Fundamentals of Genetics

Chapter 9

Trait Description Class numbers

Tongue rolling

Dimples

Widow’s peak

Hitchhiker’s Thumb

Hand clasping, left over right thumb

Arm folding fold your arms across your chest/stomach…which one is on top?

Free earlobe

Chin cleft

Hair on middle joints of fingers

Short big toe

Ear points

Round face

Curly hair

Blue Eyes

Brown Hair

Genetics is…..

• The study of heredity, how characteristics are transmitted from parents to offspring.

Gregor Mendel“Father of Genetics”

• Mendel studied garden peas and constructed the basis of genetics still used today.

• He observed 7 traits in the plants (ex. plant height )

• He noticed that traits in the offspring varied from the parent (ex. short plants came from tall plants).

7 traits- pg 167 (DO NOT COPY)

1. Position of flower along stem2. Height of plant3. Pod appearance4. Pod color5. Seed texture6. Seed color7. Flower color

Mendel’s Experiments

• Mendel grew pure plants for each of the 7 traits (pure meaning the offspring were just like the parent plants)

• He called this the P1 generation• The pure plants were then cross-

pollinated (tall plant crossed with a short plant)

• These plants were the F1 generation

• The F1 generation was allowed to self-pollinate

• These plants were called the F2 generation

Test

• P1 generation – Tall plant x short plant• F1 generation – All tall plants (where are

the short plants?)• F2 generation – Tall and short plants

present

Mendel’s Conclusions

• There are dominant and recessive traits. A dominant trait masks a recessive trait.

• During the formation of sex cells, alleles are separated (one allele for a trait per sex cell)- Law of segregation

• Alleles for different characteristics are distributed to sex cells independently – Law of independent assortment.

Genes

• A gene is a segment of DNA on a chromosome that controls a particular trait (ex. height of a plant, eye color)

• Genes occur in pairs, alleles make up the pair• Letters are used to represent alleles. Capital

letter represents a dominant allele and a lower case represents a recessive allele.

• T= tall plant; t = short plant

• When both alleles of a pair are alike it is said to be homozygous (TT or tt)

• When the alleles of a pair are different it is said to be heterozygous (Tt)

Genotype vs. Phenotype

• Genotype – genetic makeup of an individual ; ex. Bb or TT

• Phenotype – physical expression of the genotype; ex. brown eyes or tall plant

Punnett Square

A punnett square…..

• A diagram used by biologists to aid them in predicting the probability that certain traits will be inherited by offspring

• Types of crosses–Monohybrid – cross b/t one pair of traits

Ex. Tt x TT–Dihybrid – cross b/t two pair of traits

Ex. TtGG x TTgg

3 possibilities….

• Homozygous x Homozygous

• Homozygous x Heterozygous

• Heterozygous x Heterozygous

Do you know the genotype of a guinea pig just by looking at its appearance?

• Black is the dominant coat color• BB or Bb would produce a black coat• To tell which, do a test cross and

compare to offspring of the pig• Cross with a homozygous recessive

Incomplete Dominance

• Two or more alleles influence the phenotype and cause a blending of traits.

• Flower color, mouse coat, sickle cell anemia

Codominance (co= exist together)

• Two or more alleles influence the phenotype and cause both phenotypes to appear.

• Cattle coat color (spots) or Blood types (AB)

• Do the Punnett square using different letters because neither traits are dominant

There are many genes involved and eye color can range from brown to hazel to green to blue to...

How does eye color work? Eye color comes from a combination of black and yellow pigments called melanin in the iris of your eye. If you have no melanin in the front part of your iris, you have blue eyes. An increasing proportion of the yellow melanin, in combination with the black melanin, results in shades of colors between brown and blue, including green and hazel.

What we are taught in high school biology is generally true, brown eye genes are dominant over green eye genes which are both dominant over blue eye genes. However, because many genes are required and certain combinations of pigments , there many possibilities in shades and color of ones eyes.

The “real” story behind eye color......