1. Mendelian Inheritance
Learning Goal: To explore how traits are inherited and expressed according to Mendelian inheritance.
Success Criteria:
describe the experiments and discoveries of Gregor Mendel
demonstrate the role of alleles in determining traits of an offspring
explain the law of segregation and the law of dominance
define the terms homozygous and heterozygous
differentiate between phenotype and genotype
Why do we resemble our parents? (We resemble our parents because we inherit traits from them.) 2. Why does asexual reproduction result in genetic clones? (During asexual reproduction, the organism makes a copy of itself without combining its genes with those from another organism. The offspring are a genetic copy of the single parent.) 3. Why are the offspring of sexual reproduction not genetically identical to either parent? (During sexual reproduction, genes from two individuals combine to produce offspring with new combinations of genes.)

2. Mendelian Inheritance
trait: a particular version of a characteristic that is inherited, such as hair colour or blood type
we owe much of our understanding of how traits are inherited to Gregor Mendel
we owe much of our understanding of genetics to Gregor Mendel (nineteenth century)

3. Mendel’s Pea Plants Gregor Mendal studied garden pea plants
since it can self-pollinate plant, it is assured to be “true bred”
it reproduces quickly and has specific, observable traits that can be expressed only one of two ways
eg. tall or dwarf, green pods or yellow pods, ...
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

4. Mendel’s Pea Plants Cont’d…
he cross-pollinated plants with different varieties and observed results
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

5. Mendel’s Experiments eg. plant color
P generation (parent plants) he crossed purple and white plants
F1 generation (offspring of the p generation) were all purple
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

6. Mendel’s Experiments Cont’d…
Was the recessive trait gone forever?
he allowed the F1 generation to self-fertilize
F2 generation (offspring of the F1 generation) consisted of both tall and dwarf plants, in a ratio of 3 tall:1 dwarf P F1 F2
Ratio
3:1
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.
purple x white
all purple
705 purple white

7. Mendel’s Experiments Cont’d…
similar results were found for all seven traits he studied
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

8. Mendel’s Conclusions Mendel concluded…
that traits must be passed on by discrete heredity units, which he called factors (i.e. genes)
the factor that was expressed in all the F1 generations was called the “dominant factor”
the factor that remained hidden but was expressed in the F2 generation he called the “recessive factor”
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

9. Mendel’s Conclusions Cont’d…
Law of Segregation:
organisms inherit two copies of genes, one from each parent
organisms give only one copy of each gene to their gametes because the genes separate during meiosis
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

10. Alleles: Alternate Forms of a Gene
allele: a specific form of a gene
dominant allele: the allele that is always expressed when present, represented with uppercase letter
ex. allele for tall plants is dominant (T)
recessive allele: the allele that is expressed only if the individual is homozygous for the recessive allele, represented with small case letter
ex. allele for dwarf plants is recessive (t)
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

11. Alleles Cont’d…
homozygous: describes an individual that carries two of the same alleles for a given characteristic
ex. homozygous dominant (TT) or homozygous recessive plants (tt)
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

12. Alleles Cont’d…
heterozygous: describes an individual that carries two different alleles for a given characteristic
ex. heterozygous plants (Tt)
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

13. Alleles Cont’d…
genotype: the genetic makeup of an individual (ex. possible genotypes for plant height: homozygous dominant (TT), homozygous recessive (tt), or heterozygous (Tt) )
phenotype: an individual’s outward appearance with respect to a specific characteristic (ex. possible phenotypes for plant height: tall and short)
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

14. Activity: Making Reeboops!
create imaginary baby animals called Reebops by applying the principles of Mendelian inheritance
At that time, some scientists thought that traits from each parent were blended in the off spring, similar to mixing red and white paint to make pink paint. However, off spring sometimes exhibited a trait identical to that of one parent rather than blending those of both parents. To explore patterns of inheritance, Mendel crossbred thousands of plants in his garden and carefully recorded the off springs’ traits.

15. Homework
read text pages (on website)
answer 5.1 questions 1-7