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Biology Y13 > Inheritance > Flashcards

Inheritance Flashcards

1
Q

INHERITANCE

A
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2
Q

what is a homologous chromosome?

A

A pair of chromosomes of the smae length and centromere position for the genes corresponding to the same loci.

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3
Q

what is a phenotype?

A

the appearance of an organism due to expression of it’s genes. can be affected by the environment

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4
Q

what is a genotype?

A

genetic make-up of an organism

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5
Q

what is a gene?

A

a length of DNA coding (on a chromosome) for a particular protein

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6
Q

What is a loci?

A

the allele the gene is found at a fixed position is called the locus. (the position of a gene on a chromosome)

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7
Q

what is an allele?

A

one form of a gene

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8
Q

what is meant by the term recessive?

A

an allele that is only expressed if there are no dominant alleles present

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9
Q

what is meant by the term dominant?

A

an allele that is always expressed when present

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10
Q

where are chromosomes inherited from?

A

one from each parent, so we have a maternal and paternal strand.

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11
Q

what is autosomal dominant? draw an example using pedigree diagram

A

cannot be recessive as two affected parents could not have unaffected offspring. therefore parents must be heterozygous

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12
Q

what is autosomal recessive? draw a diagram showing this?

A

cannot be dominant as two unaffected parents could not have an affected offspring. therefore parents must be heterozygous

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13
Q

what are diploid organisms?

A

have two alleles for the each gene

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14
Q

what are haploid organisms?

A

gametes (sex-cells) contain only one allele for each gene

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15
Q

Monohybrid Inheritance

A
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16
Q

What is Monohybrid inheritance?

A

is the inheritance of a single gene

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17
Q

what do Monohybrid crosses show?

A

show the likelihood of different alleles of that gene being inherited by offspring of certain parents

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18
Q

what does a monohybrid cross look like?

A

parents genotypes, then gametes then the possible genotypes of offsprings then the phenotype

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19
Q

In mice, the gene for eye colour has two alleles. the alle for black eyes is dominant, while the alleles for red eyes is recessive. Choose a suitable symbols for these alleles, then draw a punnet square to show the probable results of a cross between a heterozygous black-eyes mouse and a red-eyed mouse.

A

F1 generation - 50:50 ratio

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20
Q

Co-dominance and Multiple Alleles

A
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21
Q

What is codominance?

A

alleles have equal dominance, and so they are both expressed. the traits appear together in the phenotype of hybrid organisms e.g blood groups

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22
Q

What is incomplete dominance?

A

we get a blending of the traits so that the third phenotype is something in the middle (red x white = pink)

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23
Q

Draw a diagram to show blood group phenotypes and genotypes. also practice question.

A
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24
Q

what are multiple alleles?

A

when there are more than two alleles for the same gene

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25
Q

Give an example?

A

eye-colour and blood groups

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26
Q

Sex-linked inheritance

A
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27
Q

what genes are said to be sex-linked?

A

Genes located on the sex chromosomes

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28
Q

how is sex determined?

A

Sex in mammals is determined by two chromosomes, known as sex chromosomes or heterosomes.

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29
Q

what are autosomes?

A

non- sex chromosomes)

30
Q

which sex chromosome is larger?

A

The X chromosome is larger and contains about 2000 genes, whereas the Y chromosome is smaller and contains fewer than 100.

31
Q

what type of conditions are sex-linked/ x-linked?

A

Haemophilia

Duchenne muscular dystrophy

Red–green colour blindness

32
Q

what type of conditions are Y-linked?

A

It is argued that there is little room on the Y chromosome for anything other than genes controlling testes formation and function.

33
Q

why is X-linkage more common?

A

the X chromosome is larger and part of it does not have a homologous section on the Y chromosome, therefore only one allele of a gene will be present and so will always
be expressed.

34
Q

what are homologous regions?

A

do not carry sex-determining genes

35
Q

what are non-homologous regions on a chromosome?

A

carry sex-determining genes and other genes

36
Q

When does the son inherit a sex-linked disease?

A

A son ALWAYS gets his X chromosome from his mother!

37
Q

when does the daughter inherit a sex-linked disease?

A

Daughter’s ALWAYS get the father’s X chromosome and therefore the diseased allele if her father has it.

38
Q

what is meant by X-linked dominant? draw a diagram to show this

A

Sex linkage can not be confirmed. 100% incidence of affected daughters from an affected father suggests x-linked dominance.

