Bio 203 midterm 3

What is heredity?

The transmission of traits from one generation to the next.

What is genetics?

The study of heredity and inherited variation.

What is a character?

An observable, heritable feature that may vary among individuals.

What is a trait?

A specific detectable version of a character.

What is a gene?

A DNA sequence that codes for a protein or functional product.

What is an allele?

An alternative version of a gene.

What is a locus?

The specific location of a gene on a chromosome.

What is a genotype?

An organism’s allele combination.

What is a phenotype?

The observable trait produced by a genotype and influenced by the environment.

What does homozygous mean?

Having two identical alleles for a gene.

What does heterozygous mean?

Having two different alleles for a gene.

What are homologous chromosomes?

A matching pair with one chromosome from each parent; they carry the same genes at the same loci.

What are sister chromatids?

Identical copies of one duplicated chromosome joined at the centromere.

What is a gamete?

A haploid reproductive cell, such as an egg or sperm.

What is a zygote?

The diploid cell formed when two gametes fuse.

What is the purpose of meiosis?

To reduce chromosome number by half and produce genetically unique haploid cells.

When is DNA replicated before meiosis?

During S phase of interphase.

What separates during Meiosis I?

Homologous chromosomes separate.

What separates during Meiosis II?

Sister chromatids separate.

What happens in Prophase I?

Homologs pair and crossing over occurs between nonsister chromatids.

What happens in Metaphase I?

Homologous pairs line up randomly at the equator.

What happens in Anaphase I?

Homologous chromosomes move apart; sister chromatids remain together.

What is the final product of meiosis?

Four genetically unique haploid cells.

What is crossing over?

Exchange of DNA between nonsister chromatids of homologous chromosomes.

When does crossing over occur?

During Prophase I.

What is independent assortment?

Random orientation and distribution of homologous chromosome pairs during Metaphase I.

What is random fertilization?

The random union of any sperm with any egg.

What are the three major sources of variation?

Crossing over, independent assortment, and random fertilization.

How does mitosis differ from meiosis?

Mitosis has one division and produces two usually identical cells; meiosis has two divisions and produces four unique haploid cells.

What does true-breeding mean?

A parent consistently produces offspring with the same version of a trait when self-crossed.

What is the P generation?

The parental generation.

What is the F1 generation?

The first filial generation, or offspring of the P generation.

What is the F2 generaion?

The offspring produced by crossing F1 individuals.

What is the Law of Segregation?

The two alleles for a gene separate randomly into gametes.

What is the Law of Independent Assortment?

Allele pairs for different genes can assort independently when genes are unlinked or far apart.

What is complete dominance?

The heterozygote and homozygous dominant have the same phenotype.

What is a monohybrid cross?

A cross that tracks one character.

What is a dihybrid cross?

A cross that tracks two characters.

What is a test cross?

Crossing an individual of unknown genotype with a homozygous recessive individual.

What is the genotype ratio for Aa × Aa?

1 AA : 2 Aa : 1 aa.

What is the typical phenotype ratio for Aa × Aa?

3 dominant : 1 recessive.

What is incomplete dominance?

The heterozygote has an intermediate phenotype between the two homozygotes.

What is codominance?

Both alleles are fully expressed in the heterozygote.

What are multiple alleles?

More than two alleles exist in the population, although an individual inherits only two.

What are the ABO blood-type alleles?

IA, IB, and i.

What genotype produces type AB blood?

IAIB.

What genotypes produce type O blood?

ii.

What is pleiotropy?

One gene affects multiple traits.

What is epistasis?

The phenotype of one gene affects or masks the expression of another gene.

What is polygenc inheritance?

Multiple genes contribute to one character.

What is a carrier?

A heterozygous individual who carries a recessive allele and may pass it on.

What is a wild-type phenotype?

The phenotype most commonly observed in nature.

What is an X-linked gene?

A gene located on the X chromosome.

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

Males have only one X chromosome, so one recessive allele can be expressed.

Name three X-linked recessive disorders.

Color blindness, Duchenne muscular dystrophy, and hemophilia.

What is a Barr body?

The condensed, inactive X chromosome in a mammalian female cell.

What are linked genes?

Genes located on the same chromosome that tend to be inherited together.

How does distance between linked genes affect recombination?

Genes farther apart are more likely to be separated by crossing over.

What is nondisjunction?

Failure of homologous chromosomes or sister chromatids to separate normally during meiosis.

What is aneuploidy?

An abnormal number of one particular chromosome.

What is monosomy?

Having one copy of a particular chromosome instead of two.

What is trisomy?

Having three copies of a particular chromosome.

What is polyploidy?

Having more than two complete sets of chromosomes.

What is a deletion?

Removal of a chromosome segment.

What is a duplication?

Repetition of a chromosome segment.

What is an inversion?

Reversal of a chromosome segment within the chromosome.

What is a translocation?

Movement of a chromosome segment to another chromosome.

What causes Down syndrome?

Trisomy 21, or three copies of chromosome 21.

What is Klinefelter syndrome?

XXY, an individual with an extra X chromosome.

What is Turner syndrome?

Monosomy X, written X0; the only known viable human monosomy.

What are the three parts of a DNA nucleotide?

A phosphate group, deoxyribose sugar, and nitrogenous base.

What did Hershey and Chase show?

DNA, not protein, entered bacteria and directed phage infection.

What are Chargaff’s rules?

Within a species, A is approximately equal to T and G is approximately equal to C; base composition varies between species.

What is the structure of DNA?

A double-stranded helix made of complementary nucleotide strands.

Which bases are purines?

Adenine and guanine.

Which bases are pyrimidines?

Cytosine and thymine.

What does adenine pair with?

Thymine.

What does guanine pair with?

Cytosine.

What is semiconservative replication?

Each daughter DNA molecule contains one parental strand and one newly synthesized strand.

Which DNA replication model is correct?

The semiconservative model.

What is the origin of replication?

The site where DNA replication begins.

What is a replication bubble?

The region of DNA that opens at an origin of replication as the two parental strands separate.

What is a replication fork?

The point where the two parental DNA strands are splitting and new strands are being synthesized.

How many origins of replication does E. coli usually have?

One origin of replication on its circular DNA.

What happens during replication of E. coli DNA?

A replication bubble expands outward from one origin, forming two replication forks and two daughter DNA molecules.

How does eukaryotic DNA replication differ from E. coli replication?

Eukaryotic linear DNA has multiple origins and multiple replication bubbles, while E. coli circular DNA usually has one origin.

What happens to eukaryotic replication bubbles?

They expand and eventually meet and fuse to complete replication.

What is a prokaryote?

An organism whose cells lack a membrane-bound nucleus; its DNA is typically circular.

What is a eukaryote?

An organism whose cells contain a membrane-bound nucleus; its chromosomes are typically linear.