Punnett Square Notes1. For this assignment, you are to use this PowerPoint which contains additional

videos and the packet you picked up today.

2. When you complete the entire packet, please show Mrs. Akona for credit. Failure to do so will result in zero credit.

3. After you show Mrs. Akona the completed packet, you can keep the packet and use as notes to complete review worksheets that you will get over the next couple days.

4. I strongly encourage you to ask questions when you don’t understand. Mrs. Akona is familiar with punnett squares. In addition to using her as a resource, Mrs. Bellah next door has also opened her door to you for additional help while I am away. Mr. Castro and Mr. Morales work at the Waverider Learning Center after school who can also help you with Punnett Squares. Please seek out these resources! They are awesome people who are more than willing to help you clear up any confusion.

5. Remember! All I ask is that you try. You will never learn unless you try!

Review on DNA & Intro to Geneticsclick on this link if video pauses or runs slow

What are Punnett Squares

How to draw a punnett square

Notes: ALL 2010 What is Punnett Square? 8. Biologist use a diagram called a punnett square to help predict

the probability that certain traits will be inherited by offspring.9. The punnett square used for crossing one trait (what is the

prefix for one) between two parents is called a monohybrid.10. The punnett square used for crossing two traits (what is the

prefix for two) between two parents is called a dihybrid.11. What are autosomes? The chromosomes pairs 1-22.12. Traits inherited on chromosome pairs 1-22 are called

autosomal traits.

13.What is the 23rd pair of chromosomes called? The sex chromosomes. Sex chromosomes determine gender but they also contain genes for other traits as well. For example, the gene for colorblindness is located on the X chromosome.

14.Traits that are inherited on chromosomes pair 23, the sex chromosomes are called sex-linked.

a. If the trait is on the “X” chromosomes it is called X-linked.b. If the trait is on the “Y” chromosome it is called Y-linked.c. True or false? One females can inherit X-link traits while only

males can inherit Y-linked traits?a. FALSE! Both males (XY) and females (XX) can inherit X-linked traits

because the both carry the X-chromosome. However! Males can only inherit Y-linked traits because they carry a Y-chromosome. Females cannot inherit Y-linked traits because they do not have the Y-chromosome.

15.Having the phenotype “freckles” is inherited autosomal dominant. This means that the gene for the trait freckles is found on one of the chromosome pairs 1-22. In order to “get” freckles you only have to inherit 1 copy of the freckle gene.

F f

f

f

Ff

Ff

ff

ff

Step 1 and 2 Step 5

a. When we talk about phenotype, we are talking about what is see or “features”

b. So write all the possible phenotypes that could result by crossing the genotypes of these two parents. Freckles and no freckles.

c. Now… write the above phenotypes in a ratio form. 2 freckles : 2 no freckles

d. When we talk about genotype, we are talking about the letters used to represent the genes for traits.

e. Now…write all the possible genotypes that could result by crossing the genotypes of these two parents. Ff and ff

f. Now…write the above genotypes in a ratio form. 2Ff : 2ff

FfFf F f

F

f

FF Ff

Ff ff

17.

a) Write all the possible phenotypes that could result by crossing the genotypes of these two parents. Freckles and no freckles

b) Now…write the above phenotypes in a ratio form. 3freckles : 1 no freckles

c) Write all the possible genotypes that could result by crossing the genotypes of these two parents. FF, Ff, ff

d) Now…write the above genotypes in a ratio form. 1FF : 2Ff : 1ff

e) What is the probability of producing an offspring that is homozygous dominant for freckles (hint: write first as a fraction, then as a percent)? 25%

f) What is the probability of producing an offspring that has no freckles? 25%

g) What is the probability of producing an offspring that is heterozygous for freckles? 50%

19. Problem: Let “c” represent a cleft chin. Cross a parent that is homozygous no cleft chin with a parent that has a cleft chin.

a) What is the phenotypic ratio? 4 no cleft chinb) What is the genotypic ratio? 4Ccc) What is the probability of producing an

offspring that has no cleft? 100%d) What is the probability of producing an

offspring that has a cleft chin? 0%

• Complete 20-22 on your own.

23. Some genetic diseases are inherited autosomal recessive. This means in order to be affected with specific genetic diseases, the offspring needs to inherit two “diseased” allele (one from each parent) to be affected.

24. Congenital neutropenia, severe (SCN) is a genetic

disease that is inherited autosomal recessive. In this disease, children with this condition lack neutrophils (a type of white blood cell that is important in fighting infection). These children suffer frequent infections from bacteria which in the past led to death in three-quarters of cases before 3 years of age. This disease is also known as severe congenital neutropenia (SCN). Let “d” represent the disease. Cross 2 parents who are carriers of this disease.

#24. continued

• Phenotypic ratio? 3unaffected: 1affected• Genotypic ratio? 1DD: 2Dd: 1dd• Probability of producing an unaffected

offspring? 75%• Probability of producing an affected offspring?

25%• Probability of producing a carrier of the

disease? 50%

25. Phenylketonuria (PKU) is an inherited error of metabolism caused by a deficiency in the enzyme phenylalanine hydroxylase. This is a metabolic disorder that leads to a harmful buildup of the phenylalanine in the body. Normally the “working” enzyme coverts phenylalanine into tyrosine. The severity of the symptoms can range from severe enough to cause mental retardation to mild enough not to require treatment. Severity is determined by the level of impairment of enzyme activity of phenylalanine hydroxylase. PKU is inherited autosomal recessive.

Let “P” represent unaffected while “p” represent affected. Cross an affected father with a mother that is a carrier.

#25. continued

• Phenotypic ratio? 2 unaffected : 2 affected • Genotypic ratio? 2Pp : 2pp• Probability of producing an unaffected

offspring? 50%• Probability of producing an affected offspring?

50%• Probability of producing a carrier of the

disease? 50%

• Complete the rest of the packet and correct your answers with Mrs. Akona