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Phenylkentonuria (PKU)
autosomal recessive
sickle-cell anemia
autosomal recessive
tay-sachs disease
autosomal recessive
huntington’s disease
autosomal dominant
hemophelia
sex-linked recessive
red-green color blindness
sex-linked recessive
duchenne’s muscular dystrophy
sex-linked dominant
down syndrome
nondisjunction of chromosome 21
turner syndrome
nondisjunction of sex chromosomes (missing X chromosome)
klinefelter syndrome
nondisjunction of sex chromosomes (additional X chromosome)
cri du chat syndrome
deletion in chromosome 5
prader-willi syndrome
a disorder of chromosome 15 (an example of genomic imprinting)
angelmann syndrome
inheritance of the deletion from the mother on chromosome 15 (an example of genomic imprinting)
fragile X syndrome
most common inherited mental retardation disease; inherited from the father
cystic fibrosis
the most common inherited genetic disease in Europe and the US (autosomal recessive)
blending hypothesis
the old idea of genetics where scientists thought genetic material from parents mixed like blending paint in offspring —> we now know this is not true
Gregor (Johann) Mendel
“The Father of Modern Day Genetics”
Experimented with garden peas
character
gene —> a heritable feature
trait
allele —> the variant of a character
true breeding
purely homozygous —> same allele
continuum
more than 2 options —> a wide range of traits/alleles
Why did Mendel decide to only look at either-or traits?
This is important because be was able to focus on certain things to make his discoveries
What kind of pea plants did Mendel work with?
All the varieties that he worked with were “True Breeding”
P generation
parent generation
F1 generation
1st set of kids (filial generation)
F2 generation
2nd generation of kids (F1 generation = parents)
The results of Mendel’s experiments led to the formation of what 5 main ideas?
There are alternate versions of genes called alleles
Principle of Dominance
For each character, an organism inherits 2 alleles
Law of Segregation
Law of Independent Assortment
phenotype
the result of the alleles that is physically expressed (physical tratis)
Principle of Dominance
one gene may mask another
the dominant allele determines the organism’s appearance (it is expressed)
the recessive allele has no noticeable effect on the organism’s appearance (it is masked)
2 Alleles
for each character, an organism inherits 2 alleles (one from mom (egg) and one from dad (sperm))
Law of Segregation
the 2 alleles are separated into different gametes (during Meiosis) —> this means recessive traits show up in the F2 generation
Law of Independent Assortment
members of one gene pair segregate independently of the members of the other gene pairs (homologous pairs separate independently during Anaphase I)
contributing factor to genetic diversity
genotype
the genes for the trait
testcross
used to determine if an organism is homozygous or heterozygous (never done on humans)
monohybrid cross
one characteristic/trait being crossed (traditional punnett square)
dihybrid cross
two character/traits being crossed
punnett square
the box we set up to do crosses
Reminders about Punnett square probability
a punnett square does not mean that two parents are going to have 4 kids and those are the kids they are going to have —> a punnett square simply shows what is the probability of those kinds of offspring
Rules of Probability: Rules of Multiplication
how to determine the chance that 2 independent events will occur together:
flipping a coin
chance of heads = ½
chance of tails = ½
chance of flipping heads THEN tails = ½ x ½ = ¼ = 25%
What are the odds of a couple having two biological female children then a biological male?
