Human Human GeneticsGenetics

Exploring the Human Exploring the Human GenomeGenome

Human ChromosomesHuman Chromosomes Let’s Review:Let’s Review:

– A A diploiddiploid human cellhuman cell contains contains 46 46 chromosomeschromosomes

– A A haploidhaploid gamete or sex cellgamete or sex cell has has 23 23 chromosomeschromosomes

– ChromosomesChromosomes are a condensed are a condensed form of form of DNADNA that carries all of the that carries all of the genetic informationgenetic information that makes up that makes up that organismthat organism

Human ChromosomesHuman Chromosomes Scientists have been Scientists have been

analyzing our DNA to analyzing our DNA to see see what makes us what makes us humanhuman

They take pictures of They take pictures of our DNA when it is our DNA when it is condensed into the condensed into the form of chromosomes form of chromosomes

After that they group After that they group the 23 the 23 pairspairs into into matched pairsmatched pairs

When chromosomes When chromosomes are arranged like this are arranged like this it is called it is called karyotyping karyotyping (karyotype)(karyotype)

Human Human ChromosomesChromosomes

Of the 46 chromosomes that make Of the 46 chromosomes that make up each of our cells two of them up each of our cells two of them are are sex chromosomessex chromosomes

It is our It is our sex chromosomessex chromosomes that that determine whether or not we are determine whether or not we are female or malefemale or male– Two X chromosomes and we are Two X chromosomes and we are

female (XX)female (XX)– One X and one Y and we are One X and one Y and we are male male

(XY)(XY)

Sex determinationSex determination

XX Female

XY Male

X

X

X Y

XX Female

XY Male

XX Female

XY Male

Human Human ChromosomesChromosomes

The other 44 The other 44 chromosomes are chromosomes are known as known as autosomal autosomal chromosomeschromosomes or or autosomesautosomes

This picture shows This picture shows what type of cell? what type of cell? Sex cells or Sex cells or autosomal cells?autosomal cells?

Human TraitsHuman Traits Humans inherit genes according to Humans inherit genes according to

the principles that Mendel came up the principles that Mendel came up withwith

Both parents randomly assort their Both parents randomly assort their genes into their sex cells and the two genes into their sex cells and the two sex cells are joined in sex cells are joined in fertilizationfertilization

Some traits are shown in the Some traits are shown in the phenotypephenotype of the offspring while of the offspring while other other traits are maskedtraits are masked until further until further generations generations

A Human PedigreeA Human Pedigree A A pedigreepedigree is a chart is a chart

that shows how that shows how traits are passed traits are passed from one generation from one generation to the nextto the next

Spheres or Spheres or circles circles represent femalesrepresent females while boxes or while boxes or squares represent squares represent malesmales

A half-shaded A half-shaded circle or circle or square square represents a represents a carriercarrier, a , a heterozygous heterozygous individual.individual.

Pedigrees illustrate inheritancePedigrees illustrate inheritance

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Pedigrees illustrate inheritancePedigrees illustrate inheritance A A horizontal linehorizontal line

connecting a connecting a circle and a circle and a square indicates square indicates that the that the individuals are individuals are parentsparents, and a , and a vertical linevertical line connects parents connects parents with their with their offspringoffspring..

Pedigrees illustrate inheritancePedigrees illustrate inheritance Each Each horizontal horizontal

rowrow of circles of circles and squares in and squares in a pedigree a pedigree designates a designates a generationgeneration, , with the with the most most recent recent generationgeneration shown shown at the at the bottom.bottom.

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Pedigrees illustrate inheritancePedigrees illustrate inheritance The The

generations generations are are identified identified in sequence by in sequence by Roman Roman numeralsnumerals, and , and each individual each individual is given an is given an Arabic number.Arabic number.

I

II

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A circle represents a

female.

A square represents a male.A horizontal line

connecting a male and female represents a marriage.

A vertical line and a bracket connect the parents to their children.

A half-shaded circle or square indicates that a person is a carrier of the trait.

A completely shaded circle or square indicates that a person expresses the trait.

A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. Some regular DUDE.

Section 14-1

A PedigreeA Pedigree

Human TraitsHuman Traits It can be quite difficult to trace an It can be quite difficult to trace an

actual trait through generations of a actual trait through generations of a familyfamily

Some believe that you receive your Some believe that you receive your eyes from one parent and ears from eyes from one parent and ears from anotheranother

Many traits, however, are considered Many traits, however, are considered polygenicpolygenic ; Meaning: ; Meaning: a trait that is a trait that is controlled by many genescontrolled by many genes

Human TraitsHuman Traits The second reason The second reason

that it is difficult to that it is difficult to determine where you determine where you receive your physical receive your physical characteristics from is characteristics from is because because only some of only some of your genes are your genes are controlled by controlled by inheritanceinheritance

Many traits are Many traits are strongly influenced by strongly influenced by environmental, or non-environmental, or non-genetic, factorsgenetic, factors– Nutrition and exerciseNutrition and exercise– Habitat and lifestyleHabitat and lifestyle

In arctic foxes temperature has an

effect on the expression of coat color.

