251 chapter 2

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The Influence of Heredity

on Development

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Heredity and Genetics

� Heredity

± One¶s nature based on biological transmission of traits andcharacteristics

� Genetics

± Field within the science of biology that studies heredity

� Genetics Influence our

± Physical traits ± Behavioral traits

± Psychological problems

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What Are Chromosomes and Genes?

� Chromosomes

± Found in cells

± 23pairs

� Genes

± Segments of DNA within chromosomes

± Regulate development of traits

� Transmitted by single gene or may be polygenic

± 20,000to 25,000 genes in every cell

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Double Helix of DNA

Figure 2.1

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Two Types of Cell Division

� Mitosis

± Cell division by which growth occurs

± Strands of DNA break apart, duplicate and are rebuilt

± Result is identical copies of DNA strand

� Mutations can develop throughout our lives

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� Meiosis

± Cell division by which sperm and ova are produced

± 23chromosome pairs divide

± Result is a new cell with only 23 chromosomes

� 22 pairs are autosomes

� 23rd pair are sex chromosomes

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� Meiosis

± Crossing Over

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How Are Twins Formed?

� Monozygotic Twins (MZ)

± Derived from a single zygote that has split in two

± Identical twins

� Dizygotic Twins (DZ) ± Derived from two zygotes

� Probability of twins increases

± Maternal age

± Use of fertility drugs

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How Do Genes Determine Traits?

� Traits are determined by pairs of genes

± Each member of pair is an allele

� Homozygous

± Both alleles for a trait are the same

� Heterozygous

± Alleles for a trait are different

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Mendel¶s Laws of Heredity

� Averaging

± Effects of both alleles are shown

� Law of Dominance

± Dominant allele paired with recessive allele

� Dominant allele appears in offspring

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Transmission of Dominant and Recessive Traits

Figure 2.4

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Transmission of Dominant and Recessive Traits

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Dominant and Recessive Traits

� Carriers

± Person who has one dominant and one recessive gene

� Chromosomal or genetic abnormalities

± Occur in autosomes or sex chromosomes

± May be caused by a single gene or combinations

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Chromosomal Abnormalities: Down Syndrome

� Cause: extra chromosome on 21st pair

� Probability increases with increased age of parent

� Characteristics of children

± Facial features

± Cognitive and physical deficiencies

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Down Syndrome

Figure 2.5

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Chromosomal Abnormalities: Sex-Linked

� Most are infertile

� Male with extra sex chromosome

± XYY - extra Y chromosome

± XXY - Klinefelter syndrome

� Female with abnormal number of sex chromosomes

± X (X0) - Turner syndrome ± XXX - Triple X syndrome

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Genetic Abnormalities

� Recessive gene abnormalities

± Phenylketonuria (PKU)

± Sickle-Cell Anemia

± Tay-Sachs disease

± Cystic Fibrosis

� Dominant gene abnormalities

± Huntington disease

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Sex-Linked Genetic Abnormalities

� Hemophilia

� Duchenne muscular dystrophy

� Color-Blindness

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What Is the Difference Between Our Genotypes

and Our Phenotypes?

� Canalization

± Environmental influences on genotype within reaction range

± Canalization = invariant

� Infant motor development

± Less canalization

� Intelligence

� Personality

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Genetic ± Environmental Correlation (Interaction)

� Passive Correlation (Interaction)

± Environment that child is placed into (by parents)

� Evocative Correlation (Interaction)

± Child¶s genotype elicits responses

� Active Correlation (Interaction)

± Environment child chooses

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Prenatal Testing

� Blood Tests

± Alpha-Fetoprotein(AFP) assay

� Ultrasound

± Sonogram ³picture´ of fetus

± Beneficial in

determining position of fetus and physicalcharacteristics

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Prenatal Testing

� Amniocentesis

± Routine among American women

over age 35 ± Used to detect over

100 chromosomaland geneticabnormalities

± Indicates the sex of

the baby ± Some risk of

miscarriage

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Prenatal Testing

� Chorionic VillusSampling (CVS)

± Can diagnosis

abnormalitiesearlier thanamniocentesis

± Slightly greater risk of spontaneous

abortion

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Conception

Against All Odds

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Conception

� Ova

± Begin to mature at puberty

± Monthly release of mature egg into Fallopian tube

± Egg is propelled by cilia ± If not fertilized, egg is discharged in the menstrual flow

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Female Reproductive Organs

Figure 2.8

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Conception

� Sperm

± Self propelled and smaller than ova

± Sperm with ³Y´ chromosome swim faster than sperm with ³X´

chromosome ± From 200 to 400 million in ejaculate; only 1 in 1,000 arrive in

vicinity of ovum

± Sperm are attracted by chemical odor secreted by ova

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Figure 2.9

TU1

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Slide 31

TU1 Please check that this figure is still numbered as 2.9 in 4/e. Also, please include the figure title as the heading. Thank you!TL User, 9/28/2009

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What Process Brings Together

the Genes from Each Parent?

� Only one sperm enters the zona pellucida

± Sperm secrete enzyme hyaluronidase to allow penetration of the zona pellucida

± When one sperm enters, the zona pellucida thickens, lockingout other sperm

� Chromosomes from sperm and egg combine to form 23 newpairs

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Fertilization

1 5 2814

� Egg is viable for 24 hours

� Sperm is viable for

3 to 5 days�Safe period is from

day 9 to 15 if ovulation occurs on day 14

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Infertility and Other Ways of Becoming Parents

What Are t

he Causes of Infertility?

� Fertility problems among men

± Low sperm count

± Deformed sperm

± Low sperm motility

± Diseases

± Direct trauma to testes

± Autoimmune responses

� Causes

± Genetic factors, environmental poisons, diabetes, STI¶s, overheating testes, pressure to testes, aging and effects of drugs

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What Are t

he Causes of Infertility?

� Major fertility problems among women

± Irregular or failure to ovulate

� Fertility drugs are used to cause women to ovulate

± Declining hormone levels due to aging

± Infections

� Pelvic inflammatory disease (PID)

± Endometriosis

� Obstruct fallopian tubes

± Barriers or disorders in passageways (i.e. Fallopian tubes)

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How

Are Couples Helped to Have Ch

ildren?

� 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 andimplanted in recipient¶s uterus

± Embryonic transplant

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� Surrogate Mothers

± Surrogate ³substitutes´ bring babies to term for another woman

� Adoption

± Greater diversity of adopted children and adoptive parents

± Consideration of adopted children needs

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