Human Genetics and the Pedigree

Section Objectives

• Understand how different mutations occur.

• Be able to identify different diseases and disorders.

• Some mutations seem to just happen, but many mutations are caused by factors in the environment.

• Any agent that can cause a change in DNA is called a mutagen. Mutagens include radiation, chemicals, and even high temperatures.

Causes of Mutations

Human Traits are Affected By:

• 1. Dominant and recessive genes that are inherited

• 2. Environmental Factors like diet and exercise

Mutations in Reproductive Cells

• Gamete: Sex Cells

• Zygote: Fertilized egg

• Human diploid cell has 46 chromosomes

• Human Haploid cell has 23 chromosomes

• Occurs by changing the sequence in a sperm or an egg cell.

• If this cell is involved in fertilization, the offspring has the mutation.

• The mutation may produce a new trait or it may result in a protein that does not work correctly. Sometimes, it is nonfunctional, and the embryo may not survive.

Mutations in reproductive cells

• A cell’s DNA is changed, this mutation would not be passed on to offspring.

• Damage to a gene may impair the function of the cell. Some mutations of DNA in body cells affect genes that control cell division. This can result in the cells growing and dividing rapidly, producing cancer.

Mutations in body cells/autosomes

Sex linked Traits/Disorders

• Carried on either the X or the Y chromosome

• Different diseases–Colorblindness: Caused by genes

on the X chromosome, causes people not to make pigments in the eye needed for color

Sex Linked Traits/Disorders

• Colorblindness: Most people with this disorder cannot distinguish between reds and greens

• Why does this affect mostly males?

• 8% of males less than 1% of females

Sex Linked Traits/Disorders

• Hemophilia: free bleeders, people that lack a factor for normal blood clotting

• 1:10,000 males

• 1:100,000,000 females

Sex Linked Traits/Disorders

• Muscular Dystrophy: progressive wasting of skeletal muscle. A defective gene that codes for a muscle protein dystrophin and is located on the X chromosome

Chromosomal and Gene Mutations

• A mistake on one or more of the segments in DNA in either the gene or the chromosome

• Types: deletion, inversion, translocation and nondisjunction

•In nondisjunction, both chromosomes of a homologous pair move to the same pole of the cell during meiosis I anaphase.•Types:

•Down Syndrome (trisomy 21): mental retardation, extra 21 chromosome

•Klinefelter Syndrome: extra X chromosome with the Y chromosome (male)

•Turner Syndrome: missing X chromosome (female)

NondisjunctionNondisjunction

Nondisjunction

• Turner Syndrome: appear female but are sterile (XO) no second sex chromosome present 1:1,000 births

• Klinefelter Syndrome: male in appearance but are sterile (XXY) there is a second X chromosome present 1:1,000 births

Nondisjunction

• Down’s Syndrome: nondisjunction of autosomes (trisomy 21) There is an extra copy of chromosome 21. Results in Mental Retardation mild to severe, short neck, eyes spaced apart, short webbed fingers

Tests to Detect Chromosomal Abnormalities

• 1. Amniocentesis – remove a small amount of amniotic fluid

• 2. Chorionic Villus Biopsy – sample of embryo cells from the choroin (placental tissue)

Inherited Traits

• Blood Types: A, B, AB, O

• RH Factor: + or – ( used to determine the risk of hemophilia)

• A has the A antigen on red blood cells and the B antibody in plasma

• B has the B antigen on red blood cells and the A antibody in plasma

Blood Types Cont:

• AB has bot A and B antigens in red blood cells but neither A or B antibodies in plasma

• O has neither A or B antigens in red blood cells but has both A and B antibodies in plasma

Blood Donation Rules

• Negative Blood is given to negative blood type

• Positive Blood or negative blood can be given to positive patients

• Universal red blood cell Donor is O-

• Universal plasma donor is AB+

• Red blood cells are moon shaped and deprive organs of oxygen

•Can result in death

•Mostly in African Americans

10% African Americans

40% of African Population

Sickle Cell AnemiaSickle Cell Anemia

• Huntington Disease: nervous system disorder with loss of muscle control, mental deterioration and death starts from age 30 to 40.

•Cystic fibrosis: thickening of mucus lining in lungs.

•PKU: can develop into retardation (prevented if caught at birth)

Other Genetic DisordersOther Genetic Disorders

Polygenic Traits

• Traits controlled by many genes

Examples: height, weight, skin color

• This is why children of 1 couple skin color height and weight may vary

• Interpret a pedigree.

• Identify human genetic disorders caused by inherited recessive alleles.

• Analyze the pattern of sex-linked inheritance.

Section Objectives:

• A pedigree is a diagram made up of a set of symbols that identify males and females, individuals affected by the trait being studied, and family relationships.

• Carriers (have 1 copy of the recessive allele)

Pedigrees illustrate inheritancePedigrees illustrate inheritance

Pedigrees illustrate

inheritance

Pedigrees illustrate

inheritance

Male

Female

Affected male

Affected female

Mating

Parents

Siblings

Known heterozygotes for recessive allele

Death

Section Objectives:

• Discuss new methods in genetic technology.

• A new form of manipulation that biologists created where they can engineer a set of genetic changes directly into an organisms DNA

Genetic EngineeringGenetic Engineering

CLONINGCLONING

The production of organisms with identical

genes

• Determines what genes are carried on each chromosome of

the human

•Helped in diagnosis of many inherited diseases and will lead to many advances in our future

Human Genome ProjectHuman Genome Project