2.20 Usual and Unusual Patterns of Inheritance in Genetics Flashcards
Science that deals with heredity and variation in organisms, including the genetic features and constitution of a single organism, species or group and with the mechanisms by which they are affected
Genetics
About similarities and differences
Genetics
Biological maps that tell us who we are, where we came from and how we are related to other creatures
Genes
Human genome is 75% homologous to ___; 98.7% homologous to ___; and 99% homologous to ___.
C. elegans
Chimpanzee
Mouse
Gene responsible for the gift of gab/language
FOXP2 gene at chromosome 2
22 chromosome pairs are ___ and ___
Autosome
Homologous
23rd pair contains ____
Sex chromosome
Carries genes responsible for many hereditary traits
X chromosome
Full set of chromosomes in the cell of a person
Karyotype
Genetic material
DNA
Size of human genome
3 B base pairs making up 22-25K genes varying in length
Human Genome
Less than 2% code for ___
Proteins
Human Genome
90% are sometimes called ___, important in regulation of gene expression, introns
Junk DNA
Human Genome
__ of bases are exactly the same in all people
99.9%
Variations or mutations in genes may have negative effects and lead to disease or increase susceptibility to disease
Normal protein vs. Low or nonfunctional protein
AAATTT»_space;> AATTTT
Cause no negative effect
Single nucleotide polymorphism
AAATTT»>AACTTT
Can lead to disease or higher susceptibility to disease
Low or non-functioning protein
Marfan’s syndrome
Sickle cell anemia
Cystic fibrosis
Single gene disorders
Diabetes, Hypertension
Variations in the gene, which lead to disease or increase susceptibility
Extent of interactions of various risk factors remains unknown
Complex gene disorders
Study of the set of the chemical reactions and the factors that triggers the activation/deactivation of parts of the genome at strategic times and locations
Epigenetics
Epigenetic mechanisms are affected by factors such as
Development in utero
Environmental chemicals
Drugs/pharmaceuticals
Aging
View that genes cause traits and can no longer be altered
Genetic determinism
Your genes dictate who you are
Genetic determinism
Major activity and key factor in clinical genetics
Aid in reaching a correct diagnosis
One of the most useful and accessible tools available to physicians caring for patients with genetic diseases
Family History
When taking a family history
Make it relevant to the present illness
Ask about early onset preventable diseases
Ask about first-degree relatives
Ask about informative relatives (Proband and consultand)
Record racial and ethnic background
Inquire about consanguinity
Keep it up to date
First affected individuals in a family who brings genetic disorder to the attention of the medical community
Proband
Individual presenting for genetic counseling
Not necessarily affected
Consultand
Graphic representation of a medical family history of disease using symbols
Pedigree
Provides both critical medical data and biological relationship information at a glance
Pedigree
Confounding factors in recognizing patterns of inheritance
Variable expressivity Clinical or genetic heterogeneity Sex-influenced or sex-limited gene expression Assortative mating Small paternity size
Tongue-rolling
Dominant
Cleft-chin
Dominant
Dimples
Dominant
Attached ear lobe
Recessive
Hitchhiker’s thumb
Dominant
The genotype of an affected individual in autosomal dominant inheritance
AA
Aa
True or false
Male-to-male transmission occurs in autosomal dominant inheritance
True
Each offspring has __ chance of being affected in autosomal dominant inheritance
50%
True or false
Only males are affected in autosomal dominant inheritance.
False
Males and females are affected in equal proportion
Characteristics of autosomal dominant inheritance
Affected genotype: AA or Aa
Offspring has 50% chance of being affected
Males and females affected in equal proportion
Male-to-male transmission occurs
Examples of autosomal dominant inheritance
Achondroplasia Crouzon syndrome Apert syndrome Marfan syndrome Ehlers-Danlos syndrome
Autosomal dominant inheritance usually involve ___
Structural proteins
The genotype of affected individual in autosomal recessive inheritance
aa
In autosomal recessive inheritance, each offspring has __ chance of getting affected when both parents are carriers of a single copy of the gene
25%
True or false
Autosomal recessive inheritance skips generation
True
The genotype of carrier individual in autosomal recessive inheritance
Aa
True or false
In autosomal recessive inheritance, only female is affected
False
Males and females are affected equally
Autosomal recessive:
One affected + one carrier = __ chance of being affected
One affected + one not affected = __ chance of carrier
Both are carriers = ___ affected, ___ carrier
50%
100%
25%; 50%
Characteristics of Autosomal Recessive Inheritance
Affected gene: aa
Must ask about consanguinity
Affect males and females equally
Skip generations
Examples of genetic disorders with autosomal recessive inheritance
Harlequin baby
Mucopolysaccharidosis Type I Hurler
Maple Syrup Urine Disease
Galactosemia
Affected genotypes for X-linked recessive inheritance
XaY or XaXa
True or false
In X-linked recessive inheritance, all daughters of affected males are carriers
True
True or false
In X-linked recessive inheritance, there is no mother-to-daughter transmission
False
There is no father-to-son transmission
Characteristics of x-linked recessive inheritance
Incidence higher in males
Daughters of affected males are carriers (obligate carriers)
No-father-to-son transmission
Examples of x-linked recessive inheritance
Duchenne Muscular Dystrophy
Mucopolysaccharidosis Type II Hunter
In x-linked dominant inheritance, a male or female child of an affected mother has a __ chance of inheriting the mutation and thus being affected with the disorder
50%
Example of X-linked dominant inheritance
Rett syndrome
Participation of environmental factors, not just genetic
Only those who reach threshold make up the affected population
Multifactorial inheritance
Example of disorders associated with multifactorial inheritance
Oral Clefts
Neural tube defect
Pyloric stenosis
Mother-related disease
Affected mom: all offspring will inherit the disease
Mitochondrial inheritance
Mixture of mutated and non-mutated mitochondrial DNA
Heteroplasmy
Either all mutated or all non-mutated mitochondira
Homoplasmy
Explains the variable expression of mitochondrial DNA
Homoplasmy vs. heteroplasmy
An expansion of a segment of DNA that contains a repeat of 3 nucleotides
Triple expansion disorders
Examples of triple expansion disorders
Myotonic dystrophy
Fragile X syndrome
Huntington’s disease
Only one copy of the gene is expressed
Genomic imprinting
Expression of the gene is variable depending on which parent the gene came from
The active gene is preferentially always from one parent over the other
Epigenetic phenomenon
Examples of disorders associated with genomic impirnting
Prader-Willi Syndrom
Angelman syndrome