Biology Unit 7 Genetics IHS Skavaril

Codominance

Both alleles are dominant so phenotype reflects both traits; coexist (e.g. blood type A + blood type B = AB)

Incomplete dominance

Mix/blend of alleles as they aren’t strong enough for one to be dominant (e.g. white/homo rec flower and red/homo dom flower = pink hetero flower)

Crossing over

Exchange of genetic material between paired homologous chromosomes (non-sister chromatids) during prophase I of meiosis

Gamete

A mature reproductive cell (sperm/egg)

Sex-linked gene

Genes located on the sex chromosomes (usually X, but sometimes Y)

Nondisjunction

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

Homozygous/Purebred

Homozygous dominant: AA

Homozygous recessive: aa

Same alleles

Heterozygous/Hybrid

Aa

Different alleles; one dominant one recessive

Phenotype

Physical trait produced by alleles (expression of genes)

Genotype

Combo of alleles in an individual

Fertilization

When genetic information from 2 individuals combine to result in a new individual

Genetics

The study of inheritance

Genes

Segment of DNA that codes for one specific protein

Allele

Different version of a gene/genetic code

Rule of Dominance

Only need 1 dominant allele to express that certain trait

Law of Segregation

Every cell gets 1 copy of each allele

Law of Independent Assortment

Meiosis results in unique haploid cells. Chromosomes line up randomly during metaphase I

Polygenic Trait

When one trait is affected by more than 1 gene (e.g. eye color is determined by at least 3 different genes)

Multiple Alleles

One gene has more than 2 alleles — more than one way a gene can be found on the same chromosome

Autosomes

Chromosomes 1-22 and follow simple inheritance rules

Autosomal Dominant

Only 1 copy of the dominant allele is necessary to see the phenotype

Autosomal Recessive

2 copies of the recessive allele is necessary to see the phenotype

Sex-linked Dominant

The dominant/affected gene can be found on the X chromosome of either parent

If affected:

• Females: XᴬXᴬ or XᴬXᵃ

• Males: XᴬY

Sex-linked Recessive

Only 1 copy of the allele is necessary to see the phenotype in males, but 2 copies are necessary in females

If affected:

• Females: XᵃXᵃ

• Males: XᵃY

X-chromosome inactivation

Process that “turns off” one X chromosome in each cell of females

Unaffected

Individuals with no copies of the disease allele and are not sick

Carrier

Individual with one disease allele but is not sick

Affected

Individual that has the disease allele and is sick

Pedigrees

Used to show how alleles have been passed between generations

• Females are represented as circles

• Males are represented as squares

• One level = one different generation

Female sex chromosomes

XX

Male sex chromosomes

XY

Order of genotype ratio

Homo dom : Hetero : Homo rec

Order of phenotype ratio

Dom trait : Rec trait

What do the letters on the outside of a Punnett square represent

Haploid gametes

What do the letters inside the boxes of a Punnett Square represent

Haploid offspring

Meiosis

Process that produces gametes with haploid number of chromosomes. Must occur so that zygotes will have the proper number of chromosomes after fertilization

Phases of meiosis

Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I, Cytokinesis, Prophase II, Metaphase II, Anaphase II, Telophase II, Cytokinesis

Product of meiosis

4 haploid cells

How is meiosis is different from mitosis

Meiosis: 4 haploid cells, different from each other, (mitosis 2x)

Mitosis: 2 diploid cells, identical to each other, PMAT one time

How many sets of genes are found in most adult organisms

2 sets of chromosome in every cell (diploid organisms)

Karyotypes

All the chromosomes from a cell paired together and placed in order

Monosomy

One chromosome

Trisomy

Three chromosomes

Aneuploidy

Abnormal number of chromosomes (not two of autosomes)

How many homologous PAIRS does a typical human somatic cell contain

23

How many total chromosomes does a typical human gamete have

23

Homologous chromosomes

Contains the same genes, but one comes from the mother and one comes from the father, so they might contain different alleles making them not exactly identical

Diploid organism

Has two sets of chromosomes

Haploid organism

Has one set of chromosome

Genome

Entire set of DNA instructions found in a cell

Prophase I

The chromosomes condense, and the nuclear envelope breaks down

Metaphase I

Pairs of homologous chromosomes move to the equator of the cell

Anaphase I

Homologous chromosomes move to the opposite poles of the cell

Telophase I & Cytokinesis

Chromosomes gather at the poles of the cells. The cytoplasm divides into 2 cells

Prophase II

A new spindle forms around the chromosomes

Metaphase II

Chromosomes line up at the equator

Anaphase II

Centromeres divide. Chromatids move to the opposite poles of the cells

Telophase II & Cytokinesis

A nuclear envelope forms around each set of chromosomes. The cytoplasm divides, yielding 4 cells in total