Classical Genetics

The Work and Conclusions of Gregor Mendel Father of genetics Monk in Austria 1865 Studied patterns of inheritance in peas

Why Peas?

Why Peas? Self-fertilization produces true breeding generations

Prevented self-fertilization
Manipulated reproduction
Began monohybrid crosses
Carefully examined results
Why Peas? Read Concept 1 Click Animation and View

Why Peas? Read Concept 2 Click Animation and View

Mendel’s Work Some traits are dominant and some are recessive Read concept 3 Click animation and view Read concept 4 Click animation and view

Mendel’s Work
Traits are passed on by factors (genes)
Factors (genes) have more than 1 form called alleles
There are at least 2 alleles for each trait

Mendel’s Work Alleles are represented by the first letter of the dominant trait Pea plant flower color (trait) Purple or white Purple is dominant over white Alleles are represented as P=purple p=white

You try a few…
Round seeds are dominant over wrinkled seeds
Yellow seeds are dominant over green seeds
Tall plants are dominant over short plants
1. R=round r=wrinkled
Y=yellow y=green
T=tall t= short
Mendel’s Work

Mendel’s Work Describing Traits (Tall or short plants) Genotype The actual genetic make-up of an organism the “genes” Phenotype The physical appearance or form observed the “physical”

Mendel’s Work Possible Genotypes (TT Tt tt) Homozygous The two alleles for the trait are identical TT homozygous dominant (purebred dominant) tt homozygous recessive (purebred recessive) Heterozygous The two alleles for the trait are different Tt heterozygote (hybrid)

Mendel’s Work

Mendel’s Work Read Concept 5 Click animation and view Complete visual organizer of Mendel’s pea plant experiment

1. Law of Dominance Alleles for a trait are either dominant or recessive The dominant form is expressed and the recessive form is hidden The only way to express a recessive trait is if there are two copies of the recessive allele Mendel’s Conclusions

Mendel’s Conclusions
Law of Segregation
The two alleles for a trait separate during gametogenesis

Test Cross

Dihybrid Cross

Mendel’s 3 rd Law of Independent Assortment
Alleles of different genes are assorted independently of one another during the formation of gametes
This means that calculating the probability of several traits appearing together is the product of the probability of each trait taken separately
The Rule of Multiplication

Incomplete Dominance

“ Dominant” gene does not fully express itself to mask the effect of the recessive gene A pattern of inheritance in which the phenotype of a heterozygous individual is intermediate between those of the parents Genotypic ratio is equal to phenotypic ratio

Co-Dominance Two or more alleles are fully dominant When present together they are both expressed ABO Blood Groups exhibit co-dominace

Type A Blood
• Individuals with group A blood have red blood
cells with antigen A on their surface.
Produce antibodies against antigen B,
antibody B.
• Therefore, a group A person can only receive
blood from people in groups A or O

Type B Blood
Antigen B is on their cells, and antibodies A are produced in their serum.
A group B person can only receive blood from people in groups B or O, preferably B.

Type AB
Individuals with group AB blood have red blood cells with both antigens A and B.
Do not produce antibodies A or B against either antigen in their serum.
A person with type AB blood can receive blood from any group (preferably AB) but cannot donate blood except to another AB.

Type O
Individuals with group O blood have red blood cells with neither antigen A or B.
Produce antibodies A and B against both types of antigens.
A group O person can only receive blood from group O.

Sex Inheritance Sex Chromosomes X or Y XX is female XY is male Read concept 9 Click animation and view

Sex-Linked Inheritance Genes linked to sex chromosomes

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Classical Genetics

by cgales on Mar 15, 2007

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Classical Genetics — Presentation Transcript