1. Mendel's Laws
of Genetics
How traits are passed
from parents to
offspring.

2. Genetics
 A gene is a
segment of DNA
that codes for a
protein which
determines one
particular trait
 Genetics is the
study of how genes
are passed on from
parents to offspring

3. Differentiation
 Genes signal
different cells to
create proteins
that give them
unique shapes
& functions
 These cells grow
& divide to make
tissues that form
the organs of the
developing baby

4. Fertilization: new life is formed
 Life begins when two gametes (sperm + egg) join
 A complete set of chromosomes results (23 + 23)
 The zygote starts as a single cell, but soon begins
to divide (via mitosis = identical cells)
 Genes are "turned" on and off, causing cells to
differentiate (change to have different forms/jobs)

6. Heredity & Inherited Traits
 The chromosomes from your mom and dad have
given your cells instructions to make YOU!
 Each characteristic you inherited from your
parents is called a trait (eye color, earlobe shape,
height, personality traits, etc.)
 For each trait, you have
a pair of alleles (one
from your mother and
one from your father)

7. Alleles: variations of a gene
Gene Alleles
Eye Color Blue, brown, green,
hazel
Pea height Tall, short
Pea color Yellow, green
Flower position Axial, terminal

8. Gregor Mendel
 An Austrian scientist-turned-monk
noticed patterns in the monastery's
garden
 Studied the inherited traits of pea
plants and found predictable,
numerical ratios in the offspring
 Observed some traits were
dominant over others (i.e. yellow
peas overpowered or occurred
1822-1884 more often than green pea seeds)

9. Mendel's Experiments
 He wondered if traits seen in different
generations of pea plants were
• determined by environmental factors (soil
composition, temperature, sunlight)
OR
• "handed down" by parents (chromosomes weren't
even discovered yet, so he had no idea how)
 In his highly controlled experiments, he tested the
hypothesis that each trait was determined by a
set (not one, but TWO) inherited factors from
each parent
 Do you see the Scientific Method at work here?

10. Dominant and Recessive Traits

11. Mendel’s Crosses
 Observed phenotype,
the outward expression
of the genes
 the F1 generation are
tall, showing that trait is
dominant
 The dwarf plant has the
recessive trait (it is
overpowered by the tall
allele)

12. Genotypes: Genes and Alleles
 The genetic make-up
of an organism is its
genotype
 Every organism is
diploid (has 2 copies
of each chromosome)
 Each trait is
designated by a
different letter
 DOMINANT ALLELES
ARE CAPITAL
LETTERS
 recessive alleles are
lowercase letters

13. Genotype determines Phenotype
 Homozygous means the two alleles are the same
 Heterozygous means the two alleles are different
Genotype Genotype Phenotype
Homozygous TT Dominant
dominant
Homozygous tt Recessive
recessive
Heterozygous Tt Dominant

14. Punnet Square: Monohybrid Cross
 Used to predict the outcome of a genetic cross

15. Dihybrid Cross
 What happens to two genes on
different chromosomes?
 Homologous pairs of meiotic
chromosomes line up randomly at the
equatorial plane in Metaphase I
 The two traits separate during
meiosis, resulting in offspring with
different combinations of traits
 This results in four different possible
combinations of chromosomes and
genes in the gametes

16. The Law of
Segregation
 Diploid
chromosomes of
parents undergo
meiosis
 Alleles separate as
they become
haploid egg or
sperm
 They are combined
again during
fertilization to
produce a diploid
offspring

17. Which traits are dominant?

18. Independent Assortment & Segregation