pg 112 Meiosis Crossing Over and Independant issomenet with linkage Flashcards
What is the fundamental difference between gamates and other cells
The difference is the number of chromosomes
Because if sperm and egg had full chromosome number, where humans 46 and zygote 92= zygote with 184 chromosomes, as each generation number would double.
Therefore gamates are haploid as when they fuse full number of 46 is restored so dipoid zygote is formed.
What is meiosis
is the process in producing gametes, with half the number of chromosomes, (haploid) which is neccessaru to maintain dipoid number after fertisation. this helps create genetic variation
How does meiosis help create genetic variation?
using crossing over during prophase 1 and independant assomenet during metaphase 1 and 2
Describe independant assomenet
random process whereby only one chromosome ends up in each gamete. Homologous pairs of chromosomes line up on spindle fibres and split into diffreent pairs, each daughter cell containing different assortments
Why would there never be the same combinations of chromosomes in independant assoment
This is because with a 23 pairs number, chromosome combinations are so large, their would never be the same combination.
How does meiosis help create genetic variation?
using crossing over during prophase 1 and independant assomenet during metaphase 1 and 2
Describe independant assomenet
random process whereby only one chromosome ends up in each gamete. Homologous pairs of chromosomes line up on spindle fibres and split into diffreent pairs, each daughter cell containing different assortments
What is linkage
when any two genes with a locus on same chromosomes are linked together and will be passed as a pair with the same gene
X
Describe mendels garden peas and how did it prove linkage
He crossed pure homologous tall puprle plants with short white plants and all produced were tall puprle.
From further research, Mendel concluded that inhertaince of genes is independant to inhertiance of other pairs.
how can meiosis give rise to genetic variation
Homologous chromosomes line up and DNA and Alelles are exchanged on the same loci producing a new combinantion of alleles
Describe how each gamete only receives only one allelle
Spindle fibres have homologous chromosomes which oull chromosomes to opposite poles, causing new combination of alleles
Different ways of producing genetic variation
When chromosomes are replicating, muataions in DNA sequence can occur
Combinations of genetic material, independat assosment and randomly fertisling.
What are linked genes
genes that are on the same loci and chromosome that tend to be inherited together
What to do when assessing chances of combinations
because its linked, combinations on same chromosome are more likely to happen.
Greater distance between loci, more chance of crossing over to occur.
Assess which genes are closer
Fruit Fly and linkage, Asses chances of phenotype with GgNn for mom and GgNn for dad aswell.
with body colour, dominant (G) would turn body grey
and two resccive g and g will turn black body
Same for wings as dominant (N) will give normal wings wheras two resscive n and n would give vestigial wings
Now mother is GgNn Dad is GgNn
GN gn
GN GGNN GgNn
gn GgNn ggnn
If GgNn dominant normal wings and grey body (2x)
GGNN normal wings and grey body
ggnn vestigial wings and black body
3/4 chance of having good wings and grey body
