Human Genome

Chapter 14

Sections 1-3

14-1 Human Heredity

• Karyotype – a picture of chromosomes arranged in homologous pairs.

Humans have 46 chromosomes:23 from the male23 from the female44 autosomes2 sex chromosomes

• Autosomal Chromosome – (Autosomes) the 44 chromosomes in a Karyotype that are not sex chromosomes.

• Sex Chromosomes- determine an individual’s sexFemales have 2 copies of a large X chromosome.Males have 1 X & 1 small Y chromosome.

Male vs. Female

• Males and Females are born in a roughly 50:50 ratio because of the way in which sex chromosomes segregate during meiosis.

• Females produce human egg cells that carry a single X chromosome.

• The female inherits 1 copy of every gene located on each X chromosome.

• Half of all sperm cells carry an X chromosome and half carry a Y chromosome.

(50% XX, 50%XY)

Mendelian Genetics

• Biologists must identify an inherited trait controlled by a single gene.

• Establish that the trait is inherited and not a result of environmental influence.

• Study how the trait is passed from one generation to the next.

• Use a Pedigree Chart.

Pedigree Chart

• Pedigree – chart that shows the relationships with in a family.

Ex. Pg. 342, fig. 14-3

• The inheritance of a certain trait in a family can be traces using a pedigree.

• It shows how a trait can be passed from one generation to the next.

• It determined whether an allele is dominant or recessive.

• The circle represents a Female and the square represents a Male.

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.

Figure 14-3 A Pedigree

Genetic Traits

• Polygenic – controlled by many genes. None are dominant.

Ex. Shape of eyes and ears, height, skin color, and eye color.

• Many traits are strongly influenced by environmental factors like nutrition and exercise.

Ex. Height is largely determined by genetic factors, but nutritional improvement can increase the average height.

Human Genome

• The first human genes to be identified were those that control blood type.

• Red blood cells carry 2 different antigens called A and B.

• Antigen – molecules that are recognized by the immune system.

Ex. ABO blood groups and Rh blood groups.

• ABO – single gene w/ multiple alleles (3)Ex. IA,IB ,i. IA and IB are codominant, and i is recessive.

• Rh –single gene w/ 2 alleles.Ex. Rh(+) has the antigen and Rh(-) does not have the

antigen.

Blood Types

• There are 4 possible blood types:• A, B, AB, O

Genotypes Phenotypes

IA , IB produce AB (both antigens)

IA , IA produce A

IA , i produce A

IB , IB produce B

IB , i produce Bi , i produce O (no antigens)Pg. 344, fig. 14-4

Phenotype(Blood Type Genotype

Antigen on Red Blood Cell

Safe Transfusions

To From

Section 14-1

Figure 14-4 Blood Groups

Human Genetic DisordersPg. 345, fig. 14-6

• PKU (Phenylketonuria) – One of the first discovered. – Lacks and enzyme that breaks down an

amino acid found in milk.– When phenylalanine builds up, it causes

mental retardation.– Caused by a recessive allele from both

parents.

Human Genetic Disorders

• Tay-Sachs Disease– Results in nervous system breakdown.– Death in the first few years of life.– Caused by a recessive allele.

Human Genetic Disorders

• Cystic Fibrosis– Result of a deletion of 3 bases in the middle

of the protein sequence which causes the protein to fold improperly.

– It messes up the order because bases are removed.

– Digestive problems & thick, heavy mucus clogs the lungs.

– Caused by a recessive allele.

Chromosome # 7

CFTR gene

The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein.

Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane.

The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

Section 14-1

Figure 14-8 The Cause of Cystic Fibrosis

Human Genetic Disorders

• Huntington’s Disease – Loss of muscular control and mental

deterioration.– Symptoms appear later in middle ages.– Caused by a dominant allele.

Human Genetic Disorders

• Sickle Cell Anemia– Red blood sell are shaped like sickles.– Shape causes cells to get stuck in the vessels

and blood not to flow.– Tissues are damaged and severe weakness.– Linked to malaria in Africa.– Only 1 DNA base is changed in the allele.– Codominant allele.

