1. Meiosis to the Punnett Square

2. How are haploid gamete cells produced from diploid cells?
Your parents have 46 chromosomes each and you have 46 chromosomes.
If you got half of your genes from each parent, how did this happen?
How many chromosomes do a sperm and an egg have?

3. Meiosis
The process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell that become haploid cells.
Involves two distinct divisions; Meiosis I and Meiosis II
One diploid cell becomes 4 haploid cells

4. Crossing Over Prophase I Homologous chromosomes exchange alleles
Produces new combinations of alleles
Causes randomness in gamete formation

5. Meiosis I
Prophase I- Chromosomes pair with same homologous chromosomes to form a tetrad.
Metaphase I- Homologous chromosomes meet in the middle and spindle fibers attach.
Anaphase I- Homologous chromosomes are pulled apart by spindle fibers
Telophase I- Nuclear membrane forms around separated chromosomes to form two nuclei.
Cytokinesis- The diploid cell separates into two haploid cells.

7. Meiosis II starts with two haploid daughter cells
Prophase II- haploid chromosomes with sister chromatid are in the cytoplasm.
Metaphase II- chromosomes meet in the middle of the cell
Anaphase II- Sister chromatid are pulled apart by spindle fibers
Telophase II- Nuclear envelop forms around the chromosomes
Cytokinesis- Results in 4 haploid daughter cells

9. Meiosis animation:
Pay close attention to what “meets” in each metaphase and what separates in each of the two anaphases.

10. Review
Mitosis Both Meiosis

11. Place these items into your Venn Diagram:
Produces diploid cells
Produces haploid cells
Type of cell division
Creates identical cells
Separates homologous chromosomes
Separates chromatids
Creates “daughter” cells
2 rounds of cell division
Only 1 round of cell division
Creates unique cells
Begins with diploid cells
Creates gametes
Creates “body cells”
Has crossing over

12. Genes
Genes are the characteristics contained in the DNA of every cell.
Each gene is made up of 2 alleles- one inherited from each parent.
For instance you may have one brown eye allele inherited from your dad and one blue eye allele inherited from your mom.

13. Kinds of alleles Dominant- Recessive-
These alleles always determine the physical feature of the individual.
These alleles are represented by a capital letter.
Recessive-
These alleles only determine the physical feature of the individual when there is no dominant allele.
These alleles are represented by a lower case letter.

14. Genotype and Phenotype
The genotype of an individual is the description of the actual genetic information for a trait.
The phenotype of an individual is the physical feature observed.

15. Allele Combinations
Every gene is made up of two alleles-one from each parent.
If both alleles are the same, the gene is called homozygous. (BB or bb)
If the alleles are different, the gene is called heterozygous. (Bb)

16. Label the following as homozygous dominant, homozygous recessive, or heterozygous.BB Aa nn Kk GG ff qq Hh

17. Probability and Punnett Squares
Meiosis separates the alleles of a parent into different sex cells (gametes).
For instance: Dad is heterozygous for Brown hair, with a blond hair allele as the recessive. (Bb).
Through meiosis, these alleles are copied and separated into 4 sperm. b B b B

18. Single Trait Crossing
What kind of offspring (kid) would two parents have?
A Punnett Square can help you find out!
Example: Dad is heterozygous (Bb) for Brown hair over blond hair. Mom is also heterozygous (Bb) for brown hair over blond hair.

19. Set up the Square
Dad’s Alleles B b B
Mom’s alleles b

20. Set up the Square B b B BB Bb b Bb bb Dad’s Alleles
4 possible offspring
Mom’s alleles b Bb bb

21. What do these results mean?
¼ or 25% chance of an offspring with homozygous dominant genes for brown hair.
½ or 50% chance of an offspring with heterozygous genes for brown hair.
¼ or 25% chance of an offspring with homozygous recessive genes for blond hair.

22. You try it!
1. Dad is heterozygous for Brown eyes over blue eyes. (Ee) Mom is homozygous recessive with blue eyes. (ee) What are the probabilities for the children’s genotypes. What are the probabilities for the children’s phenotypes?

23. Set up the Square
Dad’s Alleles E e e
Mom’s alleles e

24. Dad’s Alleles E e e Ee ee
4 possible offspring
Mom’s alleles e Ee ee

25. ½ or 50% of the children would inherit heterozygous genes for Brown eyes (Ee)
½ or 50% of the children would inherit homozygous recessive genes for Blue eyes (ee)

26. Hmmm…
Is it possible for two Brown haired parents to produce a blond child? Explain.
Is it possible for 2 blue eyed parents to produce a brown eyed child? Explain.
Can you figure out your genotype for hair color? How do you know?

27. Review Questions How is meiosis related to heredity?
What is the difference between heterozygous, homozygous dominant, and homozygous recessive?
Is it possible for two brown haired parents to produce a blond child? Explain.

28. Review cont… What is the difference between genotype and phenotype?
What are the chances that two heterozygous parents with Brown hair(Bb) produce a child that is also heterozygous?

29. Review cont…
In pea plants, round peas are dominant over wrinkled peas. (R and r). What would the offspring of a homozygous dominant, and a homozygous recessive cross look like?
If the offspring from question #6 were to pollinate each other (as plants often do), what would be the genotype probabilities for the offspring?

30. Two Trait Crosses
When looking at two different genes in the same cross, 4 alleles are dealt with.
For instance, a heterozygous haired(Bb), and homozygous recessive eyed(ee) parent would be Bbee.
Through meiosis, there would be 4 possible allele combinations in the sex cells.

31. FOIL!
Just like in math class, the first, outside, inside, and last rule can help you remember.
B b e e
These alleles would produce these four combinations.
Be Be be be

32. What does a two trait cross look like?
Suppose two parents who are both heterozygous haired and heterozygous eyed produce a child. What are the possible genotypes and phenotypes in the offspring?

33. You try it!
A tall (TT) pea plant that produces yellow colored peas (Yy) crosses with a short (tt) pea plant with green colored peas (yy). Create the Punnett square and list the probabilities of each genotype.