1. Genetics & Inheritance
Meiosis and Mendelian Genetics
PHA: Biology 9
Moretti and Dickson

2. Major Genetics Terms Gene: Alleles: Chromosome:
A section of DNA that holds instructions for making one protein
Ex: gene for hemoglobin protein
Alleles:
Different versions of a gene
Ex: normal hemoglobin allele vs. mutated hemoglobin allele
Chromosome:
A long strand of DNA, coiled and wrapped up, that contains many genes
Homologous Chromosomes:
 A pair of chromosomes that contain the same genes but not necessarily the same alleles

3. Human body cells contain…
Over 20,000 genes stored on 46 chromosomes
23 pairs of homologous chromosomes

4. Asexual vs. sexual reproduction
Asexual Reproduction
One parent
Parent and offspring are genetically identical (clones)
Reproduce using MITOSIS
Sexual Reproduction
Two parents
Offspring are genetically different from parents
Reproduce using MEIOSIS (makes eggs and sperm) and FERTILIZATION (egg and sperm join)

5. Sexual reproduction cycle:

6. Major Genetics Terms
Diploid: A cell that contains TWO COPIES of every chromosome (in homologous pairs)
All human body cells except gametes are diploid.
Haploid: A cell that contains ONE COPY of every chromosome
Gametes are haploid. 
 Gametes: Egg or sperm cells, used in sexual reproduction.
Contain HALF the number of chromosomes as all other body cells (they are haploid!)
Meiosis: The process of making gametes.
Separates homologous chromosomes into different cells
1 Diploid cell  4 Haploid cells

7. Studying Diagrams Activity
In your notebooks, respond to these questions:
What is the difference between Metaphase in Mitosis and Metaphase I in Meiosis? Why are the chromosomes aligned differently in both of these stages?
Are the cells diploid in Mitosis during this phase? Meiosis? Why?
What do you notice about the homologous chromosomes Metaphase II of Meiosis? Why are the chromosomes aligned the way they are?
Are the cells in Metaphase II diploid or haploid? Why?

8. 46 46 46 46 23 23 Haploid 46 Chromosomes in Humans Diploid Chromosomes
Image:
Metaphase I
Metaphase
Metaphase II 46
Chromosomes
in Humans 23
Chromosomes
in Humans 23
Chromosomes
in Humans
Haploid
46 Chromosomes in Humans
Diploid

9. Karyoptyping Dry-Lab
A karyotype is an enlarged photograph of a person’s chromosomes.
Task #1 – Circle at least 3 pairs of homologous chromosomes in the karyotype below. When you circle each chromosome, draw a line connecting it to its homologous pair.

10. Review Summary of meiosis:
DNA is replicated once
Chromosomes are divided twice:
Meiosis I: Homologous chromosomes separate
Forms 2 haploid cells
Chromosomes still have sister chromatids
Meiosis II: Sister chromatids separate
Final result:
4 haploid gametes with HALF the number of chromosomes as the original cell
Gametes

11. Meiosis generates genetic diversity between gametes
Two ways:
Independent alignment of homologous pairs during Metaphase I.
A cell with 2 homologous pairs yields 4 possible gametes.
How many are possible with 23 homologous pairs?

12. 2. Crossing over during Prophase I:
One sister chromatid trades a section of DNA with its homologous partner.
Creates new combinations of alleles on chromosomes.
Can happen at multiple places along the chromosome, allowing for a nearly infinite number of different gametes.