Chapter 12 Flashcards
list 6 reasons why Mendel used pea plants in his experiments
- easy to work with
- complete life cycle in one season
- pea plants self-pollenate
- female and male repro parts in one flower
- all truebreeding pea offspring look exactly like the parents
- there are many varieties of pea plants with many different flower colors
how did Mendel get the true-breeding parents for his experiment? (P generation)
- let purple flowering pea plants self-pollenate, so all offspring will be purple
- let white flowering plants self-pollenate so all offspring will be white
what was the first non-truebreeding cross that Mendel did and what were the results?
crossed pollen from purple flowering plants to female repro parts of white flowering plants
purple x white = offspring all purple
what is the genotype for the F1 generation of a monohybrid cross?
PP x pp = all Pp (heterozygous)
what is the phenotype of the offspring from a F1 monohybrid cross?
all dominant trait expressed
what does F1 mean?
1st filial generation
what is the genotype for the F2 generation of a monohybrid cross?
Pp x Pp = 1 (PP): 2 (Pp): 1 (pp)
what is the phenotype for the F2 generation of a monohybrid cross?
3 (dominant trait): 1 (recessive trait) expressed
what is a genotype?
tells what the members of a homologous pair carry
where do the allele of a genotype come from?
1 maternal, 1 paternal
what are the results of a monohybrid cross?
1 true-breeding dominant plant
2 not-true-breeding dominant plants
1 true-breeding recessive plant
what is a gene?
DNA coding for a trait, passed from parent to offspring
what are alleles?
alternate forms of a gene
what are the alleles for a heterozygous genotype?
2 different alleles
what are the alleles for a homozygous genotype?
2 same alleles
what is the phenotype?
the outward appearance of an individual
what is the principle of segregation?
2 alleles for a gene separate during gamete formation (meiosis) and are rejoined at random, one from each parent, during fertilization
what type of cross does the principle of segregation apply to?
monohybrid cross
how could you determine the genotype of an individual with the dominant phenotype?
test cross with a homozygous recessive individual to determine if it’s PP or Pp
what will the result of the test cross between a homozygous recessive individual and an individual with a homozygous dominant genotype be?
all offspring heterozygous, dominant trait always shown
what will the result of the test cross between a homozygous recessive individual and an individual with a heterozygous genotype be?
50/50 heterozygous/homozygous recessive offspring
what kind of inheritance is shown in monohybrid crosses?
simple gene inheritance, where some exhibit dominant inheritance and some exhibit recessive inheritance
what is pedigree analysis?
used to track inheritance patterns in families
what is a dihybrid cross?
an examination of 2 SEPARATE traits in a single cross
give an example of a genotype of a dihybrid cross
RR YY x rr yy
what is the genotype of the F1 generation of a dihybrid cross?
RrYy, heterozygous
what is the phenotypic ratio of the F2 generation of a dihybrid cross?
9:3:3:1
what is the principle of independent assortment?
in a dihybrid cross, the alleles of each gene assort independently, they don’t influence each other
what is the rule of addition?
the probability of 2 mutually exclusive events occurring simultaneously is the sum of their individual probabilities
when crossing Pp x Pp, the probability of producing Pp offspring is?
the probability of obtaining Pp (1/4) PLUS the probability of obtaining pP (1/4)
1/4 + 1/4 = 1/2
ALWAYS VERIFY WITH A PUNNET SQUARE
what is the rule of multiplication?
the probability of 2 independent events occurring SIMULTANEOUSLY is the PRODUCT of their individual probabilities
when crossing RrYy x RrYy, the probability of obtaining rryy offspring is?
probability of rr = 1/4
probability of yy = 1/4
probability of rryy = 1/4 x 1/4 = 1/16
what 3 things does the simple Mendelian model of genetic inheritance assume?
