Mendel and genetics Flashcards
blending hypothesis
idea that genetic material contributed by the two mixes
blending hypothesis predicts
over many generations a freely mating population will give rise to a uniform population of individuals
blending hypothesis fails to explain the
reappearance of traits that have skipped generations
particulate hypothesis is the
gene idea
particulate hypothesis
parents pass on discrete heritable units (genes)
with the gene idea, the genes retain their
separate identities in offspring
genes can be shuffled and passed
along generation after generation
Gregor Mendel
documented genetics with pea plants
Mendel developed his theory before
chromosomes were observed with the microscope
how did Mendel discover the basic principle of heredity
breeding pea plant
why did Mendel work with pea plants
- short generation time
- large number of offspring
- he could control the mating between plants
- distinct flower colour
why was it important Mendel could control mating between plants
he could be certain for the parentage
character
heritable trait that varies among individuals
example of a character
flower colour
trait
variant for a character
example of a trait
having purple or white flowers
a pea flower has ______ reproductive organs
both
male reproduction organ in peas
stamen
the stamen produces
pollen
female reproductive organ in peas
carpel
a pea plant will ______ fertilize
self
what is the zygote encased in
a seed (pea)
true breeding
over many generations of self pollination, plants produce the same variety as the parent
example of true breeding
the parent has a purple flower and ALL offspring have purple flowers
hybridization
mating or crossing of two true-breeding varieties
P generation
true breeding parents
F1 generation
the first hybrid offspring
F2 generation
second generation
the F2 generation arises from the
F1 generation as it self-pollinates
law of segregation
Two alleles for a heritable character segregate during gamete formation and end up in different gametes
if an organism has identical alleles for a character
the allele is present in all gametes
will the offspring look like parents if the organism has identical alleles for character
YES
dominant trait
always expressed when the allele is dominant
recessive trait
only expressed if both alleles are recessive
what happens to a recessive trait if there is only ONE allele
will show dominant phenotype
Alternative versions of genes
alleles
each parent will have _______ of the traits
one
each gene is a
sequence of nucleotides at a specific locus
how does an organism inherit two copies of a gene
one from each parent
genetic locus is represented ______ in a diploid cell
twice
what does it mean if two alleles are at a different locus
one is dominant the other is recessive
dominant allele
determines the organism’s appearance
recessive allele
has no noticeable effect on the organism’s appearance
punnet square
predicts the allele composition of offspring from a cross between individuals
what must be known for a punnet square
the genetic makeup
homozygote
organism that has a pair of identical alleles for a gene encoding a character
a homozygote is said to be _____ for that gene
homozygous
phenotype
observable traits
heterozygote
organism that has different alleles for a gene
a heterozygote is said to be
heterozygous
is true breeding homozygous or heterozugous
homozygous
phenotype is both
physiological traits and appearance
genotype
genetic makeup
testcross
breeding an unknown genotype with a RECESSIVE homozygote
what does a testcross reveal
the genotype of the organism
law of independent assortment
applies only to genes located on different chromosomes
law of independent assortment can happen on the same chromosome IF
the genes are far apart on the chromosome
monohybrid
heterozygous for the one particular character being followed in the cross
dihybrid
heterozygous for the TWO characters being followed in the cross
genes are packaged into gametes in all possible allele combinations AS LONG AS
each gamete has one allele for each gene
alleles for one gene segregate into gametes ________ of any other gene
independently
what is the key phenotypic ratio
9:3:3:1
event that is certain to occur has a probability of
1
event that is certain to NOT occur has a probability of
0
the probability of a current test is _____ by any previous attempts
unaffected
multiplication rule
multiply the probability of ONE event by the probability of the other event
each gamete has a ______ chance of carrying the dominant or recessive allele
50/50
for any heterozygous F2 plant, the dominant allele can come from
the egg OR the sperm but NEVER both
addition rule
add the individual probabilities
two ways the inheritance of a character is determined by a single gene DEVIATES from Mendel
- when a gene has more than two alleles
- when a single gene produces multiple phenotypes
alleles can show different degrees of ______ and ______ in relation to each other
dominance and recessiveness
complete dominance
the phenotype of heterozygote and the dominant homozygote are indistinguishable
incomplete dominance
neither allele is completely dominant and results in a hybrid phenotype
co-dominance
two alleles each affect the phenotype in separate ways and BOTH are shown
why is an allele dominant
its seen in the phenotype
