Transcript DEP Chapter 3 Presentation

Chapter 3
Heredity and Environment
Dr. M. Davis-Brantley
The Genetic Code
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Development that is dynamic, ongoing,
interactional, and unique; just four
chemicals are the basic building
blocks of the genetic code
What Are Genes?
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
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What Are Genes, cont.
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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
The Beginnings of Human
Life
Gamete—reproductive cell that
directs process by which genetic
information combined and
transmitted
 Father gametes—sperm
 Mother gametes—ovum
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Zygote and Genotype
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Male and female gametes fuse and become
a zygote
Zygote begins process of duplication and
division immediate
– two reproductive cells have now become one
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Genotype—the genetic information from
the 46 chromosomes
– set at human conception and endures through
life
Sex Determination and
Sex Ratio
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23rd pair is the chromosome pair that determines
the zygote’s sex
Female the 23rd pair is composed of XX chromosomes
– Females are composed of XX so they will only produce XX
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Male the 23rd pair is composed of XY chromosomes
– Males are composed of XY so they can offer either X or Y
– Therefore, critical factor in determination of sex is which
sperm penetrates the ovum first
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
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Sex Determination and Sex Ratio,
cont.
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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
Multiple Zygotes
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Monozygotic twins—identical twins
(or quadruplets) originate from one
zygote
–
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share identical instructions
possibility of cloning
1/3 of twins monozygotic
Video--Black/White Twins
Multiple Zygotes, cont.
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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
Multiple Zygotes, cont.
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Dizygotic twins
– women in late 30’s are three times more
likely to have dizygotic twins
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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)
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50 percent of the time one twin is male
Duplication, Division, and
Differentiation
The zygote contains a complete set
of instructions to create a person
 Complex instructions on duplication,
cell division, and differentiation
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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
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Additive Genes
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Additive genes—one of a number of
genes affecting a specific trait
– each additive gene contributes to the
trait
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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
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
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– gene showing the most influence is
referred to as dominant
– gene showing the least influence is
referred to as recessive
From Genotype to Phenotype, cont.
Genotype—genetic potential
 Phenotype—combination of
genetic potential and expression
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– we are all carriers of the
unexpressed genes
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we can pass them along through the
sperm or ova
Behavior Genetics
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Behavior genetics—study of effects
of genes on behavior
Chromosomal Abnormalities
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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
Chromosomal Abnormalities, cont.
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Most zygotes with chromosomal
abnormalities never come to term
– spontaneous abortion occurs in about
one-half of all fetus with chromosomal
abnormalities
Down Syndrome
Three chromosomes at gene #21
(trisomy-21)
 Syndrome—a cluster of distinct
characteristics that occur together
in a given disorder
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Abnormalities of the
23rd Pair
Location of sex chromosome
 Kleinfelters syndrome—XXY
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– seemingly normal child has delayed
puberty
Turner’s Syndrome
 Fragile X syndrome
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– hanging on by a thread (mutated gene)
– intensifies from generation to
Don’t worry about the
following slides for the test.
They are for additional
information only and to help
you understand the concepts
better.
Duplication and Division
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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
– these two cells then duplicate and divide to
Duplication and Division, cont.
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
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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
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– they take different forms
– they reproduce at different rates,
depending on where in the growing mass
they are located
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
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More Complications
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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
More Complications, cont.
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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
From Genotype to
Phenotype
Every psychological characteristic
is genetically influenced
 Every psychological characteristic
and personal trait is affected by
the environment
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Behavior Genetics
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Behavior genetics—study of effects
of genes on behavior
– personality patterns, psychological
disorders, and intellectual abilities
Alcoholism
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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
Alcoholism, cont.
Not simply a biochemical reaction—it
is psychological and physical, and
biological; thus alcoholism is
polygenetic, with alcoholics inheriting
a combination of biochemistryaffecting and temperament-affecting
genes
 Culture counts too(whether alcohol is
present in environment)
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Chromosomal and Genetic
Abnormalities
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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