Intro to GENETICS• GENETICS : The field of biology

devoted to understanding how traits are transferred (inherited) from parent to offspring

• Gregor MENDEL (1822-1884)- Austrian monk

- Left his monastery to study science and mathematics at the University of Vienna

• Upon return to the monastery, Mendel taught high school and experimented with pea plants in his garden

• “The Father of Genetics”

Mendel’s Observations• Trait - a possible appearance of a characteristic in an organism• Mendel observed 7 characteristics in his pea plants, each with 2 distinct traits

• Mendel saw that “Tall” seeds produced “Tall” plants, but also some “Short” plants

• He also saw that “Purple-flowered” seeds produced “Purple-flowered” plants, but also some “White-flowered” plants

Mendel’s Experiments• Mendel could control the pollination

(sexual reproduction) of his plants• Mendel began with PURE plants

(offspring always showed same trait as parent)

• Cross of Pea ColorP (Pure Parents) Cross : Yellow X Green

F1 (Filial) Generation : All Yellow

F2 Generation : Yellow and Green

(3:1 ratio)

• In re-doing this experiment, he obtained the same results for each characteristic !

Mendel’s Conclusions• Some “FACTOR” within the plant

must be controlling each trait

DOMINANT/RECESSIVE TRAITSFactors exist in pairs, and one factor may dominate/mask/hide the other

LAW OF SEGREGATIONPaired factors segregate (separate) during the formation of gametes

QUESTION: What process does this refer to?

LAW OF INDEPENDENT ASSORTMENTFactors for different characteristics are distributed to gametes independently

Molecular Genetics• Mendel’s findings weren’t

appreciated until much later, when new technology revealed the existence of CHROMOSOMES and GENES

• GENE : a segment on a strand of DNA that controls a particular hereditary trait

• ALLELE : each of several alternative forms of a gene (these are Mendel’s “factors”)

Genetic Crosses• Dominant Allele = capital letter• Recessive Allele = lower-case letterExample :

Yellow seeds are dominant to green seeds Y = yellow (dominant) y = green (recessive)

• Genotype: the pair of alleles that an individual possessesYY Yy yy

• Phenotype: the appearance of a trait as a result of its genotype

Genetic Makeup of an IndividualHomozygous – both alleles in a pair are alike

(YY or yy)Heterozygous – the alleles in a pair are different

(Yy) … will show a dominant phenotype

Intro to: Genetic Disorders• GENETIC DISORDERS : Diseases or debilitating

conditions that have a genetic basis

* They are in-born (inherited) *EXAMPLES:

- Huntington’s disease

- Hemophilia

- Duchenne muscular dystrophy

- Down syndrome • A person with a family history of genetic

disorders may wish to undergo genetic screening before becoming a parent

Detecting Human Genetic Disorders• AMNIOCENTESIS is a technique used to

analyze the genome of a fetus before birth

• KARYOTYPING

• BLOOD TESTING can yield some information

• Couples at risk may wish to undergo… GENETIC COUNSELING

• The job of a genetic counselor is to:– Administer and analyze genetic tests– Determine risk of inheritance of a disorder– Advise the involved parties of potential

consequences and their options

Test-Cross• FACT: We don’t always know the genotype of a particular individual

(even if we know its phenotype)• TESTCROSS: A breeding test in which an individual of unknown

genotype is crossed with a homozygous recessive individual

Incomplete Dominance• When two or more alleles influence

the phenotype of an individual • The phenotype of a heterozygous

individual is an intermediate (in-between) the dominant and recessive phenotypes

Codominance:

When both alleles are fullyfully expressed in a heterozygote (neither is recessive)

Sex-Linked Traits

REMEMBER: humans have 22 pairs of autosomes and 1 pair of sex chromosomes

XX = femaleXY = male

• SEX-LINKED TRAIT: a trait for which the allele is carried on a sex chromosome

• In this way, the phenotype of the individual may vary with the sex

Examples:• Hemophilia • Duchenne muscular dystrophy • Colorblindness

Pedigree Chart

Blood TypesAntigen – stimulates body to

produce antibodiesAntibody – causes blood to clump

ABO System• Type A – (most common) type A antigens on RBCs,

anti-B antibodies in plasma• Type B – type B antigens on RBCs, anti-A antibodies

in plasma• Type AB – (universal recipient) type A and B antigens

on RBCs, no anti-A or anti-B antibodies in plasma• Type O – (universal donor) no type A or B antigens

on RBCs, both anti-A and anti-B antibodies in plasma

Human blood type is determined by co-dominant alleles. An allele is one of several different forms of genetic information that is present in our DNA at a specific location on a specific chromosome.

There are three different alleles for human blood type:

Blood types For simplicity,we call these

IA A

IB B

i O

The Rh factor genetic information is also inherited from our parents, but it is inherited independently of the ABO blood type alleles. There are 2 different alleles for the Rh factor known as Rh+ and Rh-.

Someone who is "Rh positive" or "Rh+" has at least one Rh+ allele, but could have two. Their genotype could be either Rh+/Rh+ or Rh+/Rh-. Someone who Rh- has a genotype of Rh-/Rh-.

What are the possible blood types of the offspring in a cross between individuals that are type AB and type O? (Hint: blood type O is recessive)

Blood Donors & Recipients

Dihybrid Crosses• A cross between individuals in which the

inheritance of two traits is analyzed

F1 F2