Transcript Biol 178 Lecture 23

Bio 178 Lecture 23
Meiosis (Cntd.) and Genetics
J. Elson-Riggins
Reading
•
Chapters 12, P 1068 - 1074, & 13
Quiz Material
•
Questions on P 240, 1080, & 276-278
•
Chapter 12, 50, & 13 Quizzes on Text Website
(www.mhhe.com/raven7)
Outline
• Meiosis (cntd.)
• Gametogenesis
• Genetics
 Mendelian Patterns of Inheritance
 Non-Mendelian Patterns of Inheritance
Mitosis Vs. Meiosis
MITOSIS
# Divisions
# Daughter Cells
Final Ploidy
Cell Type
Genetic Variation?
Metaphase
Alignment
Anaphase
Separation
MEIOSIS
Mitosis Vs. Meiosis
MITOSIS
MEIOSIS
1
2
2N
Somatic
No
2
4
N
Gametes
Yes
I - Homologues
II - Chromosomes
I - Homologues
II - Sister
chromatids
# Divisions
# Daughter Cells
Final Ploidy
Cell Type
Genetic Variation?
Metaphase
Alignment
Chromosomes
Anaphase
Separation
Sister chromatids
Evolutionary Consequences of Sex
• Random Fertilization
In addition to independent assortment and crossing over,
random fertilization generates diversity because 2 gametes
(each of which is different from the parent) fuse.
• Importance for Evolution
The diversity generated by sexual reproduction results in
individuals that may be fitter than others (not always!) in a
particular environment and will therefore be selected by
that environment.
Spermatogenesis
Spermatogenesis
McGraw-Hill Video
Structure of Seminiferous Tubules
http://webanatomy.net/histology/reproductive/seminiferous_tubule.jpg
Structure of Sperm
Oogenesis
Prophase I
(Fertilization)
Metaphase II
Mature Follicle
(Metaphase II)
Initial Ideas About Heredity
• Pre-Mendel
Read about classical assumptions (P 242) & the work of
Koelreuter & Knight.
• Mendel (1822-1884)
What was different about
Mendel’s work?
Mendel’s Experiments
• Characteristics of the Study Subject
The garden pea was a good choice because:
1. Can cross or self-fertilize.
2. Produces large numbers of offspring.
3. Easy to grow.
4. Has a number of varieties with different traits.
5. Short generation times.
6. Produces hybrid varieties.
Mendel’s Experiments
• Experimental Design
Mendel worked with 7 easily distinguishable traits as follows:
1. Ensured the parental (P) generation was true-breeding.
Eg. White flowered plants  White flowered progeny
2. Crossed varieties with alternate traits.
Eg.
Mendel’s Experimental Design (Cntd.)
3. Self-fertilized the hybrid generation (F1)
Mendel’s Results
• F1 Generation
No intermediate progeny - all resembled one of the
parents. This was referred to as the dominant trait.
Eg. P:
Purple X White

F1:
Purple
Mendel’s Results (Cntd.)
• F2 Generation
F1:
F2:
Purple X Purple

3 Purple :
1 White
Mendel’s Experiments (Cntd.)
• Self-fertilize the F2  Disguised 1:2:1 Ratio
Mendel’s Experiments (Cntd.)
• Self-fertilize the F2  Disguised 1:2:1 Ratio
Mendel’s Conclusions
1. Blending (hybridization) was not occurring.
2. For each alternative trait, one alternative was
not expressed in the F1, but reappeared in the F2.
3. Pairs of alternate traits segregated among
progeny of a particular cross.
4. These alternate traits were expressed in the F2
generation as 3 dominant : 1 recessive.
Principles of Genetics
Mendel’s ideas in modern terms:
• Genes
Information about traits is transmitted from parent to
offspring in the form of genes.
• Homologous Chromosomes
A diploid individual receives 2 alleles (forms of a gene) for
each trait, one on each of 2 homologous chromosomes.
Homozygous
Heterozygous