3t chapter 7.4 monohybrid crosses

• Biologie
• Middelbare school
• vwo
• Leerjaar 3

Exercise 1

A father has brown eyes. He is heterozygous for eye colour. Mother has blue eyes. The gene for brown eyes is dominant.

a. Is mother homozygous or heterozygous for eye colour?

   

   b. Two children are born. Child 1 has brown eyes and child 2 has blue eyes. Show this in a cross. Use the letters B and b

P

P

genotype

phenotype

F1

sex cells

possibilities for F1:

Father has brown eyes. 

P

P

genotype:

phenotype:

F1

sex cells:

brown eyes

possibilities for F1:

Mother has blue eyes. 

P

P

genotype:

phenotype:

F1

sex cells:

brown eyes

blue eyes

possibilities for F1:

A father has brown eyes. He is heterozygous for eye colour. Mother has blue eyes. The gene for brown eyes is dominant.

gene is eye colour

2 alleles, they can be:

• brown - brown = homozygous
  
• blue - blue       = homozygous
  
• brown - blue    = heterozygous

brown is dominant: B

blue is recessive:   b

• brown - brown: notation =  BB
  
• blue - blue:       notation =  bb
  
• brown - blue:    notation =  Bb
  

B

b

What means homozygous?

1. a chromosome pair with two equal alleles: AA and aa
2. a chromosome pair with two equal alleles: Aa
3. a chromosome pair with two different alleles: AA and aa
4. a chromosome pair with two different alleles: Aa

What means heterozygous?

1. a chromosome pair with two equal alleles: AA and aa
2. a chromosome pair with two equal alleles: Aa
3. a chromosome pair with two different alleles: Aa
4. a chromosome pair with two different alleles: AA and aa

A father has brown eyes. He is heterozygous for eye colour. Mother has blue eyes. The gene for brown eyes is dominant.

How do you notate the genotypes of father and mother?

Father has brown eyes. He is heterozygous for eye colour. Mother has blue eyes. The gene for brown eyes is dominant.

How do you notate the genotypes of father and mother?

1. father BB, mother Bb
2. father Bb, mother BB
3. father BB, mother bb
4. father Bb, mother bb

P

P

genotype:

phenotype:

F1

sex cells:

brown eyes

blue eyes

bb                             Bb

possibilities for F1:

A father has brown eyes. He is heterozygous for eye colour. Mother has blue eyes. The gene for brown eyes is dominant.

a. Is mother homozygous or heterozygous for eye colour?

  

Is mother homozygous or heterozygous for eye colour?

1. homozygous
2. heterozygous

P

P

genotype:

phenotype:

F1

sex cells:

brown eyes

blue eyes

bb                             Bb

possibilities for F1:

And now the sex cells are made...

Sex cells are made by meiosis.
What happens during meiosis?
One answer is NOT correct. Which one?

1. a diploid (2n) cell divides into 4 haploid (n) cells
2. chromosome pairs are pulled apart into different cells
3. a diploid (2n) cell divides into 2 diploid cells (2n)
4. After meiosis there are 4 sperm cells and 2 egg cells made.

P

P

genotype:

phenotype:

F1

sex cells:

brown eyes

blue eyes

bb                             Bb

b

b

b

B

possibilities for F1:

P

P

genotype:

phenotype:

F1

sex cells:

brown eyes

blue eyes

bb                             Bb

b

b

b

B

possibilities for F1:

What eye colour do the children (F1) have?

P

P

genotype:

phenotype:

F1

sex cells:

	B	b
b
b

brown eyes

blue eyes

bb                             Bb

b

b

b

B

possibilities for F1:

spermcells 

egg cells

P

P

genotype:

phenotype:

F1

sex cells:

	B	b
b	Bb
b

brown eyes

blue eyes

bb                             Bb

b

b

b

B

possibilities for F1:

P

P

genotype:

phenotype:

F1

sex cells:

	B	b
b	Bb	bb
b

brown eyes

blue eyes

bb                             Bb

b

b

b

B

possibilities for F1:

P

P

genotype:

phenotype:

F1

sex cells:

	B	b
b	Bb	bb
b	Bb

brown eyes

blue eyes

bb                             Bb

b

b

b

B

possibilities for F1:

P

P

genotype:

phenotype:

F1

sex cells:

	B	b
b	Bb	bb
b	Bb	bb

brown eyes

blue eyes

bb                             Bb

b

b

b

B

possibilities for F1:

P

P

genotype:

phenotype:

F1

sex cells:

	B	b
b	Bb	bb
b	Bb	bb

brown eyes

blue eyes

bb                             Bb

b

b

b

B

genotype        

• 2x Bb (50%) 
  
• 2x bb (50%) 
  

possibilities for F1:

P

P

genotype:

phenotype:

F1

sex cells:

	B	b
b	Bb	bb
b	Bb	bb

brown eyes

blue eyes

bb                             Bb

b

b

b

B

genotype        

• 2x Bb (50%) 
  
• 2x bb (50%) 
  

phenotype

• brown eyes
  
• blue eyes
  

possibilities for F1:

Exercise 1

A father has brown eyes. He is heterozygous for eye colour. Mother has blue eyes. The gene for brown eyes is dominant.

a. Is mother homozygous or heterozygous for eye colour?

Mother is homozygous : she has bb

   b. Two children are born. Child 1 has brown eyes and child 2 has blue eyes. Show this in a cross. Use the letters B and b

Done.

P

P

genotype

phenotype

F1

sex cells

possibilities for F1: