Review Questions What is the difference between a genotype and a phenotype? What are the terms for genotypes AA, aa, and Aa? If a red flower (RR) is crossed with a white flower (rr), what will be the phenotype and genotype of the F1? Genotype Alleles in DNA for a certain trait Phenotype The physical trait expressed by a genotype AA homozygous dominant aa homozygous recessive Aa heterozygous Phenotype Red flower Genotype Rr

Chromosome Theory of Inheritance Sum up what we have learned from Mendel: Chromosomes occur in pairs in sexually reproducing, diploid organisms. Alleles for each gene are on these chromosomes The chromosomes of each pair are separated and delivered to different gametes. This also separates alleles of genes One-half of each chromosome pair after fertilization comes from the each parent.

Genetic Crossing

Monohybrid Crosses Punnett Square method for organizing alleles during breeding that uses statics Father on top; Mother on side All possible offspring in the middle All Statics probabilities are between 0-1 0impossible 1 completely possible Product Rule events where both A and B will occur Chance of heads vs. tails 0.5 Chance of heads twice 0.5x0.5= 0.25 Sum Rule when two or more possible ways exist to get the same outcome Chance of getting head and tail in 2 tosses 0.5x0.5=0.25 Two ways (head and tail or tail and head) 0.25+0.25= 0.5

Practice Crosses P p Pp P G g Gg P G g Gg gg What are the possible genotype ratios for a cross between homozygous dominate (purple) and homozygous recessive (white) garden pea plants? What is their phenotypes? 1.0 chance of heterozygous (Pp) All purple flowers What are all possible genotype ratios for a green seed X yellow seed? Green is dominate. 1.0 chance heterozygous (Gg) 0.5 chance heterozygous (Gg) and 0.5 homozygous recessive (gg) All green seeds OR half green and half yellow seeds. Which is correct? P p Pp P G g Gg P G g Gg gg

How do We Know AA or Aa? G g Gg G g Gg gg Test Cross determines if parent is AA or Aa based on cross with F1 F1 with recessive trait crossed with unknown parent One of two possible results: If parent is GG: GG X gg 100% Ga offspring; 100% green If parent is Gg: Gg X gg 50% Gg and 50% gg offspring; 50% green and 50% yellow F1 X P G g Gg F1 X P G g Gg gg

Non-Mendelian Inheritance Patterns Not all alleles follow dominant/recessive patterns; most do not Incomplete dominance Phenotype for heterozygous genotype is a blend of both homogenous traits Recessive trait is not completely blocked because dominate trait is incomplete CR red form of color allele CW white form of color allele CRCR x CWCW give what type of offspring ratios? 100% pink (heterozygous) What about F2? 1 Red: 2 Pink: 1 White P CR CW CRCW F1 CR Cw CRCR CRCW CW CWCW

Non-Mendelian Inheritance Patterns 2) Codominance Both alleles have equal chance expressed so heterozygotes show both traits Mosaic Flowers Cells express either Red or White allele Both alleles are present, but one is randomly not expressed Like flipping a coin; close to 50% Same inheritance patterns as incomplete dominance P= ARAR X AWAW 100% ARAW Mosaic (F1) F2= ARAW X ARAW 1:2:1; 1 AR, 2 ARAW, 1 A P AR AW ARAW F1 AR AW ARAR ARAW AWAW

Non-Mendelian Inheritance Patterns 3) Multiple Allele Inheritance More than two alleles will code for different phenotypes Human Blood-Types Allele I IA, IB, or I A Type (IAIA, IAi) Mixes with A and O type B Type (IBIB, IBi) Mixes with B and O type AB Type (IAIB) Universal acceptor Mixes with A, B, and O type O Type (ii)  Universal donor Can be given to any type IAIA IBIB IAIB ii

Sex-Linked Genes Any genes located on the sex chromosomes X or Y in humans All other 22 chromosomes are called autosomes (automatically inherited) Y Chromosome Sex-determining gene; SRY gene makes females into males XY heterogametic X Chromosome Mostly codes for non-sex related traits (ex. Color vision) XX homogametic

Sex-Linked Inheritance Often when a trait is similar to Mendelian genetics (dominant/recessive) but offspring show patterns when divided by sex Mice Body Color: B black body b white body If Bb X bb, what should be the ratio of black to white mice? 1 : 1 ratio (50% Bb and 50% bb) However you notice that females are only black and males are only white. What does this mean? B and b alleles are on X-chromosome XB Y x Xb Xb 100% XB Xb and 100% Xb Y P XB Y Xb XBXb XbY

Too Many Xs! Why do females need two Xs? They Don’t! Two X chromosomes would mean double the genetic material necessary What does the body do with the X chromosome? It randomly shuts one X chromosome down They are copied and passed on in mitosis but are never used to make proteins How can this show us X-recessive traits? Dominate X might be randomly deactivated so the X recessive is randomly present in cells Female calico cats have a mix of orange and black fur but males are always black or orange

Following Sex-linked Traits Pedigree map of parents and offspring in a family over generations ⃝ female  males  has trait  carrier; has gene but not trait Hemophilia platelets numbers so low person often bleeds to death from little body damage X-linked recessive gene Rare for XhXh why? Most males with the disease do not reproduce Lead to the Russian Revolution