Chapter 3Chapter 3Heredity and EnvironmentHeredity and Environment

Dr. M. Davis-BrantleyDr. M. Davis-Brantley

The Genetic CodeThe Genetic Code Development that is dynamic, Development that is dynamic,

ongoing, interactional, and unique; ongoing, interactional, and unique; just four chemicals are the basic just four chemicals are the basic building blocks of the genetic codebuilding blocks of the genetic code

What Are Genes?What Are Genes?

Genes are made up of Genes are made up of DNADNA——the the complex protein code of genetic complex protein code of genetic informationinformation

DNA directs the form and function DNA directs the form and function of each body cell as it developsof each body cell as it develops

What Are Genes, cont.What Are Genes, cont.

Each molecule of DNA is called a Each molecule of DNA is called a chromosomechromosome Chromosomes contain instructions to make all Chromosomes contain instructions to make all

the proteins a living being needsthe proteins a living being needs The packet of instructions is called a The packet of instructions is called a genomegenome Each person has 23 sets of chromosomes, or Each person has 23 sets of chromosomes, or

46 chromosomes 46 chromosomes The human genome contains 30,000 genesThe human genome contains 30,000 genes

The Beginnings of The Beginnings of Human LifeHuman Life GameteGamete—reproductive cell that —reproductive cell that

directs process by which genetic directs process by which genetic information combined and information combined and transmittedtransmitted

Father gametes—Father gametes—spermsperm Mother gametes—Mother gametes—ovumovum

Zygote and GenotypeZygote and Genotype

Male and female gametes fuse and Male and female gametes fuse and become a zygotebecome a zygote

Zygote begins process of duplication Zygote begins process of duplication and division immediateand division immediate– two reproductive cells have now become onetwo reproductive cells have now become one

GenotypeGenotype—the genetic information from —the genetic information from the 46 chromosomesthe 46 chromosomes– set at human conception and endures set at human conception and endures

through lifethrough life

Sex Determination and Sex Determination and Sex RatioSex Ratio

2323rdrd pair pair is the chromosome pair that is the chromosome pair that determines the zygote’s sexdetermines the zygote’s sex

FemaleFemale the 23 the 23rdrd pair is composed of pair is composed of XXXX chromosomeschromosomes– Females are composed of XX so they will only Females are composed of XX so they will only

produce XXproduce XX Male Male the 23the 23rdrd pair is composed of pair is composed of XYXY

chromosomeschromosomes– Males are composed of XY so they can offer either X Males are composed of XY so they can offer either X

or Yor Y– Therefore, critical factor in determination of sex is Therefore, critical factor in determination of sex is

which sperm penetrates the ovum firstwhich sperm penetrates the ovum first

Sex Determination and Sex Sex Determination and Sex Ratio, cont.Ratio, cont.

Females always contribute one XFemales always contribute one X Males will have 1/2 of the sperm Males will have 1/2 of the sperm

contributing an X and the other contributing an X and the other half contributing a Yhalf contributing a Y

Critical factor in determining the Critical factor in determining the sex of a zygote is which sperm sex of a zygote is which sperm reaches the ovum firstreaches the ovum first

Sex Determination and Sex Sex Determination and Sex Ratio, cont.Ratio, cont. Other factors includeOther factors include

– rarely, male sperm may only carry either X or Yrarely, male sperm may only carry either X or Y– sometimes a woman’s uterus either unusually sometimes a woman’s uterus either unusually

alkaline or acid, giving either an X or Y sperm alkaline or acid, giving either an X or Y sperm an advantagean advantage

– in a stressful pregnancy XY embryos are more in a stressful pregnancy XY embryos are more likely to be expelled than are XX embryos in a likely to be expelled than are XX embryos in a spontaneous abortion,spontaneous abortion, or miscarriage or miscarriage

– current sex ratio in United States is 52 males current sex ratio in United States is 52 males to 48 femalesto 48 females

Multiple ZygotesMultiple Zygotes

MonozygoticMonozygotic twins—identical twins—identical twins (or quadruplets) originate twins (or quadruplets) originate from one zygotefrom one zygote– share identical instructionsshare identical instructions– possibility of cloningpossibility of cloning– 1/3 of twins monozygotic1/3 of twins monozygotic– Video--Video--Black/White TwinsBlack/White Twins

Multiple Zygotes, cont.Multiple Zygotes, cont. DizygoticDizygotic twins—from two twins—from two

separate zygotesseparate zygotes– Dizygotic births occur once in every Dizygotic births occur once in every

60 births, and occur as frequently as 60 births, and occur as frequently as 1 in 6 pregnancies, but usually only 1 in 6 pregnancies, but usually only 1 twin develops past embryo stage1 twin develops past embryo stage

Multiple Zygotes, cont.Multiple Zygotes, cont.

