1. Human Growth and Development
Chapter Three
Heredity and Environment
PowerPoints prepared by Cathie Robertson, Grossmont College
Revised by Jenni Fauchier, Metropolitan Community College

2. The Genetic Code
Development that is dynamic, ongoing, interactional, and unique; just four chemicals are the basic building blocks of the genetic code

3. What Genes Are
Genes are made up of DNA—the complex protein code of genetic information
DNA directs the form and function of each body cell as it develops

4. Each molecule of DNA is called a chromosome
Chromosomes contain instructions to make all the proteins a living being needs
The packet of instructions is called a genome
Each person has 23 sets of chromosomes, or 46 chromosomes
The human genome contains 30,000 genes

5. The Beginnings of Human Life
Gamete—reproductive cell that directs process by which genetic information combined and transmitted
Father gametes—sperm
Mother gametes—ovum

6. Zygote and Genotype Male and female gametes fuse and become a zygote
Zygote begins process of duplication and division
two reproductive cells

7. Genotype—the genetic information from the 46 chromosomes
set at human conception and endures through life

8. Sex Determination and Sex Ratio
Of 22 out of 23 pairs of human chromosome, the matching chromosomes are very closely matched
but not identical
some genes come in slight, normal variations called alleles
The 23rd pair is different
in females, it is designated XX
in males, it is designated XY

9. Sex Determination and Sex Ratio, cont.
Females always contribute one X
Males will have 1/2 of the sperm contributing an X and the other half contributing a Y
Critical factor in determining the sex of a zygote is which sperm reaches the ovum first

10. Sex Determination and Sex Ratio, cont.
Other factors include
rarely, male sperm may only carry either X or Y
sometimes a woman’s uterus either unusually alkaline or acid, giving either an X or Y sperm an advantage
in a stressful pregnancy XY embryos are more likely to be expelled than are XX embryos in a spontaneous abortion, or miscarriage
current sex ratio in United States is 52 males to 48 females

11. Multiple Zygotes
Monozygotic twins—identical twins (or quadruplets) originate from one zygote
share identical instructions
possibility of cloning
1/3 of twins monozygotic

12. Dizygotic twins—from two separate zygotes
Multiple Zygotes, cont.
Dizygotic twins—from two separate zygotes
Dizygotic births occur once in every 60 births, and occur as frequently as 1 in 6 pregnancies, but usually only 1 twin develops past embryo stage

13. Dizygotic twins Multiple Zygotes, cont.
women in late 30’s are three times more likely to have dizygotic twins
as menopause approaches, ovulation becomes irregular with some cycles producing no ovas and others producing multiple ovas
share no more genes than other offspring (about 50 percent)
50 percent of the time one twin is male

14. Duplication, Division, and Differentiation
The zygote contains a complete set of instructions to create a person
Complex instructions on duplication, cell division, and differentiation

15. Zygote begins duplication and division within hours after conception
the 23 pairs of chromosomes duplicate, forming two complete sets of the genetic code for that person (zygote)
these two pair sets move toward the opposite sides of the zygote and the single cell in the zygote splits down the middle
the zygote’s outer membrane surrounds two cells, each containing a complete set of the original genetic code

16. these two cells then duplicate and divide to become four, then eight, and so on
by birth, your original zygote has duplicated and divided into 10 trillion cells by adulthood, it’s 100 trillion cells
Every cell carries an exact copy of the complete genetic instructions inherited by the one-celled zygote

17. Differentiation
Not just any cell found in the zygote can become a person
At the 8-cell stage a third process, differentiation, occurs
Cells begin to specialize
they take different forms
they reproduce at different rates, depending on where in the growing mass they are located

18. Genotype—inheritance that can be observed or is expressed
Differentiation, cont.
Certain genes affect differentiation by switching other genes on and others off so that the other genes produce the right proteins at the right times—on-off switching mechanisms
Genotype—inheritance that can be observed or is expressed

19. Gene - Gene Interactions
Multifactoral traits—inherited traits produced by interaction of genes and environment
Polygenetic traits—inherited traits produced by gene interaction
These are affected by on-off switching mechanisms, additive genes, and dominant-recessive genes

20. Additive Genes
Additive genes—one of a number of genes affecting a specific trait
each additive gene contributes to the trait
skin color and height are determined by them
every additive gene has some impact on a person’s phenotype
when genes interact this way, all the involved genes contribute fairly equally

21. Dominant and Recessive Genes
Nonadditive genes—phenotype shows one gene more influential than other genes
This is also referred to as the dominant-recessive pattern
gene showing the most influence is referred to as dominant
gene showing the least influence is referred to as recessive

