Bio 006 - 13A: Chromosomal Basis of Inheritance 1

Sex

Biological classification based on anatomical traits.

Gonads

Organs producing gametes; testes or ovaries.

Secondary Characteristics

Physical traits developed during puberty, like breasts.

Chromosomes

Structures carrying genetic information; XX or XY.

Bimodal

Classification allowing for more than two categories.

Sex Chromosomes

Chromosomes determining biological sex; X and Y for humans.

Y Chromosome

Small chromosome with ~25 proteins in humans.

Homologous Regions

Similar regions on X and Y chromosomes.

X-Linked Genes

Genes on the X chromosome, can be dominant or recessive.

Recessive Trait

Trait requiring two copies for expression in females.

Dominant Trait

Trait expressed with only one copy in males.

Alleles

Different forms of a gene, e.g., XN and Xn.

Homozygous

Having two identical alleles for a trait.

Heterozygous

Having two different alleles for a trait.

Hemizygous

Having only one allele for a gene, as in males.

Law of Segregation

Mendel's principle that alleles separate during meiosis.

Gregor Mendel

Scientist who studied inheritance using pea plants in the 1860s

Walter S.

Scientist building on Mendel's work in 1902

Chromosome Theory of Inheritance

Genes are located on specific chromosomes.

Drosophila melanogaster

• Fruit fly studied by Thomas Morgan

• Easy to breed → new generation every 2 weeks

• Only have 4 sets of chromosomes → can see all of them under a microscope

Wild type

Most common phenotype in natural populations.

Thomas Morgan

Geneticist who studied inheritance in fruit flies in 1908 and found solid evidence for specific gene

Mutant phenotype

Variation from the wild type in traits.

X-linked traits

Traits associated with genes on the X chromosome.

P generation

Parental generation in genetic crosses.

F1 generation

First filial generation from parental mating.

F2 generation

Second filial generation from F1 mating.

3:1 ratio

Observed ratio of traits in F2 generation.

Alleles

Different forms of a gene.

Loci

Specific positions of genes on chromosomes.

Meiosis

Cell division producing gametes with half chromosomes.

Crossing-over

Exchange of genetic material during Prophase I.

Independent Assortment

Genes segregate independently during gamete formation.

Sex-linked inheritance

Traits linked to sex chromosomes.

Linked Genes

Genes inherited together due to proximity on chromosome.

Recombination

Separation of genes during crossing over in meiosis.

Chromosomal Abnormalities

Changes affecting entire chromosomes, impacting organism.

Anaphase I

Homologous chromosomes separate during this meiosis stage.

Anaphase II

Sister chromatids separate during this meiosis stage.

Nondisjunction

Failure of chromosomes to separate during meiosis.

Aneuploidy

Abnormal number of chromosomes in an organism.

Monosomic

Condition of having one less chromosome than normal.

Trisomic

Condition of having one extra chromosome than normal.

Trisomy 21

Aneuploidy condition with three copies of chromosome 21.

Klinefelter Syndrome

XXY males with underdeveloped testes and breast tissue.

XYY Males

Generally normal males, might be taller than average.

Trisomy X

XXX females, usually normal but may have disabilities.

Turner's Syndrome

Monosomy X condition in females, sexually underdeveloped.

Swyer Syndrome

XY individuals with female phenotype, normal chromosomes.

Deletion

Removal of a segment from a chromosome.

Duplication

Repeating a segment within a chromosome.

Inversion

Reversing a segment within a chromosome.

Translocation

Moving a chromosome segment to a non-homolog.

Cri du Chat Syndrome

Deletion on chromosome 5 causing severe disabilities.

Fused Gene

Gene created by translocation, leading to uncontrolled growth.