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CYTOGENETICS
CYTO 13 & 14
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GENETIC COUNSELORS
- help people examine their families' histories
PEDIGREE
- one of the key steps in genetic counseling
PROBAND
- person whom the tree is initiated
AFFECTED
- person diagnosed with or having symptoms of a given disorder
HETEROZYGOTE
- person possesing one disease causing allele
CARRIER
- unaffected heterozygote in recessive disorders
HOMOZYGOTE
- person possesing 2 copies of disease causing alle
COMPOUND HETEROZYGOTE - person possesing 2 different disease- causing allele
MODE OF INHERITANCE
- way in which human genetic disorders are passed down to later generations
AUTOSOMAL INHERITANCE
- genes located on autosomes
DOMINANT TRAIT/ DISORDER
- only one allele known to cause the trait
AUTOSOMAL DOMINAT
- when a gene is carried on an autosome
EXAMPLES OF AUTOSOMAL DOMINANT DISORDERS:
Achondroplasia,
Huntington
Disease
&
Marfan
Syndrome
ACHONDROPLASIA
- form of dwarfism
HUNTINGTON DISEASE
- progressive & fatal disease affecting the brain & nervous system
MARFAN
SYNDROME
- disorder affecting the skeletal system, heart & eyes
The normal pattern of autosomal dominant inheritance has
three
exceptions
THE THREE EXCEPTIONS TO NORMAL PATTERN OF AUTOSOMAL DOMINANT INHERITANCE ARE:
New
mutations
,
Incomplete
penetrance
&
Variable expressivity
PENETRANCE
- percentage of individuals having a particular genotype
EXPRESSION
- degree to which an individual with a certain genotype exhibits the phenotypic effects of that genotype
NEW
MUTATIONS
- occur in the egg & sperm of an individual, appears for the first time in single generation
RECESSIVE TRAITS/DISORDER
- both alleles of the associated gene need to have the necessary changes order to show related phenotype
AUTOSOMAL
RECESSIVE
DISORDERS-
caused by mutations in genes
Both parents are heterozygous carriers - there is
25
% chance of both parents passing o na disease - causing allele
One parent is carrier & another is affected - each child has
50%
of being a carrier
One parent is carrier & another is affected - there is
50%
chance og having an affected child
One parent is affected & other is unaffected - there is
50%
will be
heterozygous
carriers
CONSANGUIENEOUS - meaning "
same blood
"
SEX
-
LINKED GENES
- actually located on the sex chromosomes themselves
HEMOPHILIA is a
x
-
linked
while hairy ears are
y
- linked
X
-
LINKED TRAITS
&
DISORDERS
- result of sequence variants in genes
X
-
linked recessive disorders
express the traits fully in males
X
-
INACTIVATION
- most of the genes on one female's two X chromosome are turned off
X
-
LINKED
DOMINANT
TRAITS show up more often in females
HEMIZYGOUS
- having only one copy of the chromosome
Y
-
CHROMOSOME
- is passed strictly from father to son
SEX
-
LIMITED TRAITSS
- inherited in the normal autosomal fashion but are not expressed in one sex
SEX
-
INFLUENCED TRAIT
- are coded by genes on autosomes
DIAGNOSTIC
TESTING
- performed in an affected individual in order to establish a specific diagnosis
PRENATAL
TESTING-
performed during pregnancy in order to diagnose the baby with a genetic condition
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