11 HUMAN GENETICS Flashcards
To determine the pattern of inheritance of man’s traits, the construction of family
history is performed.
pedigree analysis
By doing pedigree analysis, one can determine the possible genotypes and phenotypes of the individuals, and can predict if the trait can be _____
possibly transmitted to the next generation
The affected individual whom the pedigree is discussed is called the ____
if male, ____
if female, ____
proband
propositus
proposita
Analyzing pedigrees can reveal?
(a) whether a trait is dominant or recessive
(b) the type of chromosome (autosomal or sex) to which the trait is linked
(c) genotypes of family members
(d) probabilities of phenotypes in future generations
Generations (sometimes labeled with Roman numerals).
Rows
Top row-oldest generation
Second individual of the first generation
I-2
(family members labeled numerically from left to right
used to analyze the pattern of inheritance of a particular trait throughout a family
Pedigrees
show the
presence or absence of a trait as it relates to the relationship among parents, offspring, and siblings.
Pedigrees
By analyzing a pedigree, we can determine genotypes, identify phenotypes, and predict how a trait will be passed on in
the future.
The information from a pedigree makes it possible to determine how certain alleles are inherited: whether they ____
are dominant,
recessive,
autosomal, or
sex-linked.
Determine whether the trait is dominant or recessive
If the trait is dominant, ____ of the parents must have the trait.
Dominant traits will not skip a generation.
one
If the trait is recessive, neither parent is required to have the trait since they can be ____.
heterozygous
Determine if the chart shows an autosomal or sex-linked
For example, in ____ traits, males are much more commonly affected than females.
X-linked recessive
Determine if the chart shows an autosomal or sex-linked
In ____ traits, both males and females are equally likely to be affected (usually in equal proportions).
autosomal
2 Common mistakes and misconceptions
- The presence of many affected individuals in a family does not always mean that the trait is dominant
- You may not always be able to determine the genotype of an individual based on a pedigree.
5 Common pattern of inheritance in man
- autosomal recessive
- autosomal dominant
- sex-linked dominant
- sex-linked recessive
- sex-influenced
The trait for this type of inheritance never skips a generation
autosomal dominance
autosomal dominance Affected individual may either be
homozygous dominant or heterozygous
Marriage between 2 affected individuals produce affected offspring
Autosomal recessive
May also be produced by both unaffected person heterozygous for the character
autosomal recessive
autosomal recessive example
inability to roll tongue
ankyloglossia or nerve disorder
Affected male with unaffected wife transmit the trait to daughter only
Sex-linked dominance
Sex-linked dominance example
defective teeth enamel
Affected female with unaffected husband transmits the trait to sons only; the daughters serve as carrier of the trait
Sex-linked recessive
since male have only one X, they are already affected, but females have two so their other X can compensate: such as G6PD (both parents must be affected to produced an affected daughter)
Sex-linked recessive example
colorblindness
hemophilia
Gene exhibits high penetrance or expressivity in one sex
sex-influenced
sex-influenced example
harelip, baldness (more frequent in men than in women);
spina bifida (forked spine with open spinal cord) - more frequent in women than in men.
7 Inheritance patterns
- autosomal dominant
- autosomal recessive
- X-linked dominant
- X-linked recessive
- Y-linked
- Co-dominant
- Mitochondrial
One mutated copy of the gene in each cell is sufficient
for a person to be affected
autosomal dominant
autosomal dominant example
Huntington disease
Marfan syndrome
- both copies of the gene in each cell have mutations
- parents of an affected individual each carry one copy of the mutated gene
- typically do not show signs and symptoms
- not seen in every generation of an affected family.
autosomal recessive
between affected and unaffected
autosomal recessive example
Cystic fibrosis
Sickle cell disease
are caused by mutations in one of the two sex
chromosomes in each cell.
X-linked
dominant
X-linked Dominant
In females, a mutation in ____ copies of the gene in each cell is sufficient to cause the disorder.
In males, a mutation in the ____ of the gene in each cell causes the disorder.
one of the two
only copy
Most cases, male have severe symptoms than females.
A characteristics of ____ is that fathers cannot pass ____ traits to their sons.
X-linked Inheritance
X-linked
this is because the X trait passed to offsprings are from mothers
male always affected pass to daughters
X-linked dominant
X-linked dominant example
Fragile X Syndrome
X-linked recessive
In males, ____ mutation is sufficient to cause condition.
In females, a mutation would have to occur in ____ of the gene to cause the disorder.
one
both copies
Because it is unlikely that females will have two altered copies of this gene, males are affected more.
X-linked recessive example
hemophilia
Because only males have a Y
chromosome, in Y-linked inheritance, a mutation can
only be passed from ____
father to son.
Y-linked inheritance example
Y chromosome infertility
two different versions (alleles) of a gene are expressed, and each version makes a slightly different protein
Co-dominant
Both alleles influence
the genetic trait or determine the characteristics of the
genetic condition
Co-dominant example
ABO blood group
alpha-1 antitrypsin deficiency
applies to genes in mitochondrial DNA.
Mitochondria
mitochondrial inheritance
Conditions resulting from mutations in mitochondrial
DNA can appear in ____ of a family and can affect both males and females, but fathers do not pass these disorders to their daughters or sons
every generation
mitochondrial inheritance example
Leber hereditary optic neuropathy (LHON)
At least ____ of all spontaneous miscarriages result from gross chromosomal aberrations.
About ____ of spontaneous abortion and ____ of still births and newborn deaths are due to triploidy
25%
17%
3%
two classes of aneuploidy
autosomal aneuploidy
sexual aneuploidy
It has been found that around ____ of local clinically recognized pregnancies carry some
form of trisomy.
4%
Who first described DS in 1866?
British physician
J. Langdon Down
