14 mendelian genetics
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who discovered heredity
gregor mendel
what is heredity
how traits are passed from one gen to the next
how did mendel discover heredity
garden peas
genotype
genetic makeup or allelic combination
phenotype
physical appearance based on the genotype
homozygote
having 2 of the same alleles for a gene
heterozygote
having 2 diff alleles for a gene
dominant
allele tht over powers or masks a recessive allele
recessive
allele tht phenotypically appears only if 2 copies present
gametes
sperm/egg
what does a monohybrid cross study
one trait
what are the steps of a monohybrid cross
1. tall + dwarf varieties cross-fertilized
2. all hybrid progeny are tall
3. hybrid progeny are self-fert
4. tall + dwarf appear in 3:1 ratio
what are inheritable factors
genes
what are character variants
alleles
what are mendels principles
1. principle of dominance
2. principle of segregation
3. principle of independent assortment
what is principle of dominance
if the 2 alleles at a locus differ, the dominant allele determines
appearance
- recessive allele doesn't affect appearance
what is principle of segregation
the 2 alleles for a heritable character segregate during gamete
formation
= they end up in diff gametes
what is principle of independent assortment
alleles of diff genes segregate independently of each other
what are the exceptions to mendels principles
1. linkage
2. incomplete dominance
3. co-dominance
4. multiple alleles
5. polygenic inheritance
what is a punnett square used for
determine genotypic + phenotypic probabilities
how to use punnett square
1. determ parental gametes
2. male gametes on top, female gametes on left side
3. determine offspring genotype
4. determ genotype/phenotype ratios
what are the 4 possible birth orders for 3 unaffected and 1 affected
UUUA
UUAU
UAUU
AUUU
what are the criteria for autosomal dominant trait
- manifests itself in the heterozygote
- equally represented in males and females
- vertical inheritance
(transmission from parent to offspring)
- affected parents have atleast 50% chance their offspring will be
affected
what is polydactylism
autosomal dom
indiv has extra digit or digits on hands or feet
incomplete penetrance
= the dom allele doesnt always show up as a phenotype
features of poly
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14 mendelian genetics
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variable expressivity
= variation in strength of expression
what is phenylketonuria
autosomal recessive
indiv has mutated phenylalanine hydroxylase
= can't metabolize phenylalanine
criteria for autosomal recessive
- manifests only in the homozygote
- equal represented in males/females
- often present in siblings but not transmitted vertically
- if both parents hetero: 25% chance their offspring will be affected
how does phenylketonuria develop
infants are normal at birth, accumulate toxic metabolites over time
what are the sex chromos
X, Y
how many genes does Y chromo have
50-80
how many genes does X chromo have
>1000
what can an imbalance of genes result in
abnl phenotypes
1. 1 of 2 X chromos in females is inactivated
2. X chromo in males can be hyperactivated
3. both X chromos in females are hypoactivated
describe dosage compensation?
purpose?
fix imbalance of # of X chromos
during what stage of development does X chromo inactivation
occur
early in fetal devel
selection of what to inactivate is...
random
what happens after inactivation
all cell progeny will also have the same X chromo inactivated
what is the XIST gene
X inactive specific transcript gene
- the X chromo to be inactivated produces a RNA transcript from
this gene
what happens to the transcript prod from XIST gene
not turned into protein
instead will interact w/ the X chromo it was made from
what does the X chromo to remain active do to its XIST gene
silences its XIST gene
what happens to the inactive X chromo
condenses into Barr Body
- dark staining mass
what are the criteria for X linked dominant trait
- manifests itself in the heterozygote
- females 2x as affected as males
- vertical inheritance
- affected father has 0% chance to pass trait to son; 100% chance
to pass to daughter
- affected mother has 50% chance to pass to son or daughter
what is rett syndrome
X linked dom
mut MECP2 gene
methyl cytosine binding protein 2
what is MECP2?
function during development?
acts as transcriptional repressor in nerv sys during devel
criteria for X linked recessive
- manifests itself in homozygote but can be in heterozygotes
(RARE)
- males more affected
- often present in siblings but not transmitted vertically
- father has 0% chance to pass to son; 100% chance to pass to
daughter who is now the carrier
- affected mother has atleast 50% chance to pass trait to son or
daughter; daughter only a carrier
what is hemophilia A
x linked recessive
- mut factor VII gene
- affected can't clot blood efficiently
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14 mendelian genetics
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criteria for mitochondrial inherited disorder
- passed from mother to all offspring
- females + males affected equally
- males can't pass on
what is leigh syndrome
mitoc inherited disorder
- neurodegenerative disorder
- many diff mitochondrial muts have been linked to the disease
- usually early onset but adult onset is poss
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