1. Heredity & Reproduction
STANDARD IV: Objective I
Recognize heritable traits that are passed from parents to offspring.
Identify physical traits that are passed from parents to offspring
Recognize how genetic traits including diseases & disorders are passed through generations - including family pedigrees and monohybrid Punnett squares
Identify what happens to DNA code when a mutation occurs and identify major causes of mutations.
Recognize and evaluate the harms and benefits that result when mutations occur.

2. STANDARD IV: Objective 2
Explain how the DNA molecule transfers genetic information from parent to offspring.
Describe the relationships among DNA, genes, and chromosomes.
Describe in basic terms the structure and function of DNA.
Define the genetic purpose for meiosis from generation to generation.
Define and distinguish between dominant and recessive genes and know how each is expressed in parents and offspring.

3. In the 1860’s, Gregor Mendel first discovered the principles of genetics.
Genetics- the branch of biology that studies heredity.
Heredity- the passing on of characteristics from parents to offspring.
By observing pea plants, Mendel was able to successfully predict what traits would be passed on from parent to offspring.
Pollination- the transfer of the male pollen grain to the female organ.
Fertilization- the uniting of male and female gametes.
He also noticed that the pea plants inherited two forms of each gene; one from each parent plant.

4. From his studies, Mendel derived three basic principles:
Law of Segregation: when gametes(sex cells) are formed, the two alleles separate – one allele into one gamete and the other allele into a different gamete
States that during meiosis, the factors that control each trait separate, and only one factor from each pair is passed to the offspring.
Law of Independent Assortment: the alleles for different traits are inherited separately or independently of each other
States that the inheritance of alleles for one trait is not affected by the inheritance of alleles for a different trait if the genes for the traits are on separate chromosomes.
How does Mendel’s Law of Independent Assortment assure genetic diversity?
For most traits there is a dominant and a recessive allele. This is not true for all traits. Some traits have alleles that are equally expressed – for others, there are more than just two alleles – the combination of alleles inherited determines the offspring’s trait.
Noting that genes are located on chromosomes and that chromosomes occur in pairs, it is easy to follow Mendel’s laws. Because only one chromosome from each pair is passed through the gamete to the offspring then only one gene for that trait can be passed from the parent to the offspring. Likewise, knowing that chromosome pairs separate in a random pattern, it is easy to understand that genes too are randomly inherited.

5. Genes
Your characteristics are determined by specific portions of DNA which are called genes.
Genes carry traits to be passed on from one generation to the next.

6. Alternate forms of genes are called alleles.
An allele can be dominant or recessive. A dominant allele will mask (or hide) recessive gene. It is represented with a capital letter. A recessive allele is seen only when no dominant gene is present. It is represented with a lowercase letter.

7. Ff -- gives him freckles
Example of Alleles
An offspring has two alleles for each trait.
A mother might pass a gene for freckles (dominant - F) to her offspring, and the father might pass a gene for no freckles (recessive - f) to the offspring.
Ff -- gives him freckles

8. A pea plant has two alleles for seed color – yellow and green.
The gene for yellow seeds is dominant. The gene for green seeds is recessive.
Possible allele combinations are:
YY – yellow
Yy – yellow
yy – green
In order for the pea plant to produce green seeds, it must inherit two recessive alleles.
Yellow plant
Green plant YY yy Yy

9. The combination of alleles that an individual inherits is called the
The expression of the alleles is the
phenotype.
genotype.
This is how the trait is expressed – green, tall, hairy, etc.
These are the alleles actually present – yy, Tt, BB, etc.

10. homozygous heterozygous
If both alleles for a trait are identical the individual is
If the two alleles for a trait are different the individual is
homozygous
heterozygous
Example: YY yy
Example: Yy