14-2 Human Chromosomes

Chormosomes # 21 and # 22• The smallest chromosomes.• The first 2 chromosomes to have their sequence

identified.• #21 - 32 million DNA base pairs, 225 genes, responsible

for ALS (Lou Gehrig’s disease).• #22 – 43 million DNA base pairs, 545 genes, responsible

for many genetic diseases, Leukemia, and tumor causing diseases of the nervous system.

• Both have spaces on the chromosome that do not code for proteins. These spaces are unstable sites where rearrangements occur.

• Genes located close together on the same chromosome are linked and will be inherited together.

Sex Linked Genes

Genes that are located on the X and the Y chromosomes. Pg. 350, fig. 14-12

• X Chromosome – more than 100 sex linked genetic disorders occur here.

• Y Chromosome – smaller and has fewer disorders.• Colorblindness, Hemophilia, & Muscular Dystrophy are

expressed in males even if they are recessive.• To appear in a female, it must have 2 copies.• Are passed from fathers to daughters & to then to their

sons.

Sex Linked Genetic Disorders

Colorblindness

• Genes are defective on the X chromosome causing the inability to distinguish certain colors.

• Red – Green - 1:10 males, 1:100.

• Males have 1 X chromosome so all alleles are expressed even the recessive.

Sex Linked Genetic Disorders

Hemophilia

• Problem on the gene that controls blood clotting.

• Protein missing.

• 1:10,000 males

• May lead to death from minor cuts or internal bleeding from bumps.

• It can now be treated with injections.

Sex Linked Genetic Disorders

Duchenne Muscular Dystrophy

• Progressive weakening and loss of skeletal muscle.

• 1:3,000 males born in U.S.

X – Chromosome Inactivation

• Since males only have 1 X chromosome, the female has to make adjustments for having 2 X chromosomes.

• In females – one X chromosome is randomly turned off. • It forms a dense region in the nucleus called a Barr

body.• Males don’t have Barr bodies because their X

chromosome is active.• Ex. Calico Cats- X chromosome carries the allele for

coat color and can carry more than 1 color. The X chromosome is turned off in many different places causing several colors to appear. Anytime you see a cat with multiple colors, it will most likely be female. Males are only 1 color

Chromosomal Disorders

Nondisjunction – most common error to occur in meiosis. Pg. 352, fig. 14-15

• “Not coming apart”• If the chromosomes do not pull apart, an abnormal

numbers of chromosomes find their way into the gametes throwing off the number and order.

• Involves autosomes, sex chromosomes, and homologous chromosomes.

Downsyndrome Pg. 353, fig. 14-16

• An extra copy of chromosome # 21(3 copies – trisomy)• 1:800 babies in the U.S.• Produces mild – severe mental retardation.

Sex Chromosome Disorders

Caused by Nondisjunction• Turner’s syndrome – female inherits only 1

X chromosome. Women is sterile & her sex organs don’t develop.

• Klinefelter’s syndrome – extra X chromosome interferes with meiosis & prevents reproduction. Ex. XXXY, XXXXY.

• As long as a Y is present, the offspring will be male.

Homologous chromosomes fail to separate

Meiosis I:Nondisjunction

Meiosis II

Section 14-2

Nondisjunction

14-3 Human Molecular Genetics

DNA Fingerprinting – individuals are identified by analyzing sections of DNA.

• No 2 people, except identical twins, have exactly the same DNA.

• Determine whether blood, sperm, hair, or other materials left at crime scene matches suspects.

• 1990- Human Genome Project – Goal was to identify the DNA sequence for the entire DNA in a human cell.

• 2000- Human Genome was sequenced by looking for overlapping regions b/w sequenced DNA fragments.

Promoter Start signal

Gene Stop signal

Gene Sequence

Section 14-3

Locating Genes

Restriction enzyme

Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA varies from person to person. Here, one sample has 12 repeats between genes A and B, while the second sample has 9 repeats.

Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths.

The DNA fragments are separated according to size using gel electrophoresis. The fragments containing repeats are then labeled using radioactive probes. This produces a series of bands—the DNA fingerprint.

Section 14-3

Figure 14-18 DNA Fingerprinting

Human Genome

• Able to find causes of genetic disorders.

• Used to cure genetic disorders by using gene therapy.

• It cannot tell if an allele is dominant or recessive.