Ch 15 Flashcards
chromosome theory of inheritance
mendelian genes have specific loci (positions along the chromosome) and it is chromosomes that undergo segregation and independent assortment
wild type fruit flies have what color eyes
red as opposed to white
why are fruit flies great for genetic experiments
prolific breeders. only 4 chromosomes
wild type
the phenotype for a character most commonly observed in natural poppulations
notation for symbolizing fly alleles
w-white eyed, w+- red eyed
mutant phenotypes
traits that are alternative of wild types, assumed to be mutations
describe the white eyes in fruit flies
is recessive, located on X chromosome
types of gender chromosomal systems
X-Y; mammals, gender depends on sperm
X-0; some insects, only X, male just one X; X0 females XX
Z-W; some birds, fishes insects, female determine Gender, females ZW, males ZZ
Haplo-diploid: bees and ants, no sex chromosomes, male 16 (haploid) and unfertilized, females 32 (diploid) fertilized
signs of sex begin when
2 months, before that generic genitals
sex linked gene
gene located on either sex chromosome
Y-linked genes
genes located on Y chromosome, very few disorders are y-linked, most help determine sex
X-linked genes
genes located on X chromosome, has genes for many characters unrelated to sex; color blindness is one and is recessive
hemizygous
when referring to genes on male X chromosomes, it is not a pair, all genes (including recessive) will be , thus more X-linked disorders in males
Duchenne muscular dystrophy
characterized by weakening of the muscles, X-linked gene
Hemophilia
X-linked gene, poor blood clotting, common in European royalty
Barr Body
inactive X-chromosome in females which lies along the inside of the nuclear envelope, reactivated in ovaries for gamete formation, choice occurs randomly and independently in each female embryotic cell
females have a mosaic of
mixed X chromosome activate cells
how is the X-chromosome deactivated
modification of the DNA and the histone proteins bound to it, including attaching of methyl groups (-CH3) to one of the nitrogenous bases of DNA nucleotides, a particular region of the X chromosome has genes for inactivation, the two regions of both chromosomes associate and then one of the genes called XIST (for X-inactive specific transcript) become active only on the chromosome which will become inactive, producing an RNA product which covers the X chromosome that produced it deactivating it
linked genes
genes located near each other on the same chromosomes and tend to be inherited together during genetic crosses, thus said to be genetically linked
genetic recombination
the production of offspring with combinations of traits that differ from those found in either parent
parental type
offspring that match either of the parental (P generation) phenotypes
recombinant type (recombinants)
phenotype matches neither parent due to combinations of traits
crossing over
accounts for the recombination of linked genes, occurs while replicated homologous chromosomes are paired during prophase of Meiosis 1, a set of proteins orchestrates an exchange or corresponding segments of one maternal and one paternal chromatid. In effect, in effect end portions of two nonsister chromatids trade place each time a crossover occurs
genetic map
an ordered list of the genetic loci along a particular chromosome
the farther apart two genes are
the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency
recombinant frequency
percentage of recombinant offspring, dependent on the distance between genes on a chromosome
linkage map
genetic map based on recombinant frequencies (does not show actual distance between genes)
map units
measurement to express differences between genes, equivalent to a 1% recombinant frequency (not physical difference)
some genes which are physically connected (on same chromosome) are
genetically unlinked; because on opposite end of chromosome
linkage groups
groups of linked genes
cytogenetic map
locate genes with respect to chromosome features, such as stained bands
nondisjunction
members of a pair of homologous chromosomes do not move apart properly during meiosis 1 or sister chromatids fail to separate during meiosis 2; one gamete receives tow of chromosome and another receives none
aneuploidy
zygote has an abnormal number of a particular chromosome
monosomic
chromosome missing
trisomic
chromosome present in triplicate form
polyploidy
some organism, fairly common in plants, more than two complete chromosome sets in all somatic cells, triploidy is 3 sets; nondisjunction of all its chromosomes, tetreaploidy is 4 sets; failure of 2n zygote to properly divide after chromosome replication
deletion
chromosomal fragment is lost ( if centromere, whole chromosome lost) (especially likely to occur during meiosis)
duplication
chromosomal fragment attaches as an extra segment to another chromosome, becomes a repeat in sister chromatids (especially likely to occur during meiosis)
inversion
chromosomal fragment reattaches to original chromosome but in the reverse orientation
translocation
fragment joins nonhomologous chromosome, common type is reciprocal, both side receive, less common is non reciprocal, only one side receives
four results of chromosome breakage
deletion, duplication, inversion, and translocation
Down syndrome
aneuploid condition, often called trisomy 21 due to extra chromosome 21, facial features, short stature, developmental delays, heart defects, increased chance of Alzheimer’s and leukemia, lower chance of high blood pressure, many types of tumors and arthritis. More common in older women
XXY,XXX,X and XYY
XXY: Klinefelter syndrome, sterile, subnormal intelligence
XYY: normal but somewhat taller
XXX: at risk for learning disabilities and taller
X: Turner syndrome sterile
cri du chat
severely disabled, small head, cries like cat, dies early in childhood, caused by deletion in chromosome 5
chronic myelogenous leukemia
result of translocation, what would be white blood cells, chromosome 22, the Philadelphia chromosome
genetic imprinting
(mostly on autosomes) gene expression varies based on which parent gave it, occurs during gamete formation when one gene is silenced, always imprinted same way generation after generation, result of methylation of DNA associated histones
DNA in chloroplasts, mitochondria, and other plastids
transferred maternally, in egg cells, defects cause lower ATP, mitochondrial myopathy cause weakness, muscle intolerance and muscle deterioration, Leber’s hereditary neuropathy, causes blindness; 4 mutations found so far, may contribute to some heart disease and diabetes, also Alzheimer’s and aging
