Mendelian Genetics, Chromosome Theory, and Sex-Linked Traits

What are Mendel's hereditary factors known as today?

Genes

What does the chromosome theory of inheritance state?

Genes have specific loci on chromosomes, and chromosomes undergo segregation of alleles and independent assortment.

What process accounts for Mendel's laws of segregation and independent assortment?

The behavior of chromosomes during meiosis.

What is the phenotypic ratio of an F1 × F1 cross-fertilization?

9:3:3:1

Who provided the first solid evidence associating a specific gene with a specific chromosome?

Thomas Hunt Morgan

What organism did Morgan use for his genetic studies?

Fruit flies (Drosophila melanogaster)

What is a wild type phenotype?

The common, normal phenotype in a population.

What is a mutant phenotype?

A trait alternative to the wild type.

What did Morgan discover about the white-eyed mutant allele?

It is located on the X chromosome.

What are the two varieties of sex chromosomes in humans?

X chromosome and Y chromosome.

What gene on the Y chromosome is responsible for the development of testes?

SRY gene.

What is the chromosomal basis of sex determination in humans?

Biological females are XX and biological males are XY.

How many pairs of chromosomes do fruit flies have?

Four pairs (three pairs of autosomes and one pair of sex chromosomes).

What is a sex-linked gene?

A gene located on either sex chromosome.

How many copies of a recessive sex-linked trait does a female need to express it?

Two copies (X'X').

How many copies of a recessive sex-linked trait does a male need to express it?

One copy (X'Y).

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

Because males are hemizygous for the X chromosome.

What is color blindness in humans classified as?

A sex-linked recessive trait.

What is Duchenne muscular dystrophy?

A recessive disorder caused by a missing muscle protein coded for by a gene on the X chromosome.

What is hemophilia?

A disorder caused by recessive alleles on the X chromosome.

What is the role of the X chromosome beyond sex determination?

It has genes for many characters unrelated to sex.

What happens to sex-linked alleles passed from fathers to their children?

Fathers pass along all sex-linked alleles to all of their daughters but none to sons.

What does the law of segregation state?

The two alleles for each gene separate during gamete formation.

What does the law of independent assortment state?

Alleles of genes on nonhomologous chromosomes assort independently during gamete formation.

What is the significance of tagging isolated chromosomes with fluorescent dye?

It allows for the visualization of the location of particular genes.

What is the result of crossing two dihybrids that are heterozygous for both traits?

The phenotypic ratio will be roughly 9:3:3:1 if the traits are located on separate chromosomes.

What is the main conclusion from Morgan's experiments with fruit flies?

Chromosomes are the location of Mendel's heritable factors.

What type of trait is red/green color blindness in humans?

A sex-linked recessive trait.

If all daughters have normal vision and all sons are colorblind, what are the probable genotypes of the parents?

The mother is a carrier (X^cX) and the father is colorblind (X^cY).

What percentage of sons will be colorblind if a normal sighted woman (whose father was colorblind) marries a colorblind man?

50% of their sons will be colorblind.

What percentage of daughters will be colorblind from the same couple?

0% of their daughters will be colorblind.

What happens to one of the X chromosomes in female mammals during embryonic development?

One of the two X chromosomes is randomly inactivated.

What is formed when an X chromosome is inactivated?

The inactive X condenses into a Barr body.

What does it mean for a female to be a mosaic for a character?

She is heterozygous for a particular gene located on the X chromosome.

What are linked genes?

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

What did Morgan's experiments with fruit flies demonstrate about linkage?

Body color and wing size are usually inherited together, indicating they are on the same chromosome.

What are parental types in genetics?

Offspring with a phenotype matching one of the parental phenotypes.

What are recombinant types in genetics?

Offspring with nonparental phenotypes (new combinations of traits).

What does a 50% recombination frequency indicate?

The genes are on different chromosomes.

What is crossing over?

The process that can break the physical connection between genes on the same chromosome.

What is the significance of recombinant offspring in genetic studies?

They indicate that genes are not completely linked and can be separated by crossing over.

What is a gene linkage map?

A visual representation of the positions of genes on a chromosome.

What is the relationship between the distance of genes on a chromosome and recombination frequency?

The further apart two genes are, the more likely they will be separated by a crossing over event.

What can cause alterations in chromosome number or structure?

Physical and chemical disturbances, and errors during meiosis.

What is the expected outcome if fewer than 50% of offspring are recombinants?

The two genes are assumed to be on the same chromosome.

What is the expected outcome if the number of recombinants approaches 50%?

The two genes are assumed to be on separate chromosomes.

How did Morgan determine that body color and wing size genes were linked?

He observed that these traits were inherited together in specific combinations.

What is the significance of the Barr body in female mammals?

It represents the inactivated X chromosome and is a key aspect of dosage compensation.

What does the term 'mosaic' refer to in the context of X-inactivation?

A female with different cell populations expressing different alleles from her X chromosomes.

What is the role of crossing over in genetic diversity?

It creates new allele combinations, contributing to genetic variation in offspring.

What does it mean if genes do not assort independently?

It means they are likely located on the same chromosome and inherited together.

What is the result of a testcross in genetics?

It helps determine the genotype of an individual with a dominant phenotype.

What does the term 'nonparental phenotypes' refer to?

Phenotypes that do not match either parent, indicating genetic recombination has occurred.

What often results from large-scale chromosomal alterations?

Spontaneous abortions (miscarriages) or developmental disorders.

What is nondisjunction?

A failure of homologous chromosomes to separate normally during meiosis.

What happens to gametes during nondisjunction?

One gamete receives two of the same type of chromosome, and another receives none.

What is aneuploidy?

A condition resulting from the fertilization of gametes in which nondisjunction occurred, leading to an abnormal number of a particular chromosome.

What is a monosomic zygote?

A zygote that has only one copy of a particular chromosome.

What is a trisomic zygote?

A zygote that has three copies of a particular chromosome.

What is polyploidy?

A condition in which an organism has more than two complete sets of chromosomes.

What is triploidy?

A condition with three sets of chromosomes (3n).

What is tetraploidy?

A condition with four sets of chromosomes (4n).

Which organisms commonly exhibit polyploidy?

Plants.

What are the four types of changes in chromosome structure due to breakage?

Deletion, duplication, inversion, and translocation.

What is deletion in chromosome structure?

The removal of a chromosomal segment.

What is duplication in chromosome structure?

The repetition of a chromosomal segment.

What is inversion in chromosome structure?

The reversal of a segment within a chromosome.

What is translocation in chromosome structure?

The movement of a segment from one chromosome to another.

What is Down syndrome?

An aneuploid condition resulting from three copies of chromosome 21.

What is Klinefelter syndrome?

A condition resulting from an extra chromosome in a male (XXY), leading to sterility.

What is Turner syndrome?

A condition resulting from monosomy X (X0), producing sterile females.

What is trisomy X?

A condition where females have three X chromosomes (XXX) but are generally healthy.

What is cri du chat syndrome?

A disorder caused by a deletion in chromosome 5, characterized by mental retardation and a catlike cry.

What is the Philadelphia chromosome?

A translocated chromosome associated with chronic myelogenous leukemia (CML).

What are extranuclear genes?

Genes found in organelles in the cytoplasm, inherited maternally.

What is mitochondrial myopathy?

A condition caused by defects in mitochondrial genes, leading to muscle weakness and other symptoms.

What is Leber's hereditary optic neuropathy?

A mitochondrial disease causing bilateral loss of central vision due to optic nerve atrophy.

How are mitochondrial diseases inherited?

Maternal inheritance, as the zygote's cytoplasm comes from the egg.