• I.History of Genetics• Genetics - the scientific study of

inheritance • The domestication of dogs is one of the

earliest human experiences with genetics.• Millions of years ago there were no dogs.• Today’s domestic dogs are descended

from a wolf ancestors

• Ancient people selected traits to be passed from generation to generation.

 • Trait - a characteristic that can be

passed from parent to offspring

• It has not always been understood how traits are passed from parent to offspring.

• For many centuries scientists believed that traits were blended in offspring, they would later learn that this idea was incorrect.

• Review:• during cell division chromosomes

are replicated and distributed to daughter cells during meiosis.

• The traits that are passed from parents to offspring are in these chromosomes

• II.Gregor Mendel• Clues to

understanding inheritance came from an Austrian monk, Gregor Mendel, in the 1860’s.

 

• He used pea plants to study how traits were passed from one generation to the next.

• Mendel gathered detailed information on more than 20,000 pea plants over an eight year period.

• He applied mathematics and statistics to his findings and found that they did not support the blending hypothesis.

• III. Mendel’s Experiments• Mendel chose to work with the pea

plant for several reasons:1. the structure of the pea plant- the pea flower petals make it very easy for the pollen from the anther from a plant to fertilize it’s own pistil.

• This produced a purebred offspring.

purebred offspring - receives the same genetic traits from both parents

• Mendel was also able to transfer pollen from one plant to another by hand. This produced a hybrid.

• hybrid offspring - receives different forms of a genetic trait from each parent

2. Presence of distinctive traits 

Mendel studied several traitsEach of the traits had two

distinct forms 

ex. pea pods are either yellow or green, there is no intermediate

3. Rapid reproduction cycle 

This allowed Mendel to repeat his experiments many times to test his results

• IV. Mendel’s ObservationsMendel began his experiments using two different groups of inbred plants. He called this the parents (or P) generation.

yellow pea x green pea

• He called the offspring of that mating the first filial generation or F1 generation.

100%yellow pea plants • Mendel let the F1 plants self fertilize to

produce the F2 generation. 75% of the F2offpsring produced

were yellow while 25% were green.(3:1 ratio)

• V. Mendel’s Conclusions• Mendel’s experiments showed that

the blending hypothesis was wrong.

• Mendel hypothesized that each trait is controlled by a distinct “factor”

• We now know that Mendel’s “factors” are genes.

 • Gene - a section

of a chromosome that codes for a particular trait.

• Alleles - different forms of a gene (ex. yellow, green in peas) Alleles are represented by letters ex. Y=yellow, y= green

• dominant allele - form of the gene that is expressed fully when two different alleles are present

• recessive allele - form of the gene not expressed when two different alleles are present.

• Letters are used to represent alleles:

the dominant traits is represented by an uppercase letter ex.Y

 • the recessive allele is represented

by a lower case letter ex.y

• Mendel published his work in 1866, his work went unrecognized for 37 years.

 In 1903, Walter S.Sutton used a microscope and observed that chromosomes behaved like Mendel’s factors.

genesChromosome

• VI. Genes Affect Traits • GENOTYPE - the genetic make up of an

organism. The genotype includes both genes in a pair of homologous chromosomes.

• genotype of purebred yellow peas is YY• genotype of hybrid yellow peas is Yy• genotype of green peas_______

• PHENOTYPE - the outward expression of a trait

• phenotype for F1 generation of peas is yellow

Green seeds Yellow seeds

• If the two alleles of the gene are the same they are called homozygous. ex. YY, yy

• If the two alleles of the gene are different they are called heterozygous ex.Yy

• VII. Mendel’s Laws• The basic rules of inheritance are

called Mendel’s Laws• Law of Segregation - each pair of

genes segregates and ends up in gametes during meiosis

• half an organisms gametes contain one chromosome from a homologous pair, the other half contain the other chromosome

• Law of Independent Assortment - gene pairs separate into gametes randomly and independently of one another.

• Law of Dominance - recessive allele is expressed only when the organism has no copy of the corresponding dominant allele

• IX. Genetic InteractionsComplete dominance – the dominant allele masks the recessive allele

 

Recessive trait : Sugary kernels shown only when no dominant allele is present

Dominant trait: Yellow kernels

• incomplete dominance - when two different alleles for the same trait combine the offspring is an intermediate ex.red snap dragon x white snap dragon = pink snap dragon

• codominance - both alleles in the heterozygote express themselves fullyex. blood type

• Polygenic Traits - traits affected by more than one gene.

ex. eye color, skin color

• X. Probability• fractions, percentages, or ratios used to

predict the likelihood of an outcome, you are measuring probability.

• When you flip a coin, you can get either heads or tailsThe probability of getting heads is 1/2, 50%, 1:1

• Scientists can use probability to predict the outcome of breeding experiments.