 Genetics is the study of inheritance – the passing of traits from parent to offspring What is Genetics?

Austrian Monk - Bred pea plants cross-pollinated true breeding parents (P) P = parental generation raised offspring & then observed traits (F 1 ) F = filial gen. (offspring) allowed F 1 offspring to self- pollinate & observed traits in next generation (F 2 )

F 2 generation 3:1 75% purple-flower peas 25% white-flower peas P 100% F 1 generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate

Traits come in alternate versions: called alleles purple flower and white flower color alleles – different version of same gene. different alleles vary in the sequence of nucleotides (building blocks of DNA)

 For each characteristic, an organism inherits 2 alleles, 1 from each parent ◦ diploid organism  inherits 2 sets of chromosomes, 1 from each parent  homologous chromosomes  like using 2 different websites for research  Wikipedia  About.com What is the advantage of being diploid???

Paired genes separate during the formation of reproductive cells and the gamete only receives one gene from the pair  During meiosis, alleles segregate  When homologous chromosomes separate  During anaphase I ◦ each allele for a trait is packaged into a separate gamete

 Genes for different characteristics are distributed (sorted) to gametes independently.  This means that traits produced by dominant genes are not necessarily shown together. Does red hair ALWAYS sort with green eyes?  Genes are only inherited together if they appear on the same chromosome.

 Some traits “mask” others ◦ purple & white flower colors are separate traits that do not blend  purple x white ≠ light purple  purple masked white ◦ dominant allele  Directs the formation of a functioning protein  Creates the characteristic  masks other alleles ◦ recessive allele  Has directions for a malfunctioning protein – wrong shape (doesn’t work)  Does not affect characteristic allele producing functional protein mutant allele malfunctioning protein homologous chromosomes

 Indicate the two alleles that an individual inherited for a specific trait. ◦ One allele on each homologous chromosome ◦ Two allele conditions:  Homozygous (2 of same allele)  Must specify if they are dominant or recessive alleles  Heterozygous (2 different alleles) ◦ For peas: 3 possible genotypes for flower color  Homozygous dominant (PP)  Homozygous recessive (pp)  Heterozygous (Pp)

 Physical appearance of the trait.  Depends on the genotype  Recessive phenotype only present if genotype is homozygous recessive (pp) = white flower  Dominant phenotypes: ◦ Homozyous dominant (PP) = purple flower ◦ Heterozygous (Pp) = purple flower

 Show the possible genotypic outcomes from crossing the parents (fertilization). ◦ Gives probability of offspring genotypes  Now lets assume that Black-haired rabbits are dominant to white haired rabbits  B = black hair  b = white hair

 Probability of phenotype: 75% black 25% white

 Heterozygous black rabbit with a white rabbit What are the offspring phenotypes?

Beyond Mendel’s Laws: Other Patterns of Inheritance

 Heterozygote shows an intermediate, blended phenotype ◦ example:  RR = red flowers  rr = white flowers  Rr = pink flowers  R is not completely dominant – so does not make enough color (pigment) to completely cover “white” RRRrrr

RW male / sperm R W female / eggs RR RWWW RW 25% 1:2:1 25% 50% 25% 1:2:1 % genotype % phenotype RR RW WW 25% 50% RW x RW

 2 alleles are both equally dominant ◦ affect the phenotype equally & separately  not blended phenotype ◦ Example: ABO blood groups ◦ 3 alleles  I A, I B, i  I A & I B alleles are co-dominant to each other  both cell markers (proteins) are produced  both I A & I B are dominant to i allele ◦ Cell surface markers act as ID cards

Both red and white hairs are expressed in the phenotype – not pink hairs!

Also exhibits Multiple Alleles when there are more than two possible alleles for a trait Three alleles lead to four blood types; A, B, AB and O Blood type A is represented by I A I A or I A i Blood type B is represented by I B I B or I B i Blood type AB is represented by I A I B Blood type O is represented by ii

 Some phenotypes are determined by 2 or more genes ◦ phenotypes exist as a continuum  many more than 2 possibilities ◦ human traits include:  skin color  height  weight  eye color  intelligence  Hair color

autosomal chromosomes sex chromosomes

The sex of the offspring is determined by the presence or absence of the Y chromosome ◦ If the offspring is XX, it is a female, if it is XY, it is a male  Not all genes on the X chromosome are “gender” traits ◦ Some are for other traits that both males and females have  Traits on the X chromosome are inherited in a different pattern than those traits on the autosomes  Examples of traits that are sex-linked include baldness and red-green color blindness

 Sex-linked genes are always on the X chromosome  Lets assume that the colorblindness allele is recessive (X a )  How many children will be colorblind?