Human Genetics and Society Chapters 1-4

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Plasma membrane

-Double Layered, controls the movement of materials in & out of cell
-Genetically determined chemical markers give cell an identity
-Contains molecular sensors or receptors

cytoplasm

-Contains membrane-bound compartments & organelles
-Cell as a protein factory
-Many organelles create, modify, and transport proteins

mitochondria

-Produce energy for cell
-Carry their own DNA

nucleus

-Largest organelle
-Enclosed by a double membrane

lysosomes

-Membrane-enclosed vesicle, contains digestive enzyme for destruction of materials or cells
- >40 genetic disorders of lysosomes

ribosomes

-Produce protein for the cell

Endoplasmic Reticulum

-Network of membranes, may contain ribosomes (site of protein production)
-Proteins may be modified and folded

Golgi Apparatus

-Sorts and distributes proteins

Chromosomes

-Found in nucleus, human cells have 23 pairs (=46)
-Sperm & egg have haploid # (n)=23, they fuse to form zygote with diploid (=46)

Autosomes

-Chromosomes other than the sex-determining chromosomes

Chromosomal Sex

-For the first seven weeks of gestation, both male and
female embryos develop in identical fashion
-Begins at fertilization
-Which chromosome pair the zygote has: XX or XY
-No internal and external characteristics

Gonadal Sex

-Expression of a gene (SRY) on Y chromosome causes
the gonads to become testes
>>Testes cells secrete testosterone
>>Control development of external and internal male
reproductive organs
-XX chromosome (no Y)
>>Estrogen secretion (no testosterone)
>>Gonad develops as an ovary (female development is default) and male duct systems degenerate

Phenotypic Sex

-External appearance

Sperm Sorting

-Sperm sorted by laser based on how brightly they
glow fluoresce because X-chromosome carrying sperm are little bit heavier than Y-chromosome carrying sperm
-Sperm sorting for humans is tightly regulated by FDA
-Procedure available only to the limited case such as
having a disease with sex-linkage

Fallopian Tube

-Fusion of sperm and egg occurs in the upper thirds of the fallopian tube

Blastocyst

-Fertilized egg undergoes cell division while traveling to the uterus (3 to 4 days)
-Forms a large hollow ball of cells (blastocyst)

Inner Cell Mass

-Embryonic stem cell source

hCG

-Chorion produces hormone called human chorionic
gonadotropin (hCG)
-Prevent lining of uterus from breakdown and expelling embryo
-hCG in urine used for home pregnancy tests

Chorion

-By 12 days after fertilization, embryo forms protective membrane

3rd Trimester

-Most rapid fetal growth take place
-Circulatory system and respiratory system mature
-Fetus doubles in size during the last eight weeks

Complete Androgen Insensitivity

-Individuals with this condition have an XY chromosome
-Mutation of androgen receptor (AR) gene on the X
chromosome
-Y chromosome produces testosterone normally, but receptor for testosterone or hormones derived from testosterone is defect
-Leads to development of female duct system and external genitals, although the undescended testes remain in the abdomen
-No menstruation, Infertile because they have testes instead of ovaries, No sperm formation due to no sensitivity to androgens
-Physically appear to be females with well-developed breasts but limited pubic hair

Barr Body

-In females, one X chromosome in somatic cells is
inactivated, forms Barr Body
-The number of Barr bodies is always one less than
the total number of X chromosomes
• Female (46, XX) - one Barr body
• Male (46, XY) - no Barr body
• Male with a 47,XXY karyotype - one Barr body
• Female with a 47,XXX - two Barr bodies
• Female with a 45, XO - no Barr Body

Intersexuality

-Congenital conditions that chromosomal sex of a
person is not consistent with his or her phenotypic or
physical sex
-Or the biological sex cannot be classified clearly as
either male or female
-Conditions in this category:
• Complete androgen insensitivity (CAI)
• Klinefelter syndrome (47,XXY)
• Turner syndrome (45,X)
• Disorders or variations of sex development (DSD)

Testes

-Produce sperm and secrete androgens

Scrotum

-Where the testes descend to

Duct System

-Transports sperm out of the body
-Epididymis (storage) -> vas deferens -> urethra

Seminal Vesicles

-Provide fructose (a sugar) as an energy source and prostaglandins - chemical messengers stimulating
contractions of female reproductive system to assist in sperm movement

Prostate Gland

-Secretes a milky, alkaline fluid - neutralizes acidic
vaginal secretions and enhances sperm viability

Bulbouethral Glands

-Secrete a mucus-like substance - provides lubrication for intercourse

Spermatogonia

-(2n) divide by mitosis to form spermatocytes (2n) during spermatogenesis (which begins at puberty)

