Chapter 14 Flashcards
genetics
study of heredity
genes are considered
heritable factors
what is heredity
transmission of traits from parents to their
offspring
trait
any characteristic of an individua
what two hypotheses did Mendel prove wrong
- blending inheritance
- inheritance of acquired characteristics
blending inheritance
Parental traits blend so that
their offspring have intermediate traits
- example: blond hair x black hair–> brown hair
inheritance of acquired characteristics
Parental
traits are modified through use and then passed on
- example: parent uses right hand so offspring will use right hand
polymorphic traits
Trait that appears commonly in two or more
different forms
true breeding
plants that produce offspring of the same
variety when they self-pollinate
- same variety of parents
how did Mendel control mating
remove male organs from flower to prevent self pollination
cross pollination
used pollen from one flower to fertilize another flower
which generation are true breeding parents
p generation- grandparents
which generation are the hybrid offspring of P generation
F1 generation-parents
what occurs when F1
individuals self-pollinate
F2 generation is produced
- children of F1
- grandchildren of P generation
particulate inheritance
- Mendel proposed
- parents pass down alleles and genes to offspring in specific way
- traits don’t interact with each other
what did Mendel propose about genes
- individual has two versions of each gene
- Different alleles are responsible for variation
what are version of genes called
alleles
what do alternative versions of genes account for (first concept)
variations in inherited characteristics
- alleles
for each character, how are alleles inherited (third concept)
inherits two alleles, one from each parent
- alleles may be identical (homozygous), or
they may differ (heterozygous)
- dominant vs recessive
dominant allele
determines the organism’s appearance
recessive allele
no noticeable effect on the organism’s appearance
principle of segregation
- two members of each gene pair must segregate
- separate into different gamete cells
- during formation of egg and sperm in parents
law of segregation (fourth concept)
- accounts for the 3:1 ratio he
observed in the F2
generation - possible combinations of sperm and egg
- each gamete receives just one gene copy randomly
Monohybrid Cross
inheritance pattern of a
single trait
dihybrid crosses
inheritance patterns of two traits
that are linked
- Mendel used this cross
what does the dihybrid cross test
Independent assortment
Dependent assortment
Independent assortment
Alleles of different
genes are transmitted independently of each
other
- traits don’t interact
dependent assortment
transmission of
one allele depends on the transmission of
another
- one trait depends on the trait
principle of
independent assortment
- receive traits from parents individually
- Mendel’s results supported this hypothesis
- use dihybrid cross
testcross
homozygous recessive parent mated with a parent that has the dominant
phenotype but an unknown genotype
what can be found using a test cross
genotype of the second parent can be
inferred from the results
- further confirm principal of independent assortment
Sex Linkage
- X and Y chromosomes
- specific traits found on X and Y chromosomes
Linkage
tendency of genes to be inherited together because they are on the same chromosome
- gene stays with specific chromosome
what do linked genes violate
- principle of independent assortment
- linked genes are predicted to always be transmitted
together during gamete formation
what can be used to create a genetic map
frequency of crossing over
when are genes more likely to cross over
far apart from each other
can heritable characteristics determined by only one gene with two alleles
many cannot be
what is multiple allelism
When there are more than two alleles of a gene in a
population
what is an example of multiple allelism
Humans have three common alleles for ABO
blood types
- Each codes for a version of an enzyme that adds
polysaccharides to the membrane of red blood cells
Complete dominance
phenotypes of the
heterozygote and dominant homozygote are identical
- example: one red flower and one white flower produce red offspring. Red would be dominant over white
incomplete dominance
phenotype of F1
hybrids is somewhere between the phenotypes of the two parental varieties
- phenotype between 2 parents is blended in offspring
- example: one red flower and one white flower produce offspring that is pink in color
codominance
two dominant alleles affect the phenotype in separate, distinguishable ways
- example: one red flower and one white flower produce offspring which are partially red and partially white
what is the relationship between dominance and phenotype
- dominant allele does not subdue a recessive
allele; dominance is just what is expressed - Alleles are simply variations in a gene’s nucleotide sequence
pleiotropy
multiple phenotypic effects
- example: have a gene for a specific disease, but show different symptoms
Polygenic inheritance
additive effects
of two or more genes on a single phenotypic character
- 1 gene acts together but has multiple different outcomes
- example: human skin color
what happens in epistasis
gene at one locus alters the
phenotypic expression of a gene at a second locus
what is an example of epistasis
coat color in mammals depends on two genes
- One gene determines the pigment color
- other determines whether the pigment will be deposited in the hair
