Review Questions

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 • 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?

How do We Know AA or Aa? • Test Cross determines if parent is AA or Aabased 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% Gaoffspring; 100% green • If parent is Gg: • Gg X gg 50% Ggand 50% ggoffspring; 50% green and 50% yellow

Non-MendelianInheritance 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 • CRCRx CWCWgive what type of offspring ratios? • 100% pink (heterozygous) • What about F2? • 1 Red: 2 Pink: 1 White

Non-Mendelian Inheritance Patterns 2) Codominance • Both alleles have equal chanceexpressed 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

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 IBIB IAIA 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 genemakes 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 XbXb 100% XBXb and 100% Xb Y

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

Review Questions