Human Growth and Development

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 DNAthe 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

• Gametereproductive cell that directs process by
  which genetic information combined and
  transmitted
• Father gametessperm
• Mother gametesovum

6
Zygote and Genotype

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

7

• Genotypethe 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 womans 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 twinsidentical twins (or
  quadruplets) originate from one zygote
• share identical instructions
• possibility of cloning
• 1/3 of twins monozygotic

12
Multiple Zygotes, cont.

• Dizygotic twinsfrom 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
Multiple Zygotes, cont.

• Dizygotic twins
• women in late 30s 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 zygotes outer membrane surrounds two cells,
  each containing a complete set of the original
  genetic code

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• 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, its 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
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
  timeson-off switching mechanisms
• Genotypeinheritance that can be observed or is
  expressed

19
Gene - Gene Interactions

• Multifactoral traitsinherited traits produced by
  interaction of genes and environment
• Polygenetic traitsinherited traits produced by
  gene interaction
• These are affected by on-off switching
  mechanisms, additive genes, and
  dominant-recessive genes

20
Additive Genes

• Additive genesone 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 persons
  phenotype
• when genes interact this way, all the involved
  genes contribute fairly equally

21
Dominant and Recessive Genes

• Nonadditive genesphenotype 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 geneslocated 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 bodys
  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 imprintingtendency 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.

• Genotypegenetic potential
• Phenotypecombination 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 geneticsstudy of effects of genes on
  behavior
• personality patterns, psychological disorders,
  and intellectual abilities

30
Senility Caused by Alzheimers Disease

• Most common and feared type of senility is
  Alzheimers disease
• amyloid B protein accumulates in the brain,
  leading to dysfunction and destruction of brain
  cells and disruption of the mind
• Can be geneticbut only when early-onset

31
Senility Caused by Alzheimers 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
Alcoholism, cont.

• Not simply a biochemical reactionit 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 mothers age (over 35)
• fathers 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)
• Syndromea cluster of distinct characteristics
  that occur together in a given disorder

38
Abnormalities of the 23rd Pair

• Location of sex chromosome
• Kleinfelters syndromeXXY
• 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
  subgroupespecially 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 comeor
  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