Monohybrid crosses and Punnet square

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

male and female

male:    2 x 22 autosomes + 

                X + Y 

                = 46 chromosomes

female: 2 x 22 autosomes + 

                X + X

                 = 46 chromosomes

Different information on a chromosome pair

GENE: section of DNA with complete code for a protein

proteins

determine almost everything...

one gene = code for one protein

one or several proteins = one characteristic (hereditary trait)

Gene

A piece of DNA that contains the code for a one characteristic is what we call a gene.

Gene and allele

gene = piece of DNA that codes for 1 protein = 1 trait

• chromosomes are in pairs and thus genes as well

allele = one of the variants of a gene

homozygous = when an allele pair consists of two identical alleles

heterozygous = when an allele pair consists of two different alleles

dominant allele: allele that is always expressed in the phenotype

• A

recessive allele: allele that is only expressed in the phenotype if there is no dominant allele present

• a

Learning objectives: MONOHYBRID CROSS/ PUNNETT SQUARE

• You can create a crossbreeding diagram (Punnett square) for a monohybrid cross.
• You can find the frequency of specific genotypes and phenotypes in offspring from a Punnet square or a monohybrid cross.
  

WhAT

*read in reader page 3-9

** make 2 worksheets
** make excersizes in reader

*** study for test 

HOW

individually

in silence

NEED HELP

1. read the text again (reader or book)
2. raise your hand

get to work - IN SILENCE

Predicting genotypes

You pass your genes on with ovums and sperm cells.

These contain half of your chromosomes. 

One of each pair. 

Monohybrid Cross

The inheretence of 1 characteristic

1 characteristic = 1 genepair

inheretence = the passing on of charateristics from parent to kids

Monohybrid cross 

One characteristic: haircolour

• 2 options: 1 chocolate and 1 is yellow

Question: The gene for chocolate hair colour 

inherets dominantly. 

If two heterozygous chocolate labradors mate.

What is the chance for yellow puppy's?

What to do? Make a monohyrbid cross

Steps to follow:

1. What are the phenotypes off the parents?
2. What are the genotypen van de ouders? 
3. Which alleles do the sex cells contain?  
4. What possibilities are there for the fusion
   of the egg and spermcell?                                                                               
    => monohybrid cross/punnett square

 The gene for chocolate hair color inherets dominantly. If two heterozygous chocolate labradors mate. What is the chance for yellow puppy's?

A = chocolate, a = yellow

P:                phenotype: ............................ x ...............................

                   genotype: ........................... x ...............................

Sex cells               :      ......... of ...........         ........  of ...........

Monohybrid cross

A = chocolate, a = yellow

                                              woman          man:

P:                phenotype:   chocolate  x   chocolate

                   genotype:               Aa       x      Aa

Sexcells              :                    A of a            A of a

Monohybrid cross

	A	a
A	AA	Aa
a	Aa	aa

Monohybrid cross/

Punnett squares

1

2

3

What is de F2???

When the F1 generation start to have kids together

P = parents

F1 = first generation

F2: second generation (kids among themselves)

test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

Test cross

How to know if an organism is heterozygous (Rr) or homozygous (RR)?

--> crossing the unknown parent with a homozygous recessive parent

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.

Family tree in biology 

A family tree

What phenotype is dominant?

Intermediate phenotype

Intermediate phenotype = exists if both alleles of a gene couple are present and if they are both equally strong

Example: Andalusian chickens

Black + white = grey

Denoting an intermediate phenotype

Black feathers 

C^BC^B

White feathers

C^WC^W

Grey feathers (intermediate phenotype)

C^BC^W

intermediate phenotype

WhAT

*read in reader page 3-9

** make 2 worksheets
** make excersizes in reader

*** study for test 

HOW

individually

in silence

NEED HELP

1. read the text again (reader or book)
2. raise your hand

get to work - IN SILENCE