AP Bio Flashcards Chapters 14 and 15 - Sheet1
Who started the gene idea?
Gregor Mendel, with pea plants
Who discovered the basic principles of heredity?
Gregor Mendel, with pea plants
What makes peas conducive to genetic experiments?
The fact that they are available in many varieties, short generation time, large number of offspring, and that each trait can only be expressed one of two ways
What is a heritable features that varies among indivduals?
a character
What is a character?
a heritable feature that varies among indivudals
What is a trait?
a variant for a character, such as purple or white flowers
What is true-breeding?
plants that produce only the same variety as the parent plant
What is hybridization?
the mating/crossing of two true-breeding varieties
P generation
parental generation, the true-breeding parents
F1 generation
first filial generation, hybrid offspring of P generation
F2 generation
when F1 offspring self-pollinate or cross-pollinate with other F1s
What is Mendel’s model to explain 3:1 inheritance?
1) alternative versions of genes account for variations in inherited characters; 2) for each character, an organism inherits two copies of a gene, one from each parent; 3) if the two allelles at a locus differ, then the dominant allele determines the organism’s appearance, and the recessive allele has no noticeable phenotypic effect; 4) two alleles for a heritable character segregate during gamete formation and end up in different gametes
allele
alternative versions of a gene
law of segregation
that the two alleles for a heritable character segregate during gamete formation and end up in different gametes
testcross
breeding an organism of unknown genotype with a recessive homozygote
monohybrid
organisms that are heterozygous for one particular character being followed in the cross
dihybrid
organisms that are heterozygous for two characters being followed in the cross
law of independent assortment
each pair of alleles segregates independently of each other pair of alleles during gamete formation
What is the phenotype for a dihybrid cross?
AaBb x AaBb = 9:3:3:1
What is the genotype for a dihybrid cross?
AaBb x AaBb = 1:2:1:2:4:2:1:2:1
complete dominance
phenotypes of AA and Aa are indistinguishable
incomplete dominance
neither allele is completely dominant: red x white = pink
What is the genotype for incomplete dominant F1 hybrids?
1:2:1 (homoz dom, hetero, homoz rec)
What is the phenotype for incomplete dominant F1 hybrids?
1:2:1 (homoz dom, hetero, homoz rec)
codominance
two alleles each affect the phenotype in separate, distinguishable ways: ex: human MN blood
How is the human blood type MN phenotypically expressed?
Codominantely: with both M and N phenotypes appearing
What does Tay-Sachs disease show about genetics?
That the observed dominant/recessive relationship between alleles depends on the level of examination: Tay-Sachs allele is recessive at organismal level, but incompletely dominant at the biochemical level, and codominant at molecular level
What are multiple alleles?
Characters that exhibit more than two traits, such as blood: ABO
What are the four blood types humans can have?
A, B, AB, O
pleiotropy
when genes have more than one phenotypic effect
Give a human example of pleiotropy.
Multiple symptoms associated with cystic fibrosis and sickle-cell disease
epistasis
when the phenotypic expression of a gene at one locus alters that of a gene at a second locus
What is the phenotype for a cross of two dihybrid individuals with epistasis?
9:.3:.4
When homoz. Rec. ee is epistatis to Lab color, what happens to dogs that are homoz-dom or heteroz-dom for black?
They’re yellow anyway, since the homoz-rec ee turns the coat yellow regardless of B/b expression
quantitative characters
when characters vary in gradations rather than in the either-or behavior of pea plants
polygenic inheritance
an additive effect of two or more genes on a single phenotypic character
Polygenic inheritance is the opposite of what?
Pleiotropy
Give a human example of polygenic inheritance/quantitative characters.
Skin color
norm of reaction for a genotype
phenotypic range due to environmental influences: ex: hydrangea color
Generally, norms of reaction are broadest for what kind of characters?
polygenic characters
What does it mean when characters are multifactorial?
That many factors, both genetic and environmental, collectively influence phenotype
pedigree
the family tree describing traits of parents and children across the generations
carriers
individuals that are phenotypically normal for a disorder, but heterozygous, so that they MAY transmit the recessive allele to offspring
What does consanguinuity contribute to?
recessive disorders
What is the most common lethal genetic disease in the US?
cystic fibrosis
Give four examples of recessive disorders.
Albinism, Tay-Sachs, cystic fibrosis, sickle-cell
Give two examples of dominant disorders.
