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