Transcript Human Genetics

Human Genetics
Concepts and Applications
Tenth Edition
RICKI LEWIS
21
Reproductive
Technologies
PowerPoint® Lecture Outlines
Prepared by Johnny El-Rady, University of South Florida
Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Savior Siblings and More
Innovative ways to conceive offspring:
1) Couple in search of an oocyte donor
advertises for an attractive, athletic woman
2) Cancer patient stores her oocytes before
therapy; becomes a mother two years later
3) A paralyzed man has sperm removed
and injected into his partner’s oocyte
2
Savior Siblings and More
Lisa and Jack Nash sought to have a child for
a different reason
They conceived and selected Adam to save
his sister’s life
- She was suffering from Fanconi anemia
A month after his birth, physicians infused
Adam’ umbilical cord stem cells into Molly
3
Adam and Molly Nash
Figure 21.1
4
Assisted Reproductive
Technologies
ARTs are methods that replace the source of
a male or female gamete, aid fertilization or
provide a uterus
Developed to treat infertility but are
becoming part of genetic screening
The US Government does not regulate ARTs
- However, the British Government does
5
Infertility and Subfertility
Infertility is the inability to conceive a child
after a year of frequent intercourse without
contraceptives
Subfertility distinguishes couples who can
conceive, but require longer time than
usual
Affect one in six couples
A physical cause can be identified in 90% of
cases: 30% in males, 60% in females
6
Male Infertility
One in 25 men are infertile
Easier to detect, but often harder to treat
than female infertility
Most cases of male infertility are genetic
Causes of infertility include:
- Low sperm count (oligospermia)
- A malfunctioning immune system
- A varicose vein in the scrotum
- Structural sperm defects
7
Male Infertility
Box Figure 1
8
Most cases of male infertility are genetic
- Due to small deletions of Y chromosome
that remove genes important for
spermatogenesis
- Mutations in genes for androgen
receptors or other hormones promoting
sperm development
In cases of low sperm count, sperm can be
stored frozen, then pooled
Lack of motility in sperm prevents movement
in the female reproductive tract
9
Female Infertility
Many women with subfertility or infertility
have irregular menstrual cycles
- This makes it difficult to pinpoint when
conception is most likely
Tracking ovulation cycles aids in
determination of the most likely days for
conception
Abnormalities in any part of the female
reproductive system can cause infertility
10
Figure 21.2
11
Female Infertility
Fertility drugs stimulate ovulation but may
induce release of multiple oocytes
Blocked fallopian tubes can result in
ectopic pregnancy (tubal pregnancy).
Excess tissue growth in uterine lining may
make it inhospitable for an embryo
- Fibroids: benign tumors
- Endometriosis: buildup of uterine lining
12
Female Infertility
Secretions in the vagina and cervix may be
hostile to sperm
Infertility may also result if the oocyte fails
to release sperm-attracting chemicals
Early pregnancy loss due to an abnormal
chromosome number is more common in
older females
- May appear as infertility because
bleeding resembles a heavy menstrual
flow
13
Infertility Tests
The man is checked first, because it is
easier, less costly and less painful to
obtain sperm than oocytes
- Sperm are checked for number (sperm
count) motility and morphology (shape)
A gynecologist can then check the female
to see if reproductive organs are present
and functioning
Psychological factors may also be at play
14
Assisted Reproductive
Technologies (ARTs)
Many people with fertility problems use
alternative ways to conceive
In the US, about 1% of the 4 million births
each year are from ARTs
Several of the ARTs were developed in
nonhuman animals
15
Assisted Reproductive
Technologies (ARTs)
Examples
- Intrauterine insemination
- Surrogate motherhood
- In vitro fertilization (IVF)
- Gamete intrafallopian transfer (GIFT)
- Zygote intrafallopian transfer (ZIFT)
- Oocyte banking and donation
- Preimplantation genetic diagnosis
16
17
18
Intrauterine Insemination
