Science Warm-up 10/28/2012

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Chapter 11: Complex Inheritance and Human

HeredityAaron Wood

By PresenterMedia.com

Overview

Section 1: Basic Patterns of Human Inheritance

Section 2: Complex Patterns of Inheritance

Section 3: Chromosomes and Human Heredity

Section 1: Basic Patterns of Human InheritanceOverview

Recessive genetic disordersDominant genetic disordersPedigreesAnalyzing pedigrees

Recessive Genetic Disorders

A recessive trait is expressed when the individual is homozygous recessive for the trait.

Ex) gg

Cystic Fibrosis

Affects the mucus-producing glands, digestive enzymes, and sweat glands.

Mucus is extremely thick, and extremely hard to get rid of.

1 in 3500 chances

Treatment is daily cleaningof the lungs, and medicine.

Albinism

Genes do not produce normal amounts of the pigment melanin.

1 in 17,000 occurrence

Galactosemia

Inability to break down galactose

Mental disabilities, enlarged liver, and kidney failure.

No cure 1 in 60,000 occurence

Tay-Sacs Disease

Absence of a substance that breaks down fatty substances.

Causes a buildup of fatty deposits in the brain, and mental delaying.

1 in 2,500 occurrence, mainly affects those with Jewish descent.

Dominant Genetic Disorders

Huntington’s disease

Achondroplaisia

Huntington’s Disease

A gene affecting neurological function is defective.

Decline of mental and neurological functions, and the ability to move deteriorates.

1 in 10,000 occurance

Achondroplasia

A gene that affects bone growth is abnormal.

Effects: short arms and legs, large head

Pedigrees

A pedigree is a diagram that traces the inheritance of a particular trait through several generations.

Compared to a family tree, but for a characteristic of disease.

Males are squares, females are circles. Normal is typically a blank circle, carriers are half-filled, and expressers are completely filled.

Analyzing Pedigrees

Inferring GenotypesKnowing physical traits can determine what genes an individual is most likely to

have.

Predicting DisordersRecord keeping helps

scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and infer genotypes.

Section 2: Complex Patterns of Inheritance

Overview

Incomplete DominanceCodominanceMultiple AllelesEpistasisSex DeterminationSex-linked traits

Incomplete Dominance

This is when a heterozygous individual’s phenotype is an intermediate phenotype between the two homozygous phenotypes.

Codominance

This situation occurs when both alleles are expressed in the heterozygous condition

Ex) Sickle-cell disease

Sickle-cell disease

Changes in hemoglobin cause red blood cells to change to a sickle shape.

People who are heterozygous for the trait have both normal and sickle-shaped cells.

Sickle cell

Normal red blood cell

These sickle-cells are unable to carry as much oxygen as a normal cell. They also tend to block circulation in the hands and feet.

Why is there suchan overlap with sickle-cell andmalaria?

Individuals that are heterozygous for sickle-cell disease also have a higher resistance for malaria.

These individuals are more likely to survive and pass on the sickle-cell trait to offspring.

Multiple Alleles

Some forms of inheritance are determined by more than two alleles.

Ex) blood groups in humans (ABO)

Epistasis

Occurs when one allele hides the effects of another allele. This is the cause of coat color in Labrador retrievers.

No dark pigment present in fur Dark pigment present in fur

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Sex Determination

Sex chromosomes determine an individual’s gender.

For humans these are either the X chromosome and Y chromosome.

Sex-linked Traits

Genes located on the X chromosome

Color blindnessHemophilia

Color blindness

The trait for red-green color blindness is a recessive X-linked trait. This is very uncommon among females.

Hemophilia

A recessive sex-linked disorder, is characterized by delayed clotting of the blood.

Famous pedigree based on Queen Victoria of England (1819-1901)

Section 3: Complex Inheritance and Human Heredity

Overview

Environmental InfluencesKaryotypesTelomeresNondisjunction

Environmental Influences

The following things can impact the expression of certain characteristics

Environmental factorsDiet and exerciseSunlight and waterTemperature

Karyotype Studies

Micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.

Karyotypes can be used to predict and test for genetic alterations.

Chromosomes are stained during metaphase.

Telomeres

Telomere caps consist of DNA associated with proteins

Serves as a protective function for the structure of a chromosome.

Nondisjunction

Cell division when sister chromatids fail to separate properly.

Causes disorders such as Down’s Syndrome.

Down’s Syndrome

Also known as trisomy 21.

Individuals receive an extra copy of the 21st chromosome.

Causes mental delaying and stunted growth.

Fetal Genetic Testing

There are different ways to test the genetic makeup of a fetus in the womb.

AmniocentesisChorionic villus samplingFetal blood sampling

Amniocentesis

Prenatal diagnosis of chromosomal abnormalities, and fetal infections.

Chorionic villus sampling

Removal of a small piece of the placenta tissue to determine chromosomal or genetic abonormalities.

Fetal blood sampling

Testing of a small amount of blood from the fetus to determine certain characteristics.