Inheritance (lectures 12-14) Flashcards

1
Q

what is continuous variation?

A

phenotypes that show a large range of variation
POLYGENIC - multiple interacting genes
environmental influences

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2
Q

what is the dominant allele?

A

allele that expresses itself at the expense of an alternate allele

the phenotype expressed in the F1 generation from the crossing of 2 pure lines

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3
Q

what is the recessive allele?

A

allele whose expression is suppressed in the presence of a dominant allele

phenotype will disappear in F1 generation from the crossing of 2 pure lines but will reappear in the F2 generation

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4
Q

what is mendels first law?

A

2 copies of each gene segregate independently

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5
Q

what is mendels second law?

A

the copies of each gene segregate independently of those of other genes

doesn’t always happen - linked genes are inherited together

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6
Q

what is a monohybrid cross?

A

cross of 2 true breeding lines differing in 1 trait

looks at 1 gene/characteristic

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7
Q

what is the ratio of genotypes in the F2 generation of a monohybrid cross?

A

1 : 2 : 1

as long as the genes are not linked

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8
Q

what is the ratio of phenotypes in the F2 generation of a monohybrid cross?

A

3 : 1

as long as the genes are not linked

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9
Q

what does the hardy-weinberg equilibrium state?

A

gene frequencies and genotype ratios in a randomly breeding population remain constant from generation to generation thus populations retain genetic variability

alleles don’t disappear unless there is a selective pressure

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10
Q

what does the hardy-weinberg equilibrium assume?

A

infinitely large population

random mating

no evolutionary forces

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11
Q

what are the equations for hardy-weinberg equilibrium?

A

total frequencies of alleles in the population
p + q = 1
total frequencies of genotypes in the next generation
p^2 + 2pq + q^2 = 1

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12
Q

when does the hardy-weinberg equilibrium not work?

A

gene flow
genetic drift
non-random mating
natural selection

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13
Q

what is gene flow?

A

movement of an individual to an isolated population

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14
Q

what is genetic drift?

A

small populations - chance or inbreeding leading to a loss of infrequent alleles

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15
Q

what is non-random mating?

A

preferences for certain characteristics

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16
Q

what is natural selection?

A

ability to produce more offspring due to differential mortality (survival) or fecundity (family size)

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17
Q

examples of human autosomal recessive conditions

A
albinism 
phenylketonuria 
tay-scchs 
cystic fibrosis 
sickle cell anaemia 
haemochromotosis
18
Q

examples pf human autosomal dominant conditions

A
Huntingdon's disease 
achondroplastic dwarfism 
polydactyl
hypercholesterolemia 
FASPS - familial advanced sleep phase syndrome
19
Q

what is an autosomal recessive pedigree?

A

disease generally appears in the progeny of unaffected parents
horizontal pedigree pattern
affected progeny includes males and females

20
Q

what is an autosomal dominant pedigree?

A

appear in each generation of a pedigree
vertical pedigree pattern
usually affect 50% of offspring
affects both males and females

21
Q

how are the X and Y chromosomes different?

A

they show little homology
X has way more genes than Y
many genes on Y are involved in male sex development
many genes on X are not involved in sex development

22
Q

what is sex linkage?

A

as men only have 1X, any allele of a gene on X that causes a disease is phenotypically expressed in male offspring

23
Q

examples of X linked recessive disorders in humans

A

haemophilia - failure of blood to clot
fragile X syndrome
deuteranopia - red-green colour blindness

for serious X linked disorders all cases are in boys - always inherited from the mother who is heterozygous

24
Q

examples of X linked dominant disorders in humans

A

hypophosphatemia

affected males pass the condition to all their daughters but none of their sons
affected heterozygous females pass the condition to half their sons and daughters

25
what is codominance?
mixture of 2 phenotypes | traits show up equally in F1
26
what is incomplete dominance?
heterozygous individual looks like neither parents new phenotype formed F1 resembles neither parent
27
what is pleiotrophy?
some genes affect more than 1 unrelated characteristics they are called pleiotropic eg. Manx phenotype in cats is due to a dominant allele of a gene that severely disrupts spinal development all manx cats are heterozygous it is recessive lethal - offspring with 2 copies don't make it to birth
28
what is epistasis?
where 1 mutation hides/modifies the phenotype of another
29
what is the epistatic gene?
the gene that modifies or masks another gene
30
what is the hypostatic gene?
the gene that is being modified or masked
31
what is penetrance?
measures the proportion of the population with a particular genotype show the expected phenotype can be complete or incomplete if 15% of individuals with a particular mutation appear wild type, the penetrance is 85%
32
what is expressivity?
refers to the range and symptoms that can occur in different people with the same genetic condition depends on interaction with other genes as well as environmental influences
33
how is penetrance and expressivity in polydactyly?
incomplete penetrance - due to a dominant mutation, but children with extra digits are born to parents with the normal number variable expressivity - some individuals have 1 extra finger, other have extra digits on each hand and foot
34
what environmental effect has an affect on phenotypes?
temperature eg. siamese cats - homologous for a thermosenstive allele of a gene encoding an enzyme catalysing melanin production protein doesn't work at normal body temperature but works at slightly cooler temperatures
35
what is complementation analysis?
test for determining whether two mutations associated with a specific phenotype represent two different forms of the same gene (alleles) or are variations of two different genes can only be done with recessive alleles
36
what is a complementation group?
a set of mutations mapping to the same chromosomal locus that fail to complement each other when crossed they produce a mutant phenotype when crossed
37
what is linkage?
when genes are close on the same chromosome they can be linked and are inherited together
38
how are non parental genotypes formed when there is gene linkage?
independent asssortment of genes on different chromosomes breakage and rejoining of homologous chromosomes during meiosis - recombination
39
what is recombination frequency?
no. of recombinants / total progeny x 100
40
what is a centimorgan?
2 loci are 1 cendtimorgan (cM) apart if recombination is observed cendtimorgan is commonly called a map unit (mu) in humans, 1 cendtimorgan is around 1 million bp