Mendellian Genetics Flashcards
formula for determining # of unique gametes
2^# of heterozygotes
linkage
the tendency of alleles of particular genes to be inherited togehter
when is linkage seen?
when genes are on the same chromosome
difference between linkage and sex-linkage
linkage refers to two or more genes that are located on the same chromosome
sex-linkage refers to a single gene that is located on a sex chromosome
does sex-linkage indicate anything about location on a chromosome?
no
recombinant
alleles on chromosome are different tan the parent combinations because of crossing over
when does crossing over occur?
during prophase of meiosis I
what happens when genes are located far apart on the same chromosome?
it is more likely that crossing over will occur someplace between these genes
genetic map
a diagram showing the relative positions of genes along a particular chromosome
when are linked genes not inherited together?
when crossing over occurs
what is linkage an exception to?
Mendel’s principle of independent assortment
multiple allelism
more than two alleles of the same gene
example of multiple allelism
blood type
there are three alleles for blood type: A, B, i
codominance
simultaneous expression of the phenotype associated with each of the alleles in a heterozygote
example of codominance
the A and B alleles for blood type are codominant when together to form blood type AB
incomplete dominance
hetereozyotes show a blend of the two alleles
pleiotropic
a gene that influences many traits
are dominant traits more common?
not necessarily
is the wild type always dominant?
no
Are genes the only thing that control traits?
no
the environment plays an important role in the development of certain phenotypes
gene-gene interaction
two or more genes work together to determine a single trait
discrete traits
traits that are clearly different from each other
this is what Mendel worked with
quantitative traits
continuously varying traits
example of quantitative trait
human height and intelligence
how are quantitative traits produced?
the independent actions of MANY genes
polygenic inheritance
each of many different genes adds a small amount to the value of the trait
this is how quantitative traits are produced
central dogma
DNA - RNA - Protein
wild type
an individual that does not have mutations under study
not always the dominant genotype
the particle theory of inheritance
states that hereditary traits act like particles or units that are passed down from generation to generation
Law of Segregation
hereditary factors do not blend, but keep distinct identity during breeding
maintain two distinct alleles that can be passed down. recessive alleles do not dissapear
how is the law of segregation seen?
the separation of homologous chromosomes
1 allele from mom and 1 allele from dad separate
when do homologous chromosomes split?
anaphase of meiosis I
what is a real demonstation of the law of segregation?
true breeding
Law of Independent Assortment
character traits are not connected but are inherited independently of one another (excludes linkage)
how did Mendel determine the law of independent assortment?
performed a dihybrid cross of two traits
each trait was not dependent on other traits
true breeding
two homozygotes for different alleles are crossed
locus
particular site of chromosomal DNA where a gene resides
what is the symbol for a female in a Punnett square?
circle
mode of transmission
describes a trait as autosomal or sex-linked and the type of dominance of the allele
pedigree characteristics of an autosomal recessive trait?
if the parents of an affected individual do not have the trait, than both of the parents must be carriers for the trait
pedigree characteristics of an autosomal dominant trait?
any child with the trait must have a parent with the trait
this is because heterozygotes display the trait
identifying sex-linked recessive traits
males express the trait in question more often than females
often skips a generation because an affected male passes his X-linked trait, but they get a WT from their mother. However, these daughters have 50% chance of passing an affected X to their son
x-linked dominant trait example
rickets
identifying x-linked dominant traits
an affected male passes the trait to all his daughters and none of his sons
he gives his X to the daughters and does not give it to the sons because they only have the Y
What is baby superman an example of?
