Chapter 9Fundamentals of Genetics

What is Genetics?

The branch of Biology that studies how traits are passes down from parents to offspring.

What is Heredity?

The passing on of characteristics (traits) from parents to offspring.

Who is Gregor Mendel?

“The Father of Genetics”

Who is Gregor Mendel?

An Austrian monk in 1842. His job at the monastery was tending the garden. In 1851 he attended the University of Vienna and studied statistics. When he returned to the monastery he began experimenting with pea plants.

Why did he choose pea plants to work with?There were 7 traits that he could easily observe and study in pea plants.

Plant height

Pod color

Pod appearance

Seed texture

Seed color

Flower color

Position of the flowers

How did Mendel control the reproduction of the pea plants?

                                                                                                                                 

How did Mendel control the reproduction of the pea plants?

Pollination- the transfer of pollen from the stamen to the pistil.

Self pollination- pollen transferred within same flower

Cross pollination- pollen transferred from one flower

to another flower.

Mendel’s Experiments

Mendel began by growing plants that were Pure for each trait; plants that are pure for a trait always produce offspring with that trait.He worked with 14 strains of different traitsHe called each strain a Parental Generation or the P1 Generation

Mendel’s Experiments

4. He then cross pollinated plants with different traits.Yellow pods x Green pods- offspring were called the F1 Generation

5. He then allowed the F1 Generation to self pollinate and collected the seeds. The results of this cross were the F2 Generation

6. He performed thousands of crosses and counted and recorded the traits of every cross.

Mendel’s Results

Factors- Controls within the pea plants for the characteristics that Mendel observed.

After doing thousands of crosses he found that one factor in a pair may prevent the other factor in a pair from having an effect.

Dominant factor- Factors that masked or dominated the other factor.

Recessive factor- The factor that is masked

Mendel’s Conclusions

The Law of Segregation- a pair of factors are segregated or separated during the formation of gametes. (meiosis)

The Law of Independent Assortment- factors for different characteristics are distributed to gametes independently (randomly).

Journal Entry 2/2

On Monday, you learned about a historical scientist, what makes Gregor Mendel significant?

Sentence Starter: Gregor Mendel is significant because_____

Video

What is a gene?

A segment of DNA on a chromosome that controls a particular hereditary trait.

What is an allele?

Alternative forms of a gene or factor that code for the same trait. We now know that Mendel’s factors are actually alleles.

Letters are used to represent alleles

Dominant/Recessive

Capital letters refer to dominant allelesLower case letters refer to recessive allelesExample: unattached earlobes are dominant over attached earlobes. EE, Ee = unattached ee = attached

Alleles occur in pairs and each individual has two alleles for a trait. One of each allele is inherited from each parent.

What is homozygous?

When both alleles in a pair are alike

An organism can be homozygous dominant PP

An organism can be homozygous recessive pp

What is heterozygous?When the two alleles in a pair are different Pp

What is genotype? What is phenotype?

Genotype is the genetic makeup of an organism; it consists of the alleles that the organism inherits from its parents.

Phenotype is the physical appearance of an organism which results from its genotype.

Warm-up

What is the difference between phenotype and genotype?

What is the difference between homozygous and heterozygous?

What is probability?

Probability is the likelihood that a specific event will occur.

It can be expressed as a decimal, a percentage, or a fraction.

What is a Punnett Square?

A model used to establish the probabilities of the results of a genetic cross.

What is a Monohybrid cross?A cross between individuals that involves one pair of contrasting traits

What is complete dominance/ recessiveness?

When one allele is dominant over all other alleles

e.g Tall pea plants over short pea plants

e.g. Tongue rolling

Sample Problem

Heterozygous purple flower x heterozygous purple flower

Genotype Phenotype25% Homozygous dominant 75% Purple50% Heterozygous 25% white25% Homozygous recessive 100%100%

When crossing hetero-hetero what can we be sure of?

The offspring will always get a 75% to 25% ratio

What exactly do the results of the Punnett square show?

Predicts the probability that certain traits will be inherited by offspring.

Warm up 2/3 Stand-Up Hand-Up Pair-Up

Directions: As the music plays you will walk around the room. When the music stops you will put your hand up and tag the person that is closest to you. This will be your partner for this round.

What is incomplete dominance?

When two or more alleles influence the phenotype, resulting in a phenotype intermediate between the dominant trait and the recessive trait.

None of the alleles are dominant. The letters are written as lower case.

Also called Blending.

Sample Problem

This occurs in snapdragon and four o’clock flowers

rr=red rw=pink ww=white

Cross a pink four o’clock flowers with pink four o’clock flowers.

What is codominance?

When both alleles for a gene are expressed in a heterozygous offspring. Neither allele is dominant or recessive, nor do the alleles blend in the phenotype.

The letters are written as capitals.

Sample Problem

This occurs in some horses with their coat colorR allele = red R’ allele = white

RR = RedRR’ = Roan colored horse (red & white hairs)R’R’= White

Cross a Red horse with a Roan horse

Also Blood type is Codominant

Four blood types in humans (phenotypes): A, B, AB, O

A and B are codominant to O

What is a dihybrid cross?

A cross between individuals that involves two pairs of contrasting traits.

Predicting the results of a dihybrid cross is more complicated than predicting the results of a monohybrid cross because there are more possible combinations of alleles to work with.

Sample Problem

Cross a pea plant that is heterozygous for round, yellow seeds with another pea plant that is heterozygous for round, yellow seeds.

RrYy x RrYy

Foil!