Chapter 9 Flashcards
blending hypothesis
- the idea that the heredity materials contributed by the male and female parents mix in forming the offspring (ex: blue + yellow = green)
- rejected because it doesn’t explain how traits that disappear in one generation can reappear in later ones
true-breeding
- varieties result when self-fertilization produces all identical to the parent
- P generation
hybrids
- the offspring of two different varieties
* F1 generation
cross-fertilization
- a hybridization, or genetic cross.
* cross of F1 plant produces an F2 generation
homo- vs. hetero-
zygous
- homozygous: genotype has identical alleles
* heterozygous: genotype has two different alleles
allele
- alternative versions of genes that account for variations in inherited characters
- dominant: determines the organism’s appearance
- recessive: has no noticeable affect on the organism
phenotype
• appearance or expression of a trait (ex: blonde hair, blue eyes)
genotype
• the genetic makeup of a trait
ex: blue eyes=bb ; brown eyes=BB
monohybrid cross
• a cross between two individuals differing in a single character
dihybrid cross
• mating of parental varieties that differ in two characteristics (9:3:3:1 phenotypic ratio)
punnett square
• shows the possible combinations of alleles that could occur when gametes combine
law of segregation
• a sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other in gamete production
law of independent assortment
mendel suggested that…
- the inheritance of one character has no effect on the inheritance of another
- the dihybrid cross is equivalent to 2 monohybrid crosses
genetic relationship between homologous chromosomes
- for a pair of homo. chrom., alleles of a gene reside at the same locus (specific location of a gene along a chromosome)
- homozygous individuals have same allele on both homologues; while heterozygous individuals have different alleles on each homologue
pedigree
- shows inheritance of a trait in a family through multiple generations
- demonstrates dominant or recessive inheritance
- also be used to predict genotypes of family members
wild type traits
• those prevailing in nature, are not necessarily specified by dominant alleles ex: freckles (D), albinism (r) • recessive disorders: - albinism - sickle-cell disease • dominant disorders: - achondroplasia - huntington's disease
incomplete dominance
• results in intermediate phenotypes–heterozygous genotype (ex: red + white = pink)
codominance
• more that 2 different alleles for one particular gene exist in the wider population
• neither allele is dominant over the other
(ex: ABO blood group–A and B alleles are both expressed in heterozygous individuals = AB blood type)
environmental effects
- skin color affected by sunlight exposer
- diseases, i.e. cancer, has hereditary and environmental components
- nutrition
- pollution
pleiotropy
• when one gene influences many phenotypic characteristics
• often seen in human disease, leading to syndromes, or groups of symptoms related to a genetic mutation
(ex: sick cell disease, mar fan syndrome)
polygenic inheritance
• results from the additive affects of two or more genes
• controlled by at least 3 separately inherited genes
(ex: skin color)
sex-linked genes
• most found on X chromosome
• mostly affect males due to recessive alleles
• a male receiving a single X-linked recessive allele from his mother will have the disorder; a female must receive the allele from both parents to be affected
(ex: red-green color blindness)
chromosome theory of inheritance
• genes occupy specific loci (positions) on chromosomes, and it is the chromosomes that undergo segregation and independent assortment during meiosis–its behavior accounts for inheritance patterns
