Ch.1 Traits in pairs

• Biologie
• Middelbare school
• vwo
• Leerjaar 3

What to do:

• Read everything well!
  
• Make a glossary (begrippenlijst) from all terms you see in the text. 
• Answer all questions!

• You can ask me questions when I'm done explaining to the rest of the class.

At the end of this lesson you can:

• …describe what genotypes and phenotypes are.
  
• …name the characteristics of chromosomes.
  
• ...describe the difference between genes and alleles.

phenotype (uiterlijk)

Everyone knows they look their parents. They look a little like their father and a little like their mother. At the same time you are not half of either. You are unique.

Your appearance (visible characteristics) is called your ​phenotype​. These are the ​traits we can see on an organism.

Phenotype: the visible traits (eigenschappen) of an organism.

genotype (genetisch materiaal)

The basis for almost all traits is your ​genotype​. Your genotype is a combination of all traits that you can find on your ​DNA​.

Genotype: the DNA sequence (code) for hereditary (erfelijke) characteristics in an organism.

genotype vs fenotype

You phenotype can change by influences from your environment (omgeving). By for example dying your hair a different colour. 

Your genotype can not change. 

Phenotype = Genotype + environment

The information for your hereditary characteristics is your DNA. But what exactly is DNA?

genotype

phenotype

XY chromosomes

cannot change!

you inherit this

can sometimes change during your life

you do not inherit this

a scar

Is not always visible

Identical twins do have the same genotype but not necessarily the same phenotype

1. true
2. false

DNA: a long thin thread of a code that contains the information for all your hereditary traits. The building blocks can make many different codes for many different traits. 

A segment of DNA has the following order of nucleotides : ATTGGCAGTA. What is the order of nucleotides on the other strand?

Chromosomes

The long thin threads of DNA are bundled together into  chromosomes (Fig. 1)

Chromosomes are located in the nucleus of every cell in your body (except red blood cells).

The chromosomes contain all information for all you hereditary traits. (Fig. 2)

Fig. 1

Fig. 2

Where in your cells can you find chromosomes?

Body cells

The nucleus of the body cells of a human:

(cells that make up the body, for ex. liver cells, skin cells, muscle cells etc) contain 46 chromosomes. 

Every chromosome carries the information for different hereditary traits. 

Chromosomes occur in pairs. Two chromosomes in a pair match; they carry information for the same traits. There are 23 pairs.

Body cells

The first 22 pairs of chromosomes are present in every human (called autosomes). 

The 23rd pair is special because they are not always the same. These are the sex chromosomes.

Sex chromosomes determine whether your genetic sex is male or female. 

Males have X-Y chromosomes

Females X-X chromosomes. 

Sex cells

Sex cells are different than the body cells. 

Sex cells contain 23 chromosomes. There are no pairs. 

This is because the nucleus of the sex cell of a man and the nucleus of the sex cell of a woman fuse together. 

This way the child has 50% of its genetic information form the father and 50% of the mother. 

Pair 23 will determine the sex of the child. This depends of chromosome 23 of the spermcell  is a X or a Y chromosome. 

How many chromosomes do you have in each nucleus?

1. 44
2. 46
3. 48
4. 23

How many sex chromosomes do you have in a muscle cell?

1. 0
2. 1
3. 2
4. 46

How many X chromosomes do you have in a skin cell?

1. 0
2. 1
3. 2
4. 46

A cell with an X chromosome and a Y chromosome, can be a

1. muscle cell
2. sperm cell
3. egg cell
4. no cell

Genes

Each chromosome contains the information of a large number of hereditary traits. 

A part of a chromosome that contains the information for one trait is called a gene.

Each chromosome contains lots of genes. 

Every ​body cell​ ​in an organism has all the DNA (and all the genes) to build a complete organism. This means that all genes can be found in every cell. 

Why do we still look different then?

Genes

First it is important to understand that genes are not always active. Genes can be turned on or off. That is why your body changes over time. 

Genes can be (de-)activated by many things.

For example: 

-Gene to make you grow. Activated by hormones. No hormones? Gene not active 

Alleles

Secondly many genes have ​variants​ of the same trait. These variants are called ​alleles​.

A few examples:

- Everyone has the ​gene​ for eye colour. There are two ​alleles​ for eye colour, such as

blue or brown. ‘Eye colour’ is the gene, ‘blue’ and ‘brown’ are alleles;

- Everyone has a ​gene f​or hairstyle.‘Straight hair’ and ‘curly hair’ are​ alleles ​of this gene.

Oliver says: 'all humans have the same genes, but not the same alleles'. Charley says: 'all humans have the same alleles, but not the same genes'. Who is right?

1. Oliver
2. Charley
3. They both are
4. They are both wrong

Is it a gene or an allele?

GENE

ALLELE

skin colour

curly hair

flower colour

blue eyes

blood type

type A blood

colour-blindness

hair type

short wings in a fruit fly

Write down any questions you have or parts you still find difficult.

Done?

1. Make the exercises chapter 1 'Genes and alleles' in the document @studiewijzer 

2. Make exercises basic 5.1 at Malmberg if you haven't done that yet.

3. Start reading chapter 2 @booklet

4. Make the glossary (begrippenlijst) if you haven't yet.