Chapter 7

​Chapter 7

Genetics & Inheritance

Practice Question From Video

•Example: B = black (dominant), b = brown (recessive)

•Cross two heterozygous dogs (Bb × Bb): expected 3 black : 1 brown

•Try drawing the Punnett square yourself

What is the genotype ratio?

•What is the phenotype ratio?

Practice Question From Video

•Example: B = black (dominant), b = brown (recessive)

•Cross two heterozygous dogs (Bb × Bb): expected 3 black : 1 brown

•Try drawing the Punnett square yourself

What is the genotype ratio?

•What is the phenotype ratio?

Practice Question From Video

•Example: B = black (dominant), b = brown (recessive)

•Cross two heterozygous dogs (Bb × Bb): expected 3 black : 1 brown

•Try drawing the Punnett square yourself

What is the genotype ratio?

•What is the phenotype ratio?

What is the genotype ratio?

•1- BB, 2-Bb, 1-bb

•What is the phenotype ratio?

•3- Black, 1- brown

Multiple Choice

What is the name for a single letter in a genotype? For example B from the genotype Bb.

• Chromosome Pair

• Chromosome

• Allele

• Phenotype

Multiple Choice

When one allele prevents the second allele from affecting the phenotype that allele is

• Recessive

• Dominant

Multiple Choice

For an individual to show the recessive phenotype the must have how many copies of the recessive allele

• 0

• 1

• 2

• 3

Multiple Choice

Which of these terms describes an organism with two identical alleles for a trait?

• Homozygous

• Heterozygous

• Dominant

• Recessive

Multiple Choice

Pp would be the individuals ______ and Purple would be their _________

• Phenotype; Genotype

• Genotype; Phenotype

• Recessive allele

• Dominant allele

Multiple Choice

An individual with the genotype BB would be considered

• Dominant

• Heterozygous

• Homozygous Recessive

• Homozygous Dominant

Multiple Choice

An individual with genotype Bb would be considered

• Homozygous

• Homozygous Dominant

• Homozygous Recessive

• Heterozygous

Multiple Choice

You know a certain species of pea plant can have the dominant P trait, which is purple, or the recessive p trait, which is white. If you see a purple plant, which of the following genotypes could it possibly have?

• Homozygous dominant only

• Heterozygous only

• Homozygous dominant or Heterozygous

• Homozygous recessive or Heterozygous

Multiple Choice

Why is probability important when using a Punnett square?

• It shows that genetic outcomes are predictable for each baby

• It reminds us that offspring traits are random but follow patterns

• It helps control which traits a baby inherits

•  It tells us exactly what genotypes their first 4 offspring will have

Multiple Choice

Mendel’s pea plants produced a 3:1 ratio of purple to white flowers when heterozygotes were crossed. What does the “3” represent?

• 3 heterozygous plants

• 3 true-breeding parents

• 3 recessive phenotypes

• 3 dominant phenotypes

Punnett Square Practice

Problem: Cross a dog that is heterozygous for the black hair trait with a dog that is homozygous recessive

What is the genotype ratio?

What is the phenotype ratio?

Independent Assortment

•Alleles for different genes segregate independently (usually)

•Dihybrid cross example (RrYy × RrYy) yields 9:3:3:1 phenotypic ratio

•Useful for predicting combinations of two traits

Independent Assortment Practice

Problem : RrYy × RrYy dihybrid cross
R-round; r-wrinkley, Y-yellow, y-green

Question: Predict phenotypic ratio and list possible offspring types.

Non-Mendelian Genetics

• Mendelian Traits = traits that are controlled by a single gene and unaffected by environmental conditions

• Complex trait = a genetic trait who’s pattern of inheritance cannot be predicted by Mendel’s laws of inheritance

Non-Mendelian patterns

•Incomplete Dominance = Heterozygote shows intermediate phenotype instead of one parent or the other (e.g., IGF1 in dogs: II large, BB small, IB medium)

•Example: crossing Great Dane × Chihuahua often results in intermediate size

•Example: crossing a white flower x red flower can result in a pink flower

Non-Mendelian patterns

•Codominance = effects of both alleles are clearly visible in the phenotype of the heterozygote

•Example: Dog gum color can be pink, black or pink with black spots.

•Example: human blood type A, B or AB

•Multiple alleles exist in a population (e.g., blood group gene has 3 alleles)

Complex Traits & Interactions

•Polygenic traits: many genes contribute (eye color, skin color, height)

•Pleiotropy: when a single gene influences a number of different traits (Shape of dog’s head and shape of limb bones are controlled by single gene)

•Epistasis: one gene can mask another (Labrador coat: B/b and E/e → yellow dog when ee)

•Environment also affects phenotype (Siamese cat temperature-sensitive enzyme)

Epistasis

Scenario: Black dog (BbEe) × Yellow dog (Bb ee).

Task: What would be the Phenotype ratio for this cross?

Multiple Choice

In humans, AB blood type shows both A and B proteins equally.
What pattern is this?

• Epistasis

• Polygenic

• Incomplete dominance

• Codominance

Multiple Choice

When a heterozygote shows an intermediate phenotype instead of the phenotype of one parent or the other it is an example of

• Epistasis

• Polygenic

• Incomplete dominance

• Codominance

Multiple Choice

Eye color is determined by multiple traits, not just one. This is an example of

• Pleiotropy

• Polygenic

• Incomplete dominance

• Codominance

Multiple Choice

Siamese cats have dark ears, paws, and tails because fur pigment forms only in cool areas of the body.
This is an example of …

• Mutation

• Environmental influence on gene expression

• Codominance

• Epistasis

Multiple Choice

When one gene masks another this is an example of

• Mutation

• Environmental influence on gene expression

• Codominance

• Epistasis

Genetics & Human Health

•Many chronic diseases are complex traits (heart disease, cancer, diabetes)

•Genetic studies in dogs have helped identify genes linked to human diseases

•Personalized medicine: using genetic info to prevent or tailor treatment