1. Chapter 2 Heredity and Conception

2. The Influence of Heredity on Development
The Nature of Nature

3. What Is Meant by Heredity?
Defines one’s nature
Genetics
Field within the science of biology that studies heredity
Genetic influences
Physical traits
Behavioral traits
Psychological disorders

4. What Are Chromosomes and Genes?
Found in cells
23 pairs of rod-like structures
Genes
Segments within chromosomes
Regulate development of traits
DNA
Large strands make up genes
Double spiral (helix)
Composed of phosphate (P), sugars (S), and base pairs

5. Figure 2.1 Cells, Chromosomes, and DNA
The double helix of DNA. DNA consists of phosphate, sugar, and a number of bases. It takes the form of a double spiral, or helix.
Figure 2.1 Cells, Chromosomes, and DNA

6. What Happens During Cell Division?
Mitosis
Cell division by which growth occurs
Strands of DNA break apart and are rebuilt
Result is identical copies of DNA strand

7. Figure 2.2 Mitosis. Part A shows a segment of a strand of DNA before mitosis. During mitosis chromosomal strands of DNA “unzip” as shown in part B. As shown in part C, the double helix is rebuilt in the cell as each incomplete “rung” combines with appropriate molecules. The resulting identical copies of the DNA strand move apart when the cell divides, each joining one of the new cells.
Figure 2.2 Mitosis

8. What Happens During Cell Division?
Meiosis
Cell division by which sperm and ova are produced
23 chromosome pairs divide
Result is new cell with only 23 chromosomes
23 pairs are autosomes
23rd pair determines gender; X from mother and X or Y from father

9. How Are Twins Formed? Monozygotic Twins (MX) Dizygotic Twins (DZ)
Derived from a single zygote that has split in two
Genetically identical
Dizygotic Twins (DZ)
Derived from two zygotes
Share 50% of genetic material

10. How Do Genes Determine Traits?
Traits are determined by alleles
Pair of genes
Homozygous
Alleles for a trait are the same
Heterozygous
Alleles for a trait are different

11. Dominant and Recessive Traits: Mendel’s Laws of Heredity
Averaging
Effects of both alleles are shown
Incomplete dominance and codominance
Law of Dominance
Dominant allele paired with recessive allele
Dominant allele appears in child

12. Figure 2.4 Transmission of Dominant and Recessive Traits
Figure 2.4 Transmission of Dominant and Recessive Traits. Two brown-eyed parents, each carry a gene for blue eyes. Their children have an equal opportunity of receiving genes for brown eyes and blue eyes.
Figure 2.4 Transmission of Dominant and Recessive Traits

13. Table 2.1 Examples of Dominant and Recessive Traits

14. 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
Adjustment of children

15. Table 2.2 Risk of Giving Birth to an Infant with Down Syndrome, According to the Age of the Mother

16. Genetic Abnormalities
Recessive gene abnormalities
PKU (phenylketonuria)
Sickle-Cell Anemia
Tay-Sachs disease
Cystic Fibrosis

17. Genetic Abnormalities
Dominant gene abnormalities
Huntington’s disease
Sex-linked abnormalities
Hemophilia
Duchenne muscular dystrophy

18. Genetic Counseling and Prenatal Testing
Addresses probability of genetic abnormalities

19. Genetic Counseling and Prenatal Testing
Amniocentesis
Routine among American women over age 35
Used to detect over 100 chromosomal and genetic abnormalities
Indicates the sex of the baby
Some risk of miscarriage

20. Figure 2.6 Amniocentesis. Amniocentesis allows prenatal identification of certain genetic material sloughed off by the fetus into amniotic fluid. Amniocentesis also allows parents to learn the sex of their unborn child. Would you want to know?
Figure 2.6 Amniocentesis

21. Genetic Counseling and Prenatal Testing
Chorionic Villus Sampling (CVS)
Can diagnosis abnormalities earlier than amniocentesis
Slightly greater risk of spontaneous abortion
Ultrasound
Sonogram “picture” of fetus
Beneficial in determining position of fetus
Blood Tests
Alpha-Fetoprotein (AFP) assay

22. Heredity and the Environment
Nature versus Nurture

23. What Is the Difference Between Our Genotypes and Our Phenotypes?
Set of traits inherited from parents
Phenotypes
Actual sets of traits – product of genetics and environment

24. Using Research to Sort Out the Effects of Genetics and Environmental Influences on Development
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 versus reared apart
Adoption studies

25. Conception
Against All Odds

26. Conception: Against All Odds
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

27. Conception: Against All Odds
Sperm
Self propelled, and smaller than ova
Sperm with Y chromosome swim faster than sperm with X 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

28. Figure 2.9 Female Reproductive Organs
Figure 2.9 Female Reproductive Organs. Conception is something of an obstacle course. Sperm must survive the pull of gravity, vaginal acidity, risk winding up in the wrong Fallopian tube, and surmount other hurdles before they reach the ovum.
Figure 2.9 Female Reproductive Organs

29. 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, locking out other sperm
Chromosomes from sperm and egg combine to form 23 new pairs

30. Infertility and Other Ways of Becoming Parents:
What Are the Causes of Infertility?
Major fertility problems among men
Low sperm count
Deformed sperm
Low sperm motility
Infections diseases
Direct trauma to testes
Causes
Genetic factors, environmental poisons, diabetes, STI’s, overheating testes, pressure to testes, aging and effects of drugs

31. Infertility and Other Ways of Becoming Parents:
What Are the Causes of Infertility?
Major fertility problems among women
Failure to ovulate
Fertility drugs are used to cause women to ovulate
Infections
Pelvic inflammatory disease (PID)
Endometriosis
Obstruct Fallopian tubes
Barriers of disorders in passageways (i.e., Fallopian tubes)

32. Infertility and Other Ways of Becoming Parents:
How Are Couples Helped to Have Children?
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

33. Infertility and Other Ways of Becoming Parents
Surrogate Mothers
Surrogate “substitutes” bring babies to term for another woman
Adoption
Option chosen by singles and infertile couples

34. Selecting the Sex of Your Child
Cultural Folklore
Sperm-Separation Procedures
Preimplantation Genetic Diagnosis (PGD)
Moral and Ethical Questions