1. HEREDITY and CHROMOSOMES
GENETICS
HEREDITY and CHROMOSOMES

2. CHROMOSOMES
Contain genetic information for organism
Made of DNA

3. GENES Encode for traits of an organism
Alternate form of a gene is an allele
You have 2 alleles for each trait- one from your mother and one from your father

4. ALLELES Alleles can be dominant or recessive.
Your genotype includes all of the alleles that you carry.
Your phenotype
is the visible
evidence of your
alleles.

5. Ex: EYE COLOR Brown eyes are dominant over lighter colored eyes.
In order for brown
eyed parents to
have a blue
eyed child, they
both need to
carry the
recessive allele
for blue eyes.

6. Dominant vs. Recessive
Dominant alleles are expressed in the organism’s phenotype.
Recessive alleles are only expressed in the organism’s phenotype if there are two copies of the recessive allele.

7. PUNNETT SQUARES Monohybrid Cross (One Trait)
You are given the genotype of the male and the female of a species. You should be able to predict likely phenotypes and genotypes of the offspring.
Example: Fur color of mice
T-dominant tan
t-recessive white
Female Tt, Male Tt

8. Genotypes: What
are the allele
combinations?
TT,Tt,Tt,tt
What is the genotype
ratio?
1:2:1
Phenotypes: What
are the colors of
the mice?
Tan, white
What is the phenotype ratio?
3:1

9. YOUR TURN! B-dominant gray cheeks b-recessive pink cheeks
1. What are the
genotypes?
2. What are the
phenotypes?

10. HOMOZYGOUS VS. HETEROZYGOUS
To be homozygous for 2 alleles
means: 2 copies of the
same allele.
Homozygous dominant:
2 copies of dominant allele.
Homozygous recessive:
2 copies of recessive allele.

11. To be heterozygous for a trait:
One copy of the dominant allele,
and one copy of the recessive one.
The organism will
display dominant
traits, but still
carry the
recessive.

12. INTERPRETING GENOTYPES
Remember-you can interpret the genotype from the description.
G-dominant green feathers
g-recessive yellow feathers
L-dominant long beak
l- recessive short beak
Given: ggLl(female) X Ggll(male)
3. What are the phenotypes of the parents?

13. PREDICTING OFFSPRING in DIHYBRID CROSSES
Separate traits into separate Punnett squares: GgLl(female)X Ggll(male)
MOM
MOM g L l G l Ll G Gg Gg ll
DAD
DAD 1 2
(long) 1 2
(short)
(green)
(green) 4 3 g l 3 4 ll Ll Gg Gg
(long)
(short)
(green)
(green)
1. Green feathers, long beak 2. Green feathers, short beak
3. Green feathers, long beak Green feathers, short beak

14. QUESTIONS! 4. What is the percentage of short beaked offspring?
5. What trait is visible in all offspring?
6. Can you ever have a recessive phenotype when both of the parents have a dominant allele for the trait?

15. Using the following information, create a genotype for the male and female birds:
7.Homozygous dominant color, and heterozygous beak (female)
8.Heterozygous color, and homozygous recessive beak (male)

16. WHERE DO THE ALLELES COME FROM?
Gametes-sex cells with half the amount of genetic information.
In animals, the male sex cell is the sperm and the female is the egg.

17. KARYOTYPES Karyotypes are a map of the chromosomes of an individual.
This is a karyotype of a male human.
Note that there
are 23 pairs of
chromosomes.
The last pair are the
sex chromosomes,
and for a male, they
are XY.

18. Note that this is the karyotype of a female.
There are 23 pairs of chromosomes, the last pair being XX, a genetic female.

19. There are 22 pairs of chromosomes that encode for every trait that the organism will possess, but only 1 pair that indicates the sex of the organism.
These chromosomes encode for autosomes, (body cells).
You might also see them
referred to as somatic cells.

20. GENETIC DISORDERS
Some genetic disorders are a result of extra chromosomes being present, or deletion of some chromosomes.
Extra chromosome at the
21st= Down Syndrome

21. Turner Syndrome is a result of only one X chromosome.

22. MUTATIONS
Mutations occur as a result of a change in a protein sequence.
Some mutations are deleterious, and some are fatal, but some are not.

23. Deletion-where one base is missing
Changes in the protein sequence can occur in various ways. Some examples are:
Deletion-where one base is missing
Ex: ATTGCGAAA  ATGCGAAA
Insertion-where an extra base is added
Ex: ATTGCGAAA  ATTGCGAAGA
All mutations can alter the
amino acids in a protein
sequence, thus possibly
changing the protein
produced.

24. The only mutations that can be passed to offspring are the mutations that occur in the gametes. (Sex cells)

25. PRACTICE QUESTIONS
1. Overexposure to ultraviolet light causes mutations in the DNA of skin cells. The mutated DNA has no effect on offspring because:
A. Changes in skin cell DNA are homozygous recessive.
B. Mutations must occur within the RNA codons.
C. Offspring reject parental skin cells.
D. Only changes to gamete DNA can be inherited.

26. 2. Mutations in DNA molecules occur when:
A. Replication of DNA is exact.
B. A DNA enzyme attaches to an RNA codon.
C. RNA codons are replaced by DNA nucleotides.
D. A change occurs in a DNA nucleotide base.

27. VOCABULARY Chromosome Gene Allele Gamete Dominant Recessive
Homozygous Heterozygous
Genotype Phenotype
Karyotype Mutation
Sex chromosomes Autosomes
XX , XY

28. Answers to questions: 1. Bb, Bb, Bb, Bb 2. Gray cheeks
3.Female-yellow feathers, long beak
Male- green feathers, short beak
4. 50%
5.Green feathers
6.No
7.GGLl (female)
8. Ggll (male)
Practice questions 1 &2- Both are D

29. TEACHER NOTES
Begin with BrainPop- Cellular Life and Genetics; Genetics, Heredity, Genetic Mutations.
Have students take notes on material, as it is heavily tested on TAKS.
Have students answer embedded questions as you go along.
Have students make a vocabulary page with words, definitions and illustrations of those definitions to turn in for extra credit in their science class!