Human Blood Group Human Blood Group GenesGenes

Why is it important to know your Why is it important to know your blood type?blood type?– If you receive a transfusion of the If you receive a transfusion of the

wrong blood type there is a very wrong blood type there is a very strong chance that you will diestrong chance that you will die

– Each person has a specific blood Each person has a specific blood type and can receive donor blood type and can receive donor blood specific to the type of blood that specific to the type of blood that pumps through their veins & arteriespumps through their veins & arteries

Human Blood Group Human Blood Group GenesGenes The The ABOABO blood groups are the following: blood groups are the following:

– Type AType A , , Type BType B , , Type ABType AB , and , and Type OType O• There are There are three allelesthree alleles for the ABO blood for the ABO blood

group group

• IIAA , , IIBB , , ii

Phenotype(Blood Type) Genotype

Antigen on Red Blood Cell

Safe Transfusions

To From

Human Blood Group Human Blood Group GenesGenes IIA A andand IIBB are are codominantcodominant

This means:This means: If you haveIf you have bothboth alleles you willalleles you will

havehave Type AB bloodType AB blood If you haveIf you have Type AType A oror Type BType B with with

thethe i allelei allele you will express theyou will express the dominant traitdominant trait of Type A or Type Bof Type A or Type B

Phenotype(Blood Type) Genotype

Antigen on Red Blood Cell

Safe Transfusions

To From

Type A BloodType A Blood Type A bloodType A blood is is

the result of the the result of the genotype genotype IIAA I IAA or or IIAA ii

TheThe surface surface of of allall of the of the Type A Type A bloodblood molecules is molecules is the same the same throughout the throughout the bodybody

Type B BloodType B Blood Type B bloodType B blood is is

the result of the result of IIBB IIBB or or IIBB i i

All of the blood All of the blood in a Type B in a Type B person has the person has the same same surfacesurface

Type AB BloodType AB Blood The only way to The only way to

have have Type AB Type AB bloodblood is to have is to have the alleles the alleles IIAA I IBB

Because it has Because it has bothboth surfaces it surfaces it can can acceptaccept donor donor blood from blood from allall blood typesblood types

Human Blood Group Human Blood Group GenesGenesTheThe ii allele is allele is recessiverecessive

This meansThis means:: If it is with any other allele it will If it is with any other allele it will

be maskedbe masked If someone has both If someone has both iiii they will they will

have have Type O bloodType O blood

Phenotype(Blood Type) Genotype

Antigen on Red Blood Cell

Safe Transfusions

To From

Type O BloodType O Blood With two With two

recessive alleles recessive alleles iiii you have the you have the Blood Type OBlood Type O

Type O blood has Type O blood has a a smooth surfacesmooth surface and because of and because of that it is a that it is a universal donoruniversal donor

Human Blood Group Human Blood Group GenesGenesBlood transfusions are Blood transfusions are specificspecific

Type ABType AB is the is the universal acceptoruniversal acceptor Type ABType AB can can ONLYONLY donatedonate to to

another Type AB !!another Type AB !!Type OType O is the is the universal donoruniversal donor

Type OType O can can ONLYONLY acceptaccept another another Type O blood typeType O blood type

Phenotype(Blood Type) Genotype

Antigen on Red Blood Cell

Safe Transfusions

To From

Human Blood Group Human Blood Group GenesGenes

Human blood is governed by another Human blood is governed by another gene as wellgene as well

The The RhRh Blood group only has two Blood group only has two allelesalleles– Rh+Rh+ is is dominantdominant

RhRh++ / / RhRh++ OROR RhRh++ / / RhRh-- is is positivepositive

– Rh- Rh- is is recessiverecessiveONLY ONLY Rh- Rh- / / Rh-Rh- is a is a negativenegative blood type blood type

Human Blood Group Human Blood Group GenesGenes

When a doctor refers to your When a doctor refers to your blood type he or she will use blood type he or she will use both groupsboth groups

For example: you may have For example: you may have Type O negative blood Type O negative blood

Autosomal DisordersAutosomal Disorders There are three types of There are three types of

autosomal disorders in humans:autosomal disorders in humans:– Disorders caused by:Disorders caused by:

Recessive allelesRecessive alleles

Dominant allelesDominant alleles

Codominant allelesCodominant alleles

Recessive Autosomal Recessive Autosomal DisordersDisorders

AlbinismAlbinism – is the – is the lack of the lack of the pigment pigment melaninmelanin in the skin, hair, in the skin, hair, and eyesand eyes

In this chart it In this chart it shows that you shows that you mustmust have have both both (aa) recessive (aa) recessive allelesalleles to be to be “albino”“albino”

Recessive Autosomal DisordersRecessive Autosomal Disorders

People with People with PKUPKU (phenylketonuria) (phenylketonuria) lack the enzyme lack the enzyme needed to break needed to break down down phenylalanine phenylalanine

PhenylalaninePhenylalanine is is found in milk and found in milk and many other foodsmany other foods

PKUPKU is carried by a is carried by a recessive allele recessive allele found on found on chromosome 12chromosome 12

Simple Dominant TraitsSimple Dominant Traits

A cleft chin, A cleft chin, widow’s peak widow’s peak hairline, hairline, hitchhiker’s hitchhiker’s thumb, almond thumb, almond shaped eyes, shaped eyes, thick lips, and the thick lips, and the presence of hair presence of hair on the middle on the middle section of your section of your fingers all are fingers all are examples of examples of dominant traits.dominant traits.

