Lecture 11 Flashcards
Why is crossing over important?
-important in meiosis for the spindle alignment -somehow male drosphilas and lucillas overcome that (males:eyes further apart than females) -recombination especially double extremely uncommon but some regions of chromosomes are hot spots and other such as heterochromatin show nearly no recombination
Why is crossing over important?
-important in meiosis for the spindle alignment -somehow male drosphilas and lucillas overcome that (males:eyes further apart than females) -recombination especially double extremely uncommon but some regions of chromosomes are hot spots and other such as heterochromatin show nearly no recombination
h fz e - if change in h or fz which region crossed over?
region I
In which region is crossing over if h fz e – if change in e
region II (can also be both the h and fz change and e remains the same)
How do you map a gene?
: take two genes next to each other h-fz –region I add up all the recombinants in region I (include double recomb. Since they cross in both) - divide by the number of all the offspring (all including parental etc) - multiply by a 100 fz-e- region II add up all the recombinants in region II (plus double recomb) -divide by the total offspring - multiply by a 100
h fz e - if change in h or fz which region crossed over?
region I
Give examples of multifactorial traits? 2
-spina bifida= spinal cord not enclosed, the fluid herniates and children paralised cleft palate= when top of mouth not closed off =both result of mix of genes plus environmental factors
How do you map a gene?
: take two genes next to each other h-fz –region I add up all the recombinants in region I (include double recomb. Since they cross in both) - divide by the number of all the offspring (all including parental etc) - multiply by a 100 fz-e- region II add up all the recombinants in region II (plus double recomb) -divide by the total offspring - multiply by a 100
Is it important knowing the environment factors in multifactorial trait development?
-yes, if the traits are influenced by the environment then if we can identify them = reducing it may reduce the incidence
What are the attributes of multifactorial traits?
discontinuous distribution of phenotypes -either have it or you don’t, can be classified into discrete groups - you are type O or you’re not, either an albino or not - environmental factors -have genetic predisposition and if you have enough environmental factors and genes= reach threshold and show phenotype
What food should pregnant women avoid?
-potatoes (can prevent spina bifida and anencephaly) plus take folic acid!
What is the genetic and environmental component of developmental displasia of the hip?
-genetic: 10 fold more probable if parents had it, more common in caucasians than africans and asians -environmental: intrauterine position -breech positioning is associated with DDH, sex= female, firstborn child =first born female in breech position 1/15 probability =normally 1.5 births per 1000
What is a continuous phenotype (eg)?
-continuum of phenotypes, height= it isn’t just there or isn’t, comes on a scale -quantitative, can measure the differences between individuals
What is a quantitative trait?
continuous distribution of phenotypes -measurable and continuous range of phenotypes -height, weight, eye colour -often polygenic -affected by environmental factors
What does polygenic mean?
-controlled by many genes
What letter do we use for multifactorial traits?
A1 A2 etc, always capital as there is no dominance between them
What do we assume about the alleles of multifactorial traits?
-allele eg. A1 is a contributor -allele eg A2 is a non-contributor -the effect of the alleles is cumulative if A1 adds 1cm then A1A1 will add 2 cm
What will the F2 offspring of A1B1 x A2B2 be if A1 and B1 add red pigment?
-F1 will be medium red so looks like codominance but F2 reveals it is not! -F2 lot of phenotypes, different shades of red to complete white (A2B2)
How does increasing the number of gene loci influence the number of phenotypes of F2 offspring?
2 genes= 5 possible phenotypes 3 genes= 8 possible phenotypes to recognise= look at the number of offspring that look like parents= 1 gene =1/4 will resemble parents 2 genes= 1/16 more genes= eventually a continuum
What happens to the difference in phenotypic classes as the number of genes controlling a phenotypic character increases?
-the difference become classes becomes less distinct
How do you determine the number of polygenes involved in a genotype?
-look at F2 and and see what fraction of offspring resembles parents
Does environemnt influence the distribution of phenotypes?
-yes
What is heritability?
-a statistical measure of how strongly the phenotype of the offspring will resemble the phenotype of the parents
Why do we measure heritability?
-want to know, how much is inherited, how much due to environment
height= 65 genetic thus 35% dnvironment= can affect that
