Biology Meiosis And Mendel

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Genetics

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is the scientific study of heredity and variation

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heredity

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the transmission of traits from one generation to the next

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genes

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the units of heredity, and are made up of segments of DNA

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gametes

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Genes that are passed to the next generation through reproductive cells (sperm and egg)

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locus

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the specific location of each gene on a chromosome

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asexual reproduction

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one parent produces genetically identical offspring by mitosis

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somatic cell

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any cell other than a gamete (in humans--have 23 pairs of chromosomes

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diploid cell

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(2n) has two sets of chromosomes

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haploid

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A gamete (sperm or egg) contains a single set of chromosomes

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zygote

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a fertilized egg and has one set of chromosomes from each parent

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crossing over

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nonsister chromatids exchange DNA segments

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recombinant chromosomes

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produced by crossing over, which combine genes inherited from each parent

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chromosome theory of inheritance

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Mendelian genes have specific loci (positions) on chromosomes
Chromosomes undergo segregation and independent assortment

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law of segregation

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separate during gamete formation, and two alleles for each gene

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law of independent assortment

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Alleles of genes on nonhomologous
chromosomes assort independently during gamete formation.

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sex-linked

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A gene located on either sex chromosome. For a recessive sex-linked trait to be expressed
A female needs two copies of the allele
A male needs only one copy of the allele

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Sex-linked Disorders on X chromosome

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color blind, hemophilia, and Duchenne muscular dystrophy

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linked genes

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Genes located on the same chromosome that tend to be inherited together

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genetic recombination

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the production of offspring with combinations of traits differing from either parent (recombinant type)

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parental types

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offspring with phenotype like parents, opposed to recombinant type

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genetic map

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an ordered list of the genetic loci along a particular chromosome

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linkage map

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a genetic map of a chromosome based on recombination frequencies

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map units

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one map unit, or centimorgan, represents a 1% recombination frequency (Map units indicate relative distance and order, not precise locations of genes)

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cytogenic maps

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indicate the positions of genes with respect to chromosomal features

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nondisjunction

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pairs of homologous chromosomes do not separate normally during meiosis

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anueploity

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results from the fertilization of gametes in which nondisjunction occurred (Offspring with this condition have an abnormal number of a particular chromosome)

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monosomic

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zygote has only one copy of a particular chromosome

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trisomic

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zygote has three copies of a particular chromosome

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polyploity

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a condition in which an organism has more than two complete sets of chromosomes (common in plants)

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Barr body

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an inactive X chromosome in mammalian female that condenses

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down syndrome

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an aneuploid condition that results from three copies of chromosome 21

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genomic imprinting

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For a few mammalian traits, the phenotype depends on which parent passed along the alleles for those traits. Genomic imprinting involves the silencing of certain genes that are “stamped” with an imprint during gamete production

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hybridization

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mate two contrasting, true-breeding varieties

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homozygous

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An organism with two identical alleles for a character

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heterozygous

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An organism that has two different alleles for a gene

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F1 generation

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first generation from the P generation parents

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allele

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alternate form of a gene

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test cross

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breeding the mystery individual with a homozygous recessive individual

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monohybrid

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individuals that are heterozygous for one character

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dihybrid

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Crossing two true-breeding parents differing in two characters

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complete dominance

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phenotypes of the heterozygote and dominant homozygote are identical

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incomplete dominance

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the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties
red*white=pink

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codominance

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two dominant alleles affect the phenotype in separate, distinguishable ways
red*white=roan

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pleiotropy

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multiple phenotypic effects

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epistasis

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a gene at one locus alters the phenotypic expression of a gene at a second locus

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polygenic inheritance

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an additive effect of two or more genes on a single phenotype (eg: skin color)

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pedigree

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a family tree that describes the interrelationships of parents and children across generations

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carriers

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heterozygous individuals who carry the recessive allele but are phenotypically normal (i.e., pigmented)