Download Genetics and Inheritance - Harford Community College

PowerPoint Summary
of Chapters 23-25
• Use this PowerPoint along with the outline
notes
• If a term appears in bold and is not
defined, be sure to go look on the text for it
• Refer back to the text for any additional
info you would like to have
• Have fun!
Chapter 23
Reproductive System
• Meiosis
– A form of cell division specific to gametes that
results in only half the number of original
chromosomes (fig 21-1)
– Stem cells (46 chromosomes) divide into
functional gametes which only have 23
chromosomes
– For males, this process doesn’t start until
puberty and continues throughout the rest of
their life
• Once started, males will produce 500,000
spermatozoa per day.
• Spermatogenesis – creation of sperm
– A single stem cell divides twice to produce
four spermatozoa (sperm cell)
– This process occurs along the nearly half mile
of seminiferous tubules in each testis
– The seminiferous tubules drain into the
epididymus. There spermatozoa mature up to
2 weeks in the super coiled 23 ft of tubule.
– The next part of the pathway is the ductus
deferens (vas deferens) that runs from the
posterior of each testis to a single ejaculatory
duct.
• Sperm can be stored in the ductus deferens for
several months
• Spermatogenesis – (cont’d)
– Accessory glands add to the seminal fluid at
the ejaculatory ducts and proximal end of the
urethra.
• Seminal Vesicles
• Prostate Gland
• Bulbourethral
(see fig 23-1 for location of these glands)
– What are the functions of semen?
• Spermatogenesis – (cont’d)
– The urethra is the final path for seminal fluid
as it travels through the penis and is
ejaculated out of the body
• A typical ejaculate is 2 to 5 ml of semen and
contains 50-100 million sperm per ml
– Interstitial cells between the seminiferous
tubules produce the hormone testosterone.
• This production increase dramatically after puberty
in the presence of FSH and LH
– Refer back to Chapter 12 about the regulation and
production of these hormones
• Oogenesis – formation of an egg (ovum)
– Stem cells during prenatal development divide
twice to produce an ovum with 23 chromosomes
• Each female is born with nearly 2 million ovum, but by
the time they will start being released at puberty, the
number withers down to ~200,000. All are stored in a
pair of ovaries.
– Levels of FSH and LH stimulate the development and
release
• Even so, she will only release less than 400 in a
lifetime. One per month, alternating from the right or
left ovary.
• This process will end with menopause.
• Oogenesis – formation of an egg (ovum)
– One ovum from the left or right ovary is ovulated
into the fimbriae of the 5 inch uterine tube
• Cilia in the tube draw the ovum towards the uterus; a
trip that takes 3-4 days
– This cycle usually lasts about 28 days, but can
be longer or shorter per individual
• Increased LH levels stimulate the development of a
follicle, which will then release its ovum in 14days
• Fertilization needs to occur in the first 48 hrs after
ovulation or the ovum will disintegrate in the uterus
and be flushed out during menstration.
• If fertilizations does occur, then the cycle is stopped
until after birth
• Read both the menstrual cycle which
starts on page 466
• Review fig. 23-13 which summarizes the
hormonal events and uterus development
for this cycle.
• Read the Hot Topic (Box 23-3) and Birth
Control Strategies on pages 468 and 469
• Be familiar with the types of cancer of this
system
– Prostatic, Testicular, Breast, Endometrial,
Ovarian, Cervical
Chapter 24
Development
• Begins at fertilization, or conception and
ends at birth
– Gestation lasts approximately 38 weeks
• Prenatal development is divided into two
stages
– Embryo for the first two months
– Fetus from the ninth week to birth
• Fertilization
– Fusion of egg and sperm
– Each contain 23 chromosomes to form a
zygote containing 46 chromosomes
– 200 million sperm are
released into the vagina,
10,000 make it into the
uterine tube, and about
100 may actually make it
to the egg.
– Penetration of the egg by
a single sperm allows the
chromosomes to combine
Gestation
• Average prenatal period is 38 weeks or
266 days (divided into three trimesters)
• First Trimester
– 40% of the eggs that are fertilized produce
embryos that survive the first trimester
– Embryo formation
• Zygote undergoes rapid cell divisions called
cleavage
• By day 5, the cells have entered the uterus, and
developed into a blastocyst
• First Trimester continued
– Implantation
• About day 7, the blastocyst adheres to the surface of the
uterus and will become completely embedded within its
membrane
– The outer cells of the blastocyst develops into the placenta
• The placenta begins secreting human chorionic
gonadotropin (hGC) which signals the corpus luteum to
maintain production of estrogens and progesterone
– This hormone maintains a functional endometrial lining
• The inner cell mass of the blastocyst becomes organized into
three germ layers that will form different body tissues
• First Trimester continued
– Placenta (fig 24-2)
• Extensions from the chorion extend into maternal
tissue where chorionic blood vessels develop
• These chorionic villi enlarge as the heart starts
beating and extend further into the endometrium
where they will come in close proximity of maternal
blood vessels
• The vessels develop into two umbilical arteries and
a single umbilical vein
• The chorionic villi provide the surface area for the
exchange of gasses, nutrients and wastes
between maternal and fetal blood flow.
