1. Introduction to Genetics
Chapter 11
Introduction to Genetics
Maternal B b
Paternal BB Bb bb

2. Patterns of Inheritance
twins
sisters
brothers
Father and son
Family
Mom and offspring

3. Meiosis – The Formation of Gametes
Diploid – 2
complete sets
of chromosomes
and 2 complete
sets of genes
Haploid – 1 set
of chromosomes
and 1 set of genes

4. Meiosis I

5. Tetrads and Crossing Over
Homologous chromosomes: Same genes, but different versions, in the same location, each coming from one parent
Crossing Over: Results in the exchange of alleles between chromosomes resulting in a new combination of alleles

6. Some genes appear to be inherited together, or “linked
Some genes appear to be inherited together, or “linked.” If two genes are found on the same chromosome, does it mean they are linked forever?
Study the diagram, which shows four genes labeled A–E and a–e, and then answer the questions on the next slide.
Forever Linked?

7. 1. In how many places can crossing over result in genes A and b being on the same chromosome?
2. In how many places can crossing over result in genes A and c being on the same chromosome? Genes A and e?
3. How does the distance between two genes on a chromosome affect the chances that crossing over will recombine those genes?

8. One (between A and B)
2. Two (between A and B and A and C); Four (between A and B, A and C, A and D, and A and E)
3. The farther apart the genes are, the more likely they are to be recombined through crossing over.

9. Meiosis II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
Prophase II
Metaphase II
Anaphase II
Telophase II
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

10. Gamete Formation in Males

11. In Females . . .

12. Intro to Genetics Who was Gregor Mendel?
* Austrian monk
* Teacher of high school natural science love of evolution, nature, meteorology
* “for the fun of it”: crossed peas and mice- saw inheritance patterns
* pea plants- a formal test

13. The Experiment . . . 1. The research pea plants- why?
- structure (male and female parts on same plant)
- distinctive traits
- rapid reproduction
- ability to control pollination and fertilzation

14. The Steps. . . Used “true-breeding” plants -if self-pollination
occurs, offspring
produced that are
identical to parent
**Cross-pollination
allowed for him to
prevent self-pollination
and study the results

15. The Traits

16. 1.   Mendel studied the inheritance
of one trait (for example plant's height, color of  flowers or color and shape of seeds).
2.    Mendel first cross pollinated tall pea plants (identified asTT, height of plants in this variety were about six feet tall) with each other.
3.   Mendel then cross pollinated short pea plants (identified as tt, height of plants in this variety were about one foot tall) with each other.

17. X
In every generation of this plant only short plants were produced. He concluded that the pea plant must contain some factor for height (in that variety - for shortness).

18. 4.   The next step of Mendel's experiment was to crossed tall pea plants (TT) with short pea plants (tt). The resulting plants were labeled Tt and only tall plants were produced.

19. Genes & Segregation
F1 Generation – had the recessive alleles disappeared?
F1 generation crossed by self pollination to create F2 generation

20. Tt Tt X F1
Segregation t t T T TT Tt tt F2 Tt
Alleles segregate from each other so that each gamete carries only a single copy of each gene. Alleles pair up again when gametes fuse during fertilization

21. Dihybrid Crosses Conclusion: genes that segregate
Mendel’s next question: Does the segregation of one pair of alleles affect the segregation of another pair of alleles?
EX: Does the gene that determines whether a seed is round or wrinkled in shape have anything to do with the gene for seed color?
Conclusion: genes that segregate
don’t influence each others inheritance. This is why we have so many genetic differences in plants and animals.

22. Exceptions to Mendel's Principles
1. Incomplete Dominance – some alleles are neither dominant or recessive

23. Exceptions to Mendel's Principles
2. Codominance: both alleles contribute to the phenotype

24. Exceptions to Mendel's Principles
3. Multiple Alleles: Genes that have more than two alleles.
EX: Blood type exists as four possible phenotypes: A, B, AB, & O.
There are 3 alleles for the gene that determines blood type. (Remember: You have just 2 of the 3 in your genotype from mom & 1 from dad).
The alleles are as follows:
ALLELE IA IB i
CODES FOR Type "A" Blood Type "B" Blood Type "O" Blood

25. RESULTING PHENOTYPES Type A Type A
Bloodtypes
GENOTYPES IAIA IAi
RESULTING PHENOTYPES Type A Type A
IBIB IBi
Type B Type B
IAIB
Type AB ii
Type O

26. Let's Practice!
A woman with Type O blood and a man who is Type AB have are expecting a child.  What are the possible blood types of the kid? 

27. Step #1, figure out the genotypes of ma & pa using the given info.
"Woman with Type O" must be ii, because that is the one & only genotype for Type O.
"Man who is AB" must be IAIB, again because it is the one & only genotype for AB blood. So our cross is: ii x IAIB.  The proper p-square would look like this:  
                                                   
As you can see, our results are as follows: 50% of kids will be heterozygous with blood Type A 50% will be heterozygous with blood Type B

28. Single gene, four different alleles
C = full color dominant
Cch=chinchilla; dominant to ch & c
Ch=Himalayan; dominant to C c=albino; recessive
What allele combinations can a chinchilla rabbit have?
What are the possible offspring that would result when a chinchilla rabbit mates with a himalayan rabbit?

29. Exceptions to Mendel’s Principles
Sex-linked Inheritance: The X and Y chromosomes in mammals do not have exactly the same genes.
In mammals, the Y-chromosome is small and does not carry many genes.
Sex-linked genes linked
to X chromosome

30. X-linked Inheritance
Color blindness is one example of X-linked inheritance.

31. Exceptions to Mendel’s Principles
Polygenic Inheritance: A characteristic controlled by more than one gene (many genes shaping one phenotype)
Human Examples:
Skin Color
Eye Color
Height

32. Polygenic Inheritance: Human Skin Color
Dominant alleles
O aabbcc = very light skin
1-2 AABbcc = medium
AaBbCc
AaBBcc, etc.
3 AABBCC = very dark skin
AaBbCc x AaBbCc 