Chapter 14 Chapter 14

The Human GenomeThe Human Genome

Pg. 341Pg. 341

Section 14-1 Human HereditySection 14-1 Human Heredity

In order to learn more about humans, In order to learn more about humans, scientists started looking at our scientists started looking at our chromosomes.chromosomes.– A A ChromosomeChromosome is tightly coiled DNA is tightly coiled DNA

that becomes visible under a that becomes visible under a microscope during mitosis (cell division).microscope during mitosis (cell division).

KaryotypesKaryotypes Analyzing chromosomesAnalyzing chromosomes

– Photograph cells during mitosis (when Photograph cells during mitosis (when chromosomes are easy to see).chromosomes are easy to see).

– Cut out the picture of the chromosomesCut out the picture of the chromosomes– Group them together in pairs.Group them together in pairs.– This This picture of precisely picture of precisely

organized chromosomes organized chromosomes

is called a is called a karyotypekaryotype..

HumansHumans Humans have 46 chromosomes in a Humans have 46 chromosomes in a

typical body cell.typical body cell.– Sperm cells have 23 and egg cells have 23 so Sperm cells have 23 and egg cells have 23 so

when they combine the fertilized egg has a when they combine the fertilized egg has a complete set of chromosomes.complete set of chromosomes.

Sex ChromosomesSex Chromosomes: determine a : determine a persons gender (2).persons gender (2).– Females = XXFemales = XX– Males = XYMales = XY (the Y chromosome is much smaller than (the Y chromosome is much smaller than

an X)an X)

AutosomesAutosomes: all chromosomes except : all chromosomes except the sex chromosomes (44)the sex chromosomes (44)

How to write it out!How to write it out! Is this a girl or boy?Is this a girl or boy? To write out their To write out their

karyotype scientists karyotype scientists use the following use the following method.method.– Write the total # of Write the total # of

chromosomes.chromosomes. 4646

– Write out the sex Write out the sex chromosome chromosome combinationcombination

XX or XYXX or XY This example is 46,XYThis example is 46,XY

Try this one!Try this one!

Did you get…Did you get…

47, XX +2147, XX +21– There were 47 chromosomes in this There were 47 chromosomes in this

karyotype.karyotype.– There were 2 X chromosomes making There were 2 X chromosomes making

this person a …….this person a …….– Now we need to indicate where the Now we need to indicate where the

extra chromosome was so we do that extra chromosome was so we do that with a + since it was extra and a 21 to with a + since it was extra and a 21 to indicate where the extra chromosome indicate where the extra chromosome was found.was found.

Now you try it on the computer.Now you try it on the computer.

Type in Type in

– Karyotyping Activity Karyotyping Activity on Google.on Google. Be sure to read through the Be sure to read through the

information and fill out your information and fill out your worksheet.worksheet.

Boy or Girl?Boy or Girl? Females carry two X chromosomes = XXFemales carry two X chromosomes = XX

– This means that all human egg cells should This means that all human egg cells should carry a single X chromosome (23,X)carry a single X chromosome (23,X)

Males carry one X and one Y = XYMales carry one X and one Y = XY– Half of all sperm cells should carry an X Half of all sperm cells should carry an X

chromosome (23, X)chromosome (23, X)– The other half should carry a Y chromosome The other half should carry a Y chromosome

(23,Y)(23,Y) These factors ensure that the just about These factors ensure that the just about

half of all offspring should be 46,XX and half of all offspring should be 46,XX and half 46,XY.half 46,XY.– See Punnett Square on pg. 342.See Punnett Square on pg. 342.

