Lesson 3 Genetic Crosses

• Biologie
• Middelbare school
• havo
• Leerjaar 3,4

Lesson 3

Genetic Crosses

Learning Goals:

You can explain what hereditary traits are.

You can explain what the difference is between phenotype and genotype.

You can explain how hereditary traits are transmitted to the following generation.

You can predict what the outcome of a genetic crossing will be.

This Lesson:

1. Quiz - check concepts

2. Check homework question

3. Explanation Genetic crosses & punnett squares

4. Class work: quesions 2,3 & 4 from reader

This lesson is linked to the Lesson 3 Reader (Google Classroom).

What is the genotype of these tomatoes?

Red

We don't know

Round

Sweet

Which of the following is not a trait?

1. Colour of eyes
2. Shape of leaves
3. Sweet taste
4. Taste

In pea plants small leaves are dominant over large leaves. Which of the genotypes will have large leaves?

1. Ff
2. ff
3. FF
4. fF

In pea plants small leaves are dominant over large leaves. Which of the genotypes will have small leaves?

1. Ff and FF
2. ff
3. FF & ff
4. Only FF

Homework question

Instruction

1. Predicting Outcomes of Genetic Crossings

2. Using test crosses to work out genotypes

1. Anwers question 2 a.

2. Answer question 2b. ??????????????

1 Punnett Squares  = predicating genetic crosses

Punnett squares - used to predict outcomes of crosses:

What is the % of genotypes in F1 in a cross of heterozygous dominant X homozygous recessive?

1. 25% Aa + 75% aa
2. 50% Aa + 25% aa
3. 50% Aa + 50% aa
4. 50% AA + 50% aa

What is the ratio of phenotypes in F1 in a cross of heterozygous dominant X homozygous recessive?

1. 1:1
2. 3:1
3. 2:1
4. 4:1

Gentypes: 50% Aa + 50% aa

Phenotypes:  1:1  (Aa:aa)

2. Using a test cross to work out genotype

We want to use the small sweet tomatoes for our nieuw tomato variety:

- We know it's phenotype = sweet!

- But what is the genotype? 

- Is genotype ZZ or Zz (sweet is dominant)?

How van we test which genotype a plant has? We do a test cross using a know phenotype = homozygous recessive.

Example of a test cross with known homozygous recessive plant (zz)

Time to work!

1. Do question 2, 3 & 4 from your reader using punnett  squares.

Let op!

Make sure you check your own work & take notes as we go through the answers. 

Let op!

Make sure you check your own work & take notes as we go through the answers. 

What have we learned this lesson?