- each trait is controlled by a single gene
- each gene has only 2 alleles
- there is a clear dominant-recessive relationship between the alleles
do most genes meet the criteria of simple Mendelian genetics?
no
what is incomplete dominance?
when heterozygotes are intermediate in phenotype between the 2 homozygotes, alleles are equal, so phenotype is a combo of both
give an example of incomplete dominance
red flowers x white flowers = pink flowers
what is used to denote alleles in incomplete dominance?
superscripts
draw a punnet square for incomplete dominance
i’m serious, get out a piece of paper and a pen and DRAW IT :)
what is codominance?
the heterozygote shows the phenotypes of both homozygotes
give an example of codominance
roan horse coat color, chestnut and white both displayed
what 2 inheritance patterns does the human ABO blood group system demonstrate and how?
- multiple alleles: there are 3 alleles for the I gene (Ia, Ib, and i)
- codominance: Ia and Ib are dominant to i, but codominant to each other
list the allele combinations for each blood type
Type A: Ia Ia, Ia i
Type B: Ib Ib, Ib, i
Type AB: Ia Ib
Type O: ii
what is polygenic inheritance?
when multiple genes are involved in controlling the phenotype of a trait, is an accumulation of contributions by multiple genes
what kind of traits come from polygenic inheritance and what do they show?
quantitative traits with continuous variation
give an example of a trait controlled by polygenic inheritance
human height
list 4 factors that control the polygenic trait of human height
- growth hormones
- calcium metabolism
- muscle flexibility
- environmental factors: nutrition, activity, stress
what does polio do to human height?
depresses growth
what is pleiotropy?
when an allele has more than one effect on the phenotype
give an example of pleiotropy
human diseases like cystic fibrosis or sickle cell anemia, where multiple symptoms can be traced back to one defective allele
is sickle cell anemia strictly a homozygous recessive trait?
no, you can be heterozygous or homozygous recessive for sickle cell anemia
what is the advantage of heterozygous sickle cell anemia?
malaria resistance; malaria is a protozoa that attacks healthy red blood cells, so if your RBC’s are already fuckity, malaria doesn’t bother with your trash cells
which type of sickle cell anemia is worse to have and why?
homozygous, the decreased ability to carry oxygen throughout the body can cause learning disabilities and organ failure
what else can influence gene expression other than inheritance?
the environment
give an example of genes expression that is influenced by the environment, and how it happens
coat color in Himalayam rabbits and Siamese cats, an allele produces an enzyme that allows pigment production only at temperatures below 30 degrees celsius (room temp is about 20 degrees celsius)
what part of the Himalayan rabbits and Siamese cats are colored and why?
the extremities; they are further away from the core of the body and colder because blood flow diversion to keep them warm
what can happen sometimes when genes interact with each other?
the phenotype is influenced
what is epistasis?
one gene can interfere with the expression of another gene
give an example of epistasis
coat color in labrador retreivers
“brown” allele- eumelanin pigment color (B or b)
“eumelanin” allele- pigment present (E or e)
if a black lab has to have at least on dominant allele at each loci (for each gene) what are the possible genotypes (4)?
- EEBB
- EeBb
- EEBb
- EeBB
if a chocolate lab has to have at least one dominany eumelanin allele (E), what are the possible genotypes (2)?
- EEbb
- Eebb
homozygous recessive for fur color because lighter brown
if a yellow lab with dark skin has to have at least one brown allele, and both eumelanin alleles recessive, what are the 2 possible genotypes?
- eeBb
2. eeBB
if a yellow lab with light skin has to have both alleles recessive, what is the only possible genotype?
eebb
what chromosome pair number are the sex chromosomes?
23
what is every other chromosome pair other than the sex chromosomes called?
autosomes
what sex chromosomes do human females have?
XX
what sex chromosomes do human males have?
XY
what does the y chromosome do?
controls male sex characteristics
how did we find out about x-linked traits?
fruits fly experiments
what were the wild type and mutant traits in fruit fly eye colors?
wild type: trait normally found, red eyes
mutant: white eyes, rare
when scientists crossed a red-eyed female with a white-eyed male fruit fly, what was the expected phenotype?
red eyes
when scientists crossed F1 females and F1 male fruit flies, what were the F2 results?
