WJEC Biology:Genetic crosses.
Genetic diagrams
Gregor Mendel (1822-1884) studied the inheritance of different characteristics in pea plants. He found that when he bred red-flowered plants with white-flowered plants, all the offspring produced red flowers. If he bred these plants with each other, most of the offspring had red flowers but some had white. This was because the allele for red flowers is dominant and the allele for white flowers is recessive. Genetic diagrams help to show how this works.
In a genetic diagram, you show all of the possible alleles for a particular characteristic. There will be twoalleles from one parent and two from the other parent, making four altogether. You then draw lines to show all the possible ways that these alleles could be paired in the offspring. There will be four possible ways but some or all of them could be repeated.
A genetic diagram showing the outcome of Mendel's first cross. All the offspring have red flowers, even though they carry the recessive allele for white flowers
In genetic diagrams, the dominant allele (this allele will always have an affect) is shown as a capital letter, while the recessive allele(this allele will not be seen if a dominant is present) is shown as a lower-case letter.
A genetic diagram showing the outcome of Mendel's second cross. Three-quarters of the offspring have red flowers and a quarter have white flowers
The alleles in the organism are the genotype. What the organism looks like, eg red flower is the phenotype.
Offspring with two alleles the same are homozygous eg FF or ff. If the alleles are different eg Ff then it is heterozygous.
Cystic fibrosis
Genetic diagrams (Punnett squares)
Genetic diagrams or Punnett squares are used to show the possible outcomes of a particular cross. A dominantallele is shown by a capital letter, and a recessiveallele by a lower case letter.
Cystic fibrosis (CF) is caused by a recessive allele. In the genetic diagram below, it is written as f.
People with CF produce abnormally thick and sticky mucus in their lungs and airways. As a result, they are more likely to get respiratory infections. Daily physiotherapy helps to relieve congestion, while antibiotics can fight infection. CF also affects the gut and pancreas, so food is not digested efficiently.
Inheriting copies of the allele
You need to inherit two copies of the faulty allele to be born with CF. If you have just one copy, you are a carrier, but will not experience any symptoms. If two carriers have a child together, there is a one in four chance (or 25 per cent) of it inheriting the disorder.
The genetic diagrams shows why.
Cystic fibrosis is an inheriteddisorder caused by a recessiveallele. This genetic diagram shows the possible outcomes when both parents are heterozygous for the faulty allele. There is a one in four chance or 25 percent of the offspring being homozygous for the faulty allele, and so having cystic fibrosis.
This genetic diagram shows the possible outcomes when only one parent carries the faulty allele. There is no chance of the offspring being homozygous for the faulty allele, and so having cystic fibrosis.
WJEC Biology: Gc.
Genetic diagrams
G M (1822-1884) studied the I of different characteristics in pea plants. He found that when he b red-flowered plants with white-flowered plants, all the offspring produced red flowers. If he b these plants with each other, most of the offspring had red flowers but some had white. This was because the a for red flowers is d and the a for white flowers is r . Genetic diagrams help to show how this works.
In a genetic diagram, you show all of the possible a for a particular c. There will be ta from one parent and t from the other parent, making f altogether. You then draw lines to show all the possible ways that these alleles could be paired in the offspring. There will be four possible ways but some or all of them could be repeated.
A genetic diagram showing the outcome of Mendel's first cross. All the offspring have red flowers, even though they carry the recessive allele for white flowers
In genetic diagrams, the d a (this allele will always have an affect) is shown as a capital letter, while the recessive allele(this allele will not be seen if a dominant is present) is shown as a lower-case letter.
A genetic diagram showing the outcome of Mendel's second cross. Three-quarters of the offspring have red flowers and a quarter have white flowers
The a in the organism are the g. What the organism looks like, eg red flower is the p.
Offspring with two alleles the same are h eg FF or ff. If the a are different eg Ff then it is h.
Cystic fibrosis
Genetic diagrams (P s)
Genetic diagrams or P s are used to show the possible outcomes of a particular cross. A da is shown by a c l, and a r a by a lower case letter.
C f (CF) is caused by a r a. In the g diagram below, it is written as f.
People with CF produce abnormally thick and sticky mucus in their lungs and airways. As a result, they are more likely to get respiratory infections. Daily physiotherapy helps to relieve congestion, while antibiotics can fight infection. CF also affects the gut and pancreas, so food is not digested efficiently.
Inheriting copies of the a
You need to inherit t copies of the f a to be born with CF. If you have just one copy, you are a carrier, but will not experience any symptoms. If t carriers have a child together, there is a one in four chance (or 25 per cent) of it I the disorder.
The genetic diagrams shows why.
Cystic fibrosis is an Id caused by a ra. This genetic diagram shows the possible outcomes when both parents are h for the f allele. There is a one in four chance or 25 percent of the offspring being h for the f a , and so having c f .
This genetic diagram shows the possible outcomes when only one parent carries the fa. There is no chance of the offspring being h for the f a , and so having cystic fibrosis.