Chapter 4 & 5 Flashcards
excess mucus in lungs, digestive tract, liver; increased susceptibility to infections; dead in early childhood unless treated
Cystic fibrosis (autosomal recessive)
sickled red blood cells, damage to many tissues (homozygous)
Sickle Cell anemia (autosomal recessive)
A disorder that affects the connective tissue in many parts of the body
Marfan Syndrome (autosomal dominant)
Pattern of inheritance that results from genes located on the X chromosome
x-linked
Pattern of inheritance that results from genes located only on the Y chromosome
y-linked
A gene present on the X chromosome that is expressed in males in both the recessive and dominant condition
hemizygous
is an electrolyte disturbance in which there is an abnormally low level of phosphate in the blood.
Hypophosphatemia (x-linked dominant)
Defective color vision caused by reductions or absence of visual pigments
Colorblindness (x-linked recessive)
A group of genetic diseases that cause progressive weakness and loss of muscle mass.
Muscular Dystrophy
Mental deterioration; usually strikes later in life
Huntington’s disease (autosomal dominant)
Disorders resulting from build-up of certain chemicals related to red blood cell proteins.
porphyria (autosomal dominant and recessive)
The probability the phenotype will appear
penetrance
The range of the phenotypes from a given genotype.
expressivity
a medical condition that causes one or more fingers to be permanently bent. It involves fixed flexion deformity of the proximal interphalangeal joints. The fifth finger is always affected.
camptodactyly (autosomal dominant and recessive transmission)
Brenda and David are both heterozygous for cystic fibrosis; they should produce
children of two phenotypes in a 3:1 ratio.
When X-linked traits are considered
- a man’s genotype may be determined from his phenotype.
- a man can inherit them from his maternal grandfather.
Omar (and all other normal males) cannot be heterozygous for ________ genes.
x-linked
Incomplete penetrance refers to
a dominant allele which may not be expressed in the phenotype.
You suspect incomplete penetrance of allele B in a pedigree. You would explain to your client the dominant traits that show incomplete penetrance
can appear in some generations but not in others.
Gene expression refers to
the ability of an allele to affect the phenotype.
Two affected parents give birth to a normal child. This is an indication that the genetic trait involved is
autosomal dominant and are themselves likely to be the children of affected parents.
The human disorder that usually results in death from lung infections is
cystic fibrosis
Mutations in mitochondrial genes
result in a reduction in cellular energy.
- Edwin has a mutation in a mitochondrial gene that causes a vision problem. The gamete that carried this mutation came from Edwin’s_____________.
Mother
- A dominant allele is present in Nancy’s genotype, but she does not have the dominant phenotype. This means that the allele is
Incompletely Penetrant
- If a trait appears in every generation in a pedigree, this vertical distribution is typical of a _____________ type of inheritance.
Dominant
- Gout (arthritis combined with high levels of uric acid in the blood) is never passed from father to son, but occurs more often in males than in females. The gene for gout is probably located on the _____________ chromosome.
X
- Collecting the information to construct a pedigree is often difficult because _____________.
Knowledge about previous generations is incomplete; people are not always honest
- The inheritance pattern of Duchenne muscular dystrophy is _____________.
x-linked recessive
- Lucy is a carrier of hemophilia. This means that she _____________.
is heterozygous and does not have hemophilia
- A man may never be a carrier of an X-linked genetic disorder because men_____________.
have only one chromosome
- The SRY gene has been mapped to the Y chromosome. This gene determines ____________.
testis formation
In a family of six children, the Y-linked trait found in Joel, their father, will only be inherited by Joel’s _____________.
sons
Patricia is a heterozygous carrier of an X-linked trait. If she marries a man who does not express the trait, all of their sons will express the trait.
False; half their sons
If Abraham Lincoln had Marfan’s syndrome, his pedigree should show at least one affected parent.
True
Marfan syndrome can affect more than one part of the body because the basic problem involves a tissue that is part of several organs.
True
Out of every 5 people who have a dominant allele for a particular locus in their genotype, only two actually show the dominant phenotype. This means the allele has a penetrance of 25%.
False; 40%
Tissues most often affected by genetic defects in mitochondria have high levels of protein synthesis.
False; energy requirement
The structural protein known as collagen is defective in people with Marfans syndrome.
false; fibrillin
One problem with late-onset disorders such as Huntington disease has to do with the fact that individuals with the allele will become ill in their teens and unable to start a family.
false; pass the gene on before they know they have it
Because humans tend to have small families, information about the inheritance of human genes mostly comes from studies on a few large pedigrees.
true
Two unaffected individuals have had a child with galactosemia. As a genetic counselor, you would tell them that their chances of having a second child with the disorder is 1/2.
false; 1 in 4
In order to have a girl born with hemophilia or some other X-linked recessive disorder, both parents must show the disorder phenotype.
false; the father must show the disorder phenotype; (mother may be an unaffected carrier
If Liz has mitochondrial neuropathy, she will pass the trait to her female children only.
false; all of her children
phenotypes that fall into two or more distinct, non-overlapping classes (like Mendel’s peas)
discontinuous variation
phenotypic characters that are distributed from one extreme to another in an overlapping fashion (like
height in humans)
continuous variation
determined by the cumulative effects of genes and the influence of environment
complex traits
- traits controlled by two or more genes
- patterns of inheritance that can be measured quantitatively
polygenic traits
-Polygenic traits resulting from interactions of two or more genes and one or more environmental factors
multifactoral traits
- Averaging out the phenotype is called regression to the mean
- In a polygenic system, parents who have extreme differences in phenotype tend to have offspring that exhibit a phenotype that is the average of the two parental phenotype’s
regression to the mean
what are characteristics of multifactorial traits
- traits are polygenic
- each gene controlling the trait contributes. A small amount of the phenotype
- Environmental factors interact with the genotype to produce the phenotype (P=G+E+EG)
-The phenotypic variance of a trait in a population that is attributed to genetic differences
genetic variance
Phenotypic variation is derived from two sources:
genetic variance and environmental variance
-The phenotypic variation once of a trait in a population that is attributed to differences in the environment.
environmental variance
-The degree of phenotypic variation produced by a genotype in a specific population can be estimated by calculating what?
