1. Chapter 10
Mendel & Meiosis

2. 10.1: Mendel’s Laws of Heredity
Heredity- passing on of characteristics from parent to offspring
Traits- characteristics that are inherited
Genetics- branch of biology that studies heredity

3. Gregor Mendel Austrian monk, 1860’s
Carried out thousands of genetic experiments with garden peas

4. Why peas? Peas reproduce sexually Form gametes- sperm & eggs
Fertilization unites these gametes to form a zygote which develops into a seed

5. 2. Peas normally self-pollinate or fertilize
Mendel could cross-pollinate them manually & be sure of the parents in a given cross
3. Peas are easy to grow & reproduce quickly

6. Pea plant traits
Pea plants have many distinct traits that are either/or characteristics
Seed shape- round or wrinkled
Seed color- yellow or green
Flower color- purple or white
Plant height- tall or short
Etc.

7. Hybrids
Hybrid- offpsring of parents that have different forms of a trait
Mendel crossed parents with different traits and recorded data on what the resulting hybrid offspring were like

8. What Mendel discovered:
The rule of unit factors- each organism has 2 factors that control each of its traits
Alleles- alternate forms of a gene
Dominant allele- represented by capital letter (A, B, C…)
Recessive allele- represented by lowercase letter (a, b, c…)

9. 2. The rule of dominance- between alternate forms of a gene, one will be dominant over the other- the dominant form will show up when paired with the recessive form
3. The law of segregation
Every individual has two alleles for each gene
When gametes are produced, each gamete receives only one of these alleles

10. More vocabulary: Phenotype- the way an organism looks
Genotype- the alleles an organism has (the letters)
Homozygote (homozygous)- an organism with two alleles that are identical (AA, aa)
Heterozygote (heterozygote)- an organism with two alleles that are different from one another (Aa, Bb, Dd)

11. Let’s imagine…. We have a pea plant with purple flowers.
Purple (F) is dominant over white (f)
The plant’s genotype could be homozyote, ______, or heterozygote, ______.
The plant’s phenotype is ________.

12. If we have a pea plant with white flowers, the plant’s genotype must be ________.
It is a _____________.
The plant’s phenotype is _________.

13. Gametes
Diploid cells- cells whose nuclei contain two sets of homologous chromosomes
Diploid number- total number of chromosomes in a diploid cell
Abbreviated 2n
46 in humans, 44 autosomes & 2 sex chromosomes

14. Haploid cells- cells with a single set of chromosomes (1 of each homologous pair)
Gametes- sperm or eggs
Haploid number- total number of chromosomes in a haploid cell
Abbreviated n
23 in humans, 22 autosomes & 1 sex chromosome

15. Fertilization of egg (n) by sperm (n) results in a fertilized egg called a zygote (2n)
Gametes are the result of a division process called meiosis
Meiosis is the process that separates the letters in a genotype into separate genotypes

16. Meiosis
Meiosis is a reduction division- the number of chromosomes is reduced in the division
Occurs in reproductive organs- ovaries & testes
Involves two divisions
Four daughter cells result
Each daughter cell has only ½ as many chromosomes as the starting cell

17. Punnett Squares
Tool used by geneticists to predict expected results of crosses between parents of known genotypes.
Monohybrid cross- cross between parents that differ in one trait
Punnett squares determine the probability that a certain genotype will occur in the offspring of a certain cross

18. 10.2 Meiosis
In mitosis, each new cell produced has the exact number of chromosomes as the original cell
Meiosis- the making of sperm or eggs

19. Homologous Chromosomes
Somatic cell- typical body cell
46 chromosomes that come in 23 matched pairs
Homologous chromosomes- chromosomes in a matched pair that have genes controlling the same inherited characteristics

20. Locus- location of a particular gene on a chromosome
Homologous chromosomes have genes for the same trait at the same locus, but they may have different versions of that gene

21. Types of Chromosomes 1. Autosomes Found in both males and females
22 pairs
2. Sex chromosomes
Determine gender
1 pair- XX or XY
Only small parts are homologous, but they behave like homologous pairs during meiosis

22. We inherit one chromosome from each pair from our mother and one from our father.

23. Meiosis I: Homologous Chromosomes Separate
Interphase
Chromosomes duplicate
Prophase I
Synapsis- homologous chromosomes (each composed of 2 sister chromatids) come together as pairs to forma tetrad
Crossing over- legs of homologous chromosomes flop over each other and may exchange pieces- source of genetic variation
Spindle forms

24. Metaphase I
Tetrads line up on metaphase plate
Anaphase I
One homologous chromosome from each tetrad moves to opposite pole
Only tetrads split up, not sister chromatids

25. Telophase I and cytokinesis
Each pole has haploid set of chromosomes, one from each homologous pair
Cytokinesis occurs

26. Interphase again?
In some species, interphase occurs between Meiosis I and II
Chromosomes uncoil
Nuclear membranes reform
No chromosomal duplication

27. Meiosis II: Sister chromatids separate
Prophase II
Spindle forms
Metaphase II
Chromosomes line up on metaphase plate
Anaphase II
Sister chromatids are pulled apart
Telophase II
New nuclear membranes form
Cytokinesis occurs

28. Results of Meiosis Four new haploid daughter cells
In males- four viable sperm
In females- one viable egg, three polar bodies

30. Oogenesis