Ch. 14 The Human Genome

Ch. 14 Outline

14-1: Human Heredity Human Chromosomes Human Traits Human Genes From Gene to Molecule

Ch. 14 Outline

14-2: Human Chromosomes Human Genes and Chromosomes Sex-linked Genes X-Chromosome Inactivation Chromosomal Disorders

14-3: Human Molecular Genetics Human DNA Analysis The Human Genome Project Gene Therapy Ethical Issues in Human Genetics

Human Chromosomes Karyotypes:

A Picture of chromosomes arranged in rows is a karyotype

Human Chromosomes

Humans have 23 pairs (46 total) chromosomes.

Two of the 46 chromosomes are called sex chromosome because they determine an individual’s sex. In Human’s:

Female – two copies of large X chromosomeMale – one X and one small Y chromosome

Karyotype

Human ChromsomesAutosomes: the remaining 44

chromosomes. They do not determine the sex of the organism.

All Human egg cells carry a single X chromosome.

Half of all sperm cells carry an X chromosome and half carry the Y. This ensures that about half of the

zygotes will be female XX and half will be male XY.

Human Traits

Biologists must identify an inherited trait controlled by a single gene

Must establish that the trait is actually inherited and not the result of environmental influences

Human TraitsThey study how the trait is passed

from one generation to the next

Scientists use a pedigree chart to help study how a trait is passed from one generation to the next.Pedigree: a chart that shows the

relationships within a family.

How to read a pedigree

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.

PedigreesThese Charts are used to infer the

genotypes of family members.

They can reveal if traits are sex-linked, dominant or recessive.

Using a Pedigree

A human geneticist determined the pedigree shown in the diagram with filled symbols showing the affected individuals. How is this pattern of inheritance described?

Using a Pedigree

Below is a pedigree for an inherited lung disease.  Provide the genotypes of each of the individuals marked with lower case letters.

Using a Pedigree

Below is a pedigree for an inherited brain disease.  Provide the genotypes of each of the individuals marked with lower case letters.

Brain Disease

Human Genes Biologists were able to identify genes that directly

control a single human trait. Some of the very first genes to be identified were those that controlled blood type.

Blood Group Genes Knowing a person’s blood group is important

during transfusions. Two blood groups:

Rh groupsABO groups

The Rh Blood GroupThe Rh blood group is determined by a

single gene with two alleles: Positive and negative Rh+ is dominant to Rh-

The Rh factor is named after the Rhesus Monkey where the factor was first isolated

Very important for females to know during pregnancies.

ABO Blood Groups There are three alleles for the ABO Blood Group:

IA, IB, I “i” is the recessive allele. ii type O blood

IAIB are codominant type AB blood

IAIA or IAi type A Blood

IBIB or IBi type B Blood

ABO Blood Groups

Phenotype(Blood Type

Genotype Antigen on Red Blood Cell

Safe Transfusions

To From

Antigens and Blood

Disorders in Humans

Genetic Disorders may be caused by: Recessive Alleles

Ex. CF, PKU, Tay-Sachs

Dominant Alleles Huntington’s Disease

Codominant Alleles Sickle Cell Anemia

Concept Map

caused by

includeincludeinclude

AutosomolDisorders

Sex-Linked Genes Sex-linked genes: Genes Located on the sex

chromosomes Many genes are located on the X chromosome Males have just one X chromosome. Thus, all X

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

Sex-linked disorders are caused by genes on the X or Y chromosome Colorblindness, Hemophilia

Sex-Linked Genes : Pedigree for Color Blindness

X-Chromosome Inactivation Females have two X chromosomes but males

only have one. How do females cells “adjust” to having an extra X if males can survive with just one?

One of the X chromosomes in female cells are randomly switched off. Those are called Barr bodies.

Chromosomal Disorders

Nondisjunction: failure of chromosomes to separate correctly in meiosis

This leads to an abnormal number of chromosomes in gametes

Ex: Down Syndrome (3 copies of chromosome 21 “trisomy”)

Nondisjunction

Homologous chromosomes fail to separate

Meiosis I:Nondisjunction

Meiosis II

Nondisjunction can occur with autosomes or sex Chromosomes during meiosis

Chromosomal Nondisjunction Disorders

Down Syndrome

1 in 31,000 births

46 chromosomesXY=97%

XX=3% 1 in 1,250 births

47 chromosomesXY or XX

#21 Trisomy Nondisjunction

Down Syndrome Trisomy 21

Down Syndrome

Short, broad hands Stubby fingersRough skinImpotency in malesMentally impairedSmall round faceProtruding tongueShort lifespan

Patau’s Trisomy Syndrome

1 in 14,000 births

47 chromosomesXY or XX

#13 Trisomy Nondisjunction

Patau’s Trisomy SyndromeSmall headSmall or missing eyesHeart defectsExtra fingersAbnormal genitaliaMentally impairedCleft palateMost die a few weeks after birth

Edward’s Trisomy Syndrome

1 in 4,400 births

47 chromosomesXX =80%

XY=20%

#18 Trisomy Nondisjunction

Edward’s Trisomy SyndromeSmall headMentally impairedInternal organ abnormalities90% die before 5 months of age

Turners Syndrome

1 in 5,000 births

45 chromosomesX only #23 MonosomyNondisjunction

Turners Syndrome

96-98% do not survive to birthNo menstruationNo breast developmentNo hips (curve)Broad shoulders and neck

Jacob’s Syndrome

1 in 1,800 births

47 chromosomesXYY only

#23 Trisomy Nondisjunction

Jacob’s Syndrome

Normal physicallyNormal mentallyIncrease in testosteroneMore aggressiveNormal lifespan

?

Kleinfelter Syndrome

1 in 1,100 births

47 chromosomesXXY only

#23 Trisomy Nondisjunction

Kleinfelter Syndrome

Scarce beardLonger fingers and armsSterileDelicate skinLow mental abilityNormal lifespan

Triple X Syndrome

1 in 2,500 births

47 chromosomesXXX only

#23 TrisomyNondisjunction

Triple X Syndrome

Normally physically Normal mentallyTallFertileShort lifespan

The Human Genome Project

A research project to sequence (identify in order) all the bases in Human DNA ~3.2 BILLION pairs!

Some discoveries: A large amount of DNA does not code for

proteins

Humans only have 30,000-40,000 genes (scientists expected 100,000)

The Human Genome Project Website http://www.genome.gov/ Really interesting Information about the Human

Genome Project. It might help you understand stuff better.

EDUCATE YOURSELF!

Gene Therapy

Information about the human genome might be used to cure genetic disorders though the use of gene therapy.

Gene therapy: the process of changing a gene that causes a genetic disorder It replaces the faulty gene with a normal, working

gene

Ethical Issues

If Human cells can be manipulated to cure disease, should biologists try to engineer people with specific traits?

What will happen to the human species if we design our own bodies?

Should we clone humans?