Genetics Test #3 Flashcards
Fingerprints are also called
epidermal ridges or dermatoglyphic patters (fully formed by 17th week of pregnacy)
Who is Francis Galton?
-no two individuals have the same fingerprints
-fingerprints of relatives are more similar than unrelated people
What is ADG?
-adermatoglyphia
-due to mutation that interferes w/ epidermal ridge formation
Squares on pedigree represent
males
Circles on pedigree represent
females
Colored squares and circles represent
persons affect w/ trait
Standard symbols used in pedigree analysis
pg. 151; 6.2 and on PPT
Geneticists use pedigrees to
study the inheritance of characteristics in humans
What is a pedigree?
pictorial representation of a family history;; a family tree that outlines the inheritance of one or more characteristics
What is Proband?
the person from whom the pedigree is initiated (first affected family member)
What is Waardenburg Syndrome?
-autosomal dominant trait
-characterized by deafness, fair skin, visual problems, and white forelock
Children in each family are listed
left to right in birth order
What are autosomal recessive traits?
normally appear with equal frequency in both sexes and seem to skip generations
What is consanguinity?
mating between related people (indicated w/ two dashes)
Example of autosomal recessive traits
Tay-Sachs Disease
What is Tay-Sach’s Disease
-a recessive lysosomal storage disorder that results in the impairment of neurologic function due to the lack of an enzyme to break down a lipid that accumulates in the brain
-heterozygotes produce half the amount of that enzyme, but can break down the lipid, therefore healthy
Autosomal recessive traits often appear in pedigrees in which there have been consanguine mating because these traits
appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related
X linkage
can be x-linked dominant or x-linked recessive
Males are usually
hemizygous (one x chromosome)
What are autosomal dominant traits?
appear with equal frequency in both sexes and do not skip generations
-unaffected people do not transmit the trait…affected people have at least one affected parent
Example of an autosomal dominant trait.
familial hypercholesterolemia
What is familial hypercholesterolemia?
-blood cholesterol is greatly elevated
-defect in LDL receptor
What are X-Linked Recessive Traits?
appear more often in males than in females
-passed to sons from mothers
Example of X-Linked recessive trait.
X-linked hemophilia
What is an X-linked dominant trait?
-affects both males and females
-an affected male must have an affected mother
How are X-linked dominant traits passed on?
-affected males pass the trait on to all their daughter and non of their sons
-affected females (if heterozygous) pass the trait on to about half of their sons and half of their daughters
Example of an X-linked dominant trait.
X-linked hypophosphatemia
What is X-linked hypophosphatemia?
defective transport of phosphates, especially in kidney cells (short stature, tooth abscesses, bone and joint pain, etc.)
A male affected with an X-linked dominant trait will have what proportion of offspring affected with the trait?
all daughters and no sons
What are Y-linked traits?
-appear only in males and are passed from a father to all his sons
-do not skip generations
Genetic Mosaicism (or chimeras)
different cells of the body have different genetic constitutions
How does genetic mosaicism develop?
-error occurs early during mitosis
-variation present in large number of cells in the body
Studying twins and adoptions can help access the importance of
genes and environment
What are monozygotic twins?
identical twins
What are dizygotic twins?
non-identical (fraternal) twins
What is a concordant trait?
the trait shared by both members of a twin pair
What is concordance?
-amount of similarity
-percentage of twin pairs that are concordant for a trait
Why are monozygotic twins genetically identical, whereas dizygotic twins share only 50% of their genes on average?
