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Bio1MGC > Mendelian Inheritance > Flashcards

Mendelian Inheritance Flashcards

1
Q

reasons for working with peas

A

many varieties of characters (colour) and trait (purple)
short generation time
large number of offspring from each mating
easy to observe and record
could strictly control mating

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2
Q

true breeding

A

over many generations of self pollination plants produce only the same variety as the parent plant e.g. true breeding purple plant will give successive generations of purple flowered plants through self pollination

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3
Q

hybridisation

A

mating or crossing of two true breeding varieties
parents - P generation
F1 - first filial generation - offspring of hybrid mating
F2 - second filial generation - allowing F1 hybrids to self pollinate

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4
Q

P generation

A

parent generation in hybridisation process - mating of two true breeding varieties
YY x yy (hybrid)
F1 are their offspring

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5
Q

F1 and F2 generation

A

F1 - first filial generation / F2 second filial
F1 offspring of 2 true breeding hybridisation
F2 - offspring of 2 F1s
Mendels findings were as a result of him following through to the F2 stage

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6
Q

what enabled Mendel to discover the basic patterns of inheritance

A

If he had stopped with the F1 generation he would not have been able to work out the pattern of dominant and recessive traits as these only become evident with the F2 generation

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7
Q

what are Mendel’s two laws of hereditary

A

the law of segregation

the law of independent assortment

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8
Q

what was the main theory about inheritance before Mendel

A

the blending model which stated that genetic material contributed by two parents mixed and that over successive generations mating will led to a uniform population

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9
Q

when did Mendel do is work

A

Began in 1857

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10
Q

the law of segregation

A

alternative versions of genes account for variations in inherited characters
for each character an organism inherits two copies (two alleles) of a gene from each parent
if the two alleles at the locus differ, then one is the dominant allele (determines the organisms appearance)
the other recessive allele has no noticeable effect on the organisms appearance
the two alleles for a heritable character segregate during gamete formation and end up in different gametes

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11
Q

Give an example of the law of segregation for pea flower colour

A

cross pea flowers with purple and white flowers
F1 - all purple (the purple colour is dominant so all flowers have PP or Pp
F2 - proportion of 3:1 purple flowered to white flowered

The heritable factor for the recessive trait has not been lost but was masked by the presence of the factor for purple flowers

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12
Q

alleles

A

version of a gene e.g. purple flowers or white flowers

at a particular locus on the DNA

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13
Q

what is a gene

A

a sequence of nucleotides at specific locus along a chromosome

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14
Q

how can we have different alleles for a particular gene

A

genes are sequence of nucleotides
there can be variations in the nucleotide sequence
this variation can affect the function of the encoded protein the thus the inherited character of the organism

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15
Q

diploid

A

has two sets of chromosomes- one set inherited from each parent
a genetic locus is represented twice in a diploid cell once on each homologue of a specific pair
of chromosomes

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16
Q

somatic cell

A

all non sex cells

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17
Q

describe the arrangement of genes on chromosomes

A

each diploid cell has two sets of chromosomes - one set inherited from the mother and one from the father
so a gene is represented twice - once on the chromosome inherited from the mother and once on the chromosome inherited from the father
the variety of the gene - the allele - can be the same on both chromosomes (PP)
or they can be different (Pw)

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18
Q

what happens if the alleles for a trait differ

A

the dominant allele determines the appearance of the organism
the other allele is recessive and so not seen

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19
Q

homozygote

A

an organism that has a pair of identical alleles for a gene encoding a character
they are homozygous for that gene

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20
Q

homozygous

A

have two identical alleles for a gene e.g. PP or pp

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21
Q

heterozygote / heterozygous

A

an organism that has two different alleles for a gene
heterozygotes produce gametes with different alleles
e.g. Pp

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22
Q

phenotype

A

organism’s observable traits

this can be different to the genotype because some genes might be recessive and therefore not observable

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23
Q

genotype

A

genetic makeup
can be different from phenotype
e.g. PP and Pp plants have the same phenotype but different genotypes

