topic 10 (10.2, 10.3) Flashcards
unlinked genes ——- ———- as a result of meiosis
segregate independently
what is segregation?
the separation of the two alleles of every gene that occurs during meiosis
what is independent assortment?
the alleles of one gene segregate independently of the alleles of other genes
genes found on different chromosomes are
genes which are on the same chromosome are
the exception is
unlinked and segregate independently
linked and do not segregate independently
linked genes that are far apart on the chromosome (due to crossing over)
look at how to form a punnet square for dihybrid traits
p446
describe the difference between a monohybrid and a dihybrid trait
monohybrid cross: the cross happening in the F1 generation offspring of parents differing in one trait only, ie the inheritance of a single trait.
dihybrid cross: the cross happening in the F1 generation offspring of parents differing in two traits, the simultaneous study of the inheritance of two different traits.
when are gene loci said to be linked?
if they are on the same chromosome and hence don’t independently assort (unless synapsis occurs)
define a locus
a locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located.
define homologous chromosomes
two chromosomes that have the same sequence of genes.
why are homologous chromosomes not usually identical to each other?
for at least some of the genes on them, the alleles will be different
what is the name of non-sex chromosomes?
autosomes- these are common to both males and females
what are the two types of linkage?
autosomal gene linkage, when the genes are on the same autosome
sex linkage, when the genes are located on the X chromosome
variation can either be
discrete - no in-between categories
continuous - eg height
discrete variation
Monogenic traits (characteristics controlled by a single gene loci) tend to exhibit discrete variation, with individuals expressing one of a number of distinct phenotypes
continuous variation
Polygenic traits (characteristics controlled by more than two gene loci) tend to exhibit continuous variation, with an individual’s phenotype existing somewhere along a continuous spectrum of potential phenotypes
describe how the phenotypes of polygenic characteristics tend to show continuous variation
Increasing the number of loci responsible for a particular trait increases the number of possible phenotypes
This results in a phenotypic distribution that follows a normal distribution curve
monohybrid inheritance =
linked genes = two potential gamete combinations
dihybrid inheritance =
unlinked genes = 4 potential gamete combinations
why do offspring with unlinked genes have an equal possibility of inheriting any potential phenotypic combination?
due to the random segregation of alleles via independent assortment
Offspring with linked genes will only express the phenotypic combinations present in either parent unless
Consequently, the ‘unlinked’ recombinant phenotypes occur —– ——- than the ‘linked’ parental phenotypes
crossing over occurs
less frequently