Biology Genetics + Karyotypes (Exam 2)

Genotype

An organism's genetic makeup; the alleles it has (e.g., Aa).

Phenotype

An organism's observable traits

Recombinant phenotype

Trait in an offspring that shows a new combination of alleles not found in either parent

Gamete

A haploid reproductive cell (sperm or egg) containing one set of chromosomes, 23 chromosomes in humans. Tt genotype would make →T, t

Dominant

An allele expressed in the phenotype when at least one copy is present

Recessive

An allele usually expressed only when two copies are present in a diploid organism

Autosome

Any chromosome that is not a sex chromosome

X-linked

A trait controlled by a gene located on the X chromosome. Males get X linked diseases

Carrier

An individual with one copy of a recessive disease allele who usually does not show the condition

Allele

One version of a gene (e.g., A or a)

Karyotype

An organized display of an individual's chromosomes, arranged in pairs by size and shape

Zygote

A diploid cell formed by fertilization, containing 46 chromosomes in humans.

Fertilization

The fusion of a sperm and egg, combining their chromosomes to form a diploid zygote.

Nondisjunction

The failure of homologous chromosomes or sister chromatids to separate properly during cell division.

Meiosis I Nondisjunction

Homologous chromosomes fail to separate, producing four abnormal gametes: two with an extra chromosome and two missing one.

Meiosis II Nondisjunction

Sister chromatids fail to separate, producing two normal gametes, one with an extra chromosome, and one missing a chromosome.

Dihybrid Cross

A genetic cross that examines the inheritance of two genes.

9:3:3:1 Phenotypic Ratio

The expected F2 phenotype ratio from AaBb × AaBb when both genes assort independently and show complete dominance.

Codominance

A pattern in which both alleles are fully expressed in a heterozygote.

DNA Methylation

The addition of methyl groups to DNA, often reducing gene expression when concentrated at gene promoters.

Epigenetic Inheritance

How cells are distinguished by whether their genes are turned on or off

Epigenome

The collection of chemical modifications and regulatory marks that influence which genes are expressed in a cell.

Histone Modification

Chemical changes to histone proteins around which DNA is wrapped, affecting how accessible genes are for expression.

Gene Silencing

The turning off or reducing of gene expression.

Gene Activation

The process of allowing or increasing gene expression.

Epigenetic Modifications

Marks can be added, removed, or changed, allowing gene expression to respond to development and environmental conditions.

Oncogenes

Genes that can promote uncontrolled cell growth when abnormally activated; cancer treatments may aim to reduce their activity.