Spermatocytes

-Undergo meiosis to produce intermediate cells, spermatids (n)

Spermatids

-They form mature sperm (n) with tails

Uterus

Fertilized egg (zygote) moves into the uterus
-Holds embryo/fetus during pregnancy
-Two layers
--Outer thick layer, myometrium
--Inner uterine tissue, endometrium

Oogenesis

-Occurs in the ovary
-Controlled by cycle of hormones (GnRH, LH, FSH)
-Follicles consist of a developing egg surrounded by
an outer layer follicle cells
-Oogonia (2n) divide by mitosis and differentiate into
primary oocytes (2n).
-Primary oocytes begin meiosis in the third month of embryonic development and become secondary oocytes (n), and then stop
-At puberty, secondary oocytes arrested in meiosis
are released from follicle of ovary (ovulation)
-At birth, a girl already has a lifetime supply of developing eggs in her ovary
-About 400 to 500 eggs will be released from the ovary and move into the oviduct

Causes of Infertility in Women

-Hormone levels (most common cause of infertility)
• Estrogen
-Absent or damaged ovaries
• Surgical removal (ovariectomy)
• Damage by other surgeries, inflammation, radiation, or infections
-Premature menopause
• women who are extremely athletic and who have had low body weight for
many years
-Secondary amenorrhea (lack of menstruation)
• caused by hormonal disturbances, stress, low body weight, nutrition, and
excessive physical activities
-Fallopian tube blockage
• infections, appendicitis, bowel problem
-Endometriosis
• Unknown cause; Not affect fertilization but Leading implantation problem

Causes of Infertility in Men

-Low sperm count - most common cause
• Less than 20 million per ejaculation
• Causes: chemicals (lead, pesticide), radiation, drugs (marijuana),
• Mumps and other diseases (diabetes), alcohol consumption, injuries, heat
-Low sperm motility
• Causes: defects in structure - malformed, extra, or no tails
-Impotence (Erectile Dysfunction, ED):
• Not enough blood supply to the penis
• Causes: emotional, physical (hormonal), drug related, overweight, high blood pressure and diabetes
-No sperm - (Aspermia):
• Causes: surgery (vasectomy), injury, drugs, and birth defects such as undescended testes or no formation

Other Factors of Infertility

-Smoking:
• Men - lowers sperm count
• Women - Increases the risk of miscarriage and low-birth-weight babies
• Overall reduces the chance of conceiving by 1/3
-Environmental factors:
• Pesticides, lead, ethylene oxide (used to sterile surgical instruments and dental/medical supplies), organic solvents, dioxin, and radiation
-Woman's age
-Sexually transmitted diseases:
• Venereal diseases (Gonorrhea and Chlamydia)

Types of Assisted Reproductive Technologies

-Hormone treatment
-Donation of gametes (sperm and eggs)
-In vitro fertilization (IVF)
-Surrogacy

Hormone Treatment

-Treat estrogen to stimulate ovulation
-Treat testosterone to stimulate sperm formation
-If not successful, more complicated procedures may be applied

Donation of Sperm

-One of the first methods of ART
-Widely used for almost 50 years
-Donated by known or unknown qualified donors
-Used immediately or frozen in liquid nitrogen for
later use
-Husband/partner's sperm pre-screened for X or Y bearing sperm
-Many sperm banks offer sperm in the US
-For whom: individuals with low sperm count, low
sperm motility, or aspermia

Donation of Eggs

-Egg donation is more difficult and expensive
-Retrieval procedure is time-dependent and
involves surgery
-Egg donor undergoes hormone treatment for 7-10
days and laparoscopy to remove the eggs
-Freezing is difficult, and eggs are generally used
for IVF immediately after retrieval

In Vitro Fertilization

-Donor eggs and/or donor sperm are used for
fertilization in a dish (outside of uterus)
-Fertilized eggs (zygotes) are placed in an incubator
for further culture to reach certain stage
-Often 3 to 4 embryos are transferred to the uterus
to increase the chance of implantation

Egg Donor Surrogacy

-the surrogate contributes eggs which are fertilized by artificial insemination using sperm of infertile couple's male partner, and surrogate mom carries the embryos to term
-Surrenders the baby after term

Gestation Surrogacy

-The surrogate mom carries the embryo to term but the egg and sperm are from two other people, who may be unrelated to the infertile couple

Telomeres

-keep chromatids from sticking to each other and may play a role in aging

Meiosis I (Give stages in order)

-Interphase I
-Prophase I
-Metaphase I
-Anaphase I
-Telophase I
-Cytokinesis

Interphase I

-Before cells begin meiosis, chromosomes undergo replication

Prophase I

-As meiosis begin, chromosomes coil and shorted by
condensation, and become visible under the microscope.
-Paired homologous chromosomes may exchange parts by crossing over (recombination)

