UNIT 11 HUMAN GENETICS

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Pedigree A chart of an

individual's ancestors used in human genetics to analyze inheritance of certain traits

Nature vs. Nurture

Nature is our DNA (genes)

Nurture is our environment

The debate is over which has a greater influence

We use identical twins to study

Problems studying human genetics

1. Ethically unresponsible to conduct testcrosses on humans. Testcross: method to determine the

genotype for a dominant phenotype, always use homozygous recessive

2. Humans have long life spans and it requires decades to produce several generations to study.

3. Small number of offspring (and long gestational periods)

Techniques used to study human genetics

Population Sampling: determine how often a trait appears

in a small randomly selected group, then apply to the entire population

ex. How many people can roll their tongue?

Take this number and project for the entire population.

Pedigrees: graphical record of the inheritance of a single trait over several generations. determined based on

family/historical documents, interviews, photographs, and medical records

Techniques used to study human genetics

Pedigrees

Shapes represent individuals in pedigrees, connecting lines represent relationships

Female Without trait

Female WITH trait

Male without trait

Male WITH trait

Ticket Out the Door

1. When red cattle are bred with white cattle they produce roan (red and white spotted). Cross a roan cow with a red cow. Give phenotype percentages of the offspring.

2. Colorblindness is sex-linked recessive. Cross a colorblind male with a female carrier. What is their chance of having a colorblind son?

3. Cross a mom with type AB blood with a dad who is type O. List all possible phenotypes.

Helpful Hints for figuring out pedigrees

If the pedigree is showing a SEX-LINKED trait: No male carriers Trait cannot be passed from father to son More males will express the trait

If the pedigree is showing an AUTOSOMAL recessive trait Trait can skip a generation Trait CAN be passed from father to son

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Autosomal Trait

Trait inherited on one of the first 22 pairs of chromosomes……. NOT sex-linked

Aneuploidy

Having too many or too few chromosomes

Caused by mistakes in Meiosis--nondisjunction- homologous pairs do not separate during meiosis

Gene Disorders vs. chromosomal disorders Gene disorders: Diseases inherited as a

single gene on a single chromosome Arise from mutations on within a single

gene Chromosomes disorder: caused by

receiving a missing or extra chromosome--- like Down Syndrome Often caused by NONDISJUNCTION during

Meiosis Called ANEUPLOIDY Can be detected on a KARYOTYPE: a picture

of the chromosomes

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Pattern of Inheritance for Genetic Disorders

Autosome: the first 22 pairs of chromosomes Autosomal Dominant:

dominant trait found on any of the first 22 chromosomes

Example : Huntington’s disease, found on chromosome 4, causes brain to break down, symptoms appear in your 40’s

Genetic Disorders

Autosomal Codominant: Found on chromosomes 1-

22, and both version of trait are equally dominant

Example: Sickle-cell Anemia, leads to misshapen red blood cells, leads to poor circulation and pain, Heterozygous individuals

are resistant to malaria Primarily in African-

Americans

Genetic Disorders

Autosomal Recessive: recessive traits found on any of the first 22 chromosomes Examples: Cystic fibrosis (increased mucus in lungs and

digestive tract) caucasians Tay-Sach’s disease- break down of central nervous

system leading to premature death (die before 2) Found in jewish and pennsylvania dutch populations

PKU (phenylketonuria) Inability to break down the amino acid phenylalanine Can be controlled by diet Can build up in brain and lead to decreased mental

function

Cystic Fibrosis- autosomal recessive

Sex Chromosomes: Pair 23; XX- female, XY- Male

Sex-linked disorder: Disorder carried ON the X Examples:

Hemophilia (sex-linked recessive trait)-blood does not clot normally

colorblindness

Chromosomal Disorders

Inherited due to problems with the ENTIRE chromosome Example: Down’s

Syndrome, caused by a mistake in MEIOSIS

Nondisjunction= incorrect distribution of chromosomes; occurs during meiosis

Chromosomal Disorders

Anueploidy: an incorrect number of chromosomes in a fertilized zygote Autosomal

Chromosome Aneuploidy: having an extra autosome Example: Down’s

Syndrome is caused by an extra chromosome #21

Sex Chromosome Aneuploidy

Examples Klinefelter’s Syndrome

(XXY)--male but develops female secondary sex characteristics

-- usually sterile

--use testosterone therapy to treat

Sex Chromosome Aneuploidy

Turner’s Syndrome (XO) Female with underdeveloped

gonads, infertile

Detection of Genetic Disorders Genetic Counseling: can

help parents determine the chances of passing a harmful genetic trait to their child

Sonograms: use of sound waves to produce a picture of a fetus Used to evaluate baby’s

growth and development

Detection of Genetic Disorders Blood tests:

Screen for proteins Alpha-Feto

protein test (AFP)

Levels determine if baby is at risk for Down’s syndrome, Turner’s , or spina bifida

Detection of Genetic Disorders

Amniocentesis: Removes amniotic fluid with

fetal cells which can be cultured and produce a karyotype

Karyotype: a picture of the chromosomes

Chorionic Villi Sampling: removes tissue from the placenta for karyotyping, Can be done earlier in

pregnancy and more risky

Karyotypes

Human Genome Project

Human Genome Project: develop certain

genetic markers to detect presence of certain gene variations on the chromosomes

Knowledge of a genome unlocks the secrets of what DNA is making which proteins. This will ultimately help scientist to better understand the inner workings of biology.

Prevention/Treatment

Genetic diseases cannot be cured but treated:

Pain medication: manage pain Occupational Therapy: help people who

have conditions improve their ability to perform every day tasks

Blood Transfusions: Sickle-cell/ Hemophiliacs may require

Gene Therapy: use vectors (viruses) to replace defective genes with normal ones

Environmental Factors

Diet: can stop the progression of PKU, andlimit

the risk for genetic predispositions such as heart disease, alcoholism, and certain cancers.

Environmental Toxins: environmental factors such as UV radiation or tobacco can directly change our genes