Download development/genetics

DEVELOPMENT/GENETICS
Resources:
Textbook (glossary, clinical studies, sample quizzes) Development
Textbook (glossary, clinical studies, sample quizzes) Genetics
Textbook (sample quizzes, exercises, cadaver practicals)
Medical Research
Learning Activities
Interactions:Foundations CD (System overview, relationships with other systems)
Marieb CD (Oxytocin, Punnett Squares, Vocabulary)
Tortora Grabowski CD (Punnett Squares)
Interactive Physiology CD (None)
Lecture Notes:
I. Fertilization
A. Timing
1. Sperm lasts 1-2 days in female
2. Secondary oocyte must be fertilized with a day (within uterine tube) in order to grow mature enough to implant
in uterus
3. Intercourse must occur between 1-2 days before ovulation and 1-2 after ovulation.
B. Blocks to polyspermy
1. Sperm must penetrate cells and layers that come with the secondary oocyte in order to allow fusion of
chromosomes
2. More than one sperm penetrating oocyte (= polyspermy) causes death because of abnormal chromosome
number
3. Blocks to polyspermy
a. Oocyte changes membrane characteristics
no more sperm can penetrate easily
b. Cortical response
materials in the cell cytoplasm force attaching sperms off oocyte
C. Completion of meiosis/fertilization
1. Once sperm penetrates secondary oocyte finishes second meiotic division and loses polar body
2. New cell has 46 chromsomes (= zygote) , 23 from mom and 23 from dad
II. Embryonic processes and events
Processes begin and then continue.
A. Cleavage
mitosis without a chance for cell growth
more cells but increasingly smaller cells
not enough energy for cell growth until implantation
B. Migration
cells move from one spot to another changing the shape of the embryo, adding new embryonic structures
C. Differentiation
some cells change to form new cell types with this process allowing new cell types to form.
So...From one to many cells, and many kinds of cells and many new structures!
Events happen only once
A.Fertilization-fusion of secondary oocyte and sperm
B. Implantation-embedding of blastocyst stage in endometrium
III. Embryonic Developmental stages
A. Zygote (day 1, 1 cell, result of fertilization) Cell has chromsomes from dad but chromosomes and all other cellular
structures from mom i.e., mitochondria, etc.
B. Morula (days 3-4, solid ball of cells, >12 cells)
1. cells cleaves after 1 day to make more blastomeres
2. blastomeres are all biochemically the same and have the capability to become any tissue in adult
body (embryonic stem cells)
C. Early Blastocyst (days 7-8, hollow ball of cells after migration of cells outward)
1. Two types of cells now (differentiation of blastomeres)
a. Trophoblast cells are outer cells that become embryonic part of placenta .
b. Inner cell mass cells eventually become the embryo
2. Stage of implantation
a. Trophoblast cells digest into endometrium for nutrients
b. Trophoblast cells grow to become chorion, the embryo's part of the placenta
c. Trophoblast cells secrete HCG (Human chorionic gonadotropin) which triggers
maternal corpus luteum to continue secreting progesterone (like an embryonic LH)
d. HCG is pregnancy test hormone --can be detected within a week or so of implantation
D. Late Blastocyst (days 14-21, flat plate of embryo within ball implanted in endometrium)
1. Three types of cells (all cell ancestor types present now) form (Gastrulation)
a. Ectoderm
eventually forms skin and nervous system
b. Endoderm
eventually forms epithelial linings (mucosal layers) of digestive, urogenital and respiratory
systems
c. Mesoderm
eventually forms bone, muscle, blood and vessels, organs of reproductive and urinary
systems
2. Embryonic membranes begin to form
a. Amnionic membrane/sac (= bag of water)
sac that contains fluid surrounding embryo penetrated by umbilicus from embryo to
placenta
amniocentesis is used to determine biochemical and genetic disorders.
b. Chorion
derived from trophoblasts to form part of placenta
encloses all membranes and embryo
D. Neurula
stage when embryonic plate infolds to form central nervous system
first organ formed is brain
E. First month stageHeart present
F. Second month stage
1. Sex differentiation beginning
by week 12, sex established and detectable
2. Appendage formation
a. Limb buds appear by week 4 but recognizable as appendages at week 6-8
b. Limb proportions complete by week 17-20
V. Genetics
A. Basic information
1. Genetic information in chemical form of long DNA molecules packaged into chromosomes
2. Each DNA molecule has sequence of nucleotides that acts as a code for producing a protein (= gene)
that is often an enzyme that therefore determines a specific genetic trait.
3. 23 pairs of DNA molecules (= chromosomes) in normal body cells
Therefore, two complete sets of genes that determine the same traits ( hair shape, eye color, efficiency of
metabolic enzymes, type of chloride membrane transporter protein)-these pairs of chromosomes are
called homologous pairs.
4. 22 pairs of Chromosomes that determine only body traits are autosomal, the pair that also determines sex
characters are sex chromosomes (i.e., XX and XY) . So there are autosomal traits and sex traits.
