Exam 3: Inheritance Flashcards
humans have approx. ____ genes located on _____ chromosomes
23,000
46
chromosomes occur as _____ homologous pairs in ____ form
23
diploid
22 pairs are referred to as
autosomal
the 23rd pair is what pair??
sex-determining pair (XX, XY)
meiosis results in gametes that are ____
haploid
- containing one chromosome from each pair
what restores the diploid number
fertilization
genotype vs phenotype
genotype: genetic makeup
phenotype: physical expression
allele
variation of gene
locus
location of a gene on a chromosome
in simple inheritance, what is controlled by the interaction of one pair of alleles?
phenotype
homozygous
alleles in a pair that can be identical in expression
dominant
alleles that are expressed in phenotype
recessive
alleles that are masked by another allele’s expression
when can a recessive phenotype be expressed?
only in the homozygous state
when you have 2 diff alleles what interactions exist? (3)
complete dominance
codominance
incomplete dominance
complete dominance
one allele expressed as phenotype, the other is masked
codominance
both alleles fully expressed in phenotype
incomplete dominance
the phenotype is an intermediate expression of the 2 alleles
free earlobes, freckles, astigmatism, myopia or hyperopia, Rh+ factor, A or B blood type, Huntington’s Disease
dominant traits complete dominance
normal vision, short eyelashes, having 5 fingers, Rh-, O blood type, Tay-Sachs, Phenylketonuria
recessive traits complete dominance
2 complete dominance disorders
Huntington’s disease and Tay Sachs
Huntington’s Disease
neurodegenerative disorder, symptoms occur midlife
- motor impairments
- wild jerky movements (chorea)
- insoluble aggregates
Tay Sachs
autosomal recessive
- loss of group of enzymes that help break down lipids in CNS
- lysosome storage problem
- lazy baby syndrome
Application: Complete Dominance Disorder
Familial Hypercholesterolemia
Familial hypercholesterolemia
dominant disorder that impairs LDL removal
- high cholesterol levels due to genetics - dieting will not change this
HDL
good cholesterol
LDL
bad cholesterol
- gets distributed to cell, if high it is bad - excess deposits in blood vessels causing plaque formation
what 3 genes involved in familial hypercholesterolemia
- mutation in gene encoding for LDL receptor
- mutations in ApoB encoding gene impair ability of LDL to bind to receptor
- mutations in regulating protein can diminish recycling of receptor causing abnormally low levels
(cannot put receptors back on membrane)
Discuss how even a healthy diet these mutations in familial hypercholesterolemia would still result in high serum cholesterol levels?
- mutations prevent LDLs from going into cell - stays in bloodstream, delay in receptors getting out to surface
Risks with high cholesterol levels
- plaque build up in blood vessels - affects blood flow to heart, brain - heart attack, stroke
Would you expect the risks to be different in an individual who is homozygous vs heterozygous for one of the familial hypercholesterolemia mutatios?
no
- bc complete dominance only need one gene for this
Example of codominance
AB blood type
- both alleles for gene equally expressed
Example of Incomplete dominance
Thallassemia
Thallassemia
can occur in alpha or beta globin gene - major form = homozygous - minor form = heterozygous can cause anemia lower O2 carrying capacity - fatigue - incomplete bc carrier has symptoms
Penetrance
not all people who have a specific genotype express the phenotype
- neurofibromatosis
neurofibromatosis
- autosomal dominant
- if simple inheritance expect to see people with swellings
- only see symptoms in 50-80%
- if not 100% then it is penetrance
expressivity
the degree to which the phenotype is expressed
- severity , could be 100% penetrance
- Marfan’s syndrome
Marfan’s syndrome
connective tissue disorder
- effects elastin fiber making ligaments less flexible
- people have longer limbs, taller, lower % subcutaneous fat, connects retina to back of eye, heart problems
- can just be tall and thin but others may have life threatening conditions
X - linked Sex linked traits
red - green color vision
clotting factor VIII
hypohidrotic ectodermal dysplasia (sweat glands)
Duchenne’s muscular dystrophy
Y-linked Sex linked traits
TDF
SRY
Spermatogenesis genes
Men vs women with X linked traits
women would follow simple inheritance (may have one of these and one normal allele)
men (only get one X, so whatever is on it will show )- higher percent in men
- if give to son they would have it but if give to daughter it would depend on husband
Sex Influenced Traits: Baldness
baldness controlled by an autosomal gene on chromosome 20
- it is dominant in men but recessive in women
difference due to effect of androgens
expressed differently depending on if male or female
need one gene for baldness (women need to be homozygous)
Application: Pleiotropy - examples
one gene results in more than one phenotype
- Marfan’s
- albinism
- sickle cell anemia
example of polygenic inheritance
eye color
EYCL 1 (gey) gene
locus on 19; green/blue
EYCL 2 (gey) gene
locus on 15; central brown/blue
EYCL 3 (gey) gene
locus on 15; brown/blue
How do you get blue eyes?
have to be recessive for all colors
How do you get brown eyes?
dominant for 2 and 3
What staining do karyotypes involve?
