Q
genetic map
A
An ordered list of genetic loci (genes or other genetic markers) along a particular chromosome.
15
Q
linkage map
A
A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes.
16
Q
map unit
A
A unit of measurement of the distance between genes. One of these, also known as a centimorgan, is equivalent to a 1% recombination frequency.
17
Q
3 other chromosomal systems of sex determination
A
- X-0: grasshoppers, cockroaches, some other insects. only 1 type of sex chromosome: the X. females are XX; males are X0. sex of offspring is determined by whether the SPERM cell contains an X or no sex chromosome.
- Z-W: birds, some fishes, some insects. the sex chromosomes present in the EGG determine sex of offspring. females are ZW; males are ZZ.
- haplo-diploid: most species of bees and ants. no sex chromosomes. females develop from fertilized eggs and are thus diploid; males develop from unfertilized eggs and are haploid (they have no fathers).
18
Q
nondisjunction
A
An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other.
19
Q
aneuploidy
A
- A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.
- when an aberrant gamete unites w/ a normal one at fertilization
20
Q
common alterations of chromosome structure
A
- reciprocal translocation more common than nonreciprocal
- DELETIONS and DUPLICATIONS esp likely to occur during meiosis
- in crossing over, nonsister chromatids sometimes exchange unequal-sized DNA segments, so that one partner gives up more genes than it receives. the products of such an unequal crossover are one chromosome w/ a deletion and one chromosome w/ a duplication
21
Q
Down syndrome rate
A
- 1 in 700 children in US
- most cases result from nondisjunction during meiosis I
- some research points to an age-dependent normality in a meiosis checkpt that normally delays anaphase until all the kinetochores are attached to the spindle (similar to M phase checkpt)
22
Q
Klinefelter syndrome
A
- XXY
- 1/500 to 1/1,000 live male births
- male sex organs, but testes are abnormally small and the man is sterile
- breast enlargement and other female body characteristics; maybe subnormal intelligence
23
Q
XYY
A
- 1/1,000 males
- normal sexual development; tend to be taller than avg
24
Q
XXX
A
- 1/1,000 live female births
- healthy; tend to be slightly taller than avg
- fertile
- at risk for learning disabilities
25
Turner syndrome
- monosomy X; only known viable monosomy in humans
- 1/2,500 female births
- sterile b/c sex organs don't mature
- normal intelligence
- develop 2ndary sex characteristics w/ estrogen replacement therapy
26
cri du chat
- special deletion in chromosome 5
- "cry of the cat"; child has cry that sounds like the mewing of a distressed cat
- die in infancy / early childhood
- severely intellectually disabled
- small head, unusual facial features
27
CML
- chronic myelogenous leukemia
- when a reciprocal translocation happens during mitosis of cells that will become white blood cells. in these cells, the exchange of a large portion of chromosome 22 w/ a small fragment of chromosome 9 produces a much shortened, easily recognized chromosome 22, called the PHILADELPHIA CHROMOSOME
- such an exchange causes cancer by activating a gene that leads to uncontrolled cell cycle progression
28
genomic imprinting
- A phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent.
- occurs during gamete formation and results in the silencing of a particular allele of certain genes
- These maternal and paternal imprints are transmitted to all body cells during development.
- For a maternally imprinted gene, only the paternal allele is expressed, and vice versa.
29
Igf2
- mouse gene for insulin-like growth factor 2
- required for normal prenatal growth
- only paternal allele is expressed
- evidence came initially from normal-sized (wild type) and dwarf (mutant) mice homozygous for a recessive mutation in the Igf2 gene; the phenotypes of heterozygous offspring differed, depending on whether the mutant allele came from the mom or dad
30
chemistry of genomic imprint
- consists of methyl (-CH3) groups that are added to cytosine nucleotides of one of the alleles
- such methylation may silence the allele, an effect consistent w/ evidence that heavily methylated genes are usually inactive
- the inconsistency as to whether methylation activates or silences alleles was resolved in part when researchers found that DNA methylation operates indirectly by recruiting enzymes that modify DNA-associated proteins (histones), leading to condensation of the local DNA. depending on the original function of the condensed DNA in regulating allele expression, the result is either silencing or activation of a given allele.
31
chemistry of Igf2
- one of the few genes for which methylation has been shown to activate expression of the allele.
- methylation of certain cytosines on the paternal chromosome leads to express of the paternal Igf2 allele
32
1st hint that extranuclear genes exist
- scientists studied the inheritance of yellow or white patches on the leaves of an otherwise green plant
- he observed that the coloration of the offspring was determined only by the maternal parent; such coloration patterns are due to mutations in plastid genes that control pigmentation (in most plants, a zygote receives all its plastids from the cytoplasm of the egg)
- as the zygote develops, plastids are distributed randomly to daughter cells; the pattern of leaf coloration exhibited by a plant depends on the ratio of wild-type to mutant plastids in its various tissues
33
mitchondrial genes
- almost all the mitochondria passed on to a zygote com from the cytoplasm of the EGG
- the products of most mitochondrial genes help make up the protein complexes of the ETC and ATP synthase
- mutations may contribute to some cases of diabetes and heart disease, as well as to other disorders that debilitate the elderly, such as Alzheimer's
34
mitochondrial myopathy
causes weakness, intolerance of exercise, muscle deterioration
35
Leber's heredity optic neuropathy
- can produce sudden blindness in people as young as their 20s or 30s
- the 4 mutations found thus far to cause this disorder affect oxidative phosphorylation during cellular respiration
