chapter fifteen Flashcards
chromosome theory of inheritance
- Mendelian “factors” - genes
- specific loci on chromosomes
- replicated, segregated, independently assorted
Thomas Hunt Morgan
provided first solid evidence for chromosome theory of inheritance
- fly lab
what did Morgan use in his research
Drosophila melanogaster
- has 4 pairs of chromosomes
mutant phenotype of Drosophila melanogaster
white eyes
- alternate to wild type, originated as mutation
wild type of Drosophila melanogaster
red eyes
wild type
most commonly observed in natural populations
- could be dominant or recessive
white-eye x wild cross
F1: all red eyes (wild type)
F2: all females red eyes, 50% males red, 50% males white
sex-linked genes
a gene located on either sex chromosome
- X or Y linked
linked genes
- not sex-linked
- physically linked to other, located near each other and inherited together in genetic crosses
- don’t assort independently
what are genetic recombinations a result of?
independent assortment of chromosomes, crossing over, which sperm fertilizes which egg
sex determination of mammals
XX, XY
- depends on if sperm has X or Y
- male has Y
sex determination of Drosophila
X:autosome ratio determines male/female
- X/a < 0.5 = male
- X/a > 1 = female
- between 0.5-1 = intersex
sex determination of some insects
- females XX
- males XO
- determined if sperm contains X chromosome or not
sex determination of birds, some fish/insects
- ZW female
- ZZ male
sex determination of bees and ants
- diploid - females develop from fertilized eggs
- haploid - males develop from unfertilized eggs
potential problem for males in transmission of X-linked recessive traits
any male receiving recessive allele from mother will express the trait because they have 1 X chromosome
why don’t recessive lethals don’t normally appear in females
- they have another X chromosome, dominant masks recessive
- would need 2 copies of recessive, and would only get this from dad, but if dad had it he wouldn’t survive
ex. of recessive sex-linked traits
- Red-green color blindness
- Duchenne Muscular Dystrophy
- Hemophilia
X-inactivation
- almost all of one X chromosome becomes inactivated during early embryonic development, condenses into
Barr Body - involves modification of DNA/proteins, attaches methyl groups to nucleotides
Barr Body
inactivated X chromosome that lies inside of nuclear envelope
- reactivated in cells that give rise to eggs
nondisjunction
when members of a pair of homologous chromosomes don’t move properly apart during meiosis I
disjunction
sister chromatids fail to separate in meiosis II
- 1 gamete receives 2 of same type of chromosome, other receives no copy
aneuploidy
when aberrant gamete unites w/ normal at fertilization, zygote will have abnormal # of particular chromosome
trisomic
if chromosome is present in triplicate in zygote
- 2n + 1
monosomic
fertilization involving gamete w/ no copy (missing chromosome) in zygote
- 2n - 1
polyploidy
having an unusual number of complete chromosome sets in somatic cells
- triploidy
- tetraploidy
where is polyploidy common?
plants
where is polyploidy rare?
animals
- but more normal in appearance than aneuploids
types of alterations in chromosome structure
- deletions
- duplication
- inversion
- translocation
deletions
chromosomal fragment lost
- then misses certain genes
duplication
broken fragment may become reattached as extra segment to a sister/nonsister chromatid
inversion
chromosomal fragment may reattach to original chromosome but in reverse orientation
translocation
chromosomal fragment joins non homologous chromosome
down syndrome (Trisomy 21)
- extra chromosome 21, 47 chromosomes
- short stature, heart defects, developmental delays, shorter life span
- incidence increases with age of parent
ex. of aneuploidy of sex chromosomes
- Klinefelter’s syndrome
- XYY
- Trisomy X
- Turner’s syndrome
Klinefelter’s syndrome
- XXY
- have male sex organs but testes are small and produce little/no sperm
- male
XYY
typical sexual development, taller than average
- male
Trisomy X
- female
- taller than average, but at risk for learning disabilities
Turner’s syndrome
- monosomy X
- sterile, sex organs don’t mature, demonstrate sex characteristics when provided w/ estrogen
- female
extra-nuclear (organelle) genes
- genes located in organelles
- mitochondria/chloroplasts
mitochondrial myopathy
- weakness, intolerance of exercise, muscle deterioration
- defect in genes of mitochondria that reduce amount of ATP made in ETC/synthase
what is now being used to trace ancestry?
MtDNA
where are mitochondrial disorders inherited from?
mother
types of autosomal aneuplodies in humans
- trisomy 21 - Down syndrome
- trisomy 18 - Edward syndrome
- trisomy 13 - Pateau syndrome
- all other types end in miscarriage
