BIOL 189: Chapter 10 - Patterns of Inheritance

What is a homologous chromosome pair?

Two chromosomes containing the same genes, one maternal and one paternal.

How many chromosome pairs do humans have?

23 pairs, totaling 46 chromosomes.

Where do the two chromosomes in a homologous pair come from?

One is inherited from the mother and one from the father.

What are autosomes?

Chromosome pairs 1 through 22.

What are sex chromosomes?

The 23rd chromosome pair.

What do homologous chromosomes have in common?

They contain the same genes but may have different alleles.

What are alleles?

Different versions of the same gene.

What does diploid (2N) mean?

Having two sets of chromosomes, one from each parent.

What does haploid (N) mean?

Having only one set of chromosomes.

Which organisms are described as diploid in the lecture?

Sexually reproducing organisms.

Which organisms are described as haploid in the lecture?

Asexually reproducing organisms.

How do most mammals, birds, reptiles, and fish reproduce?

Sexually, using one male and one female parent.

How are offspring from sexual reproduction genetically different?

They are related to their parents but genetically distinct from them and each other.

How do prokaryotes reproduce, according to the lecture?

Asexually, using one parent.

What are clones?

Genetically identical offspring produced through asexual reproduction.

Who is known as the Father of Modern Genetics?

Gregor Mendel.

What organism did Mendel use for his genetics experiments?

Pea plants.

Why were pea plants useful for Mendel's experiments?

They were easy to grow in a greenhouse and easy to manipulate experimentally.

What does hermaphroditic mean?

Having both male and female reproductive structures.

What is the male reproductive structure of a pea flower?

The stamen.

What is the female reproductive structure of a pea flower?

The pistil.

What does it mean for an organism to be true-breeding?

It consistently produces offspring with the same trait when bred within its line.

How long did Mendel spend establishing true-breeding pea plants?

Two years.

What did Mendel study in pea plants?

Specific physical traits and the alleles responsible for those traits.

What is a dominant allele?

An allele that is expressed in the phenotype when present.

What is a recessive allele?

An allele whose effect is masked by a dominant allele.

What happens when dominant and recessive alleles are together?

The dominant allele determines the phenotype in complete dominance.

What does homozygous mean?

Having two identical alleles for a gene.

What does heterozygous mean?

Having two different alleles for a gene.

What is a homozygous dominant genotype?

Two dominant alleles, such as TT.

What is a homozygous recessive genotype?

Two recessive alleles, such as tt.

What is a heterozygous genotype?

One dominant and one recessive allele, such as Tt.

What is a genotype?

The specific allele combination an organism possesses.

What is a phenotype?

The observable physical characteristics of an organism.

How can phenotype help predict genotype?

Observable traits can provide clues about which alleles an organism carries.

What is a monohybrid cross?

A genetic cross that examines one gene or trait.

What is the F1 generation?

The first generation of offspring from a parental cross.

What is the F2 generation?

The offspring produced by crossing individuals from the F1 generation.

What did Mendel observe in the F1 generation?

Some traits dominated while others were hidden or receded.

How long did Mendel perform crosses on true-breeding plants to produce monohybrids?

Five years.

What phenotypic ratio did Mendel find in the F2 monohybrid generation?

3:1, with three showing the dominant phenotype and one recessive.

Approximately how many plants and generations were included in Mendel's reported experiments?

30,000 plants across eight generations.

What is a Punnett square?

A visual tool used to predict possible offspring genotypes and phenotypes.

Who created the visual representation known as the Punnett square?

Reginald Punnett, associated with Bateson.

What does TT represent in a Punnett square?

A homozygous dominant genotype.

What does tt represent in a Punnett square?

A homozygous recessive genotype.

What does Tt represent in a Punnett square?

A heterozygous genotype.

What is a test cross?

Crossing an organism with a dominant phenotype with a homozygous recessive organism.

Why is a test cross performed?

To determine whether a dominant-phenotype organism is homozygous or heterozygous.

What parent is used in a test cross?

A homozygous recessive parent.

What happens when a heterozygous dominant parent is test-crossed?

It produces offspring showing both dominant and recessive phenotypes.

What is Mendel's Law of Segregation?

