Unit 2 SAC 2 definitions Bio

Gene

Carries the code to make a protein.

Alleles

Alternative versions of a gene that arise by mutation at the same place on a chromosome.

Genome

All the genetic information in an organism; all of an organism's chromosomes.

Homologous Chromosomes

Chromosomes that share the same genes at the same loci, same size and length, same centromere position, one pair from each parent.

Autosomes

Any chromosome that is not a sex chromosome.

Sex Chromosomes

One of the 23 pairs of chromosomes in humans, containing genes that will determine the sex of the individual (X,Y).

Chromosome

A threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

Homologous Chromosomes Carrying Same Gene Loci

A matching pair of chromosomes, one from each parent, that carry the same genes at the same loci but may have different alleles.

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

Purpose of Meiosis

To make gamete cells (haploid) for sexual reproduction.

Haploid Gametes

Cells with one set of chromosomes (n).

Diploid Cells

A cell containing two sets of chromosomes (2n), one set inherited from each parent.

Crossing Over Chromatids

During meiosis 1, homologous chromosomes come together and pair up, twisting around each other, swapping bits of chromatids.

Independent Assortment

During meiosis, chromosome pairs separate randomly into gametes, increasing genetic diversity.

Zygote/Zygosity

Describes the two alleles an organism has for a gene, e.g., AA, aa, Aa.

Dominant

Describes a trait that covers over, or dominates, another form of that trait.

Recessive

An allele that is masked when a dominant allele is present.

Codominance

A condition in which both alleles for a gene are fully expressed.

Complete Dominance

A type of inheritance in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

Incomplete Dominance

Neither allele is completely dominant over the other, so a heterozygote has an intermediate/blended phenotype.

Phenotype

An organism's physical appearance or visible traits.

Genotype

An organism's genetic makeup or allele combinations, e.g., HH, Hh, hh.

Proportionate Heritability

The extent to which variation in a phenotype within a population can be attributed to genetic differences compared with environmental influences.

Patterns of Inheritance

Various ways traits are inherited from parents to offspring.

Pedigree Chart

A diagram that shows the occurrence and appearance of phenotypes of a particular gene or organism and its ancestors.

Autosomal Dominant

Inheritance pattern of a dominant allele on an autosome.

Autosomal Recessive

Two copies of an abnormal gene must be present in order for the disease or trait to develop.

X-linked Dominant

An abnormal allele that is dominant and occurs on the X chromosome.

X-linked Recessive

A recessive allele located on the X chromosome; more likely to express in males.

Y-linked

Referring to a gene located on the Y chromosome.

Monohybrid Cross

A cross between individuals that involves one pair of contrasting traits.

Meiosis 1

Separates each homologous chromosome into 2 different cells.

Meiosis 2

Separates each sister chromatid into four different cells.

Aneuploidy

Loss or gain of a single chromosome, caused by non-disjunction.

Mitosis vs Meiosis

Mitosis: one division forming 2 identical cells; Meiosis: two divisions forming 4 genetically different cells.

Non-disjunction

When chromosomes fail to separate during anaphase 1 or 2.

Non-disjunction Disorders

Disorders such as Down syndrome, Turner syndrome, Klinefelter's syndrome, and Edwards syndrome.

Monosomy

Missing a chromosome (2n-1).

Trisomy

Extra chromosome (2n+1).

Duplications

Part of the chromosome is copied.

Deletions

Part of the chromosome is removed.

Inversions

A chromosome mutation where a section of a chromosome breaks off, flips around, and reattaches in reverse order.

Translocation

: A section of one chromosome breaks off and attaches to a different, non-homologous chromosome.

Epigenetics

The study of environmental influences on gene expression that occur without a DNA change.

Transcription

A sequence of DNA is used to produce a complementary sequence of mRNA.

Translation

An mRNA sequence is used to produce a protein.

Somatically Heritable

Genetic traits/alterations inherited by daughter cells during mitotic cell division.

Gene locus / loci

The specific location of a gene on a chromosome.

homozygous dominant

Having two dominant alleles for a gene, e.g. AA.

homozygoud recessive

Having two recessive alleles for a gene, e.g. aa.

heterozygous

Having two different alleles for a gene, e.g. Aa.

genotypic ratio

The predicted proportion/ratio of each genotype among offspring, e.g. 1 AA : 2 Aa : 1 aa.

phenotypic ratio

The predicted proportion/ratio of each phenotype among offspring, e.g. 3 dominant : 1 recessive.

genetic cross

The breeding of two individuals to predict how alleles may be inherited by offspring.

sex-linked inheritance

Inheritance of a gene located on a sex chromosome, usually the X chromosome.

environmental factor

An external factor that can influence phenotype, such as nutrition, temperature or sunlight.

polygenic inheritence

When multiple genes contribute to one phenotype/characteristic.