5. Each homologous pair has two copies of a gene-each gene copy is called an allelle. Use example of hair
shape gene possibilities (straight or curly) produced by hair shape alleles.
a. Alleles can be the same (= homozygous)
e.g., one person might have both straight hair alleles while a different person might have both curly
hair alleles
b. Alleles can be different (= heterozygous)
e.g., hair shape alleles include straight and curly
6. Alleles may produce proteins with different effectiveness or durability
a. Most active version of protein (trait) is expressed over a less active protein's affect
(= dominant allele)
b. Least active version (trait) is masked (= recessive allele)
c. Either dominant or recessive can be defective allele producing a disorder. For instance, a
defective trait "bad gene" can be dominant while a "good gene" can be recessive,and vice versa.
Naming convention of allelesUse one letter for one gene and vary case of that letter to indicate recessive
or dominant.
uppercase = dominant allele, lowercase = recessive allele
Ex.: C= curly, dominant: c = straight, recessive
7. Allele naming
a. Genotype = description of actual alleles in gene pair
ex. CC = homozygous dominant , cc = homoxygous recessive, Cc = heterozygous
b. Phenotype = description of trait considering expression
must know which allele is dominant or recessive for each trait to determine ( ex. CC= curly, cc=
straight, Cc= curly)
B Patterns of inheritance
1. Complete inheritance-allele is expressed as either dominant or recessive (either/or) e.g., Cystic Fibrosis is recessive, Parkinson's is
dominant.
2. Incomplete inheritance-both alleles expressed so there is an intermediate trait. (either/or, and) e.g., sickle cell anemia
3. Codominance-both alleles are expressed so there are two traits. (and) e.g., ABO blood typing.
C. Punnett Squares
mechanism to predict possible outcomes of each crossing of male and female gametes.
1. Complete dominance (Autosomal dominant or Autosomal recessive) patterns
a) Cross of heterozygous parents (Bb) to predict offspring's traits. This hypothetical trait is autosomal
recessive.
Mother's
oocytes
B
b
Dad's
B
BB
Bb
sperms
b
Bb
bb
What are offspring genotypes? 25% are homozygous
dominant (BB), 50% are heterozygous (Bb)
and 25% are homozygous recessive (bb).
phenotypes? BB and Bb are not afflicted. In autosomal recessive disorders only bb genotypes are
afflicted. One allele comes from each parent.
b) Cross of heterozygous parents (Bb) to predict offspring's traits. This hypothetical trait
is autosomal dominant
Dad's
Z
Mother's
oocytes
Z
z
ZZ
Zz
sperms
z
Zz
zz
What are offspring genotypes? 25% are homozygous
dominant (ZZ), 50% are heterozygous
(Zz) and 25% are homozygous recessive (zz).
phenotypes? BB and Bb are afflicted. In autosomal dominant disorders all genotypes with
dominant trait are afflicted.
c. Test cross to determine parenthood
with heterozyous mom.
Mother's
oocytes
B
b
Dad's
B
Bb
Bb
sperms
?
bb
bb
What is dad's genotype- BB or Bb?
2. Test to determine whom determine offspring's gender.
Mother's
oocytes
X
X
Dad's
X
XX
XX
sperms
Y
XY
XY
What are frequencies of offspring's genders? 50% males, 50% female
Who determines the offspring's gender? The male.
3. X-linked inheritance of a recessive trait
trait is on leg of X chromosome only so missing on Y chromosomes.
example: color blindness, balding, hemophilia convention is lowercase on X shows trait (Xc)
are
recessive, uppercase on X (XC) is dominant
In terms of phenotypes, male with trait is affected ; female with one trait is a carrier but not affected ;female
with two traits is affected.
Mother's
oocytes
Xc
XC
Dad's
XC
XCXc
XCXC
sperms
Y
XcY
XCY
What are offspring genotypes (and phenotypes in parentheses)? boys:XcY (affected),
XCY (not affected)
girls: XCXC (not affected), XCXc (not affected), XcXc (affected) %50 of boys, 0% of girls
affected
Another mating.
Mother's
oocytes
Xc
XC
Dad's
Xc
XcXc
XcXC
sperms
Y
XcY
XCY
What are offspring genotypes (and phenotypes in parentheses)? boys:XcY (affected),
XCY (not affected)
girls: XCXc (not affected), XcXc (affected) 50% of boys, 50% of girls affected
2. Incomplete dominance
Sickle cell anemia
Mother's
oocytes
S
s
Dad's
S
SS
Ss
sperms
s
Ss
ss
Only SS have normal phenotypes, Ss is moderately afflicted and ss is more severely afflicted Like other recessive
traits, both parents must give offspring a recessive allele for child to have disorder.
3. Codominance
ABO blood typing
previously only one pair of alleles was considered
ABO typing involves three alleles in population but only two can be in one individual
A and B are red blood cell markers, O is lack of markers
A and B are codominant, O is recessive
genotype (Alleles)
phenotype (blood type)
AA, AO
A
BB,BO
B
AB
AB
OO
O