Giemsa staining forming G bands
which karyotype regions stain darker vs lighter?
A-T darker
C-G lighter
euploid
refers to any exact multiple of a chromosome set (n)
- monoploid or diploid
aneuploid
wen euploid does not apply -extra or missing chromosome
trisomy vs monosomy
trisomy - has extra chromosome
monosomy - missing a chromosome
nondisjunction in meiosis II
centromere did not separate, did not chromosome for pair and one cell got both from the pair
- the one with chromosomes would be the trisomy (extra) the one with nothing would be monosomy (missing)
- only half abnormal in meiosis II
Nondisjunction in meiosis I
both would be in one cell, you would get 2 gametes missing chromosomes and 2 gametes with 2 chromosomes each
- higher percentage of having fertilized embryo with problems
- all abnormal
2 types of structural abnormalities and what are they?
deletions: portion of chromosome lost due to breakage or unbalanced crossing-over (translocation)
additions: due to translocation
translocation
unequal sharing - one loses info while the other gets too much
Genetics of Down’s syndrome
most common - trisomy 21 47, XY +21 less common - translocation 46, XY t(21:21) or 46, XY t(14:21) - can have all or part of 21 on 14
Clinical effects of Down’s Syndrome
- growth retardation
- learning disabilities
- craniofacial abnormalities (eyes)
- cardiac defects: heart formation problems)
- poor muscle tone
- high risk of Alzheimer’s
Genetics of Turner’s Syndrome
only monosomy condition known to be survivable
45, X
presence of one X = female
ONLY in females!!!
Clinical aspects of Turner’s Syndrome
- short stature on average
- lymphedema of extremities
- low placed ears
- webbed neck
- infertile - only have one X will not get through checkpoint in metaphase
Genetics of Cri du chat Syndrome
unbalanced translocation
loss of short arm in chromosome 5
partial monosomy
46 XY (5p-)
- means minus the short arm (p)short arm vs long arm in cri du chat
short arm = p
long arm = q
Clinical aspects of Cri du chat Syndrome
high pitched catlike cry in infants
microcephaly
intellectual disabilities
congenital heart disease
Genomic imprinting
- expression dependent on parent or origin
- some genes always shut down in egg or always shut down in the sperm
2 types of Genomic imprinting
Angelman syndrome and Prader-Willi Syndrome
Angelman Syndrome
maternal origin deletion from mother - learning disabilities - speech disorders - poor motor development - prone to seizures - happy, frequent laughter 46, XX (15q11-15q13)
Prader-Willi Syndrome
paternal origin - deletion from father learning disabilities poor muscle tone compulsive eating obesity hypogonadism hormone issues
Barr bodies
only one X chromosome needed to survive
- in development of females one X is inactivated in somatic cells. Both X remain active in germ cell line
- inactivation mainly random
- all cells descendant from the initial inactivated X cell will express same X chromosome
Effects of Barr Bodies (2)
mosaics
fragile X syndrome
mosaics
- occurs in women who are heterozygous for X-linked traits
- result of random inactivation
- example: sweat gland distribution in patches of skin
calico cats
shut down early = big patches
shuts down late = tiny patches - tortoise shells
fragile X syndrome
- inherited from mother
- increased DNA repeats in inactivated X chromosome
- 46, XY (Xq-27) it will break
- learning disabilities
- large ears, jaw, testes
- some women carriers show cognitive effects
second most common form of learning disabilities
application: fragile X syndrome
- occurs due to a break in chromosomes, causing a low folate
- over 200 shuts down the gene and results in developmental issues
- sperm cannot carry mutated X but can pass on premutations
application: chromosomal abnormalities
turner’s and klinefelter’s
In klinefelter’s would the disorder occur in men, women, or both?`
men
How could the condition of klinefelter’s occur?
nondisjunction
- in meiosis I or II
application: pseudoautosomal genes
PAR
on ends of sex chromosomes
when make barr body they are regions that do not shut down - so these regions are active even in barr bodies
- survives with one X but problems with deficiency