monozygotic twins develop from a single egg fertilized by a single sperm, whereas dizygotic twins develop from two eggs fertilized by two different sperm
Adoption studies demonstrate that obesity has a
genetic influence
Genetic factors influence
body mass index
Dogs are a natural system for investigating the
genetics of complex traits
The breed ancestry of individual dogs is assumed to be predictive of
temperament and behavior
Genetic Variation explains more than
25% of the variation in human sociability, motor patterns, and physical traits
Biddability
how readily dog responds to human direction
Behavioral characteristic ascribed to modern breeds of dogs are
polygenic, environmentally influenced, and found, at varying prevalence
1st Law (Principle of Segregation)
alleles separate during meiosis during gamete formation
2nd Law (Independent Assortment)
alleles at one locus sort independently from alleles at other locus
Recombination
alleles sort into new combinations
Through recombination…
gametes contain new combinations of alleles
Linked genes
do not assort independently
Linked Genes
traits that are inherited together because genes are located close together on the same chromosome
Linked genes belong to the
same linkage group (are physically coupled)
Linked genes segregate together and crossing over produces
recombination between them
Complete Linkage
leads to non-recombinant gametes and non-recombinant progeny
Crossing over with linked genes leads to
recombinant gametes and recombinant progeny
If crossing over occurs between two normally linked loci
they will sort independently
With complete linkage only
non-recombinant progeny are formed
With independent assortment
half progeny is recombinant
If no crossing over takes place
each gamete receives a non-recombinant chromosome with an original combination of alleles
A crossover may take place in Prophase I
half the gametes will have an unchanged chromosome (non-recombinant) and half will have a recombinant chromosome
If crossing over does not occur, at the end of meiosis II, there will be
four linked/non-recombinant chromatids (linkage)
If crossing over occurs, at the end of meiosis II, there will be
two linked and two recombinant chromatids (recombination)
In performing a dihybrid cross, you expect to see a
9:3:3:1 ratio. What is a good explanation if you do NOT
see a 9:3:3:1 ratio in a dihybrid cross?
the two genes are linked
For single crossovers, the frequency of recombinant
gametes is half the frequency of crossing over because
each crossover takes place between only two of the
four chromatids of a homologous pair
Recombination frequency (or rate of recombination)
percentage of recombinant progeny produced in a cross
How to calculate recombination frequency?
number of recombinant progeny/total number of progeny X 100%
From the cross AB/ab×ab/ab, what is the recombination frequency if the progeny numbers are
72 AB/ab, 68 ab/ab, 17 Ab/ab, and 21 aB/ab?
0.213
In crosses for linked genes, the arrangement of alleles
on the homologous chromosomes is critical in determining the outcome of the cross
Coupling Configuration of Linked Genes (cis configuration)
wild-type alleles are found on one chromosome; mutant alleles are found on the other chromosome
Repulsion Configuration of Linked Genes (trans configuration)
wild-type allele and mutant alleles are found on the same chromosome
Inheritance of two genes in the Australian Blowfly
one locus determines color of thorax, and another determines color of puparium
Since genes are linked, there are
two possible arrangements on the chromosomes of the heterozygous fly
The phenotypes of the offspring are the same, but
their number differ, depending on whether alleles are in coupling or repulsion
Recombination frequency is the
total proportion of recombinant gametes
Predicted frequency of progeny is obtained by
multiplying the frequencies of the gametes
Genomics
the study of entire genomes, including the
complete set of genes, their nucleotide sequence and
organization, and their interactions within a species and with other species
Genome Mapping
the process of finding the locations of genes on each chromosome
Genetic Map
an illustration that lists genes and their location on a chromosome
calculated using recombinant frequencies
Genetic Markers
a gene or sequence on a chromosome that co-segregates (show a genetic linkage) with a specific trait…a.k.a linkage analysis
Physical maps
present the intimate details of smaller regions of the chromosomes
representation of the physical distance, in nucleotides, between genes and genetic markers
Gene mapping is done with
recombination frequencies (1 map unit = 1 centiMorgan = 1% recombination frequency)
What is the most likely order of the linked genes R, S,
and T if the distance between R and S is 22 m.u., the
distance between S and T is 8 m.u., and the distance
between R and T is 14 m.u.?
STR
If pedigree studies show a high incidence of cooccurrence of traits,
those genes will be located close together on a genetic map
on the garden pea, it was discovered that the color of the flower and shape of the plant’s pollen
were linked traits
The genes encoding these garden pea traits were
in close proximity on the same chromosome
Linked genes
do not assort independently
The greater the distance between two genes
the higher the chance that a recombination event will occur between them, and the higher the recombination frequency between them
If the recombination frequency between two genes is less than 50 percent
the genes are linked
genetic maps rely completely on the natural process
of recombination causing
mapping to be affected by natural increases or
decreases in the level of recombination
A two-strand double crossover between two linked genes produces
only non-recombinant gametes
