Chapter 13: Modern Understanding of Inheritance

Flashcards covering the Chromosomal Theory of Inheritance, genetic linkage, sex-linked traits, human chromosomal disorders, and structural chromosome abnormalities from Chapter 13.

Chromosomal Theory of Inheritance

Chromosomes carry genes, and meiosis explains Mendel's laws.

Walter Sutton

Connected chromosome separation during meiosis to inheritance.

Theodor Boveri

Helped establish that chromosomes carry hereditary information.

Thomas Hunt Morgan

Proved genes are on chromosomes using fruit flies.

Drosophila melanogaster

The fruit fly used in Morgan's experiments.

genetic linkage

Genes on the same chromosome tend to be inherited together.

linked genes

Genes located on the same chromosome.

unlinked genes

Genes that assort independently.

crossing over

Exchange of DNA between nonsister chromatids during prophase I.

homologous recombination

Another name for crossing over.

parental type

Has the same allele combination as a parent.

recombinant type

Has a new allele combination produced by crossing over.

recombination frequency

The percentage of offspring that are recombinant.

recombination frequency formula

$$\frac{\text{Recombinants}}{\text{Total offspring}} \times 100$$

recombination frequency and distance

Higher recombination frequency means genes are farther apart.

maximum recombination frequency

$$50\%$$

centimorgan

A chromosome distance equal to $1\%$ recombination.

map unit

Another name for a centimorgan.

genetic map

Shows gene order and relative distances on a chromosome.

Alfred Sturtevant

Created the first genetic map.

sex linkage

Inheritance of a gene located on a sex chromosome.

sex-linked gene

A gene located on the X or Y chromosome.

X-linked gene

A gene located on the X chromosome.

X-linked recessive trait

A recessive trait caused by an allele on the X chromosome.

Why X-linked recessive traits affect more males

Males have only one X chromosome.

carrier

A person who carries a recessive allele without expressing it.

hemizygous

Having only one copy of a gene.

autosome

A chromosome that is not a sex chromosome.

human autosomes

Humans have $22$ pairs, or $44$ autosomes.

sex chromosome

An X or Y chromosome.

human sex chromosomes

Humans have one pair, or two sex chromosomes.

SRY gene

A Y-chromosome gene that begins male development.

OPN1LW gene

An X-linked gene involved in red color vision.

OPN1LW mutation

Can cause red-green color vision deficiency.

Duchenne muscular dystrophy

An X-linked recessive muscle disorder.

dystrophin

The muscle protein affected in Duchenne muscular dystrophy.

autosomal recessive trait

Requires two recessive alleles on an autosome.

phenylketonuria or PKU

An autosomal recessive metabolic disorder.

PKU problem

The body cannot properly break down phenylalanine.

autosomal dominant trait

Requires only one dominant allele on an autosome.

achondroplasia

An autosomal dominant form of dwarfism.

progeria

An autosomal dominant disorder causing premature aging.

karyotype

A person's chromosome number and appearance.

karyogram

An organized photograph of chromosomes.

cytogenetics

The study of chromosomes and chromosome abnormalities.

p arm

The short arm of a chromosome.

q arm

The long arm of a chromosome.

13q12

Region $12$ on chromosome $13$'s long arm.

nondisjunction

Failure of chromosomes to separate correctly.

nondisjunction in meiosis I

Homologous chromosomes fail to separate.

meiosis I nondisjunction result

All four gametes have abnormal chromosome numbers.

nondisjunction in meiosis II

Sister chromatids fail to separate.

meiosis II nondisjunction result

Two normal gametes and two abnormal gametes form.

n + 1 gamete

A gamete with one extra chromosome.

n - 1 gamete

A gamete missing one chromosome.

euploid

Having the normal chromosome number.

aneuploid

Having an abnormal number of individual chromosomes.

monosomy

Missing one chromosome, written $2n - 1$.

trisomy

Having one extra chromosome, written $2n + 1$.

gene dosage

The number of copies of a gene.

Down syndrome

Usually caused by trisomy $21$.

polyploid

Having more than two complete chromosome sets.

triploid

Having three chromosome sets, written $3n$.

X inactivation

Silencing of extra X chromosomes.

Barr body

A condensed, inactive X chromosome.

triplo-X syndrome

A condition with genotype $XXX$.

Klinefelter syndrome

A condition commonly caused by $XXY$.

Turner syndrome

A condition caused by $X0$.

chromosomal deletion

Loss of part of a chromosome.

chromosomal duplication

An extra copy of a chromosome segment.

Cri-du-chat syndrome

Caused by a deletion on chromosome $5$.

chromosome inversion

A chromosome segment reverses direction.

pericentric inversion

An inversion that includes the centromere.

paracentric inversion

An inversion that excludes the centromere.

inversion heterozygote

Has an inversion on only one homolog.

translocation

A chromosome segment moves to another location.

reciprocal translocation

Two nonhomologous chromosomes exchange segments.