The heritability of the trait
-The fraction of genes shared by two relatives (50%)
correlation coefficient
- genetically identical twins derived from a single fertilization involving one egg and one sperm
- crucial for studying environmental factors
- twins share a single genotype
monozygotic (MZ)
- Twins derived from two separate and nearly simultaneous fertilization, each involving one egg and one sperm
- twins share about 50% of their genes
dizygotic (DZ)
can be converted to heritability by statistical methods
concordance
the hormone of energy expenditure”, is a hormone predominantly made by adipose cells that helps to regulate energy balance by inhibiting hunger. It is opposed by the actions of the hormone ghrelin, the “hunger hormone”
leptin
a total score derived from several standardized tests designed to assess human intelligence
intelligence quotient (IQ)
the ability that consistently dif- ferentiates individuals on mental abilities regardless of the cognitive task or test
General Cognitive Ability
environmental factors of IQ
- where you go to school/private vs public
- tutoring/study resources
- food/nutrition
The genes which control height in humans are different from many other genes because height genes
produce continuously varying phenotypes.
By definition, a polygenic trait which also is influenced by environmental factors
is multifactorial
Kristen and Todd are at the phenotypic extremes for a polygenic trait. Their offspring
will appear to be an average of their two parents
When four loci are involved in determining a polygenic trait, the largest number of offspring will have
four out of eight dominant alleles.
If you have a genetic predisposition to a disease,
the development of the disease will be affected by environmental factors.
If you have an aunt or uncle with a polygenic disorder
you have more dominant alleles than the average member of your population.
The total number of dominant alleles controlling the phenotype of a polygenic trait
is obtained by adding the dominant alleles at each locus.
Monozygotic twins
are the result of the union of one sperm and one egg.
Dizygotic twins
are genetically no more similar than any two children in the family.
leptin
is a signal from fat cells to the brain.
You would expect individuals with polygenic traits to
have a variety of phenotypes.
The concordance values for albinism are expected to be approximately
100% for MZ twins and 25% for DZ twins.
The difference between the height of pea plants and height in tobacco plants and humans is that in pea plants __________, whereas in tobacco plants and humans __________.
- One gene pair controls height 2. Several gene pairs control height
Two children in the same family have schizophrenia. This could be the result of heredity or_________.
environment
Heritability can be explained by the contribution of _________ to variation in phenotype.
Genetics/genes/genotype
Similarities in IQ among children who are genetically different but raised in the same family indicates the role that _________ plays in the development of intelligence.
environment
An IQ of 100 for a child of chronological age 10 indicates that the child’s mental age is ___________.
10
Skin color is a polygenic trait that seems to be controlled by genes at _________loci.
three to four
Alice’s genotype for a polygenic trait involving three loci is AABbCc. The gamete with the most dominant alleles that Alice can make is___________.
ABC
Alice’s genotype for a polygenic trait involving three loci is AABbCc. The gamete with the fewest dominant alleles that Alice can make is ________.
Abc
Alice’s genotype for a polygenic trait involving three loci is AABbCc. If Alice marries Ralph with genotype aabbCc, the most dominant alleles one of their children can have is ________.
four
Alice’s genotype for a polygenic trait involving three loci is AABbCc. Ralph with genotype aabbCc. Given the same marriage, the fewest dominant alleles one of their children can inherit is ________.
one
Alice’s genotype for a polygenic trait involving three loci is AABbCc. Ralph with genotype aabbCc. If parents are first cousins, their risk of having a child with a multifactorial trait is __________times higher than the risk for unrelated parents.
two
The genes controlling a polygenic trait are usually linked on the same chromosome.
False; independently assorting
Both polygenic and multifactorial traits are controlled by several genes.
true
If Chad who has few dominant alleles for a polygenic trait marries Diane who has several dominant alleles for the same trait, their children will all look like their mother for this trait.
False; tend to be an average of the two
When a multifactorial trait such as neural tube defect is considered, researchers know that all observed variation within a population is due to the influence of genes.
False; both genes and environment
Dizygotic twins occur when the early embryo splits into two cell masses.
False; two eggs are fertilized in the same cycle
Widow’s peak vs. straight hairline is an example of a multifactorial trait.
False; discontinuous
Eye color within a family or population would be expected to have a heritability of 0.5
False; 1.0
Continuously varying traits are distinguished by having two distinct phenotypes.
False; many different
Onset of tuberculosis has a concordance in MZ twins of 56% and a concordance in DZ twins of 22%. These concordance numbers indicate that your chance of developing TB is exclusively controlled by environment
False; controlled by both genetic and environmental factors
A pair of twins is concordant for a trait if both twins have the same appearance with respect to that trait.
true
Animal models have been used to study IQ.
False; identify genes that control learning and memory
Normal cognitive and intellectual function involves one or two genes at most.
false; several genes
Mouse genes controlling complex traits have been used to locate the same or related genes in humans.
true
Siblings adopted into different families still tend to have the similar levels of obesity. This indicates that the underlying cause of obesity is primarily environmental.
false; genetics
