V4 Inheritance 7

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Welcome!

Have the following ready:

• Notebook/document to take notes in
• Sex-linked inheritance worksheet (have it open)

Roadmap for today:

Goal: Introducing the last new topics (multiple alleles and lethal alleles) + reviewing the chapter

• Discuss sticky note question from last lesson
• Presentation: introduction to multiple alleles and lethal alleles (take notes!)
• Kahoot (review of chapter)
• Time to study/finish worksheets

Question from last lesson:

How does sex-linked inheritance affect the phenotypic ratio of the F1?

- The trait is expressed in the offspring (boys) more often than if the allele was not sex-linked.

Phenotypic ratios with sex linkage:

• If the father is XᵃY and mother XᵃX, then half of girls have the trait, half of girls are carriers, half of boys have the trait (1:1, same as if parents were aa and Aa)
• If the father is XY and the mother is XᵃXᵃ: all girls are carriers, all boys have the trait (1:1 instead of 1:0 if the parents were AA and aa).
• If the father is XY and the mother is XᵃX: half of boys have the trait, half of girls are carriers (3:1 instead of 1:0 if the parents were AA and Aa).
• What if the father is XᵃY and mother XᵃXᵃ?

What will be the genotypic and phenotypic ratio if the father is XᵃY and mother XᵃXᵃ?

Multiple alleles

A gene with more than two alleles.

Example: blood type in humans

I stands for isoagglutinogen, which is the name for the  type of antigen on red blood cells.

A heterozygous woman with blood type A is married to a man with blood type O. What are all the possible genotypes of the offspring?

Lethal alleles

Alleles which cause an organism to die only when the organism is homozygous for the allele.

You can recognize the presence of a lethal allele by looking at the phenotypic ratio of the offspring. The ratio will be different than 

Question: why do we only find lethal alleles which are recessive?

• Which phenotypic ratio would you expect to observe if the allele was not lethal?
• Which phenotypic ratio do you actually observe?

What sex ratio would you expect among the offspring of a cross between a normal male mouse and a female mouse heterozygous for a recessive X-linked lethal gene?

Write a legend for this image: 

What does square vs. circle mean?

What does grey vs. white mean?

1

2

Person 1 is female and healthy. 

Person 2 is female and has an inheritable disease. 

pedigree chart for the family Jones

5 minute break

Self-directed work time:

Use this time to prepare for the test

Study the book and the lessonups, finish any unfinished worksheets, ask questions etc.

Homework for Tuesday:

• finish the codominance worksheet
• prepare to do a practice test

You may work together (put everyone's names in the worksheet title)