Dominant Autosomal DisordersDominant Autosomal Disorders

Huntington’s disease

Huntington’s disease is a lethal Huntington’s disease is a lethal genetic disorder caused by a rare genetic disorder caused by a rare dominant allele.dominant allele.

It results in a breakdown of certain It results in a breakdown of certain areas of the brain.areas of the brain.

Huntington’s diseaseHuntington’s disease Ordinarily, a dominant allele with such Ordinarily, a dominant allele with such

severe effects would result in death before severe effects would result in death before the affected individual could have children the affected individual could have children and pass the allele on to the next and pass the allele on to the next generation.generation.

But because the onset of Huntington’s But because the onset of Huntington’s disease usually occurs between the ages disease usually occurs between the ages of 30 and 50, an individual may already of 30 and 50, an individual may already have had children before knowing whether have had children before knowing whether he or she is affected.he or she is affected.

Typical Pedigree of Huntington’s Typical Pedigree of Huntington’s DiseaseDisease

Typical Pedigree of Huntington’s Typical Pedigree of Huntington’s DiseaseDisease

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Incomplete DominanceIncomplete DominanceAppearance of a third phenotype

When inheritance follows a pattern of When inheritance follows a pattern of dominancedominance, heterozygous and homozygous , heterozygous and homozygous dominant individuals both have the same dominant individuals both have the same phenotype.phenotype.

When traits are inherited in an When traits are inherited in an incomplete incomplete dominancedominance pattern, however, the pattern, however, the phenotype of heterozygous individuals is phenotype of heterozygous individuals is intermediateintermediate between those of the two between those of the two homozygotes.homozygotes.

Incomplete DominanceIncomplete Dominance For example, if a homozygous red-flowered For example, if a homozygous red-flowered

snapdragon plant snapdragon plant (RR)(RR) is crossed with a is crossed with a homozygous white-flowered snapdragon homozygous white-flowered snapdragon plant (Rplant (R′ ′ R′), R′), all of the Fall of the F11 offspring will have offspring will have pink flowers.pink flowers.

The new phenotype occurs because the The new phenotype occurs because the flowers contain enzymes that control flowers contain enzymes that control pigment production.pigment production.

The The RR allele codes for an enzyme that allele codes for an enzyme that produces a red pigment. The produces a red pigment. The RR’ allele ’ allele codes for a defective enzyme that makes no codes for a defective enzyme that makes no pigment.pigment.

Incomplete dominance: Appearance of a third phenotype

Incomplete dominance: Appearance of a third phenotype

Red White

All pink

Red (RR)

White (R’R’)

Pink (RR’)

Pink (RR’)

All pink flowersAll pink flowers 1 red: 2 pink: 1 white1 red: 2 pink: 1 white

Incomplete dominance: Incomplete dominance: Appearance of a third phenotypeAppearance of a third phenotype Because the heterozygote has Because the heterozygote has

only one copy of the only one copy of the RR allele, its allele, its flowers appear pink because flowers appear pink because they produce only half the they produce only half the amount of red pigment that red amount of red pigment that red homozygote flowers produce.homozygote flowers produce.

Red White

All pink

Red (RR)

White (R’R’)

Pink (RR’)

Pink (RR’)

All pink flowers 1 red: 2 pink: 1 white

Because the heterozygote Because the heterozygote has only one copy of the has only one copy of the RR allele, its flowers appear allele, its flowers appear pink because they produce pink because they produce only half the amount of only half the amount of red pigment that red red pigment that red homozygote flowers homozygote flowers produce.produce.

Because the heterozygote Because the heterozygote has only one copy of the has only one copy of the RR allele, its flowers appear allele, its flowers appear pink because they produce pink because they produce only half the amount of only half the amount of red pigment that red red pigment that red homozygote flowers homozygote flowers produce.produce.

Human Genes & ChromosomesHuman Genes & Chromosomes

Genes are located on chromosomes and Genes are located on chromosomes and each chromosome in the human genome each chromosome in the human genome is a different sizeis a different size

On each chromosome can be hundreds or On each chromosome can be hundreds or even thousands of geneseven thousands of genes

Locating GenesLocating Genes

Gene Sequence

Stop signal

GeneStart signal

Promoter