11. Punnett Square
The Punnett Square is a grid used to determine the possible combinations of alleles that the parents may pass to an offspring.
Predicting Genetic Combinations
Mother1
Mother2
Father1
Father2
Mother2/Father1
Mother1/ Father1
Mother1/Father2
Mother2/Father2
A Punnett square shows the possible combinations of the parents’ genes. There are two genes for each trait (one on each homologous chromosome) – a parent will pass only one chromosome from each homologous pair and, therefore, only one gene for each trait.
[The diagram shows how each parent’s gene pair segregates and the possible combinations of the parents’ genes]
Start with Monohybrid Crosses – once all the different types of inheritance are introduced then cover dihybrid cross. (You may have your own sequence – do what works for you)
The hyperlink is to Activity 3: Predicting Genetic Combinations at the access excellence website – this is a great activity!
The arizona website below has wonderful information and problem sets for Monohybrid & Dihybrid Crosses!
Monohybrid Cross – a cross between two individuals involving (or looking at) only one trait such as flower color, lip shape, or freckles.
Dihybrid Cross – a cross between two individuals involving (or looking at) two traits such as flower color and seed shape or widow’s peak and freckles.

12. Application
In certain wasps, a hairy body is dominant over a bald body.
What would be the resulting offspring of a cross between a wasp homozygous for hairy body and a wasp homozygous for bald body?
List the genotype(s) and phenotype(s) of the possible offspring.
Specify the probabilities of each resulting genotype and each phenotypes.

13. Parents: Alleles: B B b Bb RESULTS Bb hairy body 4:0 B – hairy body
b – bald body BB bb
Parents:
B B b Bb
RESULTS
Genotype
Phenotype
Ratio Bb
hairy body
4:0

14. # of offspring with the desired trait out of total # of offspring
Probabilities
are determined by interpreting the
# of offspring with the desired trait
out of total # of offspring
How many are…
¾ or 75% are
The following is an example:
Y – yellow seeds
y – green seeds
1 YY ; 2 Yy
yellow Y y
¼ or 25% are
You may choose to do a Probabilities Lab in which students pair up (representing parents), flip a coin (representing gamete), and record their toss (heads or tails representing genes). Have them toss the coins simultaneously 100 times (you may cut this to 50 tosses but it diminishes the effect) and record their “offspring”. Have them analyze their results. How many had two heads (HH)? How many had a head and a tail (Hh)? How many had two tails (hh)? What are the percentages of each? (it will be the same as the total if they did 100 tosses) Assign a trait the coin such as chin dimple – if chin dimple is dominant (heads) and no dimple is recessive (tails), what are the probabilities of having a child with a chin dimple? No chin dimple?
[This is a wonderful illustration of probability – it makes it easier for the students to visualize what we’re talking about when we say 75% of the offspring show dominant phenotype or ½ of the offspring will be heterozygous.]
Mother
Yy – yellow
Father
Yy - yellow YY Yy yy
green
1 yy Y y
½ or 50% are
heterozygous
2 Yy

15. Monohybrid Cross Practice Problem Set Additional Problems:
Additional Problems:
In humans, tongue rolling is dominant over non-tongue rolling. If a heterozygous roller is crossed with a non-roller, what would be the results?
Find the results of a cross between a heterozygous red tomato plant and another heterozygous red tomato plant. Red is dominant over yellow.

19. Cells containing two alleles for each trait are described as diploid.
A cell with one of each kind of chromosome is called a haploid cell.
Meiosis occurs in the specialized body cells of each parent that produce gametes.
How does meiosis maintain a constant number of chromosomes in the body cell of organisms that reproduce sexually?
Meiosis reduces the number by half and when fertilization occurs the number is restored.

20. Explain how crossing over in meiosis results in genetic variation?
The gamete that contains genes contributed only by the mother is an egg.
Father = sperm
Zygote- the cell produced when a male gamete fuses with a female gamete.
Explain how crossing over in meiosis results in genetic variation?
New combinations of genes leading to an increase in genetic variation in the offspring.
How does knowledge of the events of meiosis explain Mendel’s Law of Segregation?
During meiosis, the homologous chromosome pairs line up and split; then in the second division the chromotids split. This results in only one of the pair of chromosomes(containing the “factor”) in a gamete.

21. Know Fig 10.11
When an area of chromatid is exchanged with the matching area on a chromosome, crossing over occurs.
The exchange of genetic material between homologous chromosomes.
Crossing over results in genetic recombination.
The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction.
Explain how nondisjunction can result in an individual having an extra chromosome.
When this happens one gamete can receive both homologous chromosomes. If this gamete is fertilized by a normal gamete the resulting zygote will have three copies of one chromosome.