1. Chapter Six: Meiosis and Mendel

2. Section One: Chromosomes and Meiosis
Cell Types
Somatic Cells: cells that make up your body tissues and organs
Gametes: sex cells; sperm and eggs

3. Section One: Chromosomes and Meiosis
Homologous Chromosomes: two chromosomes-one from the mother and one from the father- that have the same length and general appearance
Humans have 23 pairs of chromosomes
Have the same set of genes as well
Pairs 1-22 are autosomes: chromosomes that contain genes not directly related to the sex of an organism
Pair 23: sex chromosomes: control the development of sexual characteristics
XX=female
XY=male

5. Section One: Chromosomes and Meiosis
Haploid and Diploid
Sexual Reproduction: involves the fusion of two gametes that result in offspring that area genetic mixture of the parents
Fertilization: fusion of the sperm and egg
Dipolid: the cell has 2 copies of each chromosome
One copy from the mother and one copy from the father
Somatic cells are diploid
Haploid: the cell has only one copy of each chromsome
Sex chromsomes are haploid
X chromosome is always in the egg
Sperm can contain the X or Y chromosme

6. Section One: Chromosomes and Meiosis
Maintaining chromosome numbers is important for the body to function correctly
Meiosis: the form of nuclear division that divides the diploid cell into haploid cells for formation of gametes
Produces gametes
Reduces chromosome number by half
Creates 4 haploid cells

7. Section Two: Process of Meiosis
Homologous Chromosomes and Sister Chromatids
Sister chromatids: duplicated chromosomes that stay attached to each other
Homologous Chromosomes: two chromosomes-one from the mother and one from the father- that have the same length and general appearance

8. Section Two: Process of Meiosis
Two stages: Meiosis I and Meiosis II
Meiosis I
Prophase I, Metaphase I, Anaphase I, Telophase I
MeiosisII
Prophase II, Metaphase II, Anaphase II, Telophase II

9. Section Two: Process of Meiosis
Meiosis I
Prophase I
Nuclear membrane breaks down
Centrosomes and centrioles move
Spindle fibers assemble
Duplicated chromosomes condense
Homologous chromosomes pair up

10. Section Two: Process of Meiosis
Meiosis I
Metaphase I
Spindle fibers align the homologous chromosomes along cell equator

11. Section Two: Process of Meiosis
Meiosis I
Anaphase I
Paired homologous chromosomes separate from each other and move toward opposite ends of the cell
Sister chromatids stay attached

12. Section Two: Process of Meiosis
Meiosis I
Telophase I
Spindle fibers disassemble and the cell undergoes cytokinesis

13. Section Two: Process of Meiosis
Meiosis II
Prophase II
Nuclear membrane breaks down
Centrosomes and centrioles move to opposite ends of the cell
Spindle fibers form

14. Section Two: Process of Meiosis
Meiosis II
Metaphase II
Spindle fibers align the chromosomes along the center of the cell

15. Section Two: Process of Meiosis
Meiosis II
Anaphase II
The sister chromatids are pulled apart from each other and move to opposite ends of the cell

16. Section Two: Process of Meiosis
Meiosis II
Telophase II
Nuclear membrane forms again
Spindle fibers break apart
Cell undergoes cytokinesis

17. Section Three: Mendel and Heredity
Gregor Mendel and Genetics
Traits: distinguishing characteristics that are inherited
Genetics: the study of biological inheritance patterns and variations in organisms
Purebred: genetically uniform
The offspring of the purebred parents inherit all of the parents characteristics
Cross: the mating of two organsims
P= parental generation
F1= first generation of offspring

18. Section Three: Mendel and Heredity
Mendel’s Conclusions
Law of Segregation
Organism inherit two copies of each gene, one from each parent
Organisms donate only one copy of each gene in their gametes, thus the two copies separate during gamete formation

19. Section Four: Traits, Genes, and Alleles
Gene: a piece of DNA that provides a set of instructions to a cell to make a certain protein
Consists of two alleles: an alternate form of a gene
Homozygous: when the two alleles are the same
Heterozygous: when the two alleles are different

20. Section Four: Traits, Genes, and Alleles
Genes and Traits
Genome: all of an organism’s genetic material
Genotype: the genetic makeup of a specific set of genes
Codes for phenotype
Phenotype: physical traits

21. Section Four: Traits, Genes, and Alleles
Genotype Determination
Depends on dominant and recessive alleles
Dominant allele: the allele that is expressed when two different alleles or two dominant alleles are present
Recessive allele: the allele that is expressed only when two copies of it are present

22. Section Four: Traits, Genes, and Alleles
Phenotype
2 genotypes can produce the dominant phenotype
Ex: BB and Bb
Only 1 genotype can produce the recessive phenotype
Ex: bb

23. Section Five: Traits and Probability
Punnett Squares
A grid system for predicting possible genotypes resulting from a cross

24. Section Five: Traits and Probability
Punnett Squares
Monohybrid Cross: crosses that examine the inheritance of only one specific trait
Homozygous crossed with homozygous
Heterozygous crossed with heterozygous
Homozygous crossed with heterozygous
Test cross: a cross between an organism with an unknown genotype and an organism with the recessive phenotype

26. Section Five: Traits and Probability
Punnett Squares
Dihybrid Crosses: crosses that examine the inheritance of two different traits
Law of Independent Assortment: the allele that pairs separate independently of each other during gamete formation

27. Section Five: Traits and Probability
Heredity Patterns and Probability
Probability: the likelihood that a particular event will happen

28. Section Six: Meiosis and Genetic Variation
Unique Combinations
Sexual reproduction creates a unique variety of traits
Homologous chromosome pairing

29. Section Six: Meiosis and Genetic Diversity
Crossing Over and Genetic Diversity
Crossing Over: the exchange of chromosome segements between homologous chromosomes during prophase I of meiosis I.

30. Section Six: Meiosis and Genetic Variation
Genetic Linkage
Genes located close together tend to be inherited together