1. Unit 7: Genetics & Heredity

2. What is Heredity?
Heredity is the passing of traits from parent to offspring.
Genes on chromosomes control the traits that show up in an organism.
Genes are separated during meiosis into the egg and sperm.
The different forms of a trait that a gene may have are alleles.
The study of how traits are inherited is genetics.

3. Genetic Traits Examples

4. Who was Gregor Mendel?
Austrian monk, known as “The Father of Genetics”
Studied pea plants
Examined the color, shape and other physical characteristics of plants
Discovered that plants received genetic information from its parents passed down through generations.

5. Mendel’s Findings

6. What are Dominant & Recessive Alleles?
Dominant alleles will cover up, or dominate a recessive allele.
Represented by a capital letter (B)
Only need to inherit one dominant allele for trait to appear
Recessive alleles can be masked by a dominant allele.
Represented by a lowercase letter (b)
Need to inherit two recessive alleles for the trait to appear

7. How do Alleles Determine Traits?
Organisms inherit an allele from each parent to make an observable trait.
Homozygous: Two of the same allele (example: BB, bb)
BB would be “homozygous dominant”
bb would be “homozygous recessive”
Heterozygous: Two different alleles (example: Bb)

8. What are Genotype & Phenotype?
Genotype: the genetic make-up of an organism (represented by letters, Aa, Dd, Rr, RR, DD, etc.)
Phenotype: The way an organism looks or behaves as a result of its genotype (example: red hair, brown eyes, etc.)

9. What is a Punnett Square?
A Punnett square is a tool used to predict results of genetic crosses.

10. How do I Solve a Punnett Square Problem?
1. Determine the genotypes of the parent organisms
2. Write down your "cross" (mating)
3. Draw a Punnett square
4. Split the letters of the genotype for each parent & put them outside of the Punnett square
5. Determine the possible genotypes of the offspring by filling in the Punnett square
6. Answer what the problem is asking for based on the results of your Punnett square

11. Punnett Square Example 1
Mom is homozygous for having freckles (F) and dad (f) has none. Having freckles is dominant over not having freckles. What percentage of their children will have freckles?
The parents’ homozygous genotypes are:
Mom = FF
Dad = ff

12. F F f The parents’ homozygous genotypes are: Mom = F F Dad = f f
SPLIT the parents’ genotypes across the top and the sides of the Punnett square.
F F f
Demonstrate how both parents’ genotypes are placed on the square before determining their children’s possible genotypes.

13. Fill in the Punnett square by dragging down and across the parent genotypes.
Final Answer:
Since all of the children are Ff, 100% will have freckles.
F F Ff Ff f Ff Ff
Allow students to explore how the Punnett Square helps determine the children’s possible genotype(s) and their probability.

14. Punnett Square Example 2
Both mom and dad are heterozygous (Ff) and have freckles. What percentage of their offspring will NOT have freckles?
Their heterozygous genotypes are:
Mom = Ff
Dad = Ff
Conduct a brief question-and-answer session with the slides Coach students in using their knowledge to solve the question step by step.

15. F f
The parents’ heterozygous genotypes are:
Mom = F f
Dad = F f F f

16. F f FF Ff Ff ff F f Final Answer:
There is a 25% (1 out of 4) chance of their child NOT having freckles. FF Ff F f Ff ff
Ask or help students interpret the Punnett Square information into a probability/chance in percentages.

17. Do Mendel’s Observations Apply to all Genes?
No… some genes are neither dominant nor recessive.
Incomplete dominance: the inherited alleles from the parents are blended together in the offspring.
Codominance: both alleles are expressed in the offspring.
Multiple alleles: when a trait is controlled by more than two alleles
Polygenic inheritance: when a group of gene pairs act together to produce a trait.

18. What is Incomplete Dominance?
When two parents are homozygous for different forms of trait, the offspring shows an intermediate phenotype.
Use two different capital letters to represent alleles.
Example: four-o’clock plants

19. A red 4-o’clock flower is crossed with a white, resulting in offspring with all pink flowers. What would be the results of a Pink and White flower?
R W WW
RW x WW
Offspring:
RW: pink 50%
WW: white 50% RW W
Ask or help students interpret the Punnett Square information into a probability/chance in percentages. RW WW

20. What is Codominance? Prefix “Co” means together.
When two parents are homozygous for different forms of a trait, the offspring will express BOTH inherited alleles together.
Use two different capital letters to represent alleles.
Examples:

21. In chickens, black and white feather color are codominant
In chickens, black and white feather color are codominant. What would be the resulting genotypes and phenotypes of a cross between two black and white feathered chickens?
B W
BW x BW
Offspring:
BB: black 25%
BW: black and white 50%
WW: white 25% BB BW B W
Ask or help students interpret the Punnett Square information into a probability/chance in percentages. BW WW

22. What are Multiple Alleles?
You can only inherit 2 alleles, but more than that may exist in the population.
Example: Human Blood Type
3 alleles exist for blood type: A, B, and O.
A and B are both codominant
O is recessive

23. What is Polygenic Inheritance?
Polygenic inheritance occurs when a group of gene pairs acts together to produce a trait
Produces a wide variety of phenotypes
Examples in humans include height, hair, skin and eye color

24. What is a Genetic Disorder?
Caused by DNA mutations
Caused by mistakes in meiosis (abnormal chromosome number)
Caused by inheriting a dominant or recessive allele for the disorder
Caused by inheriting a dominant or recessive allele for the disorder on the X-Chromosome (sex-linked)

25. Chromosomal Genetic Disorders
Happens when the incorrect number of chromosomes is inherited from parents.
Examples: Down Syndrome, Turner’s Syndrome, Klinefelter’s Syndrome

26. Dominant & Recessive Genetic Disorders
Offspring must inherit two copies of recessive allele for recessive genetic disorder to appear.
Carriers carry recessive allele but do not show symptoms
Examples: Cystic Fibrosis, Albinism, Tay-Sachs Disease
Offspring only need to inherit one dominant allele for a dominant genetic disorder to appear.
No carriers
Examples: Huntington’s Disease, Marfan Syndrome

27. How is Gender Determined?
Chromosomes that determine sex in humans are XX in females and XY in males.
Females produce eggs with only one X chromosome.
Males produce sperm with either an X or a Y chromosome.
Father’s sperm determines sex of the offspring

28. Sex-Linked Genetic Disorders
Some genes are inherited on the X or Y chromosome, called sex-linked genes.
Color-blindness is a sex-linked disorder caused by a recessive allele on the X chromosome.
Sex-linked genetic disorders are more common in males.

29. What is a Pedigree?
A pedigree is a diagram that follows a trait through generations of a family. Like a “family tree”

30. Pedigree Example

31. What is Genetic Engineering?
Changing the arrangement of DNA that makes up a gene
Using a bacterium or a virus, abnormal DNA can be replaced with normal DNA. Can be used to treat genetic disorders.
Genetically Modified Organisms (GMOs) are plants and other food organisms where the DNA has been altered.