3 red-eyed, 1 white-eyed
after 2 crosses, what gender of fruit fly had white eyes and what did this suggest?
only males, suggested that eye color is on the X, not the Y chromosome
what test cross was done with fruit flies to determine if you could get white-eyed females and what was the result and what did the result prove?
white-eyed male x heterozygous female = white eyed females are viable, eye color is linked to X, and absent from Y chromosome
what is sex determination in fruit flies based on?
number of X chromosomes, XX is female, XY is male
do all organisms have X and Y chromosomes?
no
how is sex determined in birds?
Z and W chromosomes
ZZ= males (ZZ top), ZW= females
how is sex determined in grasshoppers?
number of X chromosomes, but no Y chromosome, so
XX= female, X0= male
how is sex determined in bees?
diploid= female, haploid= male
for males, from which parent does the Y chromosome come?
paternal
what parent do X chromosomes come from in humans?
male: from mom
female: from mom and dad
what is a characteristic of the X chromosome?
carries a LOT of genes
what is a characteristic of the Y chromosome?
male secondary sex characteristics
what are sex-linked traits?
controlled by genes present on the X chromosome
do sex-linked traits show the same inheritance patterns as autosomes?
no, so different pedigree patterns
who do sons inherit sex-linked traits from?
mother
who do daughters inherit sex-linked traits from?
both parents
who are carriers of sex-linked traits?
heterozygous females
what is dosage compensation?
equal expression of genes from sex chromosomes, double dose
why is dosage compensation a problem?
too much of same gene/genetic info
what happens in female cells with dosage compensation?
1 X chromosome is inactivated and highly condensed into a BARR BODY, to look more like a Y chromosome
what are females heterozygous for genes on the X chromosome called and why?
genetic mosaics, because which chromosome is activated it deactivated is totally random, and determines phenotype
what gender are most calico cats?
female
why are calico cats different patchy colors?
from activation and inactivation of fur color alleles
what is genetic mapping?
the distance between genes on a chromosome can yield information
what is genetic mapping based on?
genetic recombination (crossing over) between genes
what is true about distance between genes on a chromosome and their likelihood of crossing over TOGETHER?
genes that are closer together tend to cross over TOGETHER while genes that are father apart are less likely to cross over TOGETHER
what can cause human genetic disorders?
mutated DNA sequences leading to altered proteins
what protein is mutated in sickle cell anemia?
hemoglobin
give an example of a protein being altered at only one single amino acid causing a genetic mutation
sickle cell anemia, hemoglobin
what gene associated with sickle cell anemia that alters one amino acid to cause the disorder?
HBB gene
what is nondisjunction?
failure to separate either members of a homologous pair (meiosis I) or sister chromatids (meiosis II)
what is 2n?
diploid
what is n?
haploid
what causes miscarriage, genetically?
nondisjunction mutations that do not allow for continued development
what happens if nondisjunction occurs during meiosis I?
there are no viable cells
what does fertilization of gametes with non-normal chromosome numbers create?
trisomic or monosomic individuals
what, gentically, is down syndrome?
trisomy of chromosome 21
list 5 human genetic disorders, other than down syndrome, that can occur from nondisjunction and their genotypes
- triple-X females (XXX)
- Klinefelter syndrome (XXY)
- Turner syndrome (X0)
- 0Y nonviable zygote
- Jacob syndrome (XYY)
describe what happens to the chromosomes in triple XXX females
2 of the X chromosomes for Barr bodies
list an example of Klinefelter syndrome?
male calico cats, one X will form a Barr body
describe a physical characteristic of Turner syndrome
webbing in toes, fingers, and neck
what is Jacob syndrome known for?
producing extra male characteristics
what do Barr bodies do?
contribute to formation of sex organs
if there are no physical characteristics of some nondisjunction genetic disorders, how do most people find out they have them?
they are usually infertile/sterile