• First Trimester continued
– Placenta (cont’d)
• Also releases hormones (progesterone and
estrogen) which will take over for the declining
corpus luteum
• Prevents menstration, prepares mammary glands
to produce milk, and prepare the body for delivery
• The following slide shows embryos at
different stages and an early fetus
– Interesting note: Picture b is during a phase
where we don’t look too much different from
fish or chicken embryo
• Second and Third Trimester
– The framework for the major organ systems
have formed by the start of the second
trimester
• The fetus grows from ~1oz to 1.4lbs
– Those organ systems become mostly
functional in the third trimester
• The fetus gains most its weight and shoots up to
an average of 7lbs
Changes
• The fetus is totally
dependant on the
mother’s organ
systems
– That means that the
mother has to increase
all her norms to provide
proper nutrition to the
developing fetus
• Increase CV activity,
blood volume,
Respiratory Rate,
appetite, and excretion
Changes
• Early contractions of uterine smooth muscle are
weak, short and painless
– Late in development rising estrogen levels increase
smooth muscle sensitivity and stimulate an rise in
oxytocin levels.
– Oxytocin increases the force and frequency of
contractions in response to a stretch in the uterine
cervix
– Uterine tissues also produce prostaglandins that
increase contractions as well
• Typically at 9 months, these changes lead to
labor contractions that continue until delivery
has been completed.
Stages of Labor (Parturition)
• First Stage
– Cervix dilates and the fetus begins to slide
down the cervical canal
– Labor contractions are once every 10 to 30
min and at some point the amnion will rupture
releasing amniotic fluid (“water break”)
• Second Stage
– Starts after the cervix has dilated completely
and concludes when the fetus emerges from
the vagina
– Time varies but usually lasts two hours or less
Stages of Labor (Parturition)
• Third Stage
– This stage ends with the ejection of the placenta
(“afterbirth”) and an associated blood loss of 500600ml.
• Along with the placenta, the amniotic sac membranes, and
the umbilical cord (except the part attached to the baby which
forms the umbilicus) are ejected
• Fourth Stage
– The period the body controls the bleeding after the
birth
– Involves uterine contractions and repair of an
episiotomy, if conducted.
Stages of Labor
• An episiotomy can be performed to
prevent perineal tearing if the vaginal
opening is too small
– This procedure enlarges the vaginal opening
by placing an incision through the perineal
musculature between the vagina and anus. It
can be repaired with sutures after delivery
• A Cesarean (C) section can be performed
if complications arise
– Here the abdominal wall is opened and a 6-7
inch incision is made in the uterus to allow the
head (the widest part) to pass through
Multiple Births
• New stats on births reveals that twins occur 1 in
100 births and with African-Americans, the rate
is greater (1 in 77)
• Fraternal twins are created when two eggs are
released and fertilized at the same time. May or
may not be the same gender.
• Identical twins are produced when the fertilized
zygote cells split apart during development. The
offspring’s genetic makeup is exactly the same.
– Fraternal twins are twice as common as identical
twins and are increasing with the practice of fertility
medicine.
Genetics and Inheritance
Chapter 25
• Genetics is the study of heredity, or how
different traits are inherited.
• Families have similar traits because they are
passed on from generation to generation
through their chromosomes
Genes and Chromosomes
• Chromosomes contain
DNA (Chapter 2 if you forgot)
– No cell uses every bit of
its genetic information
– Genes are functional
segments of DNA
• Every somatic cell
carries copies of the 46
original chromosomes
that were in the zygote
– Except gametes / RBCs
figure 2
Genes and Chromosomes
• Genotype –
Chromosomes and
their component
genes
►Arrangement of
nucleotide bases –
ATGCGCCCCATA or
AGCCGCATAGCG…
• Phenotype –
physical expression
of the genotype
►Hair color, skin tone,
vision, bone structure
* The genotype dictates the phenotype
• A gene’s position on a chromosome is called a
locus
– The locus helps map the DNA strand to indicate
which section is responsible for certain traits
• Each DNA strand has a “partner” within the
nucleus
– This pairing is referred to as Homologous
Chromosomes, with one strand coming from
paternal DNA and the other from maternal DNA
Karyotyping
• a sample of amniotic
fluid is taken
(amniocentesis) and
fetal DNA is analyzed
• a Karyotype displays
homologous pairs of
chromosomes
• Sampling procedures can be dangerous to
the fetus and mother
– Amniocentesis is only performed when known
risk factors are present
• I.e. Family history, age complications, drug user, etc.