when both a dominant and recessive allele coexist, they
do not interact at ALL
for any character that observed a dominant/recessive relationship of alleles depends on
the level we examine the phenotype
Whether alleles appear to be completely dominant, incompletely dominant or codominant depends on the
level at which the phenotype is analyzed
Dominant alleles are NOT always
more frequent than recessive ones
ABO blood groups in humans are determined by that person’s
two alleles of the blood group gene
Three possible alleles for blood
- IA
- IB
i
what do the blood types refer to
carbohydrates A and B attached to a cell surface molecule on red blood cells
type O blood has _____ carbohydrate
neither
Pleiotropy
Genes can have multiple phenotypic effects
A single gene can affect a number of characteristics
Pleiotropy
Dominant relationships, multiple alleles and pleiotropy all have to do with the
effects of a single gene
Epistasis
One gene affects the phenotype of another
The two gene products interact
Epistasis
Polygenic inheritance
Multiple genes independently affect a single trait
The phenotypic expression of a gene at one locus alters the phenotypic expression of a gene at a second locus
Epistasis
a gene that determines whether or not a trait will be expressed
Epistasis
Quantitative characters
Characters that vary in population in gradations along a continuum
Usually indicates polygenic inheritance
quantitative characters
The phenotype ratio is broader
polygenic inheritance
The phenotype for a character depends on
enviroment as well as genotype
Multifactorial
Many factors collectively influence phenotype including genetic and enviromental
Refers to an organism in its entirety = all aspects of its physical appearance, internal anatomy, physiology and behaviour
phenotype
Refers to its alleles for a single genetic locus
genotype
Humans _____ a convenient subject for genetic research
aren’t
Pedigree analysis
A collection of family history for a trait
Assembled into a family tree describing the traits of parents and children across the generations
Pedigree analysis
More serious when alleles cause disabling or deadly diseases instead of differing heritable traits
Pedigree analysis
The recessively inherited disorders will ONLY show up
homozygous individual
carriers
Heterozygotes may appear normal, but they can pass along the recessive allele to their offspring
Genetic disorders _____ evenly distributed among all groups of people
aren’t
Inbreeding causes an increase in
autosomal recessive conditions
Most common lethal genetic disease in Canada
cystic fibrosis
Normal allele for the gene codes for
A membrane protein that functions in the transport of chloride ions between certain cells and extracellular fluid
Most common inherited disorder among people of Africa
Sickle-cell disease
Sickle-cell disease is a ______ disorder
recessive
At the organismal level of sickle cell
Normal allele is incompletely dominant to the sickle-cell allele
At the molecular level
Two alleles are codominant
The hereditary component is polygenic
multifactorial disorders
_____ has an effect on phenotype
lifestyle
risk of a genetic disorder can be assessed before
a child is conceived
Most children with recessive disorders are born to parents with
normal phenotypes
Amino-centesis
Inserting a needle into the uterus and extract about 10 mL of amniotic fluid
Chronic Villus Sampling (CVS)
- Inserts a narrow tube through the cervix into the uterus
- Suctions out a tiny sample of tissue from the placenta
Imagining techniques
Examine a fetus directly for major anatomical abnormalities that might not show up on genetic tests
Ultrasound
Reflected sound waves are used to produce an image of the fetus
Dominant disorders that are lethal diseases are _____ common than recessive alleles with lethal effects
less
A lethal dominant allele will often cause the
death of the individual = allele is not passed on
when can alleles for a dominantly inherited disorder be passed on
first seen after reproductive age
the pollen grain grows a ____
pollen tube
the pollen tube allows the
sperm to travel to the ovary
describe the relationship between phenotype and genotype in incomplete dominance
genotype and phenotype ratios are the same
what is the phenotype/genotype ratio in incomplete dominance of F2 generation
1:2:1 = 1 dominant, 2 mixed, 1 recessive
genotype of dominant
multiplcation rule
phenotype of dominant
add the phenotypes that show at least one dominant allele
phenotype of recessive
the same as the genotype
why does a dihybrid cross have 16 squares
4 traits have a probability of 1/16
3 traits have a probability of
1/8 (1/2 times 3)
alleles close together on the same chromosome will
segregate together
true breeding are _____
homozygous
Type O genotype
ii
Type A genotype
IA IA or IA i
Type B genotype
IB IB or IBi
Type AB genotype
IA IB
antibodies present in O type
Anti A and Anti B
antibodies present in A type
anti B
antibodies present in B type
Anti A
antibodies present in AB
NONE
Type A blood can receive
Type A or O
Type B blood can receive
type B or O
Type O blood can receive
type O only
Type AB blood can receive
all blood types
what blood is the universal DONOR
O
what blood is the universal RECEIVER
AB
norm of reaction
the phenotypic range of a genotype influenced by the environment
