1. KEY CONCEPT Genetics – the study of heredity (passing traits from parents to offspring)

2. Gregor Mendel laid the groundwork for genetics.
Genes – the chemical factors that determine traits
Trait – a distinguishing characteristic that is inherited
Gregor Mendel showed that traits are inherited as discrete units.
Mendel used pea plants because he could easily manipulate their reproductive parts.

3. Mendel’s data revealed patterns of inheritance.
Mendel made three key decisions in his experiments.
use of purebred plants
control over breeding
observation of seven “either-or” traits
Pure-bred or true-bred traits
are from a single parent or the
same from 2 parents.
Hybrid – the traits from each
parent are different.

4. Mendel used pollen to fertilize selected pea plants.
P generation; parent generation – original plants
- F1 generation; first filial generation
F2 generation; second filial generation
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.

5. Mendel allowed the resulting plants to self-pollinate.
Among the F1 generation, all plants had purple flowers
F1 plants are all heterozygous
Among the F2 generation, some plants had purple flowers and some had white

6. Mendel observed patterns in the first and second generations of his crosses.

7. Mendel drew three important conclusions.
1. traits are inherited as discrete units
2. Organisms inherit 2 copies of each
gene; one from each parent
3. Organisms donate only 1 copy of
each gene to their gametes.
So, the 2 genes separate, or
segregate, during gamete
formation
(#2 and #3 are Mendel’s First Law – the Law of Segregation) .
purple
white

8. KEY CONCEPT Genes encode proteins that produce a diverse range of traits.

9. The same gene can have many versions.
A gene is a piece of DNA that directs a cell to make a certain protein.
Each gene has a locus, a specific position on a pair of homologous chromosomes.

10. An allele is any alternative form of a gene occurring at a specific locus on a chromosome.
Each parent donates one allele for every gene.
Homozygous describes two alleles that are the same at a specific locus.
Heterozygous describes two alleles that are different at a specific locus.

11. Genes influence the development of traits.
All of an organism’s genetic material is called the genome.
A genotype refers to the makeup of a specific set of genes.
A phenotype is the physical expression of a trait.

12. ***The principle of dominance states that some alleles are dominant and some are recessive.
Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.
Dominant genes (alleles) can mask a recessive trait.
When Mendel crossed a purebred tall plant with a purebred short plant, the F1 plants inherited an allele for tall and for short.
They will have a tall phenotype because tall is dominant.

13. KEY CONCEPT The inheritance of traits follows the rules of probability.

14. Punnett squares illustrate genetic crosses.
The Punnett square is a grid system for predicting all possible genotypes resulting from a cross.
The axes represent the possible gametes of each parent.
The boxes show the possible genotypes of the offspring.
The Punnett square yields the ratio of possible genotypes and phenotypes.

15. A monohybrid cross involves one trait.
Monohybrid crosses examine the inheritance of only one specific trait.
homozygous dominant-homozygous recessive: all heterozygous, all dominant
FF X ff

16. Ff X Ff
Phenotypic ratio – 3 purple:1 white (dominant:recessive)
Genotypic Ratio —1 FF:2Ff:1ff (homozygous dominant: heterozygous:homozygous recessive)

17. A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype.
If you want to determine if a tall pea plant is homozygous or heterozygous, it should be crossed with a short plant. If all offspring are tall, then it is homozygous. If half are short, the parent plant was heterozygous.

18. Heredity patterns can be calculated with probability.
Probability is the likelihood that something will happen.
Probability predicts an average number of occurrences, not an exact number of occurrences.
Probability =
number of ways a specific event can occur
number of total possible outcomes
Probability applies to random events such as meiosis and fertilization.
**The larger the number of individuals, the closer the resulting offspring numbers will get to the expected values.

19. Dihybrid crosses examine the inheritance of two traits.
From these, Mendel formed his second law, the Principle of Independent assortment.
The law of independent assortment states that genes from different traits can segregate independently of each other during formation of gametes.
YyRr X YyRr