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Genetics > Lecture 11 > Flashcards

Lecture 11 Flashcards

1
Q

Why is crossing over important?

A

-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

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2
Q

Why is crossing over important?

A

-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

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3
Q

h fz e - if change in h or fz which region crossed over?

A

region I

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4
Q

In which region is crossing over if h fz e – if change in e

A

region II (can also be both the h and fz change and e remains the same)

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5
Q

How do you map a gene?

A

: 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

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6
Q

h fz e - if change in h or fz which region crossed over?

A

region I

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7
Q

Give examples of multifactorial traits? 2

A

-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

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8
Q

How do you map a gene?

A

: 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

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9
Q

Is it important knowing the environment factors in multifactorial trait development?

A

-yes, if the traits are influenced by the environment then if we can identify them = reducing it may reduce the incidence

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10
Q

What are the attributes of multifactorial traits?

A

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

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11
Q

What food should pregnant women avoid?

A

-potatoes (can prevent spina bifida and anencephaly) plus take folic acid!

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12
Q

What is the genetic and environmental component of developmental displasia of the hip?

A

-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

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13
Q

What is a continuous phenotype (eg)?

A

-continuum of phenotypes, height= it isn’t just there or isn’t, comes on a scale -quantitative, can measure the differences between individuals

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14
Q

What is a quantitative trait?

A

continuous distribution of phenotypes -measurable and continuous range of phenotypes -height, weight, eye colour -often polygenic -affected by environmental factors

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15
Q

What does polygenic mean?

A

-controlled by many genes

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16
Q

What letter do we use for multifactorial traits?

A

A1 A2 etc, always capital as there is no dominance between them

17
Q

What do we assume about the alleles of multifactorial traits?

A

-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

18
Q

What will the F2 offspring of A1B1 x A2B2 be if A1 and B1 add red pigment?

A

-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)

19
Q

How does increasing the number of gene loci influence the number of phenotypes of F2 offspring?

A

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

20
Q

What happens to the difference in phenotypic classes as the number of genes controlling a phenotypic character increases?

A

-the difference become classes becomes less distinct

21
Q

How do you determine the number of polygenes involved in a genotype?

A

-look at F2 and and see what fraction of offspring resembles parents

22
Q

Does environemnt influence the distribution of phenotypes?

A

-yes

23
Q

What is heritability?

A

-a statistical measure of how strongly the phenotype of the offspring will resemble the phenotype of the parents

24
Q

Why do we measure heritability?

A

-want to know, how much is inherited, how much due to environment

height= 65 genetic thus 35% dnvironment= can affect that

25
Q

,What are twin studies used for in heritability?

A

-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

26
Q

Do rate of dizygous twins vary in different places? What are the factors affecting that?

A

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)
27
Q

Are measels caused mainly by the environment or genetically?

A

-mainly environment because monozygous and dizygous get it at almost same rates

28
Q

Is schizophrenia caused genetically or environmentally?

A

-genetically because there is higher concordance in monozygotic twins than in dizygotic

29
Q

How is eye colour determined in humans?

A

-at least four polygenes

A1 B1 C1 D1= add brown pigment(contributors)

A2 B2 C2 D2= no pigment (non-contributor)

30
Q

Can brown eyed parents have a blue eyed child?

A

-yes, due to polygenic inheritance

31
Q

How is skin colour determined in humans?

A
  • similar to eye colour
  • polygenes, one allele contributor of colour the other non-contibutor
32
Q

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?

A
  • 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

33
Q

In polygenetic questions which extreme you use?

A

eithe

the smallest or biggest, doesn’t matter

Genetics (40 decks)

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