1. Gregor Mendel And The Genetic Revolution

2. Genetics What is Genetics?
The study of heredity or the passing on of traits from an organism to its offspring

3. Purebreds and Mutts — A Difference of Heredity
Heredity – The passing of traits from parents to offspring
Genetics is the science of heredity
These black Labrador puppies are purebred—their parents and grandparents were black Labs with very similar genetic makeups. Purebreds always produce offspring with the same form of a trait. In this example black coats.

4. The parents of these puppies were a mixture of different breeds also called hybrids
Their behavior and appearance is more varied as a result of their diverse genetic inheritance

5. The science of heredity dates back to ancient attempts at selective breeding
Until the 20th century, however, many biologists incorrectly believed that
characteristics acquired during lifetime could be passed on
characteristics of both parents blended irreversibly in their offspring

6. Experimental genetics began in an abbey garden
Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants
Stamen
Carpel

7. Why Peas? Mendel used peas to study inheritance because:
True breeding commercial strains were available
Peas are easy to grow
Peas have many easy to observe traits including:

8. Mendel studied seven pea characteristics
FLOWER
COLOR
Purple
White
FLOWER
POSITION
Axial
Terminal
He hypothesized that there are alternative forms of genes (although he did not use that term), the units that determine heredity
SEED COLOR
Yellow
Green
SEED SHAPE
Round
Wrinkled
POD SHAPE
Inflated
Constricted
POD COLOR
Green
Yellow
STEM LENGTH
Tall
Dwarf

9. Why Peas?
Pea flowers are constructed in such a way that they typically self fertilize
Because of this, it is relatively easy to control crosses in peas
Pea flower

10. Why Peas?
Pea flowers are constructed in such a way that they typically self fertilize
Because of this, it is relatively easy to control crosses in peas
Anthers
Pea flower
Stigma

11. Why Peas?
By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas.

12. Why Peas?
By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas.
Snip

13. Why Peas?
By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. .

14. Why Peas?
By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. .

15. Why Peas?
By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. .

16. Mendel’s Results
When crossing purebred purple pea plants with purebred white plants, Mendel got the following results:
In the first filial (F1) generation all offspring produced purple plants
In the second generation (second filial or F2):
There was approximately a 3:1 ratio of purple to white plants

17. Interpreting Mendel’s Results
Because the F1 generation did not produce light purple flowers and because white flowers showed up in the F2 generation, Mendel disproved blended inheritance.
Mendel said that the parents had two sets of genes thus two copies of the flower color gene
Each gene has two varieties called alleles
In the case of the flower color gene the two alleles are white and purple

18. Vocabulary Dominant – a trait that always shows up in the organism
Recessive – a trait that is masked or covered up by a dominant allele
Homozygous – both alleles are the same for the trait
Heterozygous – the alleles are different for the trait
Genotype – gene combination expressed as letters
Phenotype – how the trait looks --- what is visible

19. Interpreting Mendel’s Results
In the F1 generation, the white allele was hidden by the purple “dominant” allele
In the F2 generation, 1/4 of the offspring ended up with two copies of the white allele, thus they were white
Heterozygous parents make gametes either one or the other allele
Homozygous parents can only make gametes with one type of allele
Gametes from the P generation C c
F1 Generation C c
F2 Generation
The F1 Generation is all heterozygous Cc Cc CC Cc Cc Cc Cc cc

20. Mendel’s Results Trait F1 Results F2 Results
Seeds
round/wrinkled
yellow/green
full/constricted
Pods
green/yellow
axial/terminal
Flowers
violet/white
Stem
Tall/dwarf
F1 Results
All Round
All Yellow
All Full
All Green
All Axial
All Violet
All Tall
F2 Results
5,474 Round 1,850 wrinkled
6,022 Yellow 2,001 green
882 Full 299 constricted
428 Green 152 yellow
651 Axial 207 terminal
705 Violet 224 white
787 Tall 277 dwarf
Dominant traits mask recessive traits
Masked recessive traits reappear

21. Mendel’s Hypotheses
Each parent contributes one gene to the next generation from its pair
The gametes separate during formation of gametes (sex cells)
When parents form gametes (sperm or egg), the parent's gene cells separate or segregate

22. Genetic Principles Traits are passed on from one generation to another
Traits are controlled by genes
Some genes are dominant while others are recessive
Dominant genes hide recessive genes when both are inherited
Some genes are neither dominant nor recessive --- incomplete dominance

23. Put on your thinking caps!!
What part of the pea plant did Mendel remove?
Male part- anthers
A trait that always shows up is ________.
Dominant
How a trait looks is known as its________.
Phenotype
If the alleles are the same the trait is _______.
Homozygous
The study of heredity or the passing on of traits from an organism to its offspring is known as the study of ______________.
genetics
A trait that is masked, or does not show
recessive

24. Laws of Genetics Law of Segregation Law of Independent Assortment
One gene from each pair goes to each sex cell
Law of Independent Assortment
Each gene pair for a trait is inherited independently of gene pairs for other traits.
E.g. Hair color independent of height

25. Incomplete Dominance Discovered by Karl Correns – Botanist
Found some genes were not really dominant over others
Traits appear to blend
Correns crossed Red and White flowers and got pink
Ex. Palomino horse is a cross of a white horse and a chestnut horse

26. Independent Assortment
When Mendel crossed peas and looked at two different traits, he discovered that the traits assorted independently
In other words, if he was looking at the height of the plants and the color of the flowers, all four possible combinations of height and flower color were produced:
Tall Purple
Tall white
dwarf Purple
dwarf white

27. Independent Assortment
As long as genes are on different chromosomes, they will assort independently
t c
t C
T c
T C Tc tC tc TC
TtCc
TtCC
TTCc
TTCC
Ttcc
TTcc
ttCc
ttCC
ttcc