Genetics

What is the blending hypothesis? Why is the blending hypothesis incorrect?

The idea that parental traits mix together like paint, producing intermediate offspring traits.

It cannot explain how traits reappear after skipping generations.

What is the particulate hypothesis?

Traits are inherited as discrete units (genes) that do not blend.

What are alleles? What is a dominant allele?

Alternative versions of a gene

An allele that determines phenotype when present

What is a locus?

The specific location of a gene on a chromosome

How many alleles does an organism inherit per gene?

Two (one from each parent)

What is a recessive allele?

An allele whose effect is masked by a dominant allele

What is the Law of Segregation?

Two alleles separate during gamete formation; each gamete gets one allele

Mendel's law of segregation states that allele pairs segregate equally into gametes during meiosis. This means that a gamete will have only one allele of any given gene, and that the probability of a gamete having one allele or the other is equal (and therefore ½, or 50%, for either allele)

What cellular process explains segregation?

Meiosis (separation of homologous chromosomes)

What is the Law of Independent Assortment? When does independent assortment apply?

Alleles of different genes assort independently during gamete formation

When genes are on different chromosomes or far apart on the same chromosome

What is genotype? What is phenotype?

The genetic makeup (alleles)

The observable traits

What is homozygous? What is heterozygous?

Two identical alleles

Two different alleles

What is a monohybrid cross? What is a dihybrid cross?

A cross involving one trait

A cross involving two traits

What is a testcross?

Crossing an unknown genotype with a homozygous recessive to determine genotype

What is the multiplication rule? Example of multiplication rule?

Probability of two independent events = multiply probabilities

½ × ½ = ¼ chance of two heads

What is the addition rule? Example of addition rule?

Add probabilities of mutually exclusive events

Probability of heterozygous (Rr or rR) = ¼ + ¼ = ½

What does the chromosome theory state?

Genes are located on chromosomes

Who proposed chromosome theory?

Sutton and Boveri

What does meiosis explain about genetics?

Segregation and independent assortment

What is a sex-linked gene?

A gene located on a sex chromosome

Why are X-linked recessive traits more common in males?

Males have only one X chromosome

What is genetic linkage?

Genes on the same chromosome inherited together

What is crossing over? When does crossing over occur?

Exchange of DNA between homologous chromosomes

Prophase I of meiosi

What are recombinant offspring?

Offspring with new allele combinations

What are multiple alleles? Example of multiple alleles?

in a population, there are more than two common alleles for a locus

ABO blood group

What is complete dominance?

Heterozygote = dominant phenotype

What is incomplete dominance?

Blended phenotype

heterozygotes have an intermediate phenotype - more than two phenotypes are seen

What is codominance?

Both alleles expressed equally

heterozygotes have phenotypes of both alleles - more than phenotypes are seen

What is pleiotropy?

One gene affects multiple traits

What is epistasis?

an alleles of one gene mask the expression of alleles at another gene

shows that there many forms of gene interactions

What is gene-environment interaction?

Phenotype influenced by environment experienced by individuals with the same genotype

same genotype can. lead to different phenotypes

What is an autosomal recessive trait?

Requires two recessive alleles

What is a carrier?

Heterozygous individual with no symptoms

How are X-linked recessive traits inherited?

More common in males; females must be homozygous

What are quantitative traits? What causes quantitative traits?

Traits with continuous variation (e.g., height)

Polygenic inheritance (influenced by multiple genes) - each gene adds a small amount of phenotype

In a monohybrid cross between peas with alleles for purple and white flowers (Pp x Pp), what is the probability that the first offspring will have purple flowers?

A) 0

B) ¼

C) ½

D) ¾

E) 1

D) ¾

When a dominant allele coexists with a recessive allele in a heterozygous individual, how do they interact with each other?

a) the dominant allele is paired up with the recessive allele at all times and silences the latter

b) the dominant allele prevents expression from the recessive allele by an unknown mechanism

c) the recessive allele is lost through a specific nondisjunction event in mitosis I

d) they do not interact at all

e) they form a chiasmata during meiosis I that triggers crossing over and the ultimate loss of recessive allele

b) the dominant allele prevents expression from the recessive allele by an unknown mechanism

A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the male offspring?

a) ¼ will have red eyes

b) all will have white eyes

c) all will have red eyes

b) all will have white eyes