chance of biological female = ½
chance of biological male = ½
chance of 2 biological females THEN one biological male
½ x ½ x ½ = 12.5%
Rules of Addition
the probability that an event can occur in two or more different ways
used when the order is not specified and there is more than one way to get the outcome
what is the probability that in flipping a coin we would get head AND tails (in no particular order)
Heads the first time = ½
tails the 2nd time = ½
½ x ½ = ¼
tails the first time = ½
heads the 2nd time = ½
½ x ½ = ¼
¼ + ¼ = ½ = 50%
Codominance
both alleles are expressed
blood is an example (AB Blood —> both A and B are dominant and expressed)
multiple alleles
more than two alleles
ABO Blood
incomplete dominance
the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties (similar to the blending hypothesis situation)
pleiotropy
one gene has multiple phenotypic effects (meaning one gene has multiple effects in the body)
Examples are sickle cell disease and cystic fibrosis
epistasis
phenotype produced by alleles of one gene is influenced by a genotype of another
polygenic inheritance
more than one gene affects one phenotype
vary in the population along a continuum
opposite of pleitropy
A Blood
can only recieve A or O blood because it makes antigens against B
B Blood
can only recieve B or O blood because it makes antigens against A
AB Blood
can receive any blood type (universal receiver)
O Blood
can receive only O blood because makes antigens against both A and B (universal donor)
inherited disorders
some are dominant
some are recessive
some are expressed based on age
pedigrees
a family tree that describes the interrelationships of parents and children across generations
genetic testing
for a growing number of diseases tests are available that identify carriers and help define the odds more accurately
fetal testing
invasive (could possibly cause miscarriage)
amniocentesis/CVS
non-invasive
ultrasound
amniocentesis
the liquid that bathes the fetus is removed and tested
the goal is to get a karyotype
there are cells from the baby in the fluid - the cells are removed and a karyotype is produced
typically done between 14-16 weeks of pregnancy
invasive testing
chorionic villus sampling (CVS)
a sample of the placenta is removed and tested
goal is to get a karyotype
done earlier in the pregnancy (8th-11th week)
invasive testing
ultrasound
non-invasive
used for much more than pregnancies, but are a great way to check on the health of an unborn baby
the ultrasound waves bounce off solid objects and create an image
the 20th week ultrasound pregnancy is a very important test to see if there is anything wrong
alpha fetal protein (AFP)
new test
non-invasive “replacement” for amniocentesis/CVS
blood test in combo with ultrasound
blood test done to look for proteins in mom’s blood that would be released if the fetus has certain conditions
early ultrasound dome to look at brain and heart development
Chromosome theory of Inheritance
chromosomes contain the info that gives us our characteristics (we don’t just randomly have genes floating around)
Sex Linked Traits
Biological males (XY) only have one X, so they only have one “shot”. They only need one copy of the recessive allele to have that trait. This means we tend to see biological males exhibiting sex linked recessive traits
Biological females (XX) can still have sex linked recessive traits, but it isn’t as common
linked genes
genes found on the SAME chromosome
genetic recombination
creates genetic variation
genetic recombination when genes are unlinked
on two different chromosomes
due to independent assortment
genetic recombination when genes are linked
on same chromosomes
due to crossing over
crossing over and linked genes
the closer two genes are to one another on a chromosome, the higher the chance those two genes will travel together during crossing over (which means less probability that crossing over will form new combinations)
linkage maps
mapping out chromosomes
linkage map rules
if two genes are far apart, these is an increased probability that crossing over will separate them
if 2 genes are close together, there is a smaller probability that crossing over will separate them
we use recombination frequency - how often offspring show crossing over has occurred and translate that to a % called MAP UNITS (1% = 1 map unit)
sry
a gene on the y chromosome
the sex determining region of y
it turns on when the embryo is about 2 months into development
x inactivation
in biological females (XX) (must have at least 2 X chromosomes)
only occurs in autosomes not gametes
during embryonic development, one X in EACH cell is RANDOMLY inactivated
the inactivated X condenses into what is called a BARR BODY
the “blob” sits along the inside of the nuclear envelope
this means that in each cell, there is either an active X from mom OR an active X from dad
during cell division, they uncondensed and duplicate before condensing again
extranuclear genes
genes not found in the nucleus (mitochondria and plastids) —> mitochondria have their own genes and DNA
we can trace maternal lineage by looking at mitochondrial DNA because mitochondrial genes are only passed on by females NOT males
genomic imprinting
some alleles have different results depending if it came from the egg or sperm
the difference is the methylation of alleles (adding of methyl groups)
examples include prader-willi and angelmann’s syndrome
nondisjunction
in meiosis, during anaphase I or II, chromosomes/chromatids do not separate properly leading to wrong numbers of chromosomes in gametes
deletion
a chunk of chromosome does not get copied and is deleted —> missing genes
duplication
chunk of chromosome copied extra times
inversion
when copied, order of genes in mixed up/reversed
translocation
not swapped with homologous pairs, instead swapped with another random chromosome pair
aneuploidy
not right number of chromosomes (only variation by a few chromosomes)
polyploidy
whole additional/missing sets of chromosomes