CHAPTER 2: HEREDITY & CONCEPTION

the influence of heredity on development

• heredity

  • based on biological transmission of traits and characteristics from one generation to another

• genetics

  • branch of biology that studies heredity

• genetic (inherited) influences

  • physical traits

  • intelligence, emotional, and personality traits

  • behavioral traits and psychological issues

chromosomes & genes

• chromosomes

  • found in cells

  • 23 pairs of rod-shaped structures

• genes

  • segments within chromosomes

  • regulate development of traits

    • transmitted by a single gene or may be polygenic (determined by combinations of pairs)

  • 20k to 25k genes in every cell

• DNA

  • large strands make up genes

  • double spiral (helix)

  • composed of phosphate and simple sugar

  • base pairs adenine with thymine (A-T) or cytosine with guanine (C-G)

mitosis & meiosis

• mitosis

  • cell division by which growth occurs and tissues are replaced

  • strands of DNA break apart, duplicate, and are rebuilt

  • result is identical copies of DNA strand

    • mutations are exceptions

• meiosis

  • cell division by which sperm and ova are produced

  • 23 chromosome pairs divide

  • result is a new cell with only 23 chromosomes

    • 22 pairs are autosomes

    • 23rd pair are sex chromosomes

      • determines sex: x from mother and x or y from father

identical & fraternal twins

• monozygotic (identical) twins (MZ)

  • derived from a single zygote that has split in two

• dyzygotic (fraternal) twins (DZ)

  • derived from two zygotes

  • share 50% of genetic material

• probability of twins increases

  • maternal age- less regular ovulation

  • use of fertility drugs

dominant & recessive traits

• traits are determined by pairs of genes

  • each member of a pair is an allele

• homozygous

  • both alleles for a trait are the same

• heterozygous

  • alleles for a trait are different

• Gregor Mendel

  • established the laws of heredity

• averaging

  • effects of both alleles are shown

  • incomplete dominance or codominance

• law of dominance

  • dominant allele paired with recessive allele

    • dominant allele appears in offspring

• combinations of dominant and recessive genes

  • carriers

• chromosomal or genetic abnormalities

  • occur in autosomes or sex chromosomes

  • may be caused by a single gene or combinations

  • multifactorial problems

chromosomal abnormalities

down syndrome

• cause: extra chromosome on 21st pair

• probability increases with increased age of parent

• characteristics of children

  • facial features

  • deficits in cognitive, language, and motor development

• adjustment problems

sex-linked chromosomal abnormalities

• most are infertile

• male with extra sex chromosome

  • XYY: extra Y chromosomes

  • XXY: Klinefelter syndrome

• female with abnormal number of sex chromosomes

  • X: Turner syndrome

  • XXX: Triple X syndrome

genetic abnormalities

• Phenylketonuria (PKU)

• Huntington disease

• Sickle-cell anemia

• Tay-Sachs disease

• Cystic fibrosis

sex linked

• carried on X sex chromosome

  • Hemophilia

  • Duchenne muscular dystrophy

  • Diabetes

  • Color blindness

  • some types of night blindness

determining probability of abnormalities

• genetic counseling

  • addresses probability of genetic abnormalities

  • information about couple’s genetic heritage

  • prenatal testing

    • Amniocentesis

    • Chorionic villus sampling (CVS)

    • Ultrasound

    • Blood tests

genetic counseling & prenatal testing

• Amniocentesis

  • usually performed on mother about 14-16 weeks after conception

  • can detect more than 100 chromosomal and genetic abnormalities in fetus

  • indicates the sex of the baby

  • some risk of miscarriage

  • improved ultrasound and blood tests is reducing use of Amniocentesis

• Chorionic Villus Sampling (CVS)

  • can diagnose abnormalities earlier than Amniocentesis

  • equal or slightly higher risk of miscarriage compared to amniocentesis

• Ultrasound

  • sonogram “picture’ of fetus

  • used to track fetus’ growth and determine age, sex, and structural abnormalities

• Blood tests

  • can reveal presence of recessive genes in parents

  • Alpja-Fetoprotein (AFP) assay

reaction range

• range of possibilities for the expression of the trait

• genotypes

  • sets of traits inherited from parents

• phenotypes

  • actual sets of traits

  • product of genetic and environmental influences

canalization

• environmental influences on genotype within reaction range

  • canalization: sequence of development is invariant

    • infant motor development

  • less canalization

    • intelligence

    • personality

environmental correlation (genetic)

• passive correlation

  • environment that child is placed into

• evocative correlation

  • child’s genotype elicits responses

• active correlation

  • environment child chooses

epigenetic framework

• development reflects the continual bidirectional exchanges between genetics and environmental influences

effects of genetics & environmental influences

• Kinship studies

  • genetic closeness of relatives

• Twin studies

  • monozygotic twins share 100% of genes

  • dizygotic twins share 50% of genes (same as other siblings)

  • reared together vs. reared apart

• adoption studies

conception

• ovarian follicle ruptures releasing the egg

• hundreds of millions of sperm are ajaculated

  • only a few thousand survive through the cervix and uterus

  • a few hundred bombard the ovum in the fallopian tube

• sperm and ovum unite

ova

• begin to mature at puberty

• monthly release of mature eggs into fallopian tube

• egg is propelled by cilia and perhaps by contractions in the wall of the fallopian tube

• if not fertilized, egg is discharged along with endometrium

sperm cells

• each contains 46 chromosomes, including one X and one Y

• self propelled and smaller than ova

• sperm with Y chromosome swim faster than sperm with X chromosome

  • more boys are conceived than girls

• from 200 to 400 million in ejaculate

  • only 1 in 1000 arrive in vicinity of ovum

• attracted by chemical odor secreted by ova

• sperm must penetrate gelatinous layer around ova

• sperm cells secrete an enzyme that briefly thins the layer

• when one sperm penetrates, the layer thickens, locking other sperm out

• chromosomes from sperm cell combines with egg chromosomes to form 23 new pairs with unique genetic instructions

infertility

fertility problems among men

• symptoms

  • low sperm count

  • deformed sperm

  • low sperm mobility

  • diseases

  • injury of testes

  • autoimmune responses

• causes

  • genetic factors

  • environmental poisons

  • diabetes

  • STI

  • overheating testes

  • pressure to testes

  • aging

  • drugs

major fertility problems among women

• symptoms

  • irregular or absence of ovulation

    • fertility drugs are used to cause women to ovulate

  • declining hormone levels due to aging

  • endometriosis

  • obstructions or malfunctions of reproductive tract

• causes

  • hormone irregularities

  • stress

  • malnutrition

  • infections that produce obstructions, as from scarring

    • Pelvic inflammatory disease (PID)

solutions to infertility

• artificial insemination

  • sperm injected into mother’s uterus

• in vitro fertilization

  • ova and sperm are fertilized, then implanted in mother’s uterus

• donor IVF

  • ovum harvested from donor woman; fertilized in vitro and implanted in recipient’s uterus

  • embryonic transplant

• surrogate mothers

  • “substitute” who carries a baby to term for another woman

  • ethical and legal risks because the surrogate mother may not want to give up the baby

• adoption

  • greater diversity of adopted children and adoptive parents

  • consideration of adopted children needs

  • relinquishing mothers also experience effects