Biology Exam Unit 3

What is a zygote?

A fertilized egg; the first diploid cell of a new organism.

What is a morula?

A solid ball of cells formed after early cleavage.

What is a blastula?

A hollow ball of cells formed from the morula.

What is a gastrula?

An embryonic stage where the three germ layers form.

What is the ectoderm?

Outer germ layer; forms skin and nervous system.

What is the mesoderm?

Middle germ layer; forms muscles, bones, blood, and organs.

What is the endoderm?

Inner germ layer; forms digestive tract and respiratory lining.

What is histogenesis?

Formation of tissues from germ layers.

What is organogenesis?

Formation of organs during development.

What is the function of the amnion?

Protects embryo with amniotic fluid.

What is the function of the chorion?

Helps exchange materials and contributes to placenta.

What is the placenta?

Organ that exchanges nutrients, gases, and wastes between mother and fetus.

What is oxytocin?

Hormone that stimulates uterine contractions and milk release.

What is prolactin?

Hormone that stimulates milk production.

What is the correct sequence from fertilization to implantation?

Fertilization → zygote → cleavage → morula → blastula/blastocyst → implantation.

What is cleavage?

Rapid mitotic divisions without growth in size.

What is implantation?

Attachment of the blastocyst to the uterine wall.

What are the three germ layers and their fates?

Ectoderm = skin/nervous system; Mesoderm = muscles/bones/blood; Endoderm = digestive and respiratory linings.

What are the major events in embryonic development?

Cleavage, blastulation, gastrulation, organ formation.

What is the embryonic period?

Early development when organs begin forming.

What is the fetal period?

Later development when growth and maturation happen.

What are the stages of birth?

Dilation of cervix, delivery of baby, delivery of placenta.

What happens during the dilation stage?

Cervix opens and contractions begin.

What happens during the expulsion stage?

Baby is delivered.

What happens during the afterbirth stage?

Placenta is expelled.

How can fetal genetic defects be detected?

Amniocentesis, chorionic villus sampling, ultrasound, genetic screening.

What is amniocentesis?

Testing amniotic fluid for fetal cells and chemicals.

What is chorionic villus sampling (CVS)?

Testing placental tissue for genetic abnormalities.

What is heredity?

Transmission of traits from parents to offspring.

What is genetics?

Study of heredity and inherited traits.

What is a gene?

Segment of DNA that codes for a trait.

What is an allele?

Different form of a gene.

What is a dominant allele?

Allele expressed when at least one copy is present.

What is a recessive allele?

Allele expressed only when two copies are present.

What does homozygous mean?

Having two identical alleles.

What does heterozygous mean?

Having two different alleles.

What is a genotype?

Genetic makeup of an organism.

What is a phenotype?

Physical expression of a trait.

What is the P generation?

Parental generation.

What is the F1 generation?

First filial generation; offspring of P generation.

What is the F2 generation?

Offspring of F1 generation.

What is a monohybrid cross?

Genetic cross involving one trait.

What is a dihybrid cross?

Genetic cross involving two traits.

What is a test cross?

Cross with a homozygous recessive individual to determine genotype.

What is a pedigree?

Family chart showing inheritance of a trait.

What is epistasis?

One gene affects or masks the expression of another gene.

What is Mendel's law of segregation?

Allele pairs separate during gamete formation.

What is Mendel's law of independent assortment?

Different gene pairs assort independently during meiosis.

How are Mendel's laws related to meiosis?

Segregation happens in meiosis I; independent assortment comes from random chromosome alignment.

What is the reason for a test cross?

To find out if a dominant phenotype is homozygous or heterozygous.

What is the typical monohybrid genotypic ratio?

1:2:1.

What is the typical monohybrid phenotypic ratio?

3:1.

What is the typical dihybrid phenotypic ratio?

9:3:3:1.

What is incomplete dominance?

Heterozygote shows a blended phenotype.

What are multiple alleles?

A gene has more than two allele forms in a population.

What is an X-linked trait?

Trait controlled by a gene on the X chromosome.

Why are males more likely to show X-linked recessive traits?

They have only one X chromosome.

What is an autosomal recessive disorder?

Disorder expressed only with two recessive alleles.

What is an example of an autosomal recessive disorder?

Cystic fibrosis or sickle-cell disease.

What is an autosomal dominant disorder?

Disorder expressed with one dominant allele.

What is an example of an autosomal dominant disorder?

Huntington's disease.

What is an example of an X-linked trait in humans?

Red-green color blindness or hemophilia.

What is an example of an X-linked trait in fruit flies?

White eye color.

What is the autosomal dominant pedigree pattern?

Usually appears in every generation.

What is the autosomal recessive pedigree pattern?

Can skip generations.

What is the X-linked recessive pedigree pattern?

More common in males; often passed through mothers.

What is a nucleotide?

Building block of DNA and RNA.

What is a nitrogen base?

Base in nucleic acids: A, T, C, G, or U.

What is complementary base pairing?

A pairs with T (or U in RNA), C pairs with G.

What is semiconservative replication?

Each new DNA molecule has one old strand and one new strand.

What is a codon?

Three-base sequence on mRNA that codes for an amino acid.

What is an anticodon?

Three-base sequence on tRNA that matches an mRNA codon.

Which experiments showed DNA is hereditary material?

Experiments by Avery, MacLeod, and McCarty; Hershey-Chase experiment.

What did the Griffith experiment show?

Showed transformation in bacteria.

What did the Avery experiment demonstrate?

Showed DNA is the transforming material.

What did the Hershey-Chase experiment reveal?

Showed DNA, not protein, enters bacteria during viral infection.

What is the structure of DNA?

Double helix made of two antiparallel strands.

What sugar is found in DNA?

Deoxyribose.

What sugar is found in RNA?

Ribose.

What is the structure of RNA?

Usually single-stranded and contains uracil.

What are the three types of RNA?

mRNA, tRNA, rRNA.

What is the function of mRNA?

Carries code from DNA to ribosome.

What is the function of tRNA?

Brings amino acids to ribosome.

What is the function of rRNA?

Makes up ribosomes and helps build proteins.

What is the genetic code?

Rules that match codons to amino acids.

What is the universal genetic code?

Nearly all organisms use the same code.

What is transcription?

Making RNA from a DNA template.

What are the steps of transcription?

Initiation, elongation, termination.

What happens during RNA processing in eukaryotes?

5' cap added, poly-A tail added, introns removed.

What is an intron?

Noncoding segment removed from pre-mRNA.

What is an exon?

Coding segment kept in mRNA.

What is translation?

Making a protein from mRNA.

What are the steps of translation?

Initiation, elongation, termination.

What is the start codon?

AUG.

What are the stop codons?

UAA, UAG, UGA.

Where does translation happen?

At ribosomes in the cytoplasm.

What is an operon?

Group of genes regulated together in prokaryotes.

What is a regulator gene?

Gene that makes a repressor protein.

What is a repressor?

Protein that blocks transcription.

What is a promoter?

DNA site where RNA polymerase binds.