Mrs. Anna WardSeventh Grade Science

James Martin MS

Probability of InheritanceLesson 3

In rats, gray fur is dominant over white fur. Complete a

Monohybrid Cross to identify the possible fur

colors of offspring between a rat that is heterozygous for gray fur (Gg) with a rat

that is homozygous recessive (gg) for

white fur. In addtion, give the ratios of gray fur to

white fur.

DO NOW!!!!

Gg gg

gg gg

G=Gray fur Dominantg=white fur recessive

Gg x gg

1 Gg to 3 gg

1 gray rat to 3 gray rats

or

25 % gray75 white

DO NOW!!! Solution

G g

g

g

Quiz today to check for understanding

Announcements

Short video review on Punnett Squares

Quiz

Calculating Ratios from Punnett Squares Independent Practice

Ink Think Article “Genes tell old Story”

Agenda

http://www.youtube.com/watch?v=d4izVAkhMPQ

REVIEW FROM YESTERDAY:

PUNNETT SQUARES

In humans, brown eyes (B) are dominant to blue eyes (b).

1. What are the possible phenotypes for eye color as listed above?

2. What would the be genotype of: a) a homozygous dominant human?b) A homozygous recessive human?c) A heterozygous human?

3. Which genotype(s) would code for brown eyes?4. Which genotype(s) would code for blue eyes?5. Draw a Punnett Square that crosses a homozygous

dominant woman with a heterozygous man.6. What are the possible genotypes?7. Draw a Punnett Square that crosses a heterozygous

female with a homozygous recessive male.8. What are the possible genotypes?

Quiz

For Monohybrid Crosses, the ratios are always going to occur in fourths, because there are four squares.

To Calculate the GENOTYPIC RATIOS, count the number of each GENOTYPE and put that over 4.

Example: The Genotypic Ratio in the figure to the right is:

1 BB to 2 Bb to 1 bbor 1:2:1

Calculating Ratios from Punnett

Squares

BB Bb

Bb Bb

To Calculate the PHENOTYPIC RATIOS, count the number of each PHENOTYPE and put that over 4.

There are typically only two phenotypes for monohybrid crosses, the dominant & the recessive trait.

Example: The Phenotypic Ratio in the figure to the right is:

3 Brown to 1 Blueor 3:1

Calculating Ratios from Punnett

Squares

BB Bb

Bb Bb

This is something you should be very familiar with from MATH class.

For monohybrid crosses, it is always going to be a factor of 25%, because there are 4 squares.

You can calculate the percentages based on the phenotype or genotype.

Example: The genotype is 25% BB, 50% Bb, and 25%

bb. The phenotype is 75% brown, 25% blue.

Calculating Percentages from

Ratios

BB Bb

Bb Bb

Bb Bb

Bb Bb

Now you try!

Question # 1In Rabbits, Black Fur (F) is dominant to White Fur (f).

Imagine you have a Homozygous Dominant Black Male Rabbit that you are going to mate with a Homozygous Recessive White Female Rabbit.

Draw the Punnett Square to predict the offspring.

What is the genotype ratio?

What is the phenotype ratio?

Genotype Ratio: 100 % Heterozygous or BbPhenotype Ratio: 100 % Black Fur

Bb bb

Bb bb

Now you try!

Question # 2In Rabbits, Black Fur (F) is dominant to White Fur (f).

Imagine you have a Heterozygous Black Male Rabbit that you are going to mate with a Homozygous Recessive White Female Rabbit.

Draw the Punnett Square to predict the offspring.

What is the genotype ratio?

What is the phenotype ratio?

Genotype Ratio: 50% Heterozygous (Bb) Rabbits to 50% Homozygous Recessive Rabbits (bb)Phenotype Ratio: 50% Black Rabbits, 50% White Rabbits

Independent Practice

Sheets

Remember this from last week?

Underline or highlight things you want to remember or you deem important

Circle words you don’t know ? Mark thinks you don’t

understand

Attach the Passage in your Science Notebook.

INK THINK:“Old Genes Tell

the Story”

In Rabbits, Black Fur (F) is dominant to White Fur (f).

Imagine you have a Heterozygous Black Male Rabbit that you are going to mate with a Heterozygous Black Female Rabbit.

1. Draw the Punnett Square to predict the offspring.

2. What is the genotype ratio?3. What is the phenotype ratio?

EXIT TICKET OUT THE DOOR

My sister’s bunny, Basil Q. Hoppenfluff