Introduction to genetics and patterns of inheritance

Lesson 3: Applied genetics

Grade 10 ASP Biology

Applied genetics

Remember to use your digital notebook!!

Learning objective

�

Keywords

• Selective breeding
• Hybridisation
• Inbreeding
• Test cross

What do you think selective breeding is?

Think…

Do you think it would be appropriate for parents to use selective breeding to genetically alter their children?

Would it be ethical to choose a child’s eye colour? To enhance athletic ability? To prevent a painful disease?

If you were a parent, would you be more or less likely to choose your child’s genes if you knew that other parents were choosing their children’s?

​

Selective breeding

• Humans have bred animals with certain traits to get offspring that have desired traits. As a result, these traits become more common.
• Plants are bred to produce desired traits, such as larger fruits and shorter growing times.
• The process by which desired traits of plants and animals are selected and passed on to their future generations is called selective breeding.
• Through the processes of hybridization and inbreeding, desired traits can be passed on.

Advantages and disadvantages of selective breeding

Advantages

• Can increase yield and quality of crops.
• Can eliminate disease and health issues.
• Can create good genetic variety.

​

Disadvantages

• Reduced genetic variation can lead to attack by specific insects or disease.
• Rare disease genes can be unknowingly selected, leading to problems with specific organisms, eg a high percentage of Dalmatian dogs are deaf.

Discussion

Describe three traits that might be desired in camels. How can these traits be passed on to the next generation? Explain.

​

Hybridization

• Crossing parent organisms with different forms of a trait to produce offspring with specific traits results in hybrids.
• Farmers, animal breeders, scientists, and gardeners often use the production of hybrids, also known as hybridization.
• They select traits that will give hybrids a competitive edge, such as disease-resistance or faster growth.
• Example: plant breeders might choose to cross two different varieties of tomato plants to produce a hybrid that has the disease resistance of one parent and the fast growth rate of the other.
• Care must be taken to cross organisms to yield the right combination of traits from both parents.

Advantages and disavtantages of hybridization

Advantages

• Passing along favourable traits and prolonging the survival of a threatened/ endangered species.
• Can adapt to a wide range of changes in the environment.
• Can (sometimes) produce a greater number of offspring.

​

Disadvantage

• Hybrid animals have more difficulty finding mates and successfully breeding. 
• Time consuming and expensive. Example, it took rice breeders 30 years to produce hybrid rice varieties that can produce higher yields.

​

​

​

Critical thinking

Inbreeding

• Inbreeding is where two closely related organisms are bred to have the desired traits and to eliminate the undesired ones in future generations.
• Pure breeds are maintained by inbreeding.
• Clydesdale horses, and German shepherd dogs are all examples of organisms produced by inbreeding.

Horse breeders first bred the Clydesdale horse in Scotland hundreds of years ago as farm horses. Because of their strong build, agility, and obedient nature, Clydesdales originally were inbred and used for pulling heavy loads.

​

Advantages and disadvantages of inbreeding

Advantages

• Can concentrate the desired genes of a superior ancestor.
• Can fix a desired type quickly.
• Can result in animals that are more likely to transmit their own traits regularly when used for breeding.

​

Disadvantages

• Lower fertility and shorter life span
• Increase in birth defects and genetic disease
• Smaller size and slower growth
• Fewer offspring and higher mortality
• Harmful recessive traits can be passed on to future generations. Inbreeding increases the chance of homozygous recessive offspring. If both parents carry the recessive allele for a harmful trait, that harmful trait likely will not be eliminated.

​

Test cross

• Breeders must determine the genotype of the hybrid. The genotype is determined by performing a test cross.
• A test cross involves breeding an organism that has the unknown genotype with one that is homozygous recessive for the desired trait.
• If the parent’s genotype is homozygous dominant, all the offspring will have the dominant phenotype; if it is heterozygous, the offspring will show a 1:1 phenotypic ratio

Test cross

https://prod.reader-ui.prod.mheducation.com/epub/urn:com.mheducation.openlearning:enterprise.roster:prod.us-east-1:section:4ff51480-1627-11ec-bfc3-ebaedbccd682/data-uuid-27f81c8841a74a87b46df1145ef614eb

Performing a test cross

• A breeder wants to produce hybrid white grapefruits.
• The red grapefruit trees must be homozygous recessive (ww).
• The genotype of the hybrid white grapefruit tree can be homozygous (WW) or heterozygous (Ww).
• The breeder can use a test cross by transferring pollen to determine the genotype of the white grapefruit tree.
• If the white grapefruit tree is homozygous (WW) and is crossed with a red grapefruit tree (ww), then all the offspring will be heterozygous (Ww) and white in colour.
• If the white grapefruit tree is heterozygous (Ww), then half of the offspring will be white and half will be red (phenotypic ratio = 1:1).

Recessive red fruit (ww)

Dominant white fruit (WW or Ww)

Activity

Summarize how test crosses work by using the words genotype and phenotype to complete the sentence.

​

​

In a test cross, the _________ of the offspring can reveal the

_________.

​

Activity

1. Predict the phenotype of offspring from a test cross between a seedless orange (ss) and an orange with seeds (Ss).

​

2. A breeder performs a test cross to determine the genotype of a black cat. He crosses the black cat (BB or Bb) with a white cat (bb). If 50 percent of the offspring are black, what is the genotype of the black cat?

​

​

Activity

1. Predict the phenotype of offspring from a test cross between a seedless orange (ss) and an orange with seeds (Ss).

​

​

2. A breeder performs a test cross to determine the genotype of a black cat. He crosses the black cat (BB or Bb) with a white cat (bb). If 50 percent of the offspring are black, what is the genotype of the black cat?

​

​

50% will be seedless and 50% will have seeds.

The genotype of the black cat is Bb.

Summary

1. Selective breeding is used to produce organisms with traits that are considered desirable.
2. Hybridization produces organisms with desired traits from parent organisms with different traits.
3. Inbreeding creates pure breeds.
4. A test cross can be used to determine an organism’s genotype.

1. Selective breeding is used to produce organisms with traits that are considered desirable.
2. Hybridization produces organisms with desired traits from parent organisms with different traits.
3. Inbreeding creates pure breeds.
4. A test cross can be used to determine an organism’s genotype.

Activity

Analyze inbreeding and hybridization by identifying the effect, advantages and disadvantages of each.

1. Use your own ideas
2. Full sentences
3. Check your spelling!

Using genetics: Dolly the sheep

• https://www.twig-world.com/film/dolly-the-sheep-1086/

​

• Do you think this is ethical? Discuss.

​

​

​

​

Research task – answer the questions

1. What was embryologist Bill Ritchie’s procedural method for cloning an adult mammal? How many times did he have to repeat the procedure before an embryo was carried to term?
2. Several decades before Dolly’s birth, what other animal had been cloned?
3. How did the news media and politicians respond to news of Dolly’s existence?
4. What caused Dolly’s death? How old was she?
5. Why is the use of human embryos in biological research politically and culturally more sensitive than other kinds of biological research?

​