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
,What are twin studies used for in heritability?
-twin studies= tell us heritability
compare the monozygous and dizygous twins, measure the difference between phenotypes in monozygous twins- gentically identical
concordance- one twin has it the other then too
discordance- on has it while the other one doesn’t
Do rate of dizygous twins vary in different places? What are the factors affecting that?
rates vary! most common among african then european
Factors affecting DZ twins.
• genetic history, beginning to identify genes. Mutations in one of these genes (growth differentiation factor 9) are significantly more frequent in mothers of DZ twins but mutations are rare
• advanced age
- increased parity (number of previous children)
- taller mothers
- mothers with a high body mass index (>30)
Are measels caused mainly by the environment or genetically?
-mainly environment because monozygous and dizygous get it at almost same rates
Is schizophrenia caused genetically or environmentally?
-genetically because there is higher concordance in monozygotic twins than in dizygotic
How is eye colour determined in humans?
-at least four polygenes
A1 B1 C1 D1= add brown pigment(contributors)
A2 B2 C2 D2= no pigment (non-contributor)
Can brown eyed parents have a blue eyed child?
-yes, due to polygenic inheritance
How is skin colour determined in humans?
- similar to eye colour
- polygenes, one allele contributor of colour the other non-contibutor
Problem solving: how do you determine no. of polygenes:
Two races of corn averaging 96cm and 144cm in height respectively were crossed. The F1 was uniform in height averaging around 120cm. Of 500 F2 plants 2 were 96cm and 2 were 144cm. What is the number of polygenes involved and how much does it contribute to height?
- have to look at F2, find the offspring that resembles parents in this case 2 plants were 96 and 2 were 144
- know it’s four gene loci= that means 8 alleles
- the shortest plant had 8 non-contributors, the tallest had 8 contributors
F1-4 contributors
the range of plants is 144-96=48 cm, base height is 96 with no contributors, 8 contributors is the maximum and that increases height by 48 cm so 48/8= 6 cm per contributing allele
what genotype would 108 cm plant be? 108-96= 12 12/6=2 any genotyope with two contributors
In polygenetic questions which extreme you use?
eithe
the smallest or biggest, doesn’t matter
