250 Quiz 1
mutations within introns can often prevent
normal processing of the primary RNA transcript
n =
number chromosomes in genome
monohybrid cross tests how many traits
one
haplosufficient
one gene copy has enough function to produce wild-type phenotype (*null mutant allele is recessive*)
law of equal segregation
pair of inheritance unit factors (alleles) segregate with equal probability during myosis, the formation of gametes
autosomal recessive pattern
parents of progeny usually unaffected
zygote
product of two gametes (diploid)
how to demonstrate single-gene inheritancve of sterile mutants
propagate as heterozygote and self to look for 25% (if sterile recessive. sterile dominant is dead end, but can be asexually propagated in plants/fungi)
person of interest in pedigree analysis
propositus
at the molecular level, the primary phenotype of a gene is _______ produced
protein
exons
protein-coding regions of the gene
autosomal dominant disorder examples
pseudoachondroplasia, huntington disease, polydactyl (extra digits), piebald spotting
autosomal polymorphism pattern
recessive allele more common
x-linked recessive disorder examples
red-green colorblindness, hemophilia
leaky mutations
reduced enzyme function
what is development?
single fertilized cell --> mature adult
model organism traits
small size, small genome, short generation time, many offspring
law of equal segregation is based on
chromosomal segregations in meiosis
genotype
collection of all alleles
test cross
cross A/- with recessive "tester" (a/a). If 1:1, it's A/a, If all show dominant, it's AA. (you can also self the unknown)
to check for single-mutant alleles, researchers...
cross mutant with wild-type and look for 3:1 ratio if recessive mutation or 1:1 if dominant mutation
dominant vs. recessive can only be determined after
cross to get heterozygouse
which one increases genetic diversity?
cross-pollination (not self)
each gamete contains unique genetic info due to _________________
crossing-over in S phase
autosomal recessive disorder examples
cystic fibrosis, PKU
at the molecular level, alleles of the same gene differ at
only one or several nucleotides (mutations can be change, insertion, deletion)
progenitor
original cell; ancestor
autosomes
"normal" (nonsex) chromosomes
F2 name
"second filial generation"
genes in differential sex regions show
"sex linkage" inheritance patterns
meiosis
***my image***
autosomal dominant pattern
-phenotype usually appears in every generation (most affected people are heterozygotes)
single-gene inheritance ratios
1:1, 3:1, 1:2:1
3:1 phenotypic ratio in F2 of heterozygous F1 cross (monohybrid cross) is underlying...
1:2:1 (Y/Y : Y/y : yy)
homologous chromosomes, a.k.a. homologs
2 members of a chromosome pair
meiosis brief summary
2 sex cell divisions and 2 nuclear divisions (meiosis), but chromosome replication only occurs the first time, forming haploids
pseudoautosomal regions 1 and 2
2 short homologous regions at each end of human X and Y chromosomes (one or both undergoes crossing over during meiosis)
mitosis equations (for both diploid and haploid cells)
2n --> 2n + 2n, OR n --> n + n
meiosis equation
2n --> n + n + n + n (diploid to haploid)
ratio when two heterozygotes cross
3:1
how many chromosomes do humans have
46 (22 homologous autosomes and 2 sex chromosomes)
what percentage of the cell cycle is mitosis
5-10% (the rest is interphase during which DNA is replicated!)
PKU caused by
PAH deficiency in metabolic pathway (can't metabolize phenylalanine)
example of monohybrid cross
Y/y x Y/y
null mutations are located on
active site, promoter, or between intron and exon (last option could impair intron removal)
x-linked dominant pattern
affected males pass condition to all daughters but no sons ALSO affected heterozygous females x unaffected males pass condition to half sons and daughters
pure line
all offspring have identical phenotypes
genes come in two forms called
alleles
"molecular base of gene variant" is
base pair difference
autosomal polymorphism exaamples
dimorphisms brown vs. blue eyes, pigmented vs. blond hair
2n denotes a
diploid cell
leaky mutations might be located on
end region of active site
homogametic
females
zygote
fertilized egg
another name for progeny gen.
first filial generation (F1)
recessiveness is observed in
functionally haplosufficient genes; wild type is dominant
silent mutations
functionally wild-type
gp denotes
gametophyte (small structure of haploid cells that will produce gametes)
hemizygotes
genes in differential regions of sex chromosomes
are gametes haploid or diploid?
haploid
n denotes a
haploid cell
mutated allele is dominant in
haploinsufficient genes
dioecious plants
have sexual dimorphism
monohybrid explanation
heterozygote for one gene
inbreeding increases the chance that _______ will mate
heterozygous
monohybrid
heterozygous for one trait
x-linked dominant disorder examples
hypophosphatemia (a type of vitamin D-resistant rickets)
best way to study forward genetics?
identify mutant and compare to wild-type phenotype
allele phenotype won't be expressed if...
in intron region
law of equal segregation (book explanation)
in meiosis, members of gene pair separate equally into product cells (gametes, e.g. sperm and egg) so a single gamete contains only one allele
name of Mendel's first law
law of equal segregation
heterogametic
males
________ divide to produce sex cells (gametes), such as sperm and egg
meiocytes
sexual nuclear division
meiosis
equal segregation is only detectable at the genetic level in...
meiosis of heterozygote (1/2 Y and 1/2 y gametes)
somatic cell nuclear division
mitosis
somatic cell division stages
mitosis --> G1 --> S (DNA synthesis) --> G2
x-linked recessive pattern
more common in males than females because females need both sex alleles to be recessive, whereas males need only one ALSO no offspring of affected males show phenotype, but all daughters are carriers
null alleles
mutant alleles completely causing proteins to lack original function
silent mutations might be located on
non-active site region of exon
To check genotype of phenotype, use a
test cross
what happens to gametes at fertilization
they randomly fuse
dihybrid
two traits, both hybrid (e.g. XxYy)
forward genetics
understanding molecular mechanism for phenotype and phenotypic differences
in haploids, assigning dominance is...
usually not possible
haploinsufficient
wild-type allele can't provide enough product for normal function, so null mutant allele is dominant
does the law of segregation also apply to DNA sequences along the chromosome?
yes