– Amniotic fluid has to be sufficienct enough to
be taken without implication to the fetus
• Usually at a gestational age of 14 weeks
• Results take several weeks
Patterns of inheritance
• Somatic cells contain
23 pairs of
chromosomes
– All 23 are Homologous
chromosomes
– 22 pair of autosomal and
one pair of sex
chromosomes
• Various forms of a gene are called alleles
• Homozygous if homologous chromosomes
carry the same alleles - AA, or aa
• Heterozygous if homologous chromosomes
carry different alleles - Aa
• Alleles are either dominant
– Always expressed in the phenotype
– Usually represented by a capital letter (A)
• or recessive
– Expressed only when both alleles are present
– Usually represented by a lowercase letter (a)
• Incomplete Dominance
– Phenotype that is different from phenotypes of
homozygous for either allele
– Example: Sickle cell
– Recessive trait (s) that causes RBCs to fold
• ss: individual has the sickle cell disorder
• Ss: individual has RBCs that fold only when
tissue O2 levels drop
• Codominance
– Heterozygous allele that shows both traits in
its phenotype
– Example: Blood type
• IA: antigen A present
• IB: antigen B present
• i: no antigen present
•
•
•
•
ii = Type O
IB IB or IB i = Type B
IA IA or IA i = Type A
IA IB = Type AB
• Teratogens
– factors that disrupt normal development by
damaging cells, altering chromosome
structure, or by changing the pattern of gene
activation and expression.
– Examples are nicotine, radiation, and alcohol
– Fetal alcohol syndrome (FAS) produces
developmental defects caused by mothers
who drink during pregnancy
• Number 1 cause of mental retardation in the U.S.
Punnett square diagram predicts
probabilities of traits
 A = normal color, a = albino (see next slide)
• In diagram A, a homozygous dominate
male mates with a homozygous recessive
female
– The probability of them having offspring with
normal pigment is 100% (all are heterozygous
dominant)
• In diagram B, a heterozygous dominant
male mates with a homozygous recessive
female
– The probability that they will have normal
pigment offspring is 50%, the other 50% have
albinism
Inheritance
• Simple inheritance
– Phenotypic characteristics are determined by
interactions between single pair of alleles
• Polygenic inheritance
– Phenotypic characteristics are determined by
interactions among alleles on several genes
Inheritance
• More than 1200
inherited conditions
have been
identified that are
linked to 1 or 2
abnormal alleles
for a single gene
Sources of Individual Variation
• Genetic recombination
– Gene reshuffling, common, creates variations
within a gene pool
• Crossing over and translocation (fig next slide)
– Occurs during meiosis
– May produce abnormal chromosomes
• The production of chromosomes with extra or
missing segments
• Most result in miscarriages but some result in
developmental disorders
Crossover and Translocation
• Spontaneous mutations
– Random errors in DNA replication where extra
or missing code occurs
– Many of these errors are hidden as the
recessive trait, and some don’t make it past
the embryo stage
– Heterozygous for the abnormal trait would be
a carrier
Sex-Linked Inheritance
• Sex chromosomes are X chromosome and
Y chromosome
– Male = XY
– Female = XX
– X chromosome carries X-linked (sex linked)
genes
• Affect somatic structures
• The X chromosome is longer therefore no
corresponding alleles on Y chromosome (i.e. no
competition for traits)
Sex-linked Punnett
Human Genome Project
• Mapped ~24,000 of our genes
– Including some responsible for inherited
disorders
click for more Human Genome info
click for DNA sequence list
DNA Map
Genetic Disorders
• Mistakes caused during meiosis
– Extra copies or missing pieces of DNA
• Down Syndrome
– Most common chromosomal
abnormality
– Caused by an extra copy of
chromosome #21
– Marked by mental retardation of
various levels and specific
common physical features
– Most die early of cardiovascular
problems or develop neurological
problems as they age
– Incidence increases as the age of
the mother being impregnated
increases after age 35.
Genetic Disorders
• Klinefelter Syndrome
– Male with an extra X chromosome
– Reduces testosterone production so testis fail to
mature, individuals are sterile, and breasts enlarge
• Turner Syndrome
– Female with a single X chromosome
– Therefore a chromosome short
– Causes an absence of development at puberty,
ovaries are non-functional, and estrogen production is
insignificant.
– Will require hormone injections to develop adult
female characteristics
Ectopic (“displaced”) Pregnancies
• Normal implantation occurs in the endometrial
lining of the uterus, ectopics implant somewhere
else.
• 95% implant in the uterine tube which cannot
expand like the uterus.
– The developing embryo ruptures the tube which
causes internal bleeding and a risk to the mother
– In some cases, the embryo can continue to develop
full term and with surgical removal at birth
• Incidence increases with regular douching or
uterine tube infection
Placenta Problems
• Placenta Previa
– Implantation occurs in the lower portion of the uterus
– The placenta then may form near or over the cervical
opening which increases the risk of tearing and
bleeding out
– Treatment includes bed rest for the mother and a
scheduled C section when gestation has reached a
safe point
• Abrupto Placentae
– Placenta tears away from the uterus after the fifth
month of gestation
– Internal bleeding may lead to maternal anemia or
shock
– Fetal mortality is between 30 and 100%