Chapter 9

Genetics

9.1 The Work of Gregor Mendel• Mendel – crossed pea plants to study and

understand genetics– Most pea plants self pollinate (true breeding)– Mendel forced plants to cross pollinate (have 2

plants)

– Studied 7 traits of pea plants pg 176.– Took the plants that had different traits and

crossbreds them (hybrids)

The F1 Cross• First Filial (parent cross, produce the F1,

then cross the F1 making an F2)– Law of segregation: Segregation of alleles

occurs during the formation of gametes, sex cells.

– Pg 177– Law of Independent Assortment – factors for

individual characteristics are not connected. Assort independently of each other.

Came to 2 conclusions after the breeding

1. Genes, segment of DNA, occurs in pairs, controll heredity. Visual form called alleles. (noted as “factors”)

2. Found that some of the alleles are dominant and some are recessive.

1. Dominant trait always uppercase (TT, Tt)

2. Recessive always lowercase (tt)

9.2 Probability and Punnett Squares

• Punnett square – table representation of crossing alleles– TT or tt – homozygous – same alleles– Tt – heterozygous – different alleles– Phenotype – physical look, all tall (TT, Tt) have

same phenotype.– Genotype – based on alleles. (TT, and Tt) are

different now.

Probability

• Penny = ½ = .50

• A cross results in 787 pink flowers and 277 white flowers. If we cross the same P generation, the probability will be the same)

• Dominant Recessive• Curled Up Nose Roman Nose• Clockwise Hair Whorl Counter-clockwise Hair Whorl • Can Roll Tongue Can't Roll Tongue • Widow's Peak No Widow's Peak • Facial Dimples No Facial Dimples • Able to taste PTC Unable to taste PTC • Earlobe hangs Earlobe attaches at base • Middigital hair (fingers) No middigital hair • No hitchhiker's thumb Hitchhiker's thumb • Tip of pinkie bends in Pinkie straight• Oval face Square face • Cleft chin no cleft chin • Broad eyebrow Slender eyebrow • Separated eyebrows Joined eyebrows• Long eyelashes Short eyelashes• Almond eyes Round eyes • Freckles No freckles • Wet-type earwax Dry-type earwax • Left thumb on top of

interlocking fingers Right thumb on top of interlocking fingers

Punnett Squares pg 182

Homozygous x homozygous

Homozygous x heterozygous

• AA x Aa

Hetero x hetero

Summary of Mendel’s Principles pg 272

• Some alleles are neither dominant nor recessive, and many traits are controlled by multiples alleles or multiple genes.

• Incomplete Dominance – when one allele is not necessarily dominant (red and white flowers produce pink)

• Codominance – both alleles contribute to the phenotype.

• Multiple alleles – within the population of the species there are more than just 2 types of alleles. Coloration in Rabbits

• Polygenic Traits – having many genes, traits controlled by 2 or more genes. Skin color in humans.

• Incomplete Dominance

• We'll use "F" for the flower color allele. FR = allele for red flowers FW = allele for white flowers red x white -------> red & white spotted flowers FRFR  x FWFW ----> 100% FRFW

Codominance

• Problems

Explore Punnett Squares!!

• http://www.geocities.com/CapeCanaveral/Hall/1410/lab-B-19.html

Dihybrid cross – two traits