exam 3 ppt 3 Flashcards
what is the problem with Mendel’s discoveries?
genetic complexities exist that would not have allowed Mendel to make his discoveries
definition of incomplete dominance
heterozygote displays intermediate phenotype
definition of codominance
heterozygote displays BOTH phenotypes at once
definition of X-linked traits
offspring have sex-dependent inheritance patterns
definition of multiple alleles
hierarchy of dominance
definition of epistasis
gene interactions
definition of genes x environment
environment influences phenotype
what genetic complexities exist that would not have allowed Mendel to make his discoveries? (listed)
incomplete dominance, codominnce, X-linked traits, multiple alleles, epistasis, genes x environment
what do karyotypes reveal?
they reveal the biological sex of an individual
what are the female sex chromosomes?
XX
what are the male sex chromosomes?
XY
definition of sex chromosomes
one of the pair of chromosomes that determine the sex of an individual
definition of autosomes
chromosomes that are not sex chromosomes
what do many animal species have regarding sex chromosomes?
many animal species have unmatched sex chromosomes
in mammalian biological sex determination, what does the sex-determining region Y gene (SRY) gene do?
it encodes a protein called Testis determining factor (TDF), a transcription factor that turns on expression of other genes that results in development of male reproductive structure
what is the testis determining factor (TDF) in mammalian biological sex determination?
a transcription factor that turns on expression of other genes that results in the development of male reproductive structures
why is the SRY gene Y linked?
it is Y linked because it is only found on the Y chromosome
what does the segregation of sex chromosomes during meiosis predict regarding the sex of offspring?
segregation of sex chromosomes during meiosis predicts a 1:1 ratio of males to females
what does meiosis in a female result in?
meiosis in a female results in X-bearing eggs only
what does meiosis in a male result in?
meiosis in a male results in a 1:1 ratio of X-bearing and Y-bearing sperm
what does it mean that males are hemizygous?
males are hemizygous for genes on the X chromosome; what they have they got from their mother
definition of hemizygous
a gene present on the X chromosome that is expressed in males in both the recessive and dominant condition (gotten from their mothers)
definition of sex-linked inheritance
inheritance of a genetic trait located on the sex chromosomes
regarding sex-linked inheritance, how many copies do females have? what does this result in?
females have two copies, and can be homozygous or heterozygous
regarding sex-linked inheritance, how many copies do males have? what does this result in?
males have only one copy, are hemizygous, and express the phenotype of the only allele they have
exp of X-linked inheritance
human red-green color blindness
what happens with red-green color blindness regarding males vs. females?
a heterozygous female has normal vision, but a male is colorblind if he has a mutated X allele
are there Y-linked genes?
yes
definition of Y-linked genes
genes found on the Y chromosome
what discovery was the follow-up of Mendel’s?
Morgan’s discovery of X-linked genes
what is Morgan’s discovery of X-linked genes?
haploid gametes; 2 parents swap phenotypes; in the F1 generation, all of the offspring have red eyes; in the F2 generation, white eyes reappear in the next generation, but only in males, all of the females have red eyes and among the males the ratio of red:white eyes is 1:1
definition of a reciprocal cross
a cross in which the phenotypes of the male and female are reversed compared with a prior cross
what offspring can males pass their traits down to?
only can pass down to their daughters
what are the two halves of the reciprocal cross in the F1 generation?
in one half, all of them have red eyes because they all inherit the X gene from mother; in the other half, half of the offspring get it because the male is dominant
what are the two halves of the reciprocal cross in the F2 generation?
in one half, all females have red eyes and only 50% of men have red eyes (X-linked, 3:1); in the other half, 2 have red eyes and 2 have white eyes
what is Morgan’s explanation?
the w gene (for white eyes) must be on the X chromosome
in the inheritance of X-linked genes, what do XX offspring show?
XX offspring show that a male can only transmit his X chromosome to his daughter (XX)
in the inheritance of X-linked genes, what do XY offspring show?
they show that a male inherits his X chromosome from his mother
do X-linked genes show distinct patterns in pedigrees?
yes
can you distinguish between autosomal and X-linked dominant traits?
not really (look pretty similar)
definition of X-linked recessive traits
pattern in which displayed traits are due to inheritance of recessive alleles carried on the X chromosome
definition of X-linked dominant traits
all females of the affected father are diseased
exp of X-linked recessive trait
red-green color blindness
exp of X-linked dominant trait
hypophosphatemia
regarding X-linked inheritance, would it be possible for an unaffected female to have female offspring with red-green color blindness?
yes-> daughters get it from their fathers, mother just has to be a carrier
is meiosis always perfect?
no -> nondisjunction
definition of nondisjunction
when homologous chromosomes fail to seoarate properly (chromosome pairs) -> results in extra or not enough chromosomes
what fails to separate with nondisjunction?
homologs
what results from nondisjunction?
aneuploidy -> all gametes have too many or too few chromosomes
exp of aneuploidy
down syndrome/trisomy 21, etc
can nondisjunction happen in meiosis?
yes, it can happen in meiosis II if sister chromatids are not separated
definition of aneuploidy
extra or missing chromosomes in human births
definition of euploid
normal # of chromosomes; 46, XX or 46 XY
how many individuals per 10,000 human live births have extra or missing chromosomes?
33
why does it work to have extra or fewer X/Y chromosomes?
males only have one of each; only one X chromosome in each of us is being expressed anyways (not two in females)- balance with males, one X turned off/not expressed
what is down syndrome due to?
its due ro nondisjunction of chromosome 21 (gametes aren’t haploid now because of chromosome 21 having 3 copies)
is there a higher rate of down syndrome per number of births in older mothers?
yes, births from older mothers are more affected; the longer the egg is waiting in meiosis, the greater chance that the mother will have a child with down syndrome
in an X-linked recessive trait, are males or females more frequently affected?
males are affected more frequently than females
in an X-linked recessive trait, are traits passed from father to son?
no, a trait is never passed from father to son (X is given to daughters)
in an X-linked recessive trait, what is the genotype of mothers of affected sons?
affected sons are usually born to carrier mothers (heterozygous)
in an X-linked recessive trait, how many sons of a carrier mother will be affected?
about 1/3 of the sons of a carrier mother will be affected
in an X-linked recessive trait, what are the genotypes of daughters of an affected male and an unaffected non-carrier female?
all daughters of an affected male and an unaffected non-carrier female are carriers
in an X-linked recessive trait, does the trait skip generations?
yes, the trait often skips generations
in an X-linked dominant trait, are males or females more likely affected?
males and females are equally likely to be affected
in an X-linked dominant trait, are the sons and daughters of an affected father affected or unaffected?
all daughters of an affected father are affected, but np sons
in an X-linked dominant trait, what are the mothers always like of affected sons?
affected sons always have affected mothers
in an X-linked dominant trait, how much of the offspring of an affected mother will be affected?
about 1/3 of the offspring of an affected mother will be affected
in an X-linked dominant trait, can affected daughters have an affected mother or father?
yes, affected daughters can have an affected mother or father
in an X-linked dominant trait, does the trait often skip generations?
no, the trait does not skip generations
