1. Understanding Inheritance
Chapter 5 Lesson 2
Part 1

2. Understanding Inheritance
What determines the expression of traits?
How can inheritance be modeled?
How do some patterns of inheritance differ from Mendel’s model?

3. What controls traits
Mendel concluded that two factors—one from each parent—control each trait.
Mendel’s “factors” are part of chromosomes which exist as pairs—one chromosome from each parent.
Each cell in an offspring organism contains chromosomes from both parents.

4. What controls traits
A gene is a section on a chromosome that has genetic information for one trait.
The different forms of a gene are called alleles. Each chromosome has one allele for every gene on it.
The two chromosomes in an offspring cell may have the same or different alleles.

5. Important Genetic Terms
An allele is one member of a pair or series of different forms of a gene
(the different
forms of a trait
that a gene
may have)

6. What controls traits
An example is the gene for blossom color in many species of flower — a single gene controls the color of the petals, but there may be several different versions (or alleles) of the gene. One version might result in red petals, while another might result in white petals. The resulting color of an individual flower will depend on which two alleles it possesses for the gene and how the two interact.

8. Important Genetic Terms
Geneticists call how a trait appears, or is expressed, the trait’s phenotype.
The two alleles that control the phenotype of a trait are called the trait’s genotype.

9. Important Genetic Terms
Genotype - genetic makeup or allele combinations
when writing
a genotype, the
dominant trait is
always listed first
Scientists use upper-
case and lowercase
letters as symbols to
represent the alleles in a genotype.
RR or Rr

10. Important Genetic Terms
Phenotype - the physical traits of the organism (its physical appearance or visible traits)
Red Rose

11. Genotypes: GG Gg
Phenotypes:
purple-grained
white-grained

12. Important Genetic Terms
When the two alleles of a gene are the same, the genotype is homozygous.
If the two alleles of a gene are different, the genotype is heterozygous.

13. Homozygous (purebred)
an organism usually the result of many generations of such breeding (both alleles the same) (having identical factors)

14. Heterozygous (hybrid)
an offspring that was given different genetic information for a trait from each parent (alleles different)
(having factors that are different)
(has two different alleles for a trait)
a hybrid was the result of a cross between two different homozygous (purebred) organisms

15. Important Genetic Terms
FIRST CROSS
FIRST CROSS
Important Genetic Terms
cross – mating of organisms to test how they inherit traits

16. Important Genetic Terms
first filial generation (F1) - the 1st generation of offspring of a genetic cross
The word filial
comes from filia
and filius, the
Latin words for
“daughter” and
“son.”