Mendel Flashcards
before mendel, what did people believe in for heredity?
blending hypothesis - how blue and yellow make green
what did mendel introduce?
particulate hypothesis - discrete units called genes passed on from parents to offspring retain their separate identity
analogous to marbles in a bucket being passed into offspring
what did gregor mendel do as a profession?
monk
what did mendel work with?
pea plants
nickname of mendel?
Father of Genetics
what is an angiosperm?
flowering plants
parts of an angiosperm? (8)
petal
sepal - encase flower
filament - holds the pollen sack
anther - pollen sack
ovary
style - neck of ovary
stigma - sticky part of flower
stem
eggs of flowers
ovules
male parts of angiosperm
stamen - filament and anther
female parts of angiosperm
pistil/carpal - style and ovary
what is the mating of 2 varieties called?
hybridization
the mating of one character? two characters?
monohybrid; dihybrid
what did mendel’s experiment prove incorrect?
the blending model of inheritance was inccorect
what did the purple x white flowers in the p generation produce?
all purple flowers, not pale
therefore, purple flower color is dominant to white
how many characters did mendel observe the pattern of inheritance?
6 other - 7 total
what is the ratio of inheritance of mendel’s experiment?
3:1
how did mendel explain the ratio inheritance? (4)
1) alternate versions of genes account for variation (alleles)
2) organism inherits 2 alleles (mom and dad), and thus a genetic locus is represented twice in diploid organism- either heterozygous or homozygous
3) if alleles differ, dominant allele is expressed in phenotype, while recessive is not seen
4) Law of Segregation
Law of Segregation
the 2 alleles present in a cell segregate during meiosis, accounting for the haploid number in sperm and eggs
identical alleles
homozygous
alleles differ
heterozygous
how an organism looks
phenotype
genetic makeup
genotype
can we tell the genotype of a purple flower?
no it can be PP or Pp
what is test cross?
when you cross a mysterious organism with a homozygous recessive one to determine genotype
if all offspring have purple in a test cross what is the genotype?
PP
if half are purple and other half white after a test cross, what is the genotype?
Pp
how did Mendel discover his 2nd law?
performing dihybrid
he questioned whether 2 characters were inherited as a package or separately
what is mendel 2nd law?
Law of Independent Assortment
in a dihybrid, the two alleles for one character assort independently of the two alleles of another character
Law of Independent Assortment
traits separate and produce 4 gametes
4 gametes of RrYy
RY, Ry, rY, ry
genotype of RrYy x RrYy
1:2:1:2:4:2:1:2:1
phenotype of RrYy x RrYy
9:3:3:1
Law of Large Numbers
probability is closer to predicted results when sample size is increased
what does dominant really mean?
- not mean trait is more common (Polydactyly is dominant)
- it doesn’t mean the allele subdues a recessive allele
- it just is a working gene that makes a normal/functional protein
how does roundness come about in a pea rather than wrinkles?
due to the Prescence of an enzyme that converts simple sugars to starch
round peas have starch, wrinkled don’t
wrinkles store simple sugars rather than starch, so with osmosis water enters causing to to swell, and wrinkle when it dries
Incomplete Dominance
F1 hybrids have an appearance in between 2 parentals
red + white = pink
Why isn’t Incomplete Dominance evidence for blending?
blending suggests all offspring would be the intermediates-not true
what did Mendel’s pea plants exhibit?
Complete/Simple Dominance
Codominance
both alleles are expressed in phenotype
example of codominance with human blood groups
M, N, MN
M individual - MM
N individual - NN
MN individual - MN
Mutiple Alleles
exist in populations with more than 2 allelic forms
AB^O blood group has three different alleles of one gene
what do A, B, AB, O blood types represnet?
two sugars that are either present or absent on the surface of RBC’s - A substance and B substance
A blood group
Phenotype: A
Genotype: I^AI^A or I^Ai
Antibodies present: Anti-B
Compatibility with other blood types: agglutination with B and AB, A and O compatible
B blood group
Phenotype: B
Genotype: I^Bi^B or I^Bi
Antibodies present: Anti-A
Compatibility with other blood types: agglutination with A and AB, compatible with B and O
AB blood group
Phenotype: AB
Genotype: I^AI^B
Antibodies present: none
Compatibility with other blood types: compatible with all
O blood group
Phenotype: O
Genotype: ii
Antibodies present: Anti-A and Anti-B
Compatibility with other blood types: compatible only with O
Example of codominance in blood type
AB are both expressed
Pleiotrophy
gene affects an organism’s phenotype in many ways
ex. sickle cell anemia is caused by a single gene, causing RBC to change their shape, resulting in multiple symptoms
epistasis
when a gene at one locus affects the phenotypic expression of a gene at another locus
epistasis ex
Black fur dominant to brown
BB, Bb= black
but if CC, Cc (a gene that controls pigment) is present, color will show
if cc, mouse is albino regardless of genotype
Polygenic Inheritance
seen with human skin color and height - when a character varies along a continuum
what is polygenic inheritance define as?
