Phenotype - Will I look like my mum or my dad?

Part 1 Introduction: 1. Describe the genotypes given (use your notes). The first two are

already done.

A. DD homozygous, dominant B. Dd heterozygous C. dd __________________

E. Yy ______________________

D. ss ______________________

F. WW ____________________

Image source: http://www.abpischools.org.uk/page/modules/genome/dna2.cfm?coSiteNavigation_allTopic=1

2. In humans, brown eye colour (B), is dominant over blue eye colour (b).

What are the phenotypes of the following genotypes?

In other words, what colour eyes will they have?

A. BB ________________________

B. bb ________________________

C. Bb ________________________

The alleles for blue eyes are:

Source: http://en.wikipedia.org/wiki/File:Eye_iris.jpg#file

The alleles for brown eyes are:

or

Source: http://en.wikipedia.org/wiki/File:Menschliches_auge.jpg

Part 2 How to solve genetic problems using Punnett square #

Learn these 5 steps carefully.

If you take the time to follow the directions below, you will be able to solve most genetics problems. 1. Determine the genotypes of the parents or whatever is given in problem.

2. Set up your Punnett square as follows: *# sq. based on possible gametes

that can be formed.

3. Fill in the squares. This represents the possible combinations that could

occur during fertilization.

4. Write out the possible genotypic ratio of the offspring.

5. Using the genotypic (gene) ratio determine (work out) the phenotypic (the

type/features that show up) ratio for the offspring.

Now go to the next page and work out the chances of an

offspring/child inheriting certain eye colours.

Possible parent gametes

(mother’s egg cells)

Other possible parent

gametes (father’s

sperm cells)

What are the chances of a child having blue eyes? In humans, brown eye allele (B) is dominant over blue eye allele (b).

A homozygous dominant (BB) or heterozygous (Bb) offspring/child will have

brown eyes. A homozygous recessive (bb) child will have blue eyes.

A heterozygous woman marries a homozygous recessive man.

1. Work out the genotypes of the parents (parent’s genes).

Mother

Father

2. Set up a Punnett square with possible gametes (sex cells).

Explanation 1: During meiosis (the formation of sex cells) one member (allele) of each

gene pair separate. In this example, the male (Bb) produces some sperm containing

“B” (the allele for brown) and some sperm containing “b” (the allele for blue).

3. Fill in the Punnett squares above to work out the possible combination for

the offspring. Explanation 2: During fertilization sperm meets the egg. The Punnett square show us

the possible combination of genes during fertilization.

4. Count the number of possible genotypes.

Number of BB = ______

Number of Bb = ______

Number of bb = ______

5. What is the predicted phenotypic ratio for the offspring? What shows up?

Number of brown eyes child/offspring = ______

Number of blue eyes child/offspring = ______

Fill in the circles

only and go to

step 3.