Simple genetics example
Download
1 / 20

simple genetics example - PowerPoint PPT Presentation


  • 289 Views
  • Updated On :

Simple genetics example. Albino rabbits have white coats and red eyes. This is due to lack of the pigment melanin Albinos are actually rather rare in the wild, but common in pet shops!

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'simple genetics example' - liam


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Simple genetics example l.jpg
Simple genetics example

  • Albino rabbits have white coats and red eyes.

  • This is due to lack of the pigment melanin

  • Albinos are actually rather rare in the wild, but common in pet shops!

  • The original albino rabbit arose as a result of a mutation – a very rare event – due to a change in the DNA of the coat colour gene.


Simple genetics example2 l.jpg
Simple genetics example

  • Brown rabbits are the normal colour in the wild. The pigment melanin gives them colouration which enables them to blend in with their surroundings, and protects them from UV radiation.


Parents l.jpg
Parents

We shall consider what happens if we cross an albino rabbit with a brown rabbit.

  • It does not matter which one is the male, and which is the female

  • The result is the same…


F1 offspring l.jpg
F1 offspring

  • All the offspring are the same: they look brown


Using f1 offspring as parents l.jpg
Using F1 offspring as parents

If two of these rabbits are allowed to reproduce…


F2 offspring l.jpg
F2 offspring

The result is:

  • most of the offspring are brown

  • some are albino


F2 offspring7 l.jpg
F2 offspring

Actually the proportion is:

3 brown : 1 albino

(as a ratio)‏

75% brown, 25% albino

(as a percentage)‏


F2 offspring8 l.jpg
F2 offspring

We can also use these figures to give the chance of an individual rabbit being one colour or the other


F2 offspring9 l.jpg
F2 offspring

There is a 3 in 4 (¾) or 75% chance of any baby rabbit being born brown


F2 offspring10 l.jpg
F2 offspring

There is a 1 in 4 (¼) or 25% chance of any baby rabbit being born albino


Some genetics terms dominant recessive l.jpg
Some genetics terms(dominant/recessive)‏

  • Since all the F1 offspring are of one type, we have a straightforward situation.

  • We use the term dominant to describe the characteristic seen in the F1, and most of the F2 – brown

  • Because they seem to recede and are not seen in the F1, we use the term recessive for the albino forms


Some more genetics terms phenotype genotype l.jpg
Some more genetics terms(phenotype/genotype)‏

  • Phenotype is a word used to describe an organism by its observable characteristics, i.e. what it looks like, and we use ordinary words to describe it

  • Genotype is defined at the genetic level, i.e. what genes it contains. This is usually not directly visible, and we describe it using a code


Some more genetics terms genes alleles l.jpg
Some more genetics terms(genes/alleles)‏

In rabbits, the two colour forms are caused by 2 versions of a gene.

We say that the coat colour gene has 2 alleles: brown and albino


Genetics conventions l.jpg
Genetics conventions

  • It is normal to choose a particular letter to stand for the gene we are considering (could be A or B).

  • We use upper case (CAPITALS) for the dominant form and lower case for the recessive form


Genetics conventions15 l.jpg
Genetics conventions

  • The original brown parent is described using the genotype BB (could be AA)‏

  • The original albino parent is described as bb (could be aa)‏

  • These letters are in pairs because chromosomes are in pairs in adult cells


Genetics explanations l.jpg
Genetics: explanations

  • The brown rabbit (genotype BB) produces gametes (sperms or eggs, depending on its sex) containing only the allele B.

  • The albino rabbit (genotype bb) produces gametes (eggs or sperms, depending on its sex) containing only the allele b.

  • This is because meiosis separates chromosomes so that only one of each set is present in the sex cells


Genetics explanations17 l.jpg
Genetics: explanations

The brown rabbits of the F1 all have

the genotype Bb.

Their phenotype is brown because they contain a dominant allele B, and only one dominant allele is enough to give this colouration.

They have the same phenotype as their parent (brown) but a different genotype.


Genetics explanations18 l.jpg
Genetics: explanations

The white rabbits of the F2 all have

the genotype bb.

Their phenotype is white because they contain a pair of recessive alleles bb, and two recessive alleles are required to give this colouration.

They have the same phenotype as their grandparent (white) and the same genotype. Only double recessive genotypes can be forecast this way.


Genetics more terms l.jpg
Genetics: more terms

Because rabbits with the genotype Bb contain two different alleles they are called heterozygous, whereas rabbits with the genotype BB and bb are both called homozygous or true-breeding.


Genetics predictions l.jpg
Genetics: predictions

In heterozygous brown rabbits the recessive allele b is hidden, but it could reappear in the next generation…….


ad