1. Genetics
Heredity
Genes
DNA
Chapter Introduction

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?
Lesson 2 Reading Guide

3. Lesson 2 Reading Guide - Vocab
Understanding Inheritance
gene
allele
phenotype
genotype
homozygous
heterozygous
Punnett square
incomplete dominance
codominance
polygenic inheritance
Lesson 2 Reading Guide - Vocab

4. What Controls Traits
150 years ago, Mendel proposed that two factors (one from each parent) control heredity.
The factors that control heredity are contained in chromosome pairs, one from each parent.
Chromosomes
Lesson 2

5. What Controls Traits (cont.)
A gene is a section on a chromosome that has genetic information for one trait.
The different variations of a gene are called alleles. Each chromosome has one allele (variation) for every gene.
The two chromosomes in an offspring cell may have the same or different alleles (variations) of a gene.
Gene
Alleles
Lesson 2

6. “Mom”
“Dad”
Lesson 2

7. What Controls Traits (cont.)
The phenotype is how a trait is expressed and observed.
The genotype is the genetic makeup that determine the phenotype.
Phenotype
Genotype
Lesson 2

8. What Controls Traits (cont.)
phenotype
from Greek phainein, means “to show”
Lesson 2

9. What Controls Traits (cont.)
When the two alleles of a gene are the same, the genotype is homozygous.
When the two alleles of a gene are different, the genotype is heterozygous.
Homozygous
Heterozygous
Lesson 2

10. What Controls Traits (cont.)
Scientists use uppercase and lowercase letters as symbols to represent the alleles in a genotype.
How do alleles determine the expression of traits?
Lesson 2

11. Modeling Inheritance
A Punnett square is a model used to predict the probabilities of genotypes and phenotypes of an offspring.
Punnett square
Lesson 2

12. Modeling Inheritance (cont.)
How can inheritance be predicted?
Lesson 2

13. Other Patterns of Inheritance
Codominance occurs when both the parent’s traits are observed in the offspring at the same time.
Incomplete dominance occurs when the offspring appears to have a blend of both parent’s traits. (The genes are separate, not blended)
Codominance
Incomplete dominance
Lesson 2

14. Other Patterns of Inheritance (cont.)
Multiple alleles occurs when more than two alleles determine a trait.
For example, human blood type is determined by three alleles.
Multiple alleles
Two
Lesson 2

15. Other Patterns of Inheritance (cont.)
Polygenic inheritance occurs when more than one gene determine a trait.
For example, eye color is affected by at least 15 genes.
Polygenic inheritance
One
Lesson 2

16. Other Patterns of Inheritance (cont.)
How does polygenic inheritance differ from Mendel’s model?
Lesson 2

17. Genes and the Environment
The phenotype is also affected by both the genes and the environment (i.e. non-genetic or non-inheritable factors).
Some examples of environmental factors that affect phenotype are soil type that a flower is growing in, time of year that a butterfly develops, or family upbringing.
Lesson 2

18. The genes for traits are located on chromosomes.
Lesson 2

19. Geneticists use Punnett squares to predict the possible genotypes and phenotypes of offspring.
In polygenic inheritance, traits are determined by more than one gene and have many possible phenotypes.
Lesson 2

20. What is the name for different forms of a gene?
A. alleles
B. phenotypes
C. genotypes
D. chromosomes
Lesson 2

21. What is the genotype when two alleles of a gene are the same?
A. heterozygous
B. dominant
C. homozygous
D. recessive
Lesson 2

22. What occurs when both alleles can be observed in a phenotype?
A. incomplete dominance
B. homozygous
C. polygenic
D. codominance
Lesson 2

23. Homework Super Power Type Dad’s Allele (Sperm) Mom’s Allele (Egg)
Genotype
(Child’s DNA)
Phenotype
(Observed)
Spider powers S
Laser eyes L l
Telepathy t
Wings
W w
Jedi force
j j
Time travel
Not observed
Yes, observed
Fill in the blanks above, create last two super powers, then draw the super hero

24. Homework
Draw 3 Punett Squares to cross and write down the offspring probabilities of these super heroes below:
Superman (X-ray vision) with Wonder Woman (no x-ray)
Captain America and Black Widow (both heterozygous for super strength)
Spiderman (homozygous) with Mary Jane (no powers)