39
Q

what is meant by X-linked recessive? draw a diagram to show this

A

sex linkage cannot be confirmed. 100% incidence of affected sons from an affected mother suggests X-linked recessive

40
Q

Dihybrid crosses

A
41
Q

what do Dihybrid crosses show?

A

Dihybrid crosses are those where we consider the inheritance of two
characteristics at the same time.

42
Q

each characteristic is determined by..?

A

a different gene, potentially located
on a different chromosome.

43
Q

give an example?

A

Freckles and widows peak

44
Q

Who was Gregor Mendel?

A

know as the father of modern genetics. In the 1950’S AND 1960’S he established the foundations of inheritance - dominant and recessive characteristics. He had no idea about DNA, genes but knew how they were inherited

45
Q

How did he prove his findings on inheritance?

A

he used peas and studies them by crossing them together to see what offsprings they made.

46
Q

Cross a Purebreed tall (TT), purebreed yellow seed (YY) plant with a purebreed short (tt) purebreed green seed (yy) plant.

A

draw diagram, all offspeings should be heterozygous TtYy

47
Q

what is this generation called?

A

F1 generation

48
Q

if the heterozygous offsprings were to be crossed over and produce offsprings, they wold be called the ..?

A

F2 generation

49
Q

What did Mendel’s independent assortment principle state?

A

The homologous chromosomes line up randomly on the centre line in Metaphase I so the combination of alleles in the gametes is RANDOM

50
Q

Draw a genetic diagram of the heterozygous offsprings being crossed (f2 generation)

A
51
Q

what ratio do these two heterozygous parents produce in offsprings

A

9:3:3:1 always

52
Q

How did mendel figure out which phenotypes were dominant or recessive?

A

From his monohybrid trials Mendel discovered:
- allele for yellow colour was dominant to green
- allele for round peas was dominant to wrinkled peas.

53
Q

Autosomal Linkage

A
54
Q

what is autosomal linkage?

A

when two genes are located on the same chromosomes and this means that the alleles for each gene will be inherited together

55
Q

Who found out the existence of Autosomal linkage?

A

Bateson, Saunders and Punnet 1905​

56
Q

how did they do this?

A

they studied two genes:
- flower colour (P, purple and p, red)
- shape of pollen grains (L, long, l, round)
and crossed PPLL and ppll

F1 generation: All offspring were purple and long (PpLl) As expected.

However F2 generation gave suprising results

57
Q

Why were they supprised by the results of the F2 generation?

A

Gave a 3:1 ratio (just like a monohybrid cross)​

58
Q

Explain why there isn’t a perfect 3:1 ratio?

A

The parental combinations of alleles (purple long and red round) seem to be inherited as almost a 3:1 ratio ​

As though they were behaving as a single character​

These genes are called LINKED GENES (Autosomal linkage)​

i.e. The genes are transmitted together (on the same chromosome).​

59
Q

Why are there different combination of alleles? (4 to be exact)
what do we call these combinations?

A

These combinations have come about because of CROSSING OVER between the linked alleles on their chromosomes during Meiosis 1​. These are called RECOMBINANTS​

60
Q

explain what happens during crossing over?

A

Homologous chromosomes are aligned. Chromatids cross over forming bivalents and chiasmata. chromatids break off and exchange genetic material. so we are left with different combination of alleles.

61
Q

How to test if inheritance is significant?

A

always chi squared test

62
Q

Epistasis

A
63
Q

what is epistasis?

A

Epistasis is a form of a gene interaction in which one group makes a phenothopic expression of another

64
Q

what are epistatic alleles?

A

the alleles that are masking the effect. (of dominant or recessive traits)

65
Q

what are hypostatic alleles?

A

the alleles whose effect is being masked.

66
Q

how can epistatic problems be solved?

A

Dihybrid crosses

67
Q

give an example of epistasis?

A

e.g colour of labradors
gene 1 : controls colour represented by B
- labrador has a dominant B = black for BB/Bb
- Two bb (recessive) = brown for bb
gene 2: controls the expression of gene and is represented by E/e

68
Q

what does gene 1 represent?

A

the phenotype /genotype

69
Q

what does gene 2 represent?

A

the hypostatic allele represented by E.
E = no effect e = has effect of masking

70
Q

so the labradors can either be Black, brown and Golden. what are all the possible genotypes for all phenotypes.

A
71
Q

Add in epistatsis dominant,

A
72
Q

FINISH

A

Biology Y13 (13 decks)

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