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24
Q

test cross

A

breeding an organism of unknown genotype with a recessive homozygote to reveal the genotype of the organism

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25
Q

monohybrid cross

A

looking at only one genetic character e.g. colour of flowers

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26
Q

dihybrid cross

A

cross looking at two characters e.g. pea colour and shape

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27
Q

how many different combinations are possible from a dihybrid cross

A

16 (4 x 4)

Ratio 9:3:3:1

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28
Q

law of independent assortment

A

two or more genes sort independently
each pair of alleles segregates independently of any other pair of alleles during gamete formation

(some genes are inherited together if they are close to each other on the chromosome )

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29
Q

multiplication rule

A 
to determine the probability of an event - multiply the probability of one event by the probability of the other event i.e. probability of purple flowers (1:2 or half) probability of white (1:2 , half) = half multiplied by half is one quarter 
so
one quarter PP
one quarter Pp
One quarter Pp
one quarter pp
30
Q

addition rule

A

the probability that two or more mutually exclusive events will occur is calculated by adding their individual probabilities
e.g quarter of wrinkled peas + 1/4 of yellow =

31
Q

complete dominance

A

when the alleles of the gene are different the dominant allele observed in all cases
the phenotypes of the heterozygote and the dominant homozygote are indistinguishable

32
Q

incomplete dominance

A

when the alleles are different the phenotype is a blend (somewhere between the two parental varieties) e.g. snapdragons - when red snapdragons are crossed with white some of the offspring are pink (those with one dominant and one recessive)

33
Q

ratios for phenotype and genotype

A

PP x pp
results in 3 purple and 1 white in appearance so the phenotype ratio is 3:1
however the genetic ratio is different
results in 1/4 PP 1/2 Pp and 1/4 pp so the ratio is 1:2:1

34
Q

codominance

A

Codominance refers to a type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual. That is, instead of one trait being dominant over the other, both traits appear, such as in a plant or animal that has more than one pigment colour.

35
Q

codominance example

A

red flower + white flower =
RR red flower
rr white flower
Rr - red petals and white petals

36
Q

pleiotropy

A

most genes have multiple phenotypic effects
single gene affect a number of characters e.g. cystic fibrosis / sickle cell disease
Mendel - same gene that causes flower colour also causes the colour of the seed coating

37
Q

epistasis

A

one gene affects the phenotype of another because the two genes interact
the phenotypic expression of a gene at one locus alters that of another gene at a second locus
e.g. labradors - colour gene is affected by the pigment depositing gene /if the dog is recessive at the pigment locus then it is yellow - no pigment regardless of the other gene

38
Q

quantitative characters

A

characters like human skin colour or height that are graduations along a continuum

39
Q

polygenic inheritance

A

two or more genes that work together to make a single phenotypic character e.g. height - 180 genes impact on height
skin pigmentation in humans is controlled by many separately inherited genes

40
Q

pedigrees

A

collecting information about a families history for a particular trait / creating a family tree
use for calculating the probability of future children inheriting a trait / having a particular genotype or phenotype

41
Q

carriers

A

heterozygotes (two forms of the gene) though phenotypically normal can transmit the recessive allele to their offspring
most people who have recessive disorders are born to parents who are carriers of the disorder but have normal phenotype

42
Q

examples of diseases caused by recessive genes

passed on through carriers

A 
cystic fibrosis (4% are carriers)
sickle cell disease
43
Q

examples of diseases caused by dominant alleles

A

achondroplasia (dwarfism)
people who do not have it are homozygous for the recessive allele
Most lethal dominant gene diseases are not passed on because the organism dies before reproducing
some like Huntington’s disease only appear after reproductive age

44
Q

when does the segregation of alleles occur in meiosis

A

anaphase 1 - when alleles separate

45
Q

who found proof in chromosomes that supported Mendel’s theory

A

Morgan (early 1900s) working with fruit fly - Drosophilia

46
Q

why was the choice of Drosophila good

A

prolific breeders - many offspring and mate often
only 4 chromosomes
chromosomes can be seen with a light microscope
three autosomes and one pair of sex chromosomes

