1. Chapter 12 Who Was Gregor Mendel?
Gregor Mendel was a monk, born in 1822 in Austria.
He performed many scientific experiments in the monastery garden.
Discovered the principles of heredity, the passing of traits from parents to offspring.
“Father of genetics”
Chapter 12

2. Mendel’s experiments
Mendel used garden pea plants for his experiments.
Self-Pollinating Peas have both male and female reproductive structures. So, pollen from one flower can fertilize the ovule of the same flower.
stigma
anther
Pistil

3. Pea plants can also cross-pollinate
Pea plants can also cross-pollinate. Pollen from one plant fertilizes the ovule of a flower on a different plant.
The image shows
cross-pollination
and self-pollination.

4. Mendel studied the characteristic of peas.
A characteristic is a feature that has different forms in a population.
Ex. Seed shape, eye color
Different forms of a characteristic are called traits.
Ex. Round or wrinkled.

5. A Great Idea
Mendel knew that factors that affect traits exist in pairs.
The instructions for an inherited trait are called genes.
RR= gene for round peas
The different forms of a gene are alleles.
You get two for each gene. One from mom and one from dad.
R = round

6. Mix and Match
Mendel would pollinate wrinkled seed plants with round seed plants to see what would happen. RR rr

7. White flower gene disappears
Mendel’s Discoveries
One trait was always present in the first generation, and the other trait seemed to disappear.
Ex. Only purple flowers form, white would disappear.
Parents (P) pp PP
White flower gene disappears
Offspring (F1)

8. Mendel called the trait that appeared the dominant trait.
The trait that disappeared was called the recessive trait.
Parents (P) pp PP
recessive
Dominant

9. Dominant traits occur most often and masks the expression of other alleles.
A recessive trait or allele is expressed only when two recessive alleles for the same characteristic are inherited.
(P) Parents
dominant
recessive +
Kid (F1)

10. B b + Dominant allele gets a capital letter.
recessive + Bb
Dominant allele gets a capital letter.
Recessive gets a lower case. B b
gene

11. Phenotype An organism’s appearance is known as its phenotype
Phenotype An organism’s appearance is known as its phenotype. Genes affect the phenotype.
What you see
hair
height
nose
ears

12. BB = brown hair bb = red hair
Genotype The combination of inherited alleles together form an organism’s genotype.
BB = brown hair
bb = red hair
genotype
Phenotype

13. A person with two dominant or two recessive alleles is said to be homozygous.
A person that has the genotype Bb is said to be heterozygous.
bb= blond
Bb= black
homozygous
heterozygous
purebred
hybrid

14. Recessive gene disappears Recessive gene reappears
Mendel’s Final Discovery pp PP
Parents (P)
Offspring (F1)
Offspring (F2)
purebred
Recessive gene disappears
Recessive gene reappears
Lost trait always reappears in 2nd generation offspring

15. Punnet Squares

16. Punnett Squares are used to organize all the possible genotype combinations of offspring from particular parents.
Parents pp PP

17. True-breeding = homozygous P= purple, dominant p=white, recessive
* All heterozygous hybrids
Female
Male
Possible offspring
1. Pp
2. Pp
3. Pp
4. Pp
True-breeding = homozygous
P= purple, dominant
p=white, recessive

18. Possible offspring
1. PP
2. Pp
3. Pp
4. pp
Heterozygous = Pp
Flower pollinating itself

19. What Are the Chances?
Probability is the mathematical chance that something will happen.
Probability is most often written as a fraction of percentage.

20. Flower pollinating itself
Possible offspring
1. PP 1/4
2. Pp
3. Pp
4. pp 1/4
Heterozygous = Pp
Flower pollinating itself
1/2

21. True-breeding = homozygous P= purple p=white
Female
Male
Possible offspring
1. Pp
2. Pp
3. Pp
4. Pp
True-breeding = homozygous
P= purple p=white
100%
Genotypic ratio

22. Gene Interactions and Variations
Incomplete Dominance Researchers have found that sometimes one trait is not completely dominant over another.
One Gene, Many Traits Sometimes one gene influences more than one trait.
Many Genes, One Trait Some traits, such as the color of your skin, hair, and eyes, are the result of several genes acting together.

23. Phenotype vs. Genotype Genotype Pp P P p Pp Pp Phenotype Pp Pp
Purple flower Pp
P P p
Pp Pp
Phenotype
Pp Pp

24. The Importance of Environment
Genes aren’t the only influences on traits. A combination of things determine an individual’s characteristics.
Your environment also influences how you grow.
Lifestyle choices can also affect a person’s traits.

25. Sex Chromosomes carry genes that determine sex.
Human females have two X chromosomes.
Human males have one X chromosome and one Y chromosome.

26. Sex-Linked Disorders The genes for certain disorders, such as colorblindness, are carried on the X chromosome.
Genetic Counseling Genetic counselors use pedigrees to trace traits through generations of a family. These diagrams can often predict if a person is a carrier of a hereditary disease.
Selective Breeding In selective breeding, organisms with desirable characteristics are mated.