1. Mendelian Genetics
5 B - Basic Genetics

2. Mendelian Genetics
5.4
Gregor Mendel
Father of genetics

3. Gregor Mendel Born in Austria (1822) Monk (1843)
Selective breeding on pea plants (1857)
Wrote paper outlining his conclusions (1865)
Abbot of the monastery (1868)
Died of a kidney disorder (1884)
Scientist rediscover Mendel’s papers (1900)

4. Gregor Mendel
Traits Mendel studied
See Table 5-2 on page 113

5. Mendel’s Experiments P1 generation (parental generation)
Self-pollinating plants that bred true for a particular trait
F1 generation (1st filial generation)
Resulting plants from two P1 plants being cross-pollinated
F2 generation (2nd filial generation)
Resulting plants from two F1 plants being allowed to self-pollinate

6. Mendel’s Observations
The F1 generation only showed one trait.
The F2 generation always showed both traits and always in a 3:1 ratio.

7. Mendel’s Conclusions

8. 1. Concept of Unit Characteristics
Traits in a pea plant are caused by factors occurring in pairs

9. 2. Concept of Dominant & Recessive
One factor in the pair is dominant to the other factor.
The dominant factor will masked the appearance of the recessive factor when both are present.

10. 3. Concept of Segregation
Organisms form gametes for reproduction.
Each gamete has only one factor from each pair.

11. Genetic Terms
Phenotype: the expression of a gene in an organism; represented by words
Genotype: the pair of genes an organism has; represented by two letters

12. Genetic Terms
Allele: genes which have equivalent positions on homologous chromosomes
Locus: the specific site on a chromosome where a particular gene is located
Homozygous: both alleles for a trait are the same
Heterozygous: the two alleles for a trait are different
Test cross: mating an organism that has a dominant phenotype but an unknown genotype with an organism that has a recessive phenotype
Pedigree: a chart that geneticists use to trace the presence or absence of a trait in a number of generations

13. Genetic Terms
Monohybrid: a cross between two organisms in which the researcher is only interested in one set of alleles
Dihybrid: a cross between two organisms in which the researcher is interested in two sets of alleles

14. Genetic Terms
Punnett squares: depicts genetic crosses and determines the probability of an offspring having a particular trait
Named after Reginald Punnett, its designer

15. Completing Genetic Cross
Write genotypes correctly
Always have 2 letter per trait
Use 1st letter of dominant trait
Example: green/yellow pods use G or g
Capitalize dominant allele
Green pods use G
Yellow pods use g
BE CAREFUL (Not Messy) with letters!
Lowercase recessive allele
Homozygous genotype – 2 capital or 2 lowercase letters
Heterozygous genotype – 1 capital and 1 lowercase letter

16. 5 Step Method Write the genotypes of BOTH parents Do a Punnett Square
Write the possible genotypes along with the probability for each one
Write the possible phenotypes along with the probability for each one
Make sure the question has been answered
What about the ratios?

17. Practice
What type of pea plant would one expect in their fields if they cross a homozygous plant with yellow peas and a heterozygous plant with yellow peas?

18. Practice (use chart on page 113)
Write the genotype for:
Homozygous round pea
Heterozygous green pod
Homozygous white seed coat
Heterozygous green pea
A pea plant with constricted pods
A pea plant homozygous for colored seed coats
A pea plant homozygous for yellow pods
A pea plant heterozygous for round peas

19. Practice (use chart on page 113)
Write the phenotype for: Aa Gg RR Cc

20. Practice (use chart on page 113)
Show your work as you work the crosses
What offspring do you expect from two wrinkled peas of the pea plants?
What offspring would you expect from two pea plants that are both heterozygous for inflated pods?

21. Practice
How would you determine if a black cat is homozygous (BB) or heterozygous (Bb) for coat color?

22. Pedigree
Circle = female Square = male Shaded = dominant phenotype Unshaded – recessive phenotype ? = unsure