Donated sperm is placed in a woman’s
reproductive tract, typically at the cervix or
in uterus
Success rate is 5-15%
1790: first reported pregnancy from artificial
insemination
1953: methods for freezing and storing
sperm were developed
Sperm catalogs list personal characteristics
19
Surrogate Motherhood
In surrogate motherhood, a woman carries
a pregnancy to term for another woman
who cannot conceive and/or carry the
pregnancy
Custody rights are given up at birth
A surrogate mother may or may not have
contributed an oocyte
Complex legal and emotional issues must
be considered
20
In vitro Fertilization (IVF)
For in vitro fertilization, a sperm fertilizes an
oocyte in a culture dish
Embryos are transferred to the oocyte
donor’s uterus (or a surrogate’s uterus)
for implantation
1978: First IVF child born (Louise Joy Brown)
- Since then, 4 million IVF children
Intracytoplasmic sperm injection (ICSI) is
more effective than IVF alone
21
Intracytoplasmic Sperm Injection
For cases in which sperm cannot penetrate
the oocyte, IVF can be accompanied by
ICSI which injects sperm directly into the
oocyte
ICSI allows conception in cases of low
sperm count, abnormal sperm shape,
sperm motility problems,
- And in cases where male has spinal
cord injuries and cannot ejaculate
22
Intracytoplasmic Sperm Injection
Figure 21.3
23
Gamete Intrafallopian Transfer
(GIFT)
GIFT is a method in which superovulated
oocytes from a woman and sperm from
her partner are placed together in her
uterine (fallopian) tube
Fertilization occurs in the woman’s body
Allows conception in cases of fallopian tube
blockage
22% success rate and costs less than IVF
24
Zygote Intrafallopian Transfer
(ZIFT)
IVF ovum is introduced into the uterine
tube and allowed to move to the uterus
for implantation
Also about 22% successful
GIFT and ZIFT are done much less
frequently than IVF
- They often will not work for women
with scarred uterine tubes
25
Oocyte Banking and Donation
Oocytes, like sperm, can be stored frozen
Only 3% successful
New technique can freeze strips of ovarian tissue
Difficulties because oocytes pause in meiosis II until
fertilization occurs
Women can store their own oocytes to have
children later or prior to undergoing chemotherapy
Donated oocytes can be used by women with
infertility problems; 28-50% successful
Embryo adoption is a variation on oocyte donation
26
Preimplantation Genetic Diagnosis
(PGD)
This PGD technique allows detection of
genetic and chromosomal abnormalities
prior to implantation
One cell or blastomere of an 8-celled
embryo can be removed for testing
- The remaining cells will complete
normal development
About 29% success rate
27
Preimplantation Genetic Diagnosis
(PGD)
1989: First children who had PGD
- Used to select females who could not
inherit X-linked disease from mother
1992: First child born following PGD to
screen for cystic fibrosis allele present in
her family
PGD can be combined with IVF for women
who have had multiple miscarriages
28
Preimplantation Genetic Diagnosis
(PGD)
Figure 21.4
29
Table 21.1
30
Extra Embryos
Sometimes ARTs leave “extra” oocytes,
fertilized ova, or very early embryos
31
Using Extra
Embryos
Figure 21.5
32
Extra Embryos
A similar case to the Lyons’ involved a
California woman named Nadya Suleman
- She had eight fertilized ova left over
after using six to produce her six young
children
- She did not want to destroy these ova or
continue to store them
- She was implanted with them, and in
early 2009 gave birth to octuplets!
33
Polar Body Biopsy
An experimental ART that increases the
success of IVF
Based on Mendel’s first law (segregation
of alleles)
Enables physicians to perform genetic
tests on polar bodies and infer the
genotype of the accompanying oocyte
Oocytes that pass this test can be fertilized
in vitro and the resulting embryo
implanted
34
Polar Body Biopsy
Figure 21.6
35
Assisted Reproductive Disasters
ARTs introduce ownership and parentage
issues
Another controversy is that human
genome information is providing more
traits to track and perhaps control in
coming generations
- So, who will decide which traits are
worth living with, and which are not?
36
Table 21.3
Table 21.4
37