Name ___________________________________________________________ Period ______
Chapter 8 Mendel & Heredity Guided Notes
Section 1: The Origins of Genetics
Objectives
 Identify the investigator whose studies formed the basis of modern genetics.
 List characteristics that make the garden pea a good subject for genetic study.
 Summarize the three major steps of Gregor Mendel’s garden pea experiments.
 Relate the ratios that Mendel observed in his crosses to his data.
Mendel’s Studies of Traits

Heredity –
o Example:
Mendel’s Breeding Experiments

Gregor Johann Mendel –
o Worked with –

Genetics –
Useful Features in Peas
1. _
2. _
3. _
Traits Expressed as Simple Ratios

Monohybrid cross –

Mendel’s 3 steps:
1. _
Parental or P generation –
2. _
First filial or F1 generation –
3. _
Second filial or F2 generation –
Mendel’s Results

Each of Mendel’s F1 plants showed

But when the F1 generation was allowed to self-pollinate,

He found a ____:____ ratio of plants expressing the contrasting traits in the F2
generation.
Section 2: Mendel’s Theory
Objectives
 Describe the four major hypotheses Mendel developed.
 Define the terms homozygous, heterozygous, genotype, and phenotype.
 Compare Mendel’s two laws of heredity.
A Theory of Heredity

Each pea has two separate “heritable factors” for each trait-______________________.

When gametes form, each receives only ______ out of the _______factors for each trait.

When gametes fuse, the offspring has_____ factors (now called ________ for each trait.
Mendel’s Hypotheses – Mendelian Theory of Heredity:
1. For each inherited trait, an individual has ____copies of the gene—______________
2. There are alternative versions of genes. Different versions are called its ___________
3. When two different alleles occur together, one of them may be completely expressed,
while the other may have no observable effect on the organism’s appearance.
The expressed form of the trait ________________. The trait that was not
expressed when the dominant form of the trait was present is __________________
4. When gametes are formed, the alleles for each gene in an individual separate
independently of one another. Thus, gametes carry only ____ allele for each trait.
Mendel’s Findings in Modern Terms

Dominant alleles are:

Recessive alleles are:

If the two alleles are the same, the individual is said to be:

If the alleles are different, the individual is:

The set of alleles that an individual has:

The physical appearance of a trait:
The Laws of Heredity

The Law of Segregation (describes the behavior of chromosomes during meiosis).
o

The Law of Independent Assortment
o
Section 3: Studying Heredity
Objectives
 Predict the results of monohybrid genetic crosses by using Punnett squares.
 Apply a test cross to determine the genotype of an organism with a dominant phenotype.
 Predict the results of monohybrid genetic crosses by using probabilities.
 Analyze a simple pedigree.
Punnett Squares

A Punnett square -

The possible gametes are written where?
One Pair of Contrasting Traits

monohybrid cross -

Punnett squares allow for?
Determining Unknown Genotypes

test cross-
Outcomes of Crosses
 Probability -
Probability =
Probability of Specific Allele in a Gamete

The probability that a coin will land on heads is_________
Probability of the Outcome of a Cross

To find the probability that a combination of two independent events will occur________
the separate probabilities of the two events.
Inheritance of Traits

Pedigree-

Why are they helpful?
Pedigree (Video clip)

= male

= female

Lines connect parents to offspring.

Filled circles and squares indicate that the person has a certain trait.

Half filled circles and squares indicate that the person is a carrier
of the trait.

Scientists can determine several pieces of genetic information from a pedigree:
o
Autosomal or Sex-Linked?
AutosomalSex-Linked-
o
Dominant or Recessive?
Autosomal dominantRecessive-
o
Heterozygous or Homozygous?
Section 4: Complex Patterns of Heredity
Objectives
 Identify five factors that influence patterns of heredity.
 Describe how mutations can cause genetic disorders.
 List two genetic disorders, and describe their causes and symptoms.
 Evaluate the benefits of genetic counseling.
Complex Control of Characters/Characters Influenced by Several Genes
 polygenic traitExamples:
Intermediate Characters
Incomplete dominance-

Example:
Characters Controlled by Genes with Three or More Alleles

Multiple alleles-
Comparing Single Allele, Multiple Allele, and Polygenic Traits (Video clip)
What human trait is controlled by multiple alleles?
Which antigens are dominant?
Which allele produces no antigen? ____
Polygenic traits are controlled by more than one gene. Most human traits are polygenic. Ex:
Characters with Two Forms Displayed at the Same Time

Codominance -
Genetic Disorder (Video clip)
X-linked genetic disorders are usually passed from ________________________
Sickle Cell Anemia

An example of a recessive genetic disorder is __________________, a condition
caused by a mutated allele that produces a defective form of the protein hemoglobin.

Helps protect the cells of heterozygous individuals from ______________________.
Comparing X-Linked and Sex-Influenced Traits (video clip)
What chromosome corresponds to sex-linked traits?
How many recessive alleles would a male have to have to exhibit an X-linked trait?
How many recessive alleles would a female have to have to exhibit an X-linked trait?
On what type of chromosomes are sex influenced traits found?
What are sex-influenced traits actually influenced by?
Treating Genetic Disorders

Why undergo genetic counseling?
Gene Therapy

Definition:

1st step:
Ex:
Why?