Ch 15 - DNA Structure and Replication: Molecular Basis of Inheritance - Exam 2 Vocabulary

Chapters 15 vocabulary and key terminology

Incomplete dominance

Heterozygous phenotype is a blend of the two parental traits (i.e., red and white flowers producing pink offspring)

Codominance

Both alleles in a heterozygous organism are fully expressed, resulting in a phenotype that shows both traits (i.e., AB blood type, roan cattle)

Chromosomal Theory of Inheritance

suggests that Mendelian genes have specific loci (positions) along chromosomes that undergo segregation and independent assortment

True breeding

Homozygous for either the dominant or recessive trait

Law of Segregation

Alleles for one gene are separated during meiosis

Law of Independent Assortment

Alleles of genes on nonhomologous chromosomes line up independent of one another during meiosis

Recombinant gametes

• Different genotype assortment than parental gametes

• Frequency of recombination between two genes is proportional to distance

Metaphase I

stage in meiosis I where homologous chromosome pairs align along the metaphase plate

Anaphase I

stage in meiosis I where homologous chromosomes are pulled apart to opposite poles of the cell

Prophase I

stage in meiosis I where homologous chromosomes pair up, crossing over occurs, and the nuclear envelope breaks down

Telophase I

stage in meiosis I where chromosomes reach opposite poles, and the nuclear membrane may begin to reform

Cytokinesis

division of the cytoplasm, resulting in two separate daughter cells

Prophase II

stage in meiosis II where chromosomes condense, the nuclear envelope dissolves, and spindle fibers form in the two haploid cells

Metaphase II

stage in meiosis II where individual chromosomes align at the metaphase plate in each haploid cell

Anaphase II

stage in meiosis II where sister chromatids are pulled apart to opposite poles of the cell

Telophase II

stage in meiosis II where chromosomes reach opposite poles, nuclear membranes reform, and the cells prepare to divide

Sex Determining Region Y (SRY)

• Gene that encodes a transcription factor that impacts the expression level of other genes

• In the absence of SRY, female development takes place

The X-Y System

In mammals, the sex of the offspring depends on whether the sperm cell contains an X or Y chromosome.

The X-0 System

• In some insects, there is only one type of sex chromosome: X.

• Females have XX (two chromosomes) and males have X0 (one chromosome).

• Sex is determined by whether the sperm contains an X or no chromosome.

The Z-W System

• Some birds, insects, and fish have sex chromosomes in the egg that differ, rather than the sperm.

• Females are ZW and males are ZZ.

The Haplo-Diploid System

• There are no sex chromosomes in most species of bees and ants.

• Females develop from fertilized eggs and are diploid.

• Males develop from unfertilized eggs and are haploid; they have no fathers.

X-linked recessive traits

Traits that are passed onto offspring solely on the X chromosome

X-inactivation

• Only in females

• One X chromosome is randomly inactivated during development

• Mosaic of cells with different active X

Lethal X-linked recessive disorders

• Only seen in males

• Females can only be heterozygous carriers and do not develop the disorder

• Most often leads to death in utero

Sex-limited inheritance

• Expression of a specific phenotype is absolutely limited to one sex

• i.e. horns in sheep, rooster feathers

Sex-influenced inheritance

• Sex of individual influences expression of phenotype

• Not limited to one sex or the other

• i.e. male pattern baldness, thin hair in females

Conditional phenotypes

• Phenotypes affected by external factors

• i.e. temperature effects (Siamese cats and Himalayan rabbits)

Gene linkage

Two or more genes on the same chromosome are inherited together more frequently than expected according to Mendelian genetics

Polyploidy

more than 2 sets of chromosomes

Aneuploid

not a good set (trisomy or monosomy)

Chromosome deletion

removal of a chromosomal segment

Chromosome duplication

a chromosomal segment is repeated

Chromosome inversion

segment within a chromosome is reversed

Chromosome translocation

a segment from one chromosome is moved to a nonhomologous chromosome

Cytoplasmic inheritance

Genes found on structures in the cytoplasm (i.e., mitochondria and chloroplasts)