Genetics - Pedigrees Joshua Levine A 5e Lesson Bell Work Albinism - - PowerPoint PPT Presentation

Genetics - Pedigrees

Joshua Levine A 5e Lesson

Bell Work

• Albinism is a genetic trait characterized by a

lack of pigment and caused by inheritance of recessive alleles for a single gene.

• 1. Draw a Punnett Square for a cross between two

adults that are both heterozygous for Albinism.

• 2. What percentage of this couples children are

expected to have the albinism phenotype?

• 3. If this couple has 2 children, what is the

probability that:

a) Both will be albino? b) Neither will be albino?

Pedigrees

• Pedigrees are “family trees” that show the

inheritance of a trait.

Conventions?

Royal Hemophilia Pedigree

Building Pedigrees

• We are going to build a pedigree for Wet

(dominant) versus Dry (recessive) earwax.

• Wet allele

= W

• Dry allele

= w

• Which genotype(s) will have wet earwax?
• Which genotype(s) will have dry earwax?

Part 1: Find a Mate!

• Roll dice to determine how many offspring

you and your mate will produce.

• For each offspring

– Determine sex: coin flip

• Heads = female
• Tails = male

– Determine Genotype: each parent contributes

• ne allele to each offspring (everyone starts

heterozygous)

• Heterozygous parents: flip a coin (heads = W, tails = w)
• Homozygous parents: no coin flipping for you, you only

have one allele to pass!

Part 2: Next Generation!

• “Arrange” a marriage for one of you and

your mate’s offspring with another pair’s

• ffspring.
• Mate again, using same rules as before.

– Dice roll for number of offspring – Coin flip for sex

• heads = female
• tails

= male

– Coin flip for heterozygous parents

• Heads = W (wet earwax allele)
• Tails

= w (dry earwax allele)

Part 3: Diagram!

• Using proper pedigree conventions,

diagram the lineage you have created with your group.

• Display “dry earwax” as the trait of interest.

Dry Wet

Interpreting Pedigrees

• Sometimes we don’t know the underlying

genetics of a trait, but we can use pedigrees to figure them out.

• Let’s look at some examples…

Cystic Fibrosis (CF)

• CF is a disease primarily of the lungs where

sodium and chloride are not transported properly.

• Given this pedigree, what is the likely mode of

inheritance of CF? Why?

Cystic Fibrosis (CF)

• What is the probability that if the circled

couple has another child, it will have CF?

Continue Worksheet

• You may work in groups or alone
• PKU
• Tongue rolling
• DMD
• We will go over the answers tomorrow in

class!

Closure – Genetic Counseling

• Many of the examples we examined today

involve diseases that can have adverse effects on quality of life. Imagine you are analyzing a pedigree for a couple that wants to have children, but may adopt because they know there are diseases in their families. What are the pros and cons

• f knowing the probability of future

children having a disease?

END

Bell Work - Answers

1) 2) 25% 3a) 1/16 (¼ * ¼) 3b) 9/16 (¾ * ¾)

Interpreting Pedigrees - Answers

• CF

– Recessive, because two unaffected individuals (grandparents) gave birth to an affected offspring, they must both be heterozygous. – 50%

• PKU

– Recessive – No, parents of circled must be heterozygous, therefore at least one grandparent must also be heterozygous – 1/9 = 2/3 * 2/3 * 1/4

Interpreting Pedigrees - Answers

• Tongue Rolling

– Dominant – Heterozygous – ¼ = ½ * ½

• DMD

– Recessive, sex-linked – X chromosome – ¼ (½ probability that mom is carrier * ½ probability that she will pass on DMD allele) – 0 (females can not develop X linked recessive unless their father had the disease and mother was a carrier)