Metaphase I

-Paired chromosomes line up at equator of the cell
-Spindle fibers attach to the centromeres of each pair

Anaphase I

-Sister chromatids separate and move toward opposite poles of the cells

Telophase I

-Chromosome becomes uncoiled and nuclei reform

Cytokinesis

-Cytoplasm divides resulting in formation of two cells
-These cells have half the number of chromosomes of the original cells and are called haploid cells

Meiosis II (give stages in order)

-Prophase II
-Metaphase II
-Anaphase II
-Telophase II

Prophase II

-Daughter cell chromosomes become coiled again

Metaphase II

-The 23 chromosomes in each cell attach to spindle
fibers at their centromere

Anaphase II

-Each centromere and each chromosome (also called
chromatid) divide and move to opposite ends of the cell

Telophase II

-The chromosomes become uncoiled; Nuclear membrane reforms
-After meiosis, four daughter cells form, each has the half number (haploid) of chromosomes (n)

Nondisjunction

-Chromosomes fail to separate equally during meiosis
-Results in gametes with an abnormal chromosome
number:
• extra (n+1, 24) chromosome
• missing (n-1, 22) chromosome
-Fertilization by abnormal gametes
-Resulting in zygotes with abnormal chromosome number

Amniocentesis

-At 14-16 weeks
-Collects amniotic fluid (liquid surrounding fetus)
• Fetal cells grown and karyotype produced
-Only done under certain circumstances:
• Mother age > 35
• History of child with chromosomal abnormalities -
1-2% recurrence risk in such case
• Either parent has abnormal chromosomes
• Mother is a carrier of a X-linked genetic disorder
• Parents have history of infertility or multiple
miscarriages

Amniotic Fluid

-Fetal urine, water, enzyme proteins,
and shed fetal cells

Chorionic villus sampling (CVS)

- At 10-12 weeks
• Rapidly dividing cells
• Karyotype within few days

Aneuploidy

-Abnormal condition of chromosomal number
• gain of one chromosome (three copies of one chromosome) -trisomy (2n + 1, 47): Down syndrome, Jacobs syndrome
• loss of one chromosome (only one copy of a chromosome) -monosomy (2n - 1, 45): Turner syndrome

Karyotype

-Display of chromosomes in pairs by size, the position of the centromeres, banding pattern
• During mitotic metaphase

Euploidy

-Normal two copies of each chromosome (2n, 46)

Polyploidy

-Multiple full sets of chromosomes
• Triploidy (3n, 69)
• Tetraploidy (4n, 92)
• In humans, this is rare and lethal
• Fertilization of an egg with two or more sperm

Autosomal Monosomies

-Always fatal resulting in miscarriage early in pregnancy

Autosomal Trisomies

-Also mostly fatal in early stage but a few conditions result in live birth
• Trisomy 13 (Patau syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 21 (Down syndrome)

Patau Syndrome (47,+13)

-1/15,000 live births
-Survival: 1-2 months
-Symptoms:
• facial malformation
• eye defect
• extra digits
• heart defects (80%)
• severe defects in brain and nervous system

Edwards Syndrome (47,+18)

-1 in 11,000 in live birth
-80% females
-Survival: 2-4 months
-Symptoms:
• retarded development
• mental disabilities
• finger defects
• heart malformation
-Die from heart failure or
pneumonia

Down Syndrome (47,+21)

-1 in 800 live births (depending on mother's age)
-Survival up to age 50 - only autosomal trisomy in
which patients can survive into adulthood
-Childhood mental retardation and heart defects (40%)
-Wide, flat skulls; eyelid folds; large tongues; physical,
mental, and development retardation
-May live rich, productive lives
-Maternal age is the main risk factor

Turner Syndrome (45,X)

-Aneuploidy in sex chromosome
-1 in 10,000 female births
-Most cases (95-99%) lead
miscarriage
-Survival to adulthood
-75% paternal X is missing
-Symptoms (female):
• short stature
• wide-chested
• undeveloped ovaries
• normal intelligence

Klinefelter Syndrome (47,XXY)

-Trisomy involving sex chromosomes
-1 in 500-1,000 males births
-Survival to adulthood
-Symptoms (Male):
• Features do not develop until puberty
• Usually sterile (small testes)
• Female-like features (broad hips, lack of body hair, female type nipples)
• May have learning disabilities

Jacobs Syndrome (47,XYY)

-Trisomy involving sex chromosomes
-1 in 1,000 male births
-Extra Y chromosome
-Survival to adulthood
-Symptoms:
• Thin and tall
• Personality disorders
• Some form of mental disabilities
• Adolescent acne
• Some may have very mild symptoms

