how characteristics (traits) pass from parents to offspring Genetics The study of Heredity how characteristics (traits) pass from parents to offspring

What does genetics have to do with DNA? Genes stated clearly. 5 mins

Gregor Mendel - A monk who studied peas in his garden and developed our basic understanding of heredity.

Allele Mendel’s term for Alternate forms of a trait. Most traits have 2 alleles Ex. Yellow or green pea

Blue eye or brown eye allele

Mendel said traits could be Dominant or recessive Dominant – The trait that is stronger or masks the other trait Recessive – The trait that is weaker or hidden in presence of dominant one

If there are both a dominant and recessive traits together, only the dominant one appears

Ex. Dominant gene Black fur is usually dominant to white

Ex. Recessive genes Blue eyes and blond hair

Mendel’s Law of segregation Offspring can only receive one allele or the other. They segregate from each other during meiosis When gametes (sperm and egg) form, only one of the 2 possible genes for each trait will be in each gamete

Mendel’s Law of independent assortment Alleles separate independently. During meiosis, each homologous pair of chromosomes separate independently. Different combinations possible

What Mendel did NOT know about ? Genes DNA Chromosomes Meiosis He still figured out how it worked with out knowing the details

Genes A single unit of hereditary information (DNA) located on a chromosome

Locus (loci) A gene’s specific location on a chromosome

Pure Strain Called True Breeding When crossed with in strain, all the offspring have the same trait The genes are all the same Often called “Pure bred”

Hybrid When an organism has both forms of the gene (both alleles) Ex. Heterozygous pepper has one gene for yellow and one gene for red

G g Genotype The genes an organism carries Ex: Gg = a green (G) and yellow (g) gene G g

Phenotype How the genes are expressed (what it looks like) Ex: Aa peas have both green and yellow genes but the phenotype is yellow because yellow is dominant

G Homozygous Dominant Two Dominant Genes Genotype = GG Phenotype = Green GG G G

g Gg G Heterozygous 1 Dominant gene and 1 recessive gene Genotype = Gg Phenotype = Green g Gg G

gg g g Homozygous Recessive Two recessive Genes Genotype = gg Phenotype = Yellow gg g g

Monohybrid cross Look at one single trait Cross RR X rr  get all Rr Cross Rr X Rr  get 1RR + 2Rr + 1rr 3:1 ratio of dominant phenotype

Generations of a cross P1 Generation – The original parents F1 Generation – The first offspring (Children) F2 Generation – The offspring from the F1 gen. (grandchildren)

P1 = BB (brown) X bb (blond) F1 Offspring: BB = Bb = B b

P1 = BB (brown) X bb (blond) F1 Offspring: BB = Bb = B b Bb

P1 = BB (brown) X bb (blond) F1 Offspring: BB = Bb = B b Bb

P1 = BB (brown) X bb (blond) F1 Offspring: BB = Bb = B b Bb

P1 = BB (brown) X bb (blond) F1 Offspring: BB = Bb = B b Bb

P1 = BB (brown) X bb (blond) F1 Offspring: BB = 0% Brown Bb = 100% Brown bb = 0% Blond B b Bb

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = Bb = bb = B b

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = Bb = bb = B b BB

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = Bb = bb = B b BB Bb

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = Bb = bb = B b BB Bb

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = Bb = bb = B b BB Bb bb

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = 25% Brown Bb = bb = B b BB Bb bb

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = 25% Brown Bb = 50% Brown bb = B b BB Bb bb

Cross two hybrids Bb X Bb from F1 generation F2 Offspring: BB = 25% Brown Bb = 50% Brown bb = 25% blond B b BB Bb bb

Dihybrid cross Look at 2 traits at same time when crossing 2 hybrids

DiHybrid example http://www.siskiyous.edu/class/bio1/genetics/dihybrid_v2.html

9 : 3 : 3 : 1 ratio 9 Dom / Dom Tall/Red 3 Dom / res short/Red 3 res / Dom Tall/yellow 1 res / res short/yellow

Other inheritance patterns

Incomplete dominance When a the phenotype is a mixture of the two alleles. Causing Blending! Ex: Red and White make Pink

Ex. Incomplete dominance snap dragons Cr X Cw

Co- dominance - When both traits show up. Both dominant Blood type is Co Dominant Ex: AB blood type has both A and B proteins

Ex. Co dominance in chickens Have both color feathers

Ex. Codominance in cattle Red and white make roan

Multiple alleles More than 2 alleles Blood type has 3 alleles IA – Type A IB – Type B i – Type O

Blood types AB - Universal receiver O - Universal donor

Blood types in America

Polygenic inheritance traits When there is more than one gene for a trait. Ex. Eye color, height

Epistasis When the effects of one gene are modified by another gene. Ex. Albino gene - overrides other genes that determine color

Labrador retrievers are polygenic                         Black (B) is dominant to chocolate (b) BUT Yellow is recessive epistatic ee changes all yellow Phenotype- Possible Genotypes BBEE BbEE BBEe BbEe bbEE bbEe BBee Bbee bbee

X - linked traits When a trait is carried on the X chromosome Females (XX) need both genes Males (XY) need only one gene to have trait