47
Q

wild type

A

phenotype for a character most commonly observed

in natural populations

48
Q

mutant phenotypes

A

alternatives to wild type

49
Q

homologous chromosomes

A

two chromosomes in a pair carry genes controlling the same inherited characters
carry the same genes

50
Q

somatic cells

A

all the cells in the body except gametes

51
Q

sex chromosomes

A

chromosomes involved in sex determination

all other chromosomes are called autosomes

52
Q

diploid cell

A

any cell with two chromosome sets
has a diploid number of chromosomes -2n
humans - diploid number is 46
drosophila - 8 (2 x 4)

53
Q

haploid cell

A

cells tat have a single set of chromosomes
gametes are haploid cells
for humans the haploid number is 23
drosophila - 4

54
Q

X - Y system for sex determination

A 
Females have XX
Males XY (Y smaller)

each egg receives one x
each sperm can have x or Y
Fathers pass X to all their daughters but none to their sons

55
Q

sex linked gene

A

a gene located on either sex chromosome
chromosomes on the X chromosome are called X linked (1100 in humans)
chromosomes in the Y chromosome are Y linked
(78 in humans) - mainly related to function of testicular function
X chromosome genes for many characteristics

56
Q

hemizygous

A

because females have XX they can be homozygous or heterozygous for a particular allele on a X chromosome
because males have only on X chromosome they only have one form of the allele - they are hemizygous (hemi - they only have half)

57
Q

why do more males than females have X linked disorders

A

Females have two X chromosomes so can be XX Xx Xx and xx
if x is recessive have 1/4 chance of inheriting
If a male has only one X it can be X or x - so have 1/2 chance
if the male receives a recessive six linked gene from their mother they will express the trait

58
Q

examples of sex linked traits

A

colour blindness
muscular dystrophy
haemophilia
baldness

59
Q

Barr body

A

females have XX so twice as many of the genes located on the X chromosome as males
in females one X is inactivated during embryonic development
As a result males and females have the same effective dose (protein making ability) of most X linked genes
the inactive X forms the Barr body

60
Q

why don’t females - XX- produce double the proteins for genes on the X chromosome as males (XY)

A

inactivation of one X chromosome during embryonic development
As a result both males and females have the same dosage of most X linked genes.

61
Q

linked genes

A

genes located near each other on the same chromosome tend to be inherited together in genetic crosses
genes that are genetically linked
(different from Mendel’s law of independent assortment

62
Q

parental types

A

offspring that have a phenotype that matches either of the phenotypes of the parents
e.g. round yellow pea X green wrinkly pea = round yellow and green wrinkly offspring which are parental types but also yellow wrinkly and green round which are recombinants
this is for genes that are not linked

63
Q

recombinants

A

offspring that have new combinations of phenotypes
e.g. round yellow pea X green wrinkly pea = round yellow and green wrinkly offspring which are parental types but also yellow wrinkly and green round which are recombinants

64
Q

nondisjunction

A

when members in a pair of homologous chromosomes do not move apart properly during meiosis 1 or sister chromatids fail to separate during meiosis II. One gamete receives two of the same type of chromosome and another gamete receives no copy

65
Q

aneuploidy

A

a zygote with an abnormal number of chromosomes
monosomic - missing one chromosome
trisomic - having three of a chromosome
monosomy and trisomy are estimated to occur in 10-25% of human conceptions and are the main reason for pregnancy loss

66
Q

monosomic

A

aneuploid with a missing chromosome

67
Q

trisomic

A

aneuploid with an extra chromosome

68
Q

down syndrome

A

trisomy21

69
Q

polyploidy

A 
have more than two complete chromosome sets 
triploidy - 3n
tetraploidy - 4n
Common in the plant kingdom
some fish and amphibians are polyploid
70
Q

monohybrid ratios

A

P- true breeding HH X hh
F1 - all express dominant allele 1 : 1 : 1 = Hh Hh Hh Hh
F2 - 3 : 1 HH Hh Hh hh

Bio1MGC (11 decks)

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