Tuesday, April 24, 2012- Punnett Square checkup (end of) Block Day

MendelSim Data ReviewGoes in entry from Friday-Entry 39: MendelSim Simulation- 4/20/12

Parent 1 Parent 2 Offspring (after 50 crosses)

Red Blue

Data Table 1: Pure Red X Pure Blue

Parent 1 Parent 2 Offspring (after 50 crosses)

Red Blue

Data Table 2: Cross of Two Red Offspring

Data Table 3: Cross of Two Blue OffspringParent 1 Parent 2 Offspring (after 50 crosses)

Red Blue

Red Blue

Red Red

Blue Blue

50 0

38 12

This one varied

0 50

PARENT 2BLUE

X 50 (ALL) RED OFFSPRING

=

PARENT 1RED

PARENT 2RED

X =

38 RED 12 BLUE

X = 50 (ALL) BLUEOFFSPRING

PARENT 1RED

PARENT 1BLUE

PARENT 1BLUE

TAPE in these questions and answer them in your logbook

1. What is the trait we observed?2. What are the results of crossing the red

flowers with the blue flowers?3. Based on the results, what do we know about

the flower color gene?4. What are the results for the second crossing

—red crossed with red?5. The flowers in the second crossing look red—

but what do we know about their genetics?6. What happened to the blue trait and how did

it show up again in the third generation?

Entry 40: Heredity and Genetics 1-4/23

See attached notes page

Chromosome structure - genes

Human chromosome # 7

• Contains about 1,800 genes

• Contains over 150 million nucleotides

Link to view genes and DNA sequence

• Parts of chromosomes that code for proteins are called genes

• Genes, and specifically the proteins made from them, help determine your characteristics RGene for

RED flowers

How does your DNA determine your traits?

DNA mRNA protein Observed trait

transcr

iption

transla

tion

Example1: A person has DNA that has instructions to make LACTASE (a protein) which allows them to digest milk

Example 2: The Labrador Retriever has DNA that has the instructions to make TRP-1 which converts brown pigment to black—so they have black fur.

Trait – a characteristic of an organism– Example: “flower color”

Gene – part of a chromosome that helps determine a specific trait– Example: “flower color gene”

Allele – a form of a gene – Example:• One allele is the “blue” form of the gene• One allele is the “red” form of the gene

• Humans = 23 chromosome pairs, or 46 total. We have about 24,000 genes.

Some other examples: (do not need to memorize)

• Pea flower = 7 chromosome pairs (14 total)• Fruit fly = 4 chromosome pairs (8 total) 13,601

genes identified so far!• Potato = 24 pairs (total 48)• Horse = 32 pairs (total 64)

How many chromosomes?

Chromosomes come in pairs (one from Mom and one from Dad)

• This pair of chromosomes is called a “homologous pair” because they have the same genes on them -

Flower chromosome 3

(from computer simulation)From Dad

From Mom

flower color gene

IMPORTANT: homologous pairs are NOT IDENTICAL, but they have the same genes, – Alleles can be different

flower color gene

From Dad

From Mom

“Blue” alleleof flower colorgene

“Red” alleleof flower colorgene

The combination of alleles determines the observed characteristics

Chromosomecombination

Allelecombination

Observedcharacteristic

REDallele

RED allele

REDallele

BLUE allele

BLUEallele

BLUE allele

red, red red, blue(or blue, red)

blue, blue

RED RED BLUE

Dominant and recessive allelesOnly one red allele is needed for the flower to look

red.• Scientists call this a DOMINANT allele

Two blue alleles are needed for the flower to look blue.

