V4 Inheritance 1

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Planning until the test week:

- Today (1 Feb): inheritance (genes, alleles & loci, dominant/ recessive, homozygous/heterozygous, genotype/phenotype)

- Friday (4 Feb): inheritance (monohybrid inheritance, continuous and discontinuous variation)

- Tuesday (7 Feb): preparation for test (last questions, 30 seconds with terms)

Goals for today:

- Know the difference between a gene, an allele and a locus

- Know what dominant and recessive alleles are

- Know the difference between genotype and phenotype

- Be able to calculate the probability of inheriting a certain trait in monohybrid inheritance

Gregor Mendel (1822-84)

                 :

Genes, alleles, loci and chromosomes

Recall: a gene codes for a protein. This protein will have certain traits, determined by the gene.

Every gene is located at a fixed place in the genome. This place is called a locus (plural: loci).

Different versions of a gene can be found in every population. Each different version is called an allele. 

To inherit = to receive a characteristic from an ancestor by genetic transmission. 

• Genotype = complete set of all inherited characteristics. 
• Example: the plant has one allele for purple flowers (P) and one allele for white flowers (p)

• Phenotype = set of characteristics that are seen/expressed. 
• Example: the plant produces purple flowers.

Phenotype = genotype + pattern of gene expression + environmental factors. 

Letter notation for genes en alleles

Complete dominance

A letter is assigned to the gene *

dominante allele: capital letter   (A)

recessive allele: lowercase letter   (a)

Genotypes

homozygous dominant:    AA

heterozygous:                       Aa (convention: you never write aA)

homozygous recessive:      aa

* = if you choose a letter yourself, choose a letter that has a clearly different capital letter vs. lowercase letter (e.g. Aa and Hh are better than Ss or Oo). 

Incomplete dominance

Sometimes the recessive allele also influences the phenotype just slightly

Sometimes both alleles are evenly dominant in determining the phenotype

A homozygous plant with two alleles for red flowers produces red flowers.

A homozygous plant with two alleles for white flowers produces white flowers.

A heterozygous plant with both an allele for red flowers and for white flowers produces pink flowers.

Because both alleles are evenly dominant, both are determining the phenotype together.

The resulting phenotype is called an intermediate phenotype.

small revision 

What's the difference between ... 

• an allele and a gene?
• genotype and phenotype?
• homozygous and heterozygous?
• dominant and recessive? 

Monohybrid cross worksheet

- no phones (unless permission asked)

- yes music (using computer)

- no distracting each other

- yes working together

Convention rules in genetics:

USE CAPITAL LETTERS FOR DOMINANT ALLELES

and

lower case letters for recessive alleles

(Tip: avoid using non distinct letter like Ww or Ss rather use Hh)