Two copies of a gene separate so each gamete receives only one copy.

How does meiosis support the Law of Segregation?

Homologous chromosomes separate during meiosis I, separating the gene copies.

What happens to gene copies during meiosis I?

The homologous chromosomes carrying the gene copies separate.

How does nondisjunction violate the Law of Segregation?

A gamete may receive zero or two copies of a particular gene instead of one.

What is a dihybrid cross?

A genetic cross that examines two different genes or traits.

What did Mendel produce when studying two genes together?

Dihybrids.

What phenotypic ratio is expected from a typical F2 dihybrid cross?

9:3:3:1.

What does each number in the 9:3:3:1 ratio represent?

The four possible phenotype groups among offspring.

What is Mendel's Law of Independent Assortment?

Copies of different genes assort independently of one another.

Which stage of meiosis supports independent assortment?

Metaphase I.

What is being sorted independently during independent assortment?

Different homologous chromosome pairs carrying different genes.

What happens during metaphase I that creates independent assortment?

Homologous chromosome pairs align randomly and independently.

When can Mendel's Law of Independent Assortment be violated?

When two genes are located close together on the same chromosome.

What is genetic linkage?

Two genes located close together on the same chromosome that do not assort independently.

What process can separate genetically linked alleles?

Crossing over during prophase I of meiosis.

Which researchers illustrated genetic linkage in 1905?

Bateson and colleagues.

What problem did Bateson observe with genetic linkage?

The offspring did not fit the predicted 9:3:3:1 ratio.

What did an excessive number of parental phenotypes suggest?

That certain alleles were associated or coupled together.

What is the predicted offspring ratio for the linked-gene example in the lecture?

1:1:1:1.

What ratio was actually observed in the linked-gene example?

5:1:1:5.

Why were unique allele combinations observed in the linked-gene example?

Crossing over during prophase I created new combinations.

What is incomplete dominance?

A pattern where a heterozygote has an intermediate phenotype.

What happens to the heterozygote phenotype in incomplete dominance?

It appears intermediate between the two homozygous phenotypes.

What F2 phenotypic ratio occurs with incomplete dominance?

1:2:1 instead of the typical 3:1 ratio.

What flower is used as the incomplete dominance example?

The snapdragon flower.

What does the R allele code for in the snapdragon example?

A red protein.

What does the r allele code for in the snapdragon example?

No functional protein.

Why are Rr snapdragons pink?

They produce about half the red protein produced by RR individuals.

Do alleles literally blend in incomplete dominance?

No. The intermediate phenotype results from the amount of functional protein produced.

Where is the human ABO blood-type gene located?

On chromosome 9.

What are the three main alleles of the ABO blood-type gene?

Iᴬ, Iᴮ, and i.

What do the A, B, and O blood types refer to?

Different glycolipids on the surface of red blood cells.

What does the Iᴬ allele code for?

The A-type glycolipid on red blood cells.

What does the Iᴮ allele code for?

The B-type glycolipid on red blood cells.

What does the i allele produce?

No functional glycolipid; it is non-functional.

Which blood-type allele is dominant over i?

Iᴬ.

Which blood-type allele is also dominant over i?

Iᴮ.

What genotypes produce type A blood?

IᴬIᴬ and Iᴬi.

What genotypes produce type B blood?

IᴮIᴮ and Iᴮi.

What genotype produces type O blood?

ii.

What is codominance?

A pattern where both alleles are fully expressed in a heterozygote.

What happens when Iᴬ and Iᴮ are inherited together?

Both are expressed, producing AB blood type.

Why is AB blood an example of codominance?

Both A and B glycolipids appear on red blood cells.

What is a multifactorial trait?

A trait influenced by multiple factors, including genes and the environment.

What is continuous variation?

A range of phenotypes rather than a few distinct categories.

What is penetrance?

The proportion of individuals with a genotype who actually show its expected phenotype.

What is pleiotropy?

One gene affects multiple phenotypic traits.

What is epistasis?

Interactions between genes affect the resulting phenotype.

What is the difference between polygenic and polyallelic traits?

Polygenic traits involve multiple genes; polyallelic traits involve more than two alleles of one gene.