22. X-linked genes—located on X chromosome
if recessive gene is X-linked, that it is on the X chromosome is critical
female has one X chromosome and one Y; males have only 2 X
females’ recessive genes can be counterbalanced by Y chromosome, but males’ recessive genes can not because they have only the X chromosome
if X-linked gene recessive, may cause color blindness, many allergies, several diseases, and learning disabilities

23. More Complications
Genes direct the creation of 20 amino acids that produce thousands of proteins forming the body’s structure and directing biochemical functions
proteins of each body cell are continually affected by other proteins, nutrients, and toxins that influence the cell functioning

24. More Complications, cont.
genetic imprinting—tendency of certain genes to be expressed differently when inherited from mother than from father (tagging)
some of the genes which influence height, insulin production, and several forms of mental retardation affect a child differently depending on which parent they came from

25. Mechanisms of Genetic Diversity
Since each gamete contains only 23 chromosomes, why is every conception genetically unique?
8 million chromosomally different ova x 8 million of the same = 64 trillion different possibilities of children from each couple

26. Health Benefits of Genetic Diversity
Genetic diversity safeguards human health
Minute differences can affect the ability to stave off certain diseases
Genetic diversity maintains the species

27. From Genotype to Phenotype
Every psychological characteristic is genetically influenced
Every psychological characteristic and personal trait is affected by the environment

28. From Genotype to Phenotype, cont.
Genotype—genetic potential
Phenotype—combination of genetic potential and expression
we are all carriers of the unexpressed genes
we can pass them along through the sperm or ova

29. Behavior Genetics
Behavior genetics—study of effects of genes on behavior
personality patterns, psychological disorders, and intellectual abilities

30. Senility Caused by Alzheimer’s Disease
Most common and feared type of senility is Alzheimer’s disease
amyloid B protein accumulates in the brain, leading to dysfunction and destruction of brain cells and disruption of the mind
Can be genetic—but only when “early-onset”

31. Senility Caused by Alzheimer’s Disease, cont.
If “late-onset,” may be a combination of genes and environment
other predictors may include hypertension, diabetes, high cholesterol, diet, exercise, not smoking, weight control, mental alertness, and physical health

32. Alcoholism
Inherited biochemistry makes some people highly susceptible to alcohol addiction
addictive pull can be overpowering, or weak, or something in the middle
may explain ethnic variations

33. Culture counts too(whether alcohol is present in environment)
Alcoholism, cont.
Not simply a biochemical reaction—it is psychological and physical, and biological; thus alcoholism is polygenetic, with alcoholics inheriting a combination of biochemistry-affecting and temperament-affecting genes
Culture counts too(whether alcohol is present in environment)

34. Chromosomal and Genetic Abnormalities
We now give attention to these because we can recognize
disruptions of normal development
origins of genetic and chromosomal abnormalities
misinformation and prejudice add to problems of people with these abnormalities

35. Chromosomal Abnormalities
A gamete with more than or less than 23 chromosomes creates a zygote with chromosomal abnormalities
most likely variable that creates chromosomal abnormalities is mother’s age (over 35)
father’s age (over 40) also a variable

36. Chromosomal Abnormalities, cont.
Most zygotes with chromosomal abnormalities never come to term
spontaneous abortion occurs in about one-half of all fetus with chromosomal abnormalities

37. Down Syndrome Three chromosomes at gene #21 (trisomy-21)
Syndrome—a cluster of distinct characteristics that occur together in a given disorder

38. Abnormalities of the 23rd Pair
Location of sex chromosome
Kleinfelters syndrome—XXY
seemingly normal child has delayed puberty
Fragile X syndrome
hanging on by a thread (mutated gene)
intensifies from generation to generation

39. Genetic Testing and Genetic Counseling
Individuals with a parent, sibling, or child with a serious genetic condition known to be dominant or recessive
Couples with history of early spontaneous abortions, stillbirths, or infertility
Couples from the same ethnic group or subgroup—especially if closely related
Women over 35 and men over 40

40. The Process of Genetic Counseling
Counselor constructs couples’ family history
charts patterns of health and illness over generations
Some tests provide information before conception

41. The Process of Genetic Counseling, cont.
Other tests are prenatal
alpha-fetoprotein assay
ultrasound (AKA sonogram)
amniocentesis
chorionic villi sampling
pre-implantation testing (used in in vitro fertilization)
gamete selection; ova/and or sperm are screened to select ones free of particular problems

42. A Basis for Decision Many want to know ahead of time Some do not
There is a more knowledge of what is to come—or not

43. Alternatives
If both partners are carriers of a serious condition or are at high risk because of age or family characteristics, they may turn to
in-vitro fertilization (IVF)
gamete intrafallopian transfer (GIFT)
zygote intrafallopian transfer (ZIF)
artificial insemination donor (AID)
postponement of pregnancy until promising treatments are further developed