Dominant

-Trait present in the first-generation offspring (tall)

Recessive

-Trait absent in first generation but reappeared in the next generation (short)

Alleles

-Variations of a gene

Homozygous

-Organisms that carry identical alleles of a gene - TT (tall) or tt (short)

Heterozygous

-Organisms that carry non-identical alleles of a gene - Tt

Phenotype

-What an organism looks like - tall or short

Genotype

-Actual genetic makeup

Law of Segregation

-Two copies of each gene separate from each other during meiosis
-Only one copy of each gene is present in the sperm or egg, and is contributed to the offspring
-Each parent gives one copy of each gene

Law of Independent Assortment

-Members of a gene pair segregate into gametes independently
• S/s - tail length
• B/b - coat color
-Gametes can have different combinations of parental genes
-For two traits, four combination possible in F2 - 9:3:3:1 ratio

Pedigree Symbols

see photo

Autosomal Recessive Inheritance

-Trait is carried by autosome and inherited trait is not
marked in heterozygous person like Albinism

Autosomal Recessive Mutation

-Unaffected heterozygote parents (Aa; carriers) can have affected children (aa)
-All children of affected parents (aa) are affected (aa)
-Both parents Aa, risk of affected child is 25%
-Equal affected male and female
-Both parents must transmit the gene for a child to be affected
-Recessive traits vary from mild conditions such as hair color and eye color to life-threatening or fatal disorders

Sickle Cell Anemia

-High frequency in areas of West Africa, India, and
Mediterranean Sea
-Abnormal hemoglobin, blood vessel blockage

Autosomal Dominant Inheritance

-Trait is carried by autosome and inherited trait is
marked in heterozygous person like HD
-Needs one copy of allele (Aa) - an abnormal gene from one parent is capable of causing disease, even though matching gene from the other parent is normal
-Dominant genetic disorders present in a homozygous condition (AA)
-Fatal early in life
-aa: Unaffected individuals carry two recessive alleles
-Affected individual has at least one affected parent

X-Linked Recessive Inheritance

-In females, recessive gene (a) can be covered by dominant gene (A) in heterozygote (Aa)
-Males carrying a mutant gene (a) on X chromosome
cannot carry a normal, dominant allele of the gene (no A) to mask expression of recessive allele
• This means that males cannot be heterozygous for any gene on X chromosome
• X-linked recessive genes are always expressed in males
• Males are affected by X-linked recessive genetic disorders much more often than females

Neurofibramatosis

-Autosomal dominant genetic disorder
-Pigmented spots on skin
-Or non-cancerous tumors in nervous system
-Can press against nerves causing paralysis or blindness
-Often appears in children of normal parents (because the gene mutates spontaneously)

Huntington Disease

-Autosomal dominant genetic disorder
-Causes destruction in certain areas of brain
-Symptoms come on slowly and get worse progressively
-No treatment

Achondroplasia

-Autosomal dominant genetic disorder
-Dwarfism

Brachydactyly

-Autosomal dominant genetic disorder
-Hands with short fingers

Marfan Syndrome

-Autosomal dominant genetic disorder
-Connective tissue disorder
-Possible aortic aneurysm

Porphyria

-Autosomal dominant genetic disorder
-Inability to metabolize porphyrin
-Episodes of mental disturbance (paranoia or hallucinations)

Hemizygous

-Males cannot be homozygous or heterozygous, they
are hemizygous for all genes on X chromosome

Muscular Dystrophy

-X Linked recessive genetic disorder
-DMD gene on the end of X chromosome
-Encodes protein dystrophin that supports plasma
membrane during contraction
-If dystrophin absent or defective, cells are torn apart
-Another form, Becker MD (BMD) has partially
functional dystrophin, and thus develops less
serious condition and live longer

Hemophilia A

-X Linked recessive genetic disorder
-XH = normal; Xh = affected (hemophilia)
-Problem in blood clotting
-Danger of non-stop bleeding to death from even minor cut or from hemorrhage caused by bruise
-Clotting factor called factor VIII is absent in blood
-Hemophilia A most common form of X-linked hemophilia
-Females affected only if they are homozygous for
recessive gene (XhXh), both parents must carry the trait (rare)
-More males have hemophilia than females

Red-Green Color Blindness

-Inability to see red and green colors
-X Linked recessive genetic disorder

Lesch-Nyhan Syndrome

-X Linked recessive genetic disorder
-Lack of HGPRT protein
-Mental retardation
-Self mutilation

GINA

-Genetic Information Non-discrimination Act (GINA)
-People cannot be discriminated by their genetic
information

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