Chapter 10 Patterns of Inheritance. 10.1 Genetics trait: a variation of a particular character Ex...
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Transcript of Chapter 10 Patterns of Inheritance. 10.1 Genetics trait: a variation of a particular character Ex...
10.1 Genetics
trait: a variation of a particular characterEx yellow or red flowers
gene: a unit of inherited information
Blending Hypothesis1800
Explains how offspring inherit traits from both parents Ex. yellow flower + red flower = orange flower
Discarded because it could not explain traits disappearing and reappearing in another generation
Gregor Mendel19th century Austrian
Monk
First to apply an experimental approach to the question of inheritance
genetics: the study of heredity Used pea plant
breeding
Particulate HypothesisParents pass on
to their offspring separate and distinct factors (genes) that are responsible for inherited traitsHeritable factors
retain their identity through generations
Mendel’s Experiment
1. Identify pea plants that were true-breeding When self-fertilized, only produces identical offspring
2. To insure self-fertilization, Mendel tied cloth bags around each plant’s flowers to prevent cross pollination
3. Mendel crossed true-breeding plants with two distinct traits (color and roundness)
cross-fertilization: sperm from the pollen of one flower fertilizes the eggs in the flower of a different plant
4. The fertilized eggs developed into embryos within seeds (peas) that were planted
5. These then grew to produce flowers Purple crossed with white flowers
10.2 Mendel’s Principle of Segregation
hybrids: the offspring of two different true-breeding varieties
P generation= parental
F1 generation = the hybrid offspring
F2 generation = offspring when F1 self-fertilize each other
Monohybrid Cross monohybrid cross: a
pairing in which parent plants differ in only one character Mendel found that F1
produced all purple flowers but F2 3/4 purple and 1/4 white
He repeated this for other traits (seed color, shape, pod shape & color, flower position, and stem length)Same result
Mendel’s 4 Hypotheses1. There are alternate forms of genes
alleles: the alternate forms of genes Ex. Purple and white
2. For each inherited character, an organism has 2 alleles for the gene controlling that character, one from each parent
homozygous: 2 alleles are the same for that character
heterozygous: the 2 alleles are different
3. dominant: only one allele appears to affect the trait
recessive: the allele that does not appear to affect the traitPp; P = dominant, p = recessive
4. Principle of SegregationTwo alleles for a character separate during
formation of gametes (meiosis) so that each gamete carries only one allele for each character
Phenotype and Genotype phenotype: an observable trait
Hair color, height, tongue rollingThe dominant trait shows upBb and BB = dominant; brown bb = recessive; blond
genotype: the genetic makeup (combination of alleles)
1/2 Bb; 1/2 bb = 2:2
Test Crosstest cross: breeds
an individual of unknown genotype but dominant phenotype with a homozygous recessive individual
Principle of Independent Assortment
During gamete formation in an F2 cross, a particular allele for one character can be paired with either allele of another
Intermediate Inheritance(Incomplete Dominance)
intermediate inheritance: the heterozygotes have a phenotype that is intermediate between the two homozygotesEx. Red + white
flowers = pink, red & white
Codominance codominance: a heterozygote
expresses both traits
Ex. Blood Type A, B, AB, O A & B refer to 2 carbohydrates that are
found on the surface of red blood cells
O = ii = neither carbohydrates Universal donor
A= IAIA or IAi = A carb (A)
B= IBIB or IBi = B carb
AB= IAIA or IAi = both A & B Universal receiver
Polygenic Inheritance polygenic inheritance:
two or more genes affect a single character Ex. Eye color, skin,
height
Eye color = tone of pigment , amount, and position
pleiotropy: a single gene affects more than one trait Ex sickle cell anemia
Importance in the Environment
Temperature can have an effect on animal coloringEx siamese cats,
rabbits
Height can be affected by nutrition and exerciseEx. Dancers
Nature vs Nurture
10.4 Meiosis Explains Mendel’s Principles
Chromosome Theory of InheritanceStates that genes
are located on chromosomes and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns
Genes gene locus: the
alleles of a gene reside at the same location on homologous chromosomesThe homologous
chromosomes may bear the same or different alleles
Genetic Linkage genetic linkage: the
tendency for the alleles on one chromosome to be inherited together The closer the genes are on
a chromosome, the greater the genetic linkage and crossing over will not separate them
The probability of genetic linkage is measured in centiMorgans (cM)Represents 1% of the
probability of crossing over1 cM apart = 1% chance of
separation20 cM = 20% chance
10.5 Sex-Linked Genes
sex-linked gene: any gene located on a sex chromosome Most are found on the X
chromosome
Thomas Hunt Morgan Discovered sex-linked genes
while studying fruit flies Normal fruit flies have red eyes
which is carried on the X, but sometimes males have white (recessive)