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

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Human growth and development

Human Growth and Development

Chapter Three

Heredity and Environment

PowerPoints prepared by Cathie Robertson, Grossmont College

Revised by Jenni Fauchier, Metropolitan Community College

The genetic code
The Genetic Code

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

What genes are
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

  • 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
The Beginnings of Human Life

  • Gamete—reproductive cell that directs process by which genetic information combined and transmitted

  • Father gametes—sperm

  • Mother gametes—ovum

Zygote and genotype
Zygote and Genotype

  • Male and female gametes fuse and become a zygote

  • Zygote begins process of duplication and division

    • two reproductive cells

  • Genotype—the genetic information from the 46 chromosomes

    • set at human conception and endures through life

Sex determination and sex ratio
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

Sex determination and sex ratio cont
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

Sex determination and sex ratio cont1
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

Multiple zygotes
Multiple Zygotes

Monozygotic twins—identical twins (or quadruplets) originate from one zygote

share identical instructions

possibility of cloning

1/3 of twins monozygotic

Multiple zygotes cont
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

Multiple zygotes cont1
Multiple Zygotes, cont.

  • Dizygotic twins

    • 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

Duplication division and differentiation

The zygote contains a complete set of instructions to create a person

Complex instructions on duplication, cell division, and differentiation

Duplication, Division, and Differentiation

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 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

Differentiation then eight, and so on

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

Differentiation cont
Differentiation, cont. then eight, and so on

  • 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

Gene gene interactions
Gene - Gene Interactions then eight, and so on

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

Additive genes
Additive Genes then eight, and so on

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

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

Dominant and Recessive Genes

  • X-linked genes—located on X chromosome influential than other genes

    • 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

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

More Complications

More complications cont
More Complications, cont. thousands of proteins forming the body’s structure and directing biochemical functions

  • 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

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

Mechanisms of Genetic Diversity

Health benefits of genetic diversity

Genetic diversity safeguards human health conception genetically unique?

Minute differences can affect the ability to stave off certain diseases

Genetic diversity maintains the species

Health Benefits of Genetic Diversity

From genotype to phenotype
From Genotype to Phenotype conception genetically unique?

Every psychological characteristic is genetically influenced

Every psychological characteristic and personal trait is affected by the environment

From genotype to phenotype cont
From Genotype to Phenotype, cont. conception genetically unique?

  • 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

Behavior genetics
Behavior Genetics conception genetically unique?

Behavior genetics—study of effects of genes on behavior

personality patterns, psychological disorders, and intellectual abilities

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”

Senility Caused by Alzheimer’s Disease

Senility caused by alzheimer s disease cont
Senility Caused by Alzheimer’s Disease, cont. disease

  • 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

Alcoholism disease

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
Alcoholism, cont. disease

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)

Chromosomal and genetic abnormalities

We now give attention to these because we can recognize disease

disruptions of normal development

origins of genetic and chromosomal abnormalities

misinformation and prejudice add to problems of people with these abnormalities

Chromosomal and Genetic Abnormalities

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

Chromosomal Abnormalities

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

Chromosomal Abnormalities, cont.

Down syndrome

Three chromosomes at gene #21 (trisomy-21) term

Syndrome—a cluster of distinct characteristics that occur together in a given disorder

Down Syndrome

Abnormalities of the 23rd pair

Location of sex chromosome term

Kleinfelters syndrome—XXY

seemingly normal child has delayed puberty

Fragile X syndrome

hanging on by a thread (mutated gene)

intensifies from generation to generation

Abnormalities of the 23rd Pair

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

Genetic Testing and Genetic Counseling

The process of genetic counseling

Counselor constructs couples’ family history genetic condition known to be dominant or recessive

charts patterns of health and illness over generations

Some tests provide information before conception

The Process of Genetic Counseling

The process of genetic counseling cont
The Process of Genetic Counseling, cont. genetic condition known to be dominant or recessive

  • 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

A basis for decision

Many want to know ahead of time genetic condition known to be dominant or recessive

Some do not

There is a more knowledge of what is to come—or not

A Basis for Decision

Alternatives genetic condition known to be dominant or recessive

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