1. 5.1-Understanding Inheritance
SBI3U

2. Early ideas about inheritance
Humans have used selective breeding to develop numerous breeds of dogs with specific attributes.
For example the dachshund (hunting) and toy poodle (intelligence and sensitivity).
For thousands of years, many plants and animals species have been selectively bred to have desirable traits.

3. Early ideas about inheritance
Aristotle
B.C.
Theory of pangenesis
sperm and egg contained tiny particles from all body parts.
Antony Van Leewenhook
1677
Discovered living sperm in semen
He believed to see a miniature person inside the head of the sperm
Other Scientists
1800s
They settled on the idea that traits from the parents were irreversibly blended in the offspring

4. Gregor Mendel Austrian monk
used scientific evidence to prove how traits are inherited
Studied inheritance of traits by breeding in carefully planned experiments.
He used pea plants

5. The Experiment
Mendel used 7 different traits in his experiment. These experiments were called monohybrid crosses because only one trait was monitored at a time.

6. Key Terms
Cross: fertilizing a female gamete with a male gamete to control the experiment Trait: specific characteristic or feature exhibited in an organism (i.e. eye colour) P generation: the organisms initially crossed; parent generation F1 generation: the offspring of a cross between the P generation; first filial generation F2 generation: the offspring of a cross between the F1 generation; second filial

7. The Results of Mendel’s True Breeding Crosses…
P generation was crossed (yellow-male X green-female peas)
Results?? F1 generation was all yellow
P Generation
F1 Generation

8. The Results of Mendel’s F1Crosses..
F1 generation was crossed (self-fertilization)
(Yellow pea X Yellow pea)
Results?? F2 generation had a 3:1 ratio of yellow to green
3:1 ratio is called Mendelian Ratio

9. Law of Segregation Each gamete receives one allele from each parent
There are 2 hereditary “factors” for each trait a.k.a. alleles
Diploid organisms have 2 alleles for each gene (maternal/paternal)
Traits are determined by pairs of alleles that segregate during meiosis
Each gamete receives one allele from each parent

10. Law of Segregation Cont’d
Dominant: form of a trait that always appears when an individual has at least ONE allele for it (i.e. yellow peas are dominant)
Recessive: form of a trait that only appears when an individual has TWO alleles for it (i.e. green peas are recessive)

11. Genotype and Phenotype
Alleles are represented using letters:
Uppercase letters = dominant (Y=yellow)
Lowercase letters = recessive (y=green)
3 possible combinations:
YY(homozygous dominant, yellow)
Yy (heterozygous, yellow)
yy (homozygous recessive, green)
*Note: Capital letter is always written first

12. Genotype and Phenotype Cont’d
Genotype: the combination of alleles for a given trait ( ie. YY, Yy, yy)
Phenotype: the physical traits of an organism ( ie. Yellow or green)

13. CHECK YOUR UNDERSTANDING…
1. When Mendel put pollen from tall plants into the flowers of short plants, the seeds produced an F1 generation with all tall plants. But the short trait was not lost. How did Mendel demonstrate this?
He showed that self-pollinating F1 plants produced all medium size plants
He showed that self-pollinating F1 plants produced 1/4 short and 3/4 tall plants
He knew that the short plants had recessive genes
He showed that self-pollinating plants produced plants of all sizes from tall to short
He knew that the tall gene covered up the short gene
C and E are both correct

14. CHECK YOUR UNDERSTANDING…
2. We can deduce (figure out) from Mendel's data that heredity as one allele from each parent, because
you can see the individual genes for the two traits under the microscope.
Mendel told us that this was true from his experimental findings with crossed pea plants
a trait that disappears in the F1 generation reappears in the F2 generation from self-pollinated F1 plants (at the ratio of 1:3)
a trait that blends in the second generation will separate in the third generation
plants in the F2 generation don't breed true

15. CHECK YOUR UNDERSTANDING…
3. Match the following:
i) allele
ii) homozygous
iii) heterozygous
Plants with green seeds produce only green seeded offspring in the next generation.
The gene controlling height comes in two forms, one producing tall plants, the other producing short plants.
Plants with yellow seeds produce yellow and green seeded offspring in the next generation.

16. CHECK YOUR UNDERSTANDING…
4. An allele that is expressed even when paired with a different allele is the version of that gene.
normal
abnormal
recessive
dominant
chromosome

17. CHECK YOUR UNDERSTANDING…
5. An allele that is not expressed when paired with a different allele is the version of that gene.
normal
abnormal
recessive
dominant
chromosome

18. What You Should Know… Early theories Gregor Mendel’s experiment
P, F1, and F2 generation
Law of Segregation
Difference between dominant and recessive
Genotype vs. phenotype

19. Homework:
Read and make notes 5.1
Pg. 205 #1-6
pg 207 #1-2, 6, 11, 12