Mendel’s
Laws:
Patterns of
Inheritance
Introduction
•
Attempts to explain inheritance
date back at least to the ancient
Greek physician Hippocrates. He
suggested that particles called
“pangenes” travel from each part of
an organism’s body to the eggs or
sperm and then are passed to the
next generation.
01
• Objectives •
• Variations on Mendel’s Laws
• The Chromosomal Basis of
•
Inheritance
Sex Chromosomes and SexLinked Genes
BEFORE WE START DO YOU
KNOW WHAT HEREDITY MEANS?
The transmission of traits
(inherited features) from one
generation to the next.
The field of genetics, began in the
1860’s, when an Augustinian
named Gregor Mendel
deduced the fundamental
principles of genetics by
breeding garden peas.
Genes, retain their
individuality
generation after
Mendel probably chose to
study garden peas because
they had short generation
times, produced large numbers
of offspring from each mating,
and came in many readily
distinguishable varieties.
• Hmmm, Mendel.
A
heritable feature that varies among
individuals within a population, such as
flower color in pea plants or eye color in
humans.
A variant of a character found
within a population, such as
purple or white flowers in pea
plants.
The offspring of two different varieties are called
hybrid.
The cross-fertilization itself is referred to as a
hybridization, or simply a genetic cross
The true-breeding parents are called the “P”
generation (P for parental)
Their hybrid offspring are called the generation
F1 (F for filial)
When plants self-fertilize or fertilize each other,
their offspring are the F2 generation.
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CLASS
OBJECTIVES
Understand Mendel’s first and second laws and how they apply to the
heredity patterns Mendel observed in pea plants.
Understand the term allele and the relationship between dominant and
recessive alleles.
Know the difference between monohybrid and dihybrid crosses.
Understand the link between genotype and phenotype.
Understand the difference between a character and a trait.
VOCABULARY
Develop the following words, using the correct meaning and
Illustrate 10 of them (each illustration should have a title)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Heredity
Dominant Allele
Recessive Allele
Probability
Genotype
Phenotype
Quantity
Factor
Experiment
Genetics
Traits
DNA
RNA
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
Genes
Punnet Square
Chromosomes
Variations
Mitosis
Meiosis
Chromatids
Cells
Replications
Somatic Cell
Sex-Linked Genes
Mutations
Meiosis and
Crossing Over
Chromosomes are matched in
homologous pairs
In humans, a typical body cell,
called a somatic cell, has 46
chromosomes. Chromosomes
undergoing mitosis are
condensed enough to be
viewed with a microscope and
arranged into matching pairs
HOMOLOGOUS
CHROMOSOMES
Two chromosomes in a pair –
normally one inherited from
the mother and one from the
father.
Using a testcross to determine genotype
Testcross: The mating
between an individual of
unknown genotype for
particular character and an
individual that is
homozygous recessive for
that same character.
Suppose you have a
chocolate Lab. Referring to
Figure 9.5B, you can tell that
its genotype must be bb. But
what if you had a black Lab?
It could have one of two
possible genotypes—BB or
Bb—and there is no way to
tell simply by looking at the
dog
Variations on
Mendel’s Laws