Incomplete dominance
his mother was a heterozygote who showed abnormal strength
Baby superman disease
lacked myostatin protein
this is a protein that regulates / controls muscle growth through negative feedback
Wild-type
an individual that does not have mutations in the allele under study
often the most common phenotypes observed in nature
The Particle Theory of Inheritance
states that hereditary traits act like particles, units, or factors and they are passed from generation to generation
law of segregation
hereditary factors do not blend, but stay distinct during breeding
keep a copy of the recessive allele that does not get blended with the dominant allele
when does the law of segregation take place?
when homologous chromosomes separate during meiosis
what demonstrates the law of segregation?
true breeding shows this in the second generation of heterozygotes
true breeding
crossing homozygous individuals
law of independent assortment
traits are not connected but are inherited independently of one another
SsYy x SsYy ratio
9: 3: 3: 1
test cross
determine if an individual with a dominant phenotype is heterozgyous or homozygous dominant by crossing with a homozygous recessive
If genes are linked what is more likely to be seen in higher ratios?
the parental genotypes since recombination does not occur
map unit
distance between genes
one map unit corresponds to a recombination frequency of 1%
how to calculate map units
total # of recombinants / total # of progeny * 100
Do recombination frequencies of 50% indicate linkage?
no
50% is approaching the 1:1:1:1 ratio which would indicate that linkage did not occur and all the phenotypes are observed with the same frequency
why does incomplete dominance not support the blending theory?
recessive alleles maintain their own distinct identity and can reappear in later generations
what is hemophilia an example of?
x-linked recessive disorder
SNP
single-nucelotide polymorphisms
are DNA markers that can show genes that are linked to certain traits
Why are SNPs used as genetic markers?
they are close to the gene of interest
Polymorphous SNPs
if a SNP and a gene are physically very close linkage can occur between a version of a SNP and a specific allele
the type of SNP can indicate the allele when linked
Why is linkage between SNPs and alleles never 100%?
no matter how physically close and linked the SNP and the allele are there is always a possibility that recombination can occur
An example of a SNP that is linked to an allele
huntingtons
cis- alleles
recessive alleles that are on the same chromosome
trans- alleles
recessive alleles that are on different chromosomes
aggulitination
clumping of blood
can indicate the ABO type
Why does blood clump around certain antibodies?
type A blood makes B antibodies, so it will clump around the A antibody
If a person’s blood clumps around the A antibody but not the B antibody what does this indicate?
that they have there body produces the B antibody and they have type A blood
What antibodies do people with type O blood produce?
anti-A and anti-B
their blood does not clump around A or B antibodies
What antibodies do people with type AB blood produce?
neither anti-A or anti-B
their blood clumps around A and B antibodies
Complementation
two mutants can breed to restore the normal phenotypes if the mutation occurs on different genes
since both parents are recessive for different genes and dominant for the other, when they make they will produce individuals with heterozygous genotype and the dominant, “normal”, phenotype will be present
What genotype must parents have for complementation to work?
homozygous recessive
What is non-complementation indicated by?
-
What is complementation indicated by?
+
How to count the number of genes working together to produce a trait through complementation
group all individuals that complementation occurred between as one and leave individuals that complementation did not occur with on their own
count the number of groups and single individuals and that is the number of genes that are working together
Why do mutations tend to be recessive?
it is improbable to get a working mutated version of a gene because so many things need to happen correctly
therefore, often times the working allele will be dominant by nature because the other version of the gene simply does not function
PKU
an autosomal recessive disease that cannot convert phenylalanine to tyrosine
if left untreated mental diseases can occur
BUT, if placed on a low phenylananine diet an individual can not develop mental disease
this is an example of environment influencing phenotype
What shows the Law of Independent Assortment?
dihybrid cross
the genes for different traits are not inherited together
two-point testcross
heterozygous x homozygous recessive
what does a two-point testcross indicate?
linkage
the 1:1:1:1 ratio will not be observed
what type of disease is cystic fibrosis?
autosomal recessive
What are the effects of Huntington’s disease?
motor disturbances that effect both voluntary and involuntary movement
How can Huntington’s stay dominant?
it affects individuals after they reproduce
What is an example of incomplete dominance?
sickle-cell anemia
heterozygotes will have a mix between some normal and some sickled red blood cells
hemizygous
refers to males having X and Y chromosome
makes them more suspectible to X-linked recessive diseases