Dizygotic Dizygotic twinstwins– women in late 30’s are three times women in late 30’s are three times

more likely to have dizygotic twinsmore likely to have dizygotic twins as menopause approaches, ovulation as menopause approaches, ovulation

becomes irregular with some cycles becomes irregular with some cycles producing no ovas and others producing producing no ovas and others producing multiple ovasmultiple ovas

– share no more genes than other share no more genes than other offspring (about 50 percent)offspring (about 50 percent)

50 percent of the time one twin is male50 percent of the time one twin is male

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

Complex instructions on duplication, Complex instructions on duplication, cell division, and differentiationcell division, and differentiation

Duplication, Division, Duplication, Division, and Differentiationand Differentiation

Gene - Gene Gene - Gene InteractionsInteractions Multifactoral traitsMultifactoral traits—inherited traits —inherited traits

produced by interaction of genes produced by interaction of genes and environmentand environment

Polygenetic traitsPolygenetic traits—inherited traits —inherited traits produced by gene interactionproduced by gene interaction

These are affected by on-off These are affected by on-off switching mechanisms, additive switching mechanisms, additive genes, and dominant-recessive genes, and dominant-recessive genesgenes

Additive GenesAdditive Genes

Additive genesAdditive genes—one of a number of —one of a number of genes affecting a specific traitgenes affecting a specific trait– each additive gene contributes to the traiteach additive gene contributes to the trait

skin color and height are determined by themskin color and height are determined by them every additive gene has some impact on a every additive gene has some impact on a

person’s phenotypeperson’s phenotype

– when genes interact this way, all the when genes interact this way, all the involved genes contribute fairly equallyinvolved genes contribute fairly equally

Nonadditive genes—phenotype Nonadditive genes—phenotype shows one gene more influential shows one gene more influential than other genesthan other genes

This is also referred to as the This is also referred to as the dominant-recessive patterndominant-recessive pattern– gene showing the most influence is gene showing the most influence is

referred to as referred to as dominantdominant– gene showing the least influence is gene showing the least influence is

referred to as referred to as recessiverecessive

Dominant and Dominant and Recessive GenesRecessive Genes

From Genotype to Phenotype, From Genotype to Phenotype, cont.cont.

GenotypeGenotype—genetic potential—genetic potential PhenotypePhenotype—combination of —combination of

genetic potential and genetic potential and expressionexpression– we are all we are all carrierscarriers of the of the

unexpressed genesunexpressed genes we can pass them along through the we can pass them along through the

sperm or ovasperm or ova

Behavior GeneticsBehavior Genetics

Behavior geneticsBehavior genetics—study of effects —study of effects of genes on behaviorof genes on behavior

A gamete with more than or less A gamete with more than or less than 23 chromosomes creates a than 23 chromosomes creates a zygote with chromosomal zygote with chromosomal abnormalitiesabnormalities– most likely variable that creates most likely variable that creates

chromosomal abnormalities is chromosomal abnormalities is mother’s age (over 35)mother’s age (over 35)

– father’s age (over 40) also a variablefather’s age (over 40) also a variable

Chromosomal Chromosomal AbnormalitiesAbnormalities

Most zygotes with chromosomal Most zygotes with chromosomal abnormalities never come to termabnormalities never come to term– spontaneous abortion occurs in about spontaneous abortion occurs in about

one-half of all fetus with chromosomal one-half of all fetus with chromosomal abnormalitiesabnormalities

Chromosomal Abnormalities, Chromosomal Abnormalities, cont.cont.

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

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

Down Syndrome Down Syndrome

Location of sex chromosomeLocation of sex chromosome Kleinfelters syndromeKleinfelters syndrome—XXY—XXY

– seemingly normal child has delayed pubertyseemingly normal child has delayed puberty Turner’s SyndromeTurner’s Syndrome Fragile X syndromeFragile X syndrome

– hanging on by a thread (mutated gene)hanging on by a thread (mutated gene)– intensifies from generation to generationintensifies from generation to generation

Abnormalities of the Abnormalities of the 23rd Pair23rd Pair

Don’t worry about the Don’t worry about the following slides for the test. following slides for the test.

They are for additional They are for additional information only and to help information only and to help you understand the concepts you understand the concepts

better.better.

