1. Genetics: the Scientific Study of Inheritance
Mendelian Genetics

2. Gregory Mendel: Father of Genetics
1860’s people supported one of two notions
Blending theory of Inheritance
Pangenesis
The work of Gregory Mendel would refute both!

3. Gregory Mendel: Father of Genetics
Austrian Monk ( )
Studied how traits were passed
from one generation to another
Used pea plants since:
Express contrasting traits (tall/short, smooth/wrinkled)
Easy to grow and control reproduction
Self pollination or cross-pollination (pollen from one plant to pistil of another plant)

4. Gregory Mendel: Father of Genetics
First Experiment:
Used Pure bred Tall and Pure Bred Short
Cross-pollinated them, harvested seeds and planted them
First Generation plants (F1), were ALL tall
He repeated with several contrasting traits, each time the F1 showed only one trait

5. Contrasting Traits in pea plants
Page 156, fig 6.5
Conclusion:
Law of Dominance: Traits shown in the F1 generation were Dominant and traits that were masked were Recessive
Dominant traits: capital letters, eg T for tall
Recessive traits: lower case letter, eg t for short

6. Some others,
see handout

7. Recall: You have two copies of each chromosome
One Maternal and one Paternal copy of each of the 22 chrom.
Thus for any gene located on the maternal chromosome 1, you have a copy of it on the paternal chromosome 1!

8. A Couple Key Terms
Gene: specific packets of DNA, units of inheritance, passed from one generation to another. All genes have 2 forms called alleles.
Allele: one form of a gene for a specific trait. E.g. blue vs brown eyes
Phenotype: Observable trait, what we see
Genotype: types of alleles present; e.g. TT, Tt produce tall plant, tt short plant

10. Gregory Mendel: Father of Genetics
Second Experiment:
Allowed self pollination of Tall F1 generation plants to see if traits were lost forever or not being expressed
F2 generation had 75% tall and 25% short
Phenotypic Ratio of 3:1;
3 tall: 1 short

11. Gregory Mendel: Father of Genetics
His Hypothesis
Contrasting traits caused by internal ‘factors’ (known as genes)
Each offspring inherits 2 types of factors, now known as alleles

12. Gregory Mendel: Father of Genetics
If purebred, plant inherits 2 identical copies, said to be
Homozygous: genotype with identical alleles, e.g. TT (tall) or tt (short)
Hybrid plants inherit 2 contrasting traits, said to be
Heterozygous: genotypes with different alleles, e.g. Tt
These plants will appear tall since tall is dominant

13. Gregory Mendel: Father of Genetics
Mendel’s First Law: The Law of Segregation
An individual contains genes in pairs. These pairs segregate and are distributed into different sex cells. Each parent can only contribute one member of a pair to offspring

14. SUMMARY Terms to know: Gregory Mendel: Gene Alleles Genotype Phenotype
Homozygous
Heterozygous
Dominant
Recessive
Gregory Mendel:
Father of Genetics
Law of Dominance
Law of Segregation

15. Let’s have a look at how Mendel did this!
Monohybrid Crosses:
A cross involving a single trait, e.g. Height, thus only one pair of alleles
Punnett Square:
A chart used by geneticists to show the possible combinations of alleles in offspring . Helps organize results of a cross between individuals.

16. Using a Punnett Square Determine the Dominant and Recessive trait
Write down genotypes of the parents
List possible gametes each parent produces
Complete the Punnett square