the additive/quantitative effect of two or more genes on a single phenotypic character
polygenic inheritance example
with skin color, each dominant allele contributes to darker skin color and each recessive gene to lighter color
AABBCC - six units of darkness, so skin will be very tan
aabbcc - six units of lightness, skin will be very pale
AaBbCc and AABbcc - both have 3 units of darkness, so skin will be same tone
what is phenotype also determined by?
environment
nature (gene) and nurture (environment) both influence all traits
example of nature
genotype
example of nurture
nutrition, exercise, expose to sunlight
what is the nurture side of the debate the broadest for?
polygenic traits like skin color and height
example of how environment affects an organism is seen in flowers
hydrangea - same genetic varieties produce a range of colors from pink to white to purple based upon the soil pH
how to geneticist analyze mating of humans?
pedigrees
what can pedigrees be used for?
track a trait across generations to understand the past and to predict the future
when an allele causes a genetic disorder, what are the possible reasons?
either a malfunction of a protein or no protein at all
why do heterozygous individuals regarding recessive disorders express the “normal” phenotype?
one copy of the normal allele produces some of a specific protein
what are heterozygotes that are phenotypically normal called?
carriers
when does a recessively inherited disorder show up in?
homozygous recessive individuals
why are genetic disorders not evenly distributed among all groups of humans?
past conditions when the world was less industrialized, and people were more geographically isolated
most common recessive lethal genetic disease in white in the US
cystic fibrosis
what is cystic fibrosis
affects Cl- transport between cells and the interstitial fluid
the protein channels that transport chloride in and out of the cell are defective or absent in people with cystic fibrosis
causes Cl- to build up that leads to mucus build up around organs and air pathways as well as bacterial infection
Tays Sechs
recessive disorder where a dysfunctional enzyme fails to break down lipids in the brain - causes seizures, blindness, and degeneration of motor and mental perfomrance
sickle cell anemia is common in what descent? why?
African descent
1/10 African Americans are carriers of this allele
in certain environments in Africa, heterozygotes have an advantage over hom. dom as they have resistance to malaria
plasmodium only infect normal RBC
what is sickle cell anemia?
substitution of 1 amino acid in the hemoglobin protein RBC’s causes to sickle
sickled cells hold less oxygen
what type of dominance is sickle cell anemia?
incomplete as individuals who are heterozygous suffer some of the symptoms due to a fraction of their RBC sickled
most harmful alleles are?
recessive
example of dominant disorder
Achondroplasia = form of dwarfism expressed in individuals with AA or Aa
99.99% of population is aa
AA = fetal death
many lethal dominant alleles results due to?
mutations
example of dominant disorder that does not show up until age 35-35
Huntington’s disease - degeneration of the nervous system
amniocentesis
inserting needle into amniotic fluid surrounding the fetus around the 14th-16ht week of pregnancy
how is the fluid taken from amniocentesis tested?
1) tested with chemicals for certain disorder
2) the cells from the fluid are grown in a lab and within weeks a karyotype can identify chromosomal defects
CVS
chronic villus sampling
doctor suctions out fetal tissue from the placenta around the 8th to 10th week of pregnancy
fetal tissue is then karyotyped immediately, giving results within 24 hours
what type of means are CVS and aminocentesis to check for abnormalities?
invasive means
noninvasive way to check for abnormalities?
ultrasound - uses sound waves to prdce image of fetus
risk of invasive procedures
som risk of maternal bleeding or fetal death, and therefore are reserved for only extreme risk cases
how big was Mendel’s sample?
many varieties
how were the pea plants easy to control?
remove make stamens of parentals so they could not self-fertilize
how were the traits of the pea plants?
either - or
how did mendel start his experiment?
true breeding/purebred varieties
all parentals were homozygous
how long did mendel follow his experiment?
at least 3 generations
P (parental), F1(first filial) that self-pollinate, F2
what type of analysis did mendel use?
quantitative analysus
what did the large number of offspring/sample provide?
high probablilty
how were the peas easy maintain?
short life cycles
