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Ch. 14 & 15: Mendel and the Gene Idea & The Chromosomal Basis of…
Ch. 14 & 15: Mendel and the Gene Idea & The Chromosomal Basis of Inheritance
mendel's experiments
gregory mendel
alleles
alternative versions of a gene
law of segragation
dominant allele
exerts it's effects whenever present (capital letter) ex: Y:Yellow
YY
homozygous dominant
two identical alleles for the same gene
Yy
heterozygous
two different alleles for the same gene
genotype
genetic makeup, "what genes it has" (written as pair of letters)
recessive allele
has no effect if a dominant allele is present (lowercase letter) ex: y: green
yy
green peas
phenotype
character that is expressed, "way it looks"
homozygous recessive
test cross
crossing unknown genotype with homozygous recessive
father of genetics
law of independent assortment
chromosomes line up randomly
occurs in metaphase I
law of segragation
refers to the splitting of the homologous pairs of chromosomes
occurs in anaphase I & II
mendel's experiments
self-fertilization
self-fertilization produces offspring with the same phenotypes as the parent
true-bredding plants (homozygous)
cross-fertilization
self-fertilization produces offspring with mixed phenotypes
hybrid (heterozygous)
monohybrids are heterozygous for one specifc trait/gene
parental generation (P)
first filial generation (F1): their offspring
second filial generation (F2): offspring of the F1 generation
dihybrid cross
cross-fertilization between two dihybrid organisms
dihybrid
organism that is heterozygous for two specifc genes (RrYy)
phenotypic ratio 9:3:3:1
chromosome abnormalities
nondisjunction
pairs of homologous chromosomes do not separate normally during meiosis
leads to aneuploidy or polyploidy
trisomy 21 (down syndrome)
occurs when chromosome 21 fails to separate
gain of one chromosome
aneuploidy
results from the fertilization of gametes in which nondisjunction occurs
abnormal # of chromosomes
monosomy
loss of one chromosome
turner's syndrome
only monosomy the fetus can survive
polyploidy
extra sets of chromosomes
more common in plants than animals
organism has more than two complete sets of chromosomes
non-mendelian inheritance
incomplete dominance
heterozygotes show a blended intermediate phenotype
R: Red, r: white ; heterozygotes = pink
codominance
both alleles are expressed at same time
roan horse with both white & red hair; AB blood type
sex-linked genes
Y-linked
carried on Y chromosome
hairy pinnae
X-linked
carried on X chromosome
color blindness, hemophilia
males can't be carriers of a sex linked trait
women usually the carrier of the trait
morgan's fruit fly experiments
wild type = red eyes ; mutant = white eyes
white eye mutation found on x chromosome
first evidence linking genes directly to chromosomes
multiple allele trait
more than two choices
A, B, O blood alleles produce A, B, O, or AB blood types
polygenic trait
trait determined by more than one gene
skin color, eye color, interlligence
epistasis
one gene controls the expression of another
coat color pigment not deposited in hair without color gene
multifactorial
genetic component + enviromental facors influence disease (risk factors)
heart disease, diabetes, cancer
pedigree
diagram that shows how traits are passed over generations
circles = females; whereas squares = males
individual with trait gets filled in
carrier = half filled in
