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Explain Mendel's contribution to genetics:

Gregor Mendel- Austrian Monk

Theory of inheritance based on 7 years of work w/ 24,034 plants

By 1900s, meiosis had been observed

-Meiosis was a physical explanation for Mendel's results

Mendel worked w/ pea plants

Peas usually self-pollinate

Mendel forced cross pollination

Mendel followed 7 characters each with two traits

Flower color : purple or white

Plant height: tall or short

Seed color: yellow or green

Seed shape: round or wrinkled

Pod color: green or yellow

Pod shape: inflated or constricted

Flower position: axial or terminal

Character: observable physical features (color,shape)

Trait: form of a character(yellow or green flower)

True breeding crosses

Parents(P generation) were true breeders of different traits

F1 generation(offspring)were monohybrids

Results: 1 trait was lost

Monohybrid crosses

Offspring are the F2 generation

Results: trait is returned

For all 7 traits, results were the same...

In F1, one trait disappeared- the trait that remains is dominant, the trait that lost is recessive

In F2, the recessive trait returns in 3:1 dominant:recessive ratio

Mendel figured out:

2 "particles" determines a trait

1 "particle" from each parent (via gametes)

ID the two laws proposed by Mendel & match to meiosis:

Mendel's 1st law:

Law of segregation- when gametes are made, the 2 gene versions (homologues or particles) separate. Gametes get 1.

States that these two alleles will be separated from each other during meiosis causing the two distinct alleles located on those chromosomes to segregate from one another

Mendel's particles turned out be alleles.

Alleles are different versions of a gene.

Diploid cells have 2 alleles for every gene

Gametes have one b/c of meiosis

In diploid cells,

if amino acid sequence of alleles are identical, the gene is homozygous

if alleles differ, genes is heterozygous

Each gene occurs on a chromosome at a unique locus

Punnet square is a fertilization matrix- line up possible gametes from each parent on each side

Mendel's 2nd law:

The law of independent assortment: Alleles different genes assort independently during gamete formation

We know this law does not apply for genes on the same chromosome but because of crossing over sometimes it does

After meiosis, each haploid cell contains a mixture of genes from the organism's mother and father

Exception is for genes that are located very close to one another on the same chromosome bc of the genetic linkage

Predict phenotypes and genotypes based on crosses:

Phenotype: physical appearance (spherical wrinkled seed)

Genotype: the genetic makeup (RR or rr)

Upper case- dominant allele

Lower case- recessive allele

1 or 2 dominant alleles--- dominant phenotypes

2 recessive allels-- recessive phenotype

Mendel tested his hypothesis with test cross:

used find dominant individual genotypes

you will cross homozygous recessive x dominant

If offspring include recessive phenotypes than dominant parent's genotype.. is heterozygous

If offspring are all dominant, then dominant parent's genotype.. is homozygous dominant

Dihybrid cross:

F1 dihybrids

F2- products of dihybrids

Results: each character was inherited separately

9:3:3:1 ratio

Seite 2

Identify mutation types:

Mutations are change to the nucleotide sequence of DNA & phenotype may or may not be affected

Somatic mutations- occurs in body cells-- not passed to offspring

Germ line mutations- occurs in gamete-- offspring receives

Mutations that lead to nonfunctional proteins are loss of function mutations

are usually recessive

If 1 or 2 genes still work, then the protein is expressed

Sickle cell anemia is caused by a missense mutation on the hemoglobin gene

Those that lead to protein with a different function are gain of function mutations

usually dominant

Only need 1 new protein to do the new job. Common in cancers.

Mutations outside the protein coding regions can have significant effects too

Example: promoter mutations may alter the rate of transcription of the gene(switches)

Predict how mutations affect AA sequence:

Silent mutations- do not affect the AA sequence

Missense mutations-base substitution results in different AA

Nonsense mutations -stop the AA sequence

Frame shift mutations- results in completely new AA sequence

C&C mutation types:

Mutations are either:

Point mutations- change to a single base pair

Point mutations occur when a base is modified:

Tautomeres: normal variants (spontaneous)

deamination- loss of NH2 group-changes C to U or T (spontaneous or induced)

Chromosomal mutations- change to larger segments of DNA

4 types of point mutations:

Silent

Missense

Nonsense

Frame-shift

Silent mutations- do not affect amino acid sequence (Wobble) - mutation goes unnoticed

Missense mutations- base substitutions results in different AA

Nonsense mutations- base substitution results in stop codon

Frame shift mutation -single bases inserted or deleted

4 types of chromosomal mutations:

Deletions

Duplications

Inversions

Translocations

Deletions- remove part of the genetic material functions like frame shift

Duplications- occur when homologous chromosomes break in different places and recombine with the wrong partners. One chromosome has a deletion, and the other has two copies of the DNA segment

Inversions- break and rejoin during crossing over, but segment is "flipped"

Translocation- segment of DNA breaks off and is inserted into another chromosome. Can cause sterility if chromosomes pairing in meiosis is impossible

Mutations are spontaneous or induced

Spontaneous mutations: are natural mutations, occurring with no outside influence

Induced mutations: are caused by an outside agent called a mutagen

Induced mutations can be caused by:

Chemical mutagens

Ex: benzopyrene(cigarette smoke) modifies guanine- DNA polymerase cannot recognize

Radiation

X rays create free radicals that can change bases

UV modifies thymine- disrupts DNA replication

Mutagens can be natural or artificial

Natural

Toxins produced for defense (ex aflatoxin)

UV from the sun

Artificial

Synthetic pesticides

Radiation from nuclear reactions

Interpret results from DNA fingerprinting analyses:

ID causes of genetic disorders discussed in class

Some are caused by one dysfunctional enzyme

Point mutations example PKU

sickle cell anemia

Both are recessive diseases (loss of function mutations)

In PKU, phenylalanine hydroxylase(PAH) is faulty

PAH converts phenylalanine to tyrosine

When PAH does not work...

phenylalanine builds up & damages neurons in the brain-- mental retardation a symptom if not controlled

Another symptom is light skin & light hair -- tyrosine is a precursor to Melanin

Some genes are more suscpectible to loss of function mutations

Diseases caused by chromosomal mutations:

Cystic fibrous

Muscular dystrophy

Hemophilia A

Muscular dystrophy

Deletions in the dystrophin gene (organizes muscular structures) cause muscular dystrophy

Severity depends on the length of deletion

Seite 3

Recognize the order of events in Signal Transduction Pathway:

C&C long distance & short distance signals:

Predict the receptors location in the cell based on the ligand:

C&C the types of plasma membrane receptors

C&C the types of responses

Seite 4

Putting it all together- Cancer: