Unit 8: Human Heredity Mrs. Howland Biology 10 Rev. Feb 2016

What can be INHERITED? TRAITS

Why LOOK at inheritance? Can predict DISORDERS Pedigree analysis Inheritance patterns Phenotypes  Genotypes

Information about INHERITANCE Inheritance may be studied by looking at: Karyotypes Pedigrees Physical traits to determine genotypes Patterns: sex-influenced, X-chromosome inactivation Heterozygous advantage Mistakes in meiosis (nondisjunction) Prenatal genetic screening

PEDIGREES A pedigree is a diagram that tracks inheritance of a trait through multiple generations of offspring in a family

Information From Pedigrees Genotypes of individuals Determination of trait inheritance: Autosomal or X-linked? Dominant or recessive?

Interpreting a pedigree…

Helpful Videos ~ Pedigrees Overview of pedigrees: Interpreting a pedigree: Ztzi6pAh5M Ztzi6pAh5M

TIPS

Remember! Recessive disorders can skip a generation!

Example:

PRACTICE! Pedigrees Complete the following:

Detecting Genetic Disorders GENETIC SCREENING allows for early detection of chromosomal disorders in fetuses Carried out during 1 st or 2 nd trimester of pregnancy Can be used for karyotyping Amniocentesis Chorionic Villus Screening (CVS)

Genetic Screening Amniocentesis = Medical procedure used to diagnose chromosomal abnormalities Needle aspirates sample of amniotic fluid (the fluid contains particles of fetal tissues). Ultrasound is used as visual guide for needle insertion.

Genetic Screening Chorionic Villus Sampling (CVS) = Medical test that samples placental tissue through the cervix or abdomen

X-Chromosome Inactivation Males have only ONE “X” chromosome, while females have TWO EACH X chromosome has ~1000 genes It could be a problem if those genes are expressed TWICE! Dosage compensation= X-chromosome inactivation “turns off” one X chromosome in females

X-Chromosome Inactivation Which X chromosome gets shut off? It is randomly selected! FUN FACT: Some marsupials preferentially inactivate the father’s X chromosome! WHEN does this occur? EARLY in life ~ during embryonic development ANIMATION:

Barr Body With X-chromosome inactivation, what happens to the INACTIVE X chromosome? INACTIVE X chromosome condenses into a Barr body, which maintains a silent state

Blood Type Inheritance ABO blood type is inherited by multiple alleles

Overview of Blood Types

Blood Type Inheritance ABO blood type is inherited by multiple alleles Rh blood type (+ or -) is inherited independently of ABO blood type Coded by TWO genes: RHD and RHCE Rh+ is DOMINANT Rh is also an antigen on the surface of the red blood cell

Rh Incompatibility Some of baby’s blood may enter mother’s bloodstream Sometimes, mother and child differ in Rh blood type May result in ‘rejection’

Blood Type Compatibility Who can donate/receive blood?

Epigenetics Genes do not change once they are inherited Gene expression may be influenced by environment or stages of life Epigenetics studies differences in gene expression (nature vs. nurture) NOT due to changes in DNA

Epigenetics ~ What can be learned? VIDEO: ACTIVITY: Diverging Twins

Heterozygote Advantage Why might it be a GOOD THING to be a carrier for a disease or disorder? VIDEO:

Heterozygote Advantage EXAMPLE: Malaria & Sickle Cell Anemia

How MALARIA affects the body What’s the connection between BLOOD and MALARIA? SOURCE:

Heterozygote Advantage Heterozygote advantage = Individuals with heterozygous genotypes (two different alleles) is more ‘fit’ than those with homozygous genotypes Natural selection maintains existence of both copies of alleles EXAMPLES: Sickle cell / malaria (sickle cells inhibit reproduction of parasite) Cystic fibrosis and cholera (cystic fibrosis prevents dehydration)