Human TraitsHuman Traits

PedigreePedigree charts show relationships charts show relationships within a family and are used to within a family and are used to determine if a trait is inherited rather determine if a trait is inherited rather than a result of environmental than a result of environmental influences.influences.– Genetic counselors use pedigree charts Genetic counselors use pedigree charts

to infer genotypes of family members.to infer genotypes of family members.http://www.accessexcellence.org/RC/VL/GG/http://www.accessexcellence.org/RC/VL/GG/

nhgri_PDFs/pedigree.pdfnhgri_PDFs/pedigree.pdfSee example on pg. 342See example on pg. 342

Genes and the EnvironmentGenes and the Environment

Some human traits are almost impossible Some human traits are almost impossible to associate with single genes.to associate with single genes.– Some traits are controlled by many genes.Some traits are controlled by many genes.

Eye shape, ear shape, etc.Eye shape, ear shape, etc.

– Many traits are strongly influenced by Many traits are strongly influenced by environmental factors including nutrition and environmental factors including nutrition and exercise.exercise.

Good nutrition has lead to an increase in height by Good nutrition has lead to an increase in height by 10cm since the 1800’s in Americans and British.10cm since the 1800’s in Americans and British.

Human GenesHuman Genes

Human genome – the complete set of Human genome – the complete set of our genetic information.our genetic information.– Includes tens of thousands of genes.Includes tens of thousands of genes.– Difficult to do because of our long Difficult to do because of our long

generation times, complex life cycle, generation times, complex life cycle, and produce few offspring.and produce few offspring.

- Completed in early 2000’s- Completed in early 2000’s

Genetic DisordersGenetic Disorders

Genetic disorders have helped Genetic disorders have helped scientists learn more about genes.scientists learn more about genes.– Some disorders are autosomal Some disorders are autosomal

recessive.recessive.Albinism, cystic fibrosis, etc.Albinism, cystic fibrosis, etc.

– Others are autosomal dominant.Others are autosomal dominant.Dwarfism, Huntington’s disease, etc.Dwarfism, Huntington’s disease, etc.

– Some are even codominantSome are even codominantSickle cell disease.Sickle cell disease.

Cracking the Code of LifeCracking the Code of Life

Watch the following video clips and Watch the following video clips and take notes on the things you learn take notes on the things you learn from each section.from each section.

http://www.pbs.org/wgbh/nova/genohttp://www.pbs.org/wgbh/nova/genome/program.htmlme/program.html

Section 14-2 Section 14-2 Human ChromosomesHuman Chromosomes

Almost every human cell contains more Almost every human cell contains more than 3 billion base pairs of DNA.than 3 billion base pairs of DNA.– All of our DNA is packaged into 46 All of our DNA is packaged into 46

chromosomes.chromosomes.Genes make up a small part of your Genes make up a small part of your

chromosomes. chromosomes. Only 2% of the DNA in your Only 2% of the DNA in your chromosomes functions as genes, which chromosomes functions as genes, which make proteins, that give us our traits.make proteins, that give us our traits.

– Genes located close on the same chromosome Genes located close on the same chromosome are usually passed on together.are usually passed on together.

Chromosomes 21 and 22Chromosomes 21 and 22 Smallest human autosomes.Smallest human autosomes. These were the first two chromosomes to These were the first two chromosomes to

be sequenced.be sequenced. Chromosome 22Chromosome 22

– Contains around 545 genesContains around 545 genes– Very important to human health.Very important to human health.– Contains long stretches of repetative DNA that Contains long stretches of repetative DNA that

do not code for proteins.do not code for proteins. Unstable sites that can easily rearrange Unstable sites that can easily rearrange

Chromosome 21 is similar, also having Chromosome 21 is similar, also having many regions with no genes.many regions with no genes.

Chromosome 21 SequenceChromosome 21 Sequence

Chromosome 22Chromosome 22

Sex Linked GenesSex Linked Genes

Genes located on the sex chromosomes (X Genes located on the sex chromosomes (X and Y). These are called and Y). These are called sex-linked sex-linked genes.genes.– More than 100 genetic disorders have been More than 100 genetic disorders have been

mapped to the X chromosome.mapped to the X chromosome. Males have just one X chromosome. Thus ALL X-Males have just one X chromosome. Thus ALL X-

linked alleles are expressed in males, even if they are linked alleles are expressed in males, even if they are recessive.recessive.

