Genetics review

The probability of a yellow-seed plant (YY) forming a Y gamete is_____ % because the principle of segregation - one_____ of each gene pair goes to a____ ; it only has "Y" alleles.

100,

If you have a heterozygous yellow-seed plant (Yy), the probability of forming a "Y" gamete is _____. The probability of forming a "y" gamete is _____. This follows the principle of segregation.

50 ,50

Chromosome

A "thread-like" molecule in the nucleus, composed of DNA. A chromosome possesses one allele for a given trait, therefore chromosomes occur in pairs. Each originates from the male and female gamete (parent)

Mutation

A change in the genetic information code

Crossing Over

A condition where non-sister chromatid of homologous chromosomes exchange genes

Chromatid

A double-stranded chromosome following replication attached by a centromere

Recessive

A gene or trait which is masked when a dominant allele is present

Trait

A genetic characteristic of the idividual

Punette Square

A grid system used to predict possible combinations of genes due to random fertilization

Spindle Fibers

A number of threadlike filaments formed between poles of the cell during cell division to which the centromeres of chromosomes attach; used to pull chromosomes apart and segregate them during anaphase.

Pure-bred

A phenotype (trait) resulting from homozygous genes from the offspring of true breeding

Gene

A portion of DNA which codes a specific hereditary trait

Gamete

A reproductive cell produced by the male or female parent, which contains the haploid number of chromosomes

Y Chromosome

A sex chromosome found in males; influencing the degree of maleness

X Chromosome

A sex chromosome; in human males only one is present and in females two are present

Centromere

A structure on the chromosome that holds a pair of chromatids together during replication

Meiosis

A type of cell division used to produce gametes and there is a reduction in the chromosome number from the diploid to the haploid number

Gene Pool

All of the genes present in a specific population

Allele

Alternative forms for a specific gene (either dominant or recessive)

Hybrid

An offspring from a cross between parents which has different phenotypes for a specific trait

Autosome

Any pair of chromosomes other than the sex chromosome

Diploid

Both members of a pair of chromosomes are present

Dihybrid Cross

Breeding of individuals which have two genes for two different characteristics

Tetrad

During metaphase I the two pairs of chromatids of the homologous pair of chromosomes comes together; crossing-over can occur at this time.

Nondisjunction

Failure of chromosomes to segregate during the formation of gametes, resulting in extra or a shortage of chromosomes in the gamete

Sex-linked

Genes that are located in the sex chromosome

Dominant

In a pair of genes, one may prevent the allele from being expressed

Principle of Segregation

Members of a gene pair separate during meiosis and are found in separate gametes

Haploid

One member of a pair of homologous chromosomes is present, such as in a gamete

Sex-Chromosomes

One of the chromosomes which determine the sex of the individual

Polar Body

One of three small cells produced during oogenesis, each contain the haploid number of chromosomes.

Oogenesis

Process of development of haploid female gametes.

Pedigree

The ancestral history of an individual; a chart showing the history of a trait in the family

Incomplete Dominance

The blending of two traits in a heterozygous individual

Monohybrid Cross

The breeding of two organisms which differ in a single trait

Probability

The chance that a given event will occur usually expressed between the number 0 (will not occur) and 1 (the event will occur)

Codominance

The condition in heterozygotes where both members of an allelic pair contribute to phenotype producing a mixture of phenotypic traits

Genotype

The genes present in an organism

Phenotype

The outward appearance of the organism which is the product of gene action

True-Breeding

The process of crossing two organisms, both having homozygous genes for the same trait

Spermatogenesis

The production of haploid male gametes by the male parent.

Prophase I

The stage in the first meiotic division where the doubled chromosomes become visible and nuclear membrane disappears.

Metaphase I

The stage in the first meiotic division where the homologous chromosomes line up as a pair, forming a tetrad of chromatids, at the equator of the cell

Metaphase II

The stage in the second meiotic division where the chromatid pair lines up at the equator of the cell..

Anaphase II

The stage in the second meiotic division where the sister chromatids of a chromosome split and migrate to opposite poles

Telophase I

The stage of the first meiotic division where the cell divides into two cells each containing one member of each pair of homologous chromosomes.

Telophase II

The stage of the second meiotic division when the cell divides into two cells with each being haploid; these cells become the gametes.

Anaphase I

The stage on the first meiotic division when the homologous chromosomes move to opposite poles but the sister chromatids remain together

Multiple Alleles

Where more than two alternatives for a gene exist

Heterozygous

Refers to a pair of genes from a specific trait in an organism which are different

Homozygous

Refers to a pair of genes in an organism which are identical in the way they influence a trait