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

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

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

Meiosis I

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

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?

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?

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.

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.

Gamete Formation in Males

In Females . . .

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

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

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

The Traits

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.

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).

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.

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

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

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.

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

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

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 --- 1 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

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

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? 

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

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?

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

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

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

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 