– Color blindness, hemophilia, muscular dystrophy, etc.Color blindness, hemophilia, muscular dystrophy, etc.

– The Y chromosome is much smaller and carries The Y chromosome is much smaller and carries only a few genes.only a few genes.

X ChromosomeX Chromosome Contains around 1,000 Contains around 1,000

genes!genes!– Learning disabilitiesLearning disabilities– Colorblindness Colorblindness pg.350pg.350

– HemophiliaHemophilia– Muscular DystrophyMuscular Dystrophy– Etc…Etc…

Hemophilia and Colorblindness are sex linked Hemophilia and Colorblindness are sex linked traits, the punnett square below shows how a traits, the punnett square below shows how a woman who is a carrier passes the trait to her woman who is a carrier passes the trait to her

son, but not her daughtersson, but not her daughters..

X-Chromosome InactivationX-Chromosome Inactivation

Females = XXFemales = XX Males = XYMales = XY If one X is enough in males why do If one X is enough in males why do

females need 2?females need 2? In female cells, one X chromosome is In female cells, one X chromosome is

randomly switched off.randomly switched off.This turned off chromosome turns into a This turned off chromosome turns into a

dark spot in the nucleus called a dark spot in the nucleus called a Barr bodyBarr body..

Cat Coat ColorCat Coat Color

In cats, a gene that controls coat In cats, a gene that controls coat color is on the X chromosome. color is on the X chromosome. – One X may have an allele for orange spots, the One X may have an allele for orange spots, the

other X may have an allele for black spots. other X may have an allele for black spots. XoXbXoXb

– Females can be calico because in some parts Females can be calico because in some parts of their body the Xo is activated and of their body the Xo is activated and

in other areas the Xb is activated.in other areas the Xb is activated.– Males can only have spots of Males can only have spots of

one color.one color.

Chromosomal DisordersChromosomal Disorders

During meiosis, errors can happen.During meiosis, errors can happen.– The most common error is called non-The most common error is called non-

disjunction. disjunction. NondisjunctionNondisjunction is when is when homologous pairs of chrmomosomes fail to homologous pairs of chrmomosomes fail to separate.separate.

– If nondisjunction occurs an abnormal number If nondisjunction occurs an abnormal number of chromosomes will end up in a sex cell.of chromosomes will end up in a sex cell. If If fertilized, a child may be born with a fertilized, a child may be born with a chromosomal disorder.chromosomal disorder.

– http://www.biostudio.com/d_%20Meiotic%20Nohttp://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htmndisjunction%20Meiosis%20I.htm

Down’s SyndromeDown’s Syndrome

Trisomy means three bodies. Trisomy means three bodies. ““Trisomy 21” means that a person has 3 number 21 Trisomy 21” means that a person has 3 number 21

chromosomes.chromosomes. This gives a person Down Syndrome.This gives a person Down Syndrome.

In the US 1 out of 800 babies has Downs.In the US 1 out of 800 babies has Downs. SymptomsSymptoms

– Mental retardationMental retardation– Increased susceptability to diseases.Increased susceptability to diseases.– Higher incedince of birth defects.Higher incedince of birth defects.

Sex Chromosome DisordersSex Chromosome Disorders Turner’s Syndrome: only 1 XTurner’s Syndrome: only 1 X

– Sterile females Sterile females (don’t go through puberty)(don’t go through puberty)

– Affects 1 in 2,500 girlsAffects 1 in 2,500 girls– Short stature 4’7Short stature 4’7– Webbed neckWebbed neck– Abnormal bone developmentAbnormal bone development

Klinefelter’s SyndromeKlinefelter’s Syndrome

In Males they have XXY (or XXXY)In Males they have XXY (or XXXY)– SterileSterile– Affects physical, language and social Affects physical, language and social

development.development.– Taller, less muscle, less facial hair, Taller, less muscle, less facial hair,

breasts all due to low testosterone.breasts all due to low testosterone.