• Scientists call this a RECESSIVE allele

Symbols used for alleles• The traditional symbols used for alleles are

big and small letters• The letter chosen usually refers to the

dominant alleleExample: R = Red allele

r = Blue allele

The combination of alleles determines the observed characteristics

Chromosomecombination

Allelecombination

Observedcharacteristic

REDallele

RED allele

REDallele

BLUE allele

BLUEallele

BLUE allele

red, red red, blue(or blue, red)

blue, blue

RED RED BLUE

The combination of alleles determines the observed characteristics

RChromosomecombination

Allelecombination

Observedcharacteristic

RR Rr rr

RED RED BLUE

R R r r r

Genotype – the two alleles that an organism has for a trait (genetics)

Phenotype – the observed (or measurable) trait of an organism that relates to one gene (physical)

Example: Trait = “flower color”Genotype = “RR” or “Rr” or “rr”Phenotype = “RED” or “BLUE”

The combination of alleles determines the observed characteristics

RChromosomecombination

GENOTYPE

PHENOTYPE

RR Rr rr

RED RED BLUE

R R r r r

Representing genotype and phenotype based on DNA/genes

DNA mRNA protein Observed trait

transcr

iption

transla

tion

BLUE PIGMENT RED PIGMENT

Blue Pigment

Functional Enzyme Y

Red Pigment

Blue Pigment

Non-Functional Enzyme Y

Red Pigment

No Red Pigment for You!!

GENOTYPE for flower type 1:

Allele of chromosome 2A= Y1 (functional enzyme)

PHENOTYPEof flower type 1:

nucleus

Y1 Y1

Draw the enzymes and pigment molecules present in the cells of each type of flower below.

Yes or no, is any functional enzyme Y in the cell?

Allele of chromosome 2B= Y1 (functional enzyme)

2A

2B

1B

1A

YES

RED

RR

Draw the enzymes and pigment molecules present in the cells of each type of flower below.

GENOTYPE for flower type 2:Allele of chromosome 2A= Y1 (functional enzyme)

PHENOTYPEof flower type 2:

nucleus

Y1

Y2

Yes or no, is any functional enzyme Y in the cell?

Allele of chromosome 2B= Y2 (non-functional enzyme)

2A

2B

1B1A

GENOTYPE for flower type 3:Allele of chromosome 2A= Y2 (non-functional enzyme) PHENOTYPE

of flower type 3:

nucleus

Y2

Y2

Yes or no, is any functional enzyme Y in the cell?

Allele of chromosome 2B= Y2 (non-functional enzyme)

2A

2B1B

1A

YES

RED

NO

BLUE

Rr

rr

• ATB: NEW LOGBOOK ENTRY “HEREDITY AND GENETICS 2”• PLANNER: SHORT CHECKUP ON

PUNNETT SQUARES/HEREDITY AT END OF BLOCK DAY• MAKE UP ANY MISSED WORK!

Homozygous – the two alleles are the same • RR and rr are homozygous genotypes

Heterozygous – the two alleles are different• Rr is a heterozygous genotype

Draw the enzymes and pigment molecules present in the cells of each type of flower below.

GENOTYPE for flower type 2:

Allele of chromosome 2A= Y1 (functional enzyme)

PHENOTYPEof flower type 2:

nucleus

Y1

Y2

Yes or no, is any functional enzyme Y in the cell?

Allele of chromosome 2B= Y2 (non-functional enzyme) 2A 2B

1B

1A

YES RED

WHAT DOES Rr ACTUALLY MEAN?Rr

Possible combinations of inherited chromosomes/genes

R rR r

Dad Mom

R

r

Parents

PossibleOffspring r

r

R

R

r

R

X

Order doesn’t matter, these two are the same (Rr)

What are all possible genotypes produced from the parents?

RR, Rr, rr

Punnett squares organize all possible offspring combinations

R r R rX

R r

R

r

RR

Rr rr

Rr

Dad Mom

1 out of 4 possibilities is rr = What is probability of Rr?• How many out of 4 are red? • What is the probability of red? • What is the probability of blue?

R r

R RR Rr

r Rr rrGenotypic ratio = 1RR: 2Rr:1rr

25 %50 %

3/475 %

25 %

R= red flower alleler= blue flower allele

Phenotypic ratio = 3 Red:1 blue

Your turn:• What are all possible genotypes and phenotypes

produced by crossing Rr with rr?

Complete the Punnett Square

r r

R Rr Rr

r rr rr

Punnett squares predict ratios of all genotypes and phenotypes produced

Genotypic ratio = 2 Rr:2 rr or 1Rr : 1 rrPhenotypic ratio = 2 Red:2 Blue or 1 Red : 1 Blue

r r

R Rr Rr

r rr rr

R= red flower alleler= blue flower allele