This document discusses Gregor Mendel's pioneering work in genetics and heredity. Through controlled experiments breeding pea plants, Mendel discovered that traits are passed from parents to offspring through discrete units (now known as genes). He found that some traits are dominant over others, and that traits assort independently during reproduction according to predictable numerical ratios. Mendel's work established the foundations of classical genetics and demonstrated that heredity obeys basic scientific laws.

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