Duplication and Duplication and DivisionDivision Zygote begins duplication and division within Zygote begins duplication and division within

hours after conceptionhours after conception– the 23 pairs of chromosomes duplicate, forming two the 23 pairs of chromosomes duplicate, forming two

complete sets of the genetic code for that person (zygote)complete sets of the genetic code for that person (zygote)– these two pair sets move toward the opposite sides of the these two pair sets move toward the opposite sides of the

zygote and the single cell in the zygote splits down the zygote and the single cell in the zygote splits down the middlemiddle

– the zygote’s outer membrane surrounds two cells, each the zygote’s outer membrane surrounds two cells, each containing a complete set of the original genetic codecontaining a complete set of the original genetic code

– these two cells then duplicate and divide to become four, these two cells then duplicate and divide to become four, then eight, and so onthen eight, and so on

Duplication and Division, cont.Duplication and Division, cont.

by birth, your original zygote by birth, your original zygote has duplicated and divided into has duplicated and divided into 10 trillion cells . . . by 10 trillion cells . . . by adulthood, it’s 100 trillion cellsadulthood, it’s 100 trillion cells

Every cell carries an exact copy Every cell carries an exact copy of the complete genetic of the complete genetic instructions inherited by the instructions inherited by the one-celled zygoteone-celled zygote

DifferentiationDifferentiation

Not just any cell found in the Not just any cell found in the zygote can become a personzygote can become a person

At the 8-cell stage a third process, At the 8-cell stage a third process, differentiation, occursdifferentiation, occurs

Cells begin to specializeCells begin to specialize– they take different formsthey take different forms– they reproduce at different rates, they reproduce at different rates,

depending on where in the growing depending on where in the growing mass they are locatedmass they are located

Differentiation, cont.Differentiation, cont.

Certain genes affect differentiation Certain genes affect differentiation by switching other genes on and by switching other genes on and others off so that the other genes others off so that the other genes produce the right proteins at the produce the right proteins at the right times—right times—on-off switching on-off switching mechanismsmechanisms

Genotype—Genotype—inheritance that can be inheritance that can be observed or is expressed observed or is expressed

Genes direct the creation of 20 amino Genes direct the creation of 20 amino acids that produce thousands of acids that produce thousands of proteins forming the body’s structure proteins forming the body’s structure and directing biochemical functionsand directing biochemical functions– proteins of each body cell are continually proteins of each body cell are continually

affected by other proteins, nutrients, and affected by other proteins, nutrients, and toxins that influence the cell functioningtoxins that influence the cell functioning

More ComplicationsMore Complications

More Complications, cont.More Complications, cont. genetic imprintinggenetic imprinting—tendency of —tendency of

certain genes to be expressed certain genes to be expressed differently when inherited from differently when inherited from mother than from father (tagging)mother than from father (tagging)– some of the genes which influence some of the genes which influence

height, insulin production, and several height, insulin production, and several forms of mental retardation affect a forms of mental retardation affect a child differently depending on which child differently depending on which parent they came fromparent they came from

From Genotype to From Genotype to PhenotypePhenotype Every psychological Every psychological

characteristic is genetically characteristic is genetically influencedinfluenced

Every psychological Every psychological characteristic and personal trait characteristic and personal trait is affected by the environmentis affected by the environment

Behavior GeneticsBehavior Genetics

Behavior geneticsBehavior genetics—study of effects —study of effects of genes on behaviorof genes on behavior– personality patterns, psychological personality patterns, psychological

disorders, and intellectual abilitiesdisorders, and intellectual abilities

AlcoholismAlcoholism

Inherited biochemistry makes some people Inherited biochemistry makes some people highly susceptible to alcohol addictionhighly susceptible to alcohol addiction– addictive pull can be overpowering, or weak, or addictive pull can be overpowering, or weak, or

something in the middlesomething in the middle– may explain ethnic variationsmay explain ethnic variations

Alcoholism, cont.Alcoholism, cont.

Not simply a biochemical reaction—it Not simply a biochemical reaction—it is psychological and physical, and is psychological and physical, and biological; thus alcoholism is biological; thus alcoholism is polygenetic, with alcoholics inheriting polygenetic, with alcoholics inheriting a combination of biochemistry-a combination of biochemistry-affecting and temperament-affecting affecting and temperament-affecting genesgenes

Culture counts too(whether alcohol is Culture counts too(whether alcohol is present in environment)present in environment)

We now give attention to these because We now give attention to these because we can recognizewe can recognize– disruptions of normal developmentdisruptions of normal development– origins of genetic and chromosomal origins of genetic and chromosomal

abnormalitiesabnormalities– misinformation and prejudice add to misinformation and prejudice add to

problems of people with these abnormalitiesproblems of people with these abnormalities

Chromosomal and Chromosomal and Genetic AbnormalitiesGenetic Abnormalities