Review Questions1) What is the difference between a genotype and a

phenotype?

2) What are the terms for genotypes AA, aa, and Aa?

3) 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 traitPhenotype 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:1) Chromosomes occur in pairs in

sexually reproducing, diploid organisms. Alleles for each gene are on these chromosomes

2) The chromosomes of each pair are separated and delivered to different gametes. This also separates alleles of genes

3) 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

• 0impossible• 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 Crosses1) 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

2) 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 Pp Ppp Pp Pp

P G Gg Gg Ggg Gg Gg

P G gg Gg ggg Gg gg

How do We Know AA or Aa?• 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:1) If parent is GG:– GG X gg 100% Ga offspring;

100% green2) If parent is Gg:– Gg X gg 50% Gg and 50% gg

offspring; 50% green and 50% yellow

F1 X P G gg Gg ggg Gg gg

F1 X P G Gg Gg Ggg Gg Gg

Non-Mendelian Inheritance Patterns• Not all alleles follow

dominant/recessive patterns; most do not

1) 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 CR

CW CRCW CRCW

CW CRCW CRCW

F1 CR Cw

CR CRCR CRCW

CW CRCW CWCW

Non-Mendelian Inheritance Patterns2) 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 AR

AW ARAW ARAW

AW ARAW ARAW

F1 AR AW

AR ARAR ARAW

AW ARAW AWAW

Non-Mendelian Inheritance Patterns3) 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

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– ⃝K 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