exam 3 ppt 2 Flashcards
how did Mendel discover the principle of independent assortment?
he discovered this by studying dihybrid crosses with 2 true breeding traits (homozygous genotypes)
what were the dihybrid crosses that Mendel studied?
yellow vs. green and round vs. wrinkled
what gametes does the genotypes AA bb produce?
gametes Ab
what gametes does the genotype aa BB produce?
gametes aB
what ratio did Mendel always observe in the F2 generation in dihybrid crosses?
9:3:3:1
what do dashes in a genotype mean?
it means that either allele can be present
definition of Mendel’s principle of segregation
individuals inherit two copies of each gene, one from the mother and one from the father, and when individuals form reproductive cells, the two copies separate equally in the eggs and sperm (equal amounts of each type of gametes)
what type of cross is associated with the principle of segregation?
monohybrid crosses
what type of cross is associated with the principle of independent assortment?
dihybrid crosses
definition of the principle of independent assortment
the two copies of each gene segregate into gametes independently of the two copies of another gene
what happens to the pairs of alleles in the principle of segregation?
the pairs of alleles are separated during meiosis I in the formation of gametes (equal gamete types of both alleles)
in the principle of independent assortment, is each gamete combo equally likely?
yes
why do the genes for seed shape and seed color assort independently?
because 1) they are located on different chromosomes, and 2) these chromosomes have two equally likely ways of lining up before they are segregated (each gamete type is equally likely to occur)
is there an exception to the principle of independent assortment?
yes
what are the exceptions to the principle of independent assortment?
if two genes are close together on the same chromosome, they will likely not assort independently -> they are linked
what does it mean if two genes are linked?
this means that the genes are close enough together on the same chromosome that they will likely not assort independently
do yellow, green, wrinkled, and round assort independently regarding the dihybrid crosses?
yes
what is an example of complete dominance seen in Mendel’s crosses?
in his yellow vs. green seed trait, yellow is dominant because the protein produced by the green allele is non-functional; we only see the result of the protein produced by the yellow allele
are all alleles completely dominant or recessive?
no -> there can be codominance or incomplete dominance
definition of complete dominance
a relationship in which one allele is completely dominant over another
definition of codominance
situation in which both alleles of a gene contribute to the phenotype of the organism
when does codominance occur?
it occurs when an individual displays phenotypes of BOTH alleles
definition of incomplete dominance
a pattern of inheritance in which two alleles, inherited from the parents, are neither dominant or recessive; the resulting offspring have a phenotype that is a blending of the parental traits
what are heterozygotes like in incomplete dominance?
heterozygotes have a phenotype in between the homozygous phenotypes (intermediate phenotype)
exp of incomplete dominance
parental has red and white flowers; produce 1/4 red, 2/4 pink, and 1/4 white
what phenotypic ratio always appears in incomplete dominance?
1:2:1
why does incomplete dominance occur?
one R allele doesn’t produce enough pigment to produce full red color; as opposed to complete dominance, one allele is sufficient
what can patterns of inheritance in humans be drawn as?
it can be drawn as a pedigree
in a pedigree, are affected traits empty or filled in?
affected traits are filled in
definition of an autosome
chromosome that is not a sex chromosome
definition of autosomal dominant trait
inheritance pattern of a dominant allele on an autosome
exp of an autosomal dominant trait
Huntington disease
definition of an autosomal recessive trait
inheritance pattern of a recessive allele on an autosome
exp of an autosomal recessive trait
sickle-cell disease
will we have half shaded in individuals in our pedigrees we see?
no
in autosomal recessive traits, are males or females more likely to be affected?
males and females are equally likely to be affected
in autosomal recessive traits, what parents do affected offspring often have?
affected offspring often have unaffected parents
in autosomal recessive traits, what are the characteristics of unaffected parents of affected offspring?
unaffected parents of affected offspring are heterozygous (carriers)
in autosomal recessive traits, what is the genotype of affected offspring?
affected offspring are homozygous
in autosomal recessive traits, what will be offspring be if both parents are heterozygous?
if both parents are heterozygous, about 1/4 of the offspring will be affected
in autosomal recessive traits, do traits appear in every generation?
no, traits often skip generations
in autosomal dominant traits, are males or females more likely to be affected?
males and females are equally likely to be affected
in autosomal dominant traits, do affected offspring have affected parents?
affected offspring have at least one affected parent
in autosomal dominant traits, if only one parent is affected, what are the genotypes of affected offspring?
affected offspring are heterozygous if only one parent is affected
in autosomal dominant traits, what is the genotype for unaffected offspring?
unaffected offspring are homozygous recessive
in autosomal dominant traits, how many offspring will be affected if one parent is heterozygous?
if one parent is heterozygous, about 1/2 of the offspring will be affected
in autosomal dominant traits, do the traits skip generations?
no, the trait does not skip generations