Dwarfism (achondroplasia) and Huntingdon’s disease
Which is more likely to result in early death, lethal rec-disorders or lethal dom-disorders?
Dominant disorders, since heterozygous rec-disorder carriers don’t exhibit the disorder, whereas the only survivors of lethal dom-disorders are the homoz-rec.
What allows lethal dom-disorders to be passed on?
If onset of death occurs at a later age
amniocentesis
physicians insert a needle into the uterus and extract amniotic fluid for genetic testing
CVA (chorionis villus sampling)
physicians insert narrow tube through cervix into uterus and suction out a sample of placenta tissue for genetic testing: faster results, can be done earlier than amniocentesis
What is one common newborn screening for?
PKU
chromosome theory of inheritance
developed by sutton and Boveri: Mendelian genes have specific loci/positions along chromosomes and these chromosomes undergo segregation and independent assortment, which accounts for those genetic properties
Who gave the first evidence that chromosoems are the location of Mendel’s inheritable factors?
TH Morgan, with drosophila melanogaster
wild type
the phenotype for a character most commonly obersved in natural populations
mutant
phenotype opposite to what’s most commonly observed in natural populations
How does Morgan’s notation differe from Mendel’s notation?
Morgan uses + for wildtype and nothing for mutant, whereas Mendel uses capital for dominant and lowercase for recessive
What is one fly characteristic that is sex-linked?
Eye colors: red or white
In embryos, the absence of what allows the development of ovaries?
the SRY gene
sex-linked gene
a gene located on either sex-chromosome
X-linked gene
~1,000 genes conatined in the human X chromosome
Why are so few disorders Y-linked?
Because the Y chromsome has so few genes on it
Most Y-linked genes determine ___, but many X-linked genes code for what?
Y-linked: sex; but X-linked: lots of things unrelated to sex
hemizygous
term used for males to refer to the recessive x-linked allele, since they have only one X chromosome and tehrefore homoz or heteroz don’t really apply
Give three examples of X-linked disorders.
color-blindness, Duchenne muscular dystrophy, hemophilia
Why do males and females have the same effective “dose” or X-linked genes?
One of the X-chromosomes in female mammals becomes inactivated during early embryonic development: condeses into a Barr body
What happenes to Barr bodies in cells that become gametes?
Reactivated so that each gamete has an X chromosome
Why do females consist of a mosaic of two types of cells: active X from father vs. active X from mother?
The X-chromosome inactivated into a Barr body is selected randomly in each embryonic cell
If a female is hereterozygous for a sex-linked trait, what percentage of her cells exhibit each trait?
50% each
What is the XIST gene?
a gene that becomes active only on the chromosome that will become the Barr body to inactivate the chosen X chromosome
linked genes
genes located near each other on the same chromosome that tend to be inherited together in genetic crosses
genetic recombination
the production of offspring with combinations of traits that differ from those found in either parent
parental types vs. recombinant types
look like parents vs. look like combination of parents
When 50% of all offspring are recombinant, geneticists say that there is a ___ frequency of recombination.
50%
What percent frequency of recombination in testcrosses is observed for any two genes that are not linked?
50%
If two genes are recombined with 50% frequency, then the genes are what?
Not linked
How do you calculate the recombination frequency?
total recombinants over total offspring times 100
What accounts for the recombination of linked genes?
crossing over
genetic map
an ordered list of the genetic loci along a particular chromosome
What determines recombination frequency?
the distance between genes on a chromosome
The farther apart two genes are, the ___ the probability that a crossover will occur between them and therefore the ___ the recombination frequency.
Higher, higher
linkage map
genetic map based on recombination frequences
How does one express distances between genes?
With map units
T/F: genes that are physically connected are always genetically linked
False, they can be genetically unconnected if they’re far enough apart to be almost certainly separated during crossing-over
T/F: map units correspond to actual physical distances between genes/
False, because the frequency of crossing over is not actually uniform over the length of the chromosome
cytogenetic maps
locate genes with respect to chromosomal features, such as stained bands, that can be seen in the microscope
nondisjunction
members of a pair of homologous chromosomes do not move apart properly during meiosis I, or sister chromatids fail to separate during meiosis II
aneuploidy
when zygotes have an abnormal number of a particular chromosome
monosomic
when a cell only has one of a chromosome instead of two (2n-1)
trisomy
when a cell has an extra of a chromosome instead of two (2n+1)
polyploidy
when organisms have more than two complete chromosome sets in all somatic cells
