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OCR Biology A Level Module 6 > 6.2 Patterns of Inheritance > Flashcards

6.2 Patterns of Inheritance Flashcards

1
Q

Define monogenic

A

determined by a single gene, two distinct alleles

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2
Q

If you crossed a homozygous recessive genotype with a homozygous dominant genotype, for example for eye colour (B= brown, b=blue) what is the resulting phenotypic ratio?

A

100% heterozygous

Therefore 100% brown eyes

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3
Q

If you crossed two heterozgygous genotypes for eye colour for example (B = brown, b= blue), what is the resulting phenotypic ratio?

A

3:1 brown eyes to blue eyes

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4
Q

Define homozygous and heterozygous

A

Homo: identical alleles at a particular gene locus on a pair of homologous chromosomes
Hetero: different alleles at a particular gene locus on a pair of homologous chromosomes

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5
Q

What does dihybrid unlinked mean?

A
  • inheritance of two characteristics simultaneously, involving 2 gene loci.
  • if unlinked, there are 2 genes on two diff homologous pairs of chromosomes
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6
Q

Cross two pea plants that are heterozygous for seed shape and colour - what is the phenotypic ratio?

(yellowis dominant, green is recessive)
(round is dominant, wrinkle is recessive)

A

9:3:3:1

yellow round seed: yellow wrinkle seed: green round seed: green wrinkle seed

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7
Q

What is phenotype vs genotype?

A

pheno: visible characteristic
geno: genetic makeup

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8
Q

What are mutagens? What are some examples?

A

chemicals that increase mutation rate

physical: X-rays, gamma rays, UV
chemical: mustard gas, dyes, free radicals, aromatic amines

biological: viruses, transpoons, food contaminants from fungi

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9
Q

Mutations that occur during gamete formation are also: (2)

A

persistent: transmitted through generations without change
random: not directed by a need for it

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10
Q

What are non-disjunction chromosome mutations? WHat is an example?

A

failure to segregate - one gamete (and therefore zygote) has an extra chromosome. E.G DOWN SYNDROME/ TRISOMY 21

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11
Q

Define aneuploidy

A

abnormal chromosome number in a cell

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12
Q

Define polyploidy

A

if diploid gamete is fertilised by haploid gamete = triploid. 3 diploid gametes = tetraploid

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13
Q

How does sexual reproduction increase genetic variation? (4)

A
  1. allele shuffling during crossing over of non sister chromatids in prophase I
  2. independent assortment of chromosomes in metaphase I
  3. independent assortment of chromatids in metaphase II
  4. random fusion of gametes that are already genetically unique increases genetic diversity
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14
Q

How do environmental factors play into phenotypes? (2)

A
  1. ONLY ENVIRO include speaking with a dialect, scar after injury
  2. ENVIRO AND GENES: chlorotic plants don’t make enough chlorophyll due to environmental factors such as dim light or insufficient Mg
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15
Q

What is the genotype for males and females?

A

Male: XY
Female: XX

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16
Q

What is sex linkage? What is significant about male inheritance of certain sex linked characteristics? What are some examples?

A
  • where genes are located on sex chromosomes
  • if a male inherits an X chromosome with an abnormal allele for a particular gene from his mother, he will suffer from a genetic disease.
  • hameophilia A and colour blindness and Duchenne muscular dystrophy
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17
Q

Males are —- for X linked genes

A

hemizygous

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18
Q

Describe haemophilia A

A
  • unable to clot blood fast enough = bleeding or internal haemorrhage
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19
Q

Draw a genetic diagram of a haemophilia A carrier female with a normal male. Calculate the probability the offspring will suffer from haemophilia

A

25%

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20
Q

Describe colour blindness. When will a male suffer?

A
  • recessive sex linked
  • can’t tell difference between red and green
  • a male with one abnormal allele on his X WILL since no protective allele on Y chromosome
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21
Q

in every female cell ——-, one ——- is inactivated during early —— development

prevents —— no of ——– genes being expressed

A

nucleus, X chromosome, embyronic

twice, X-linked

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22
Q

Define codominant

A

where both alleles present in the genotype of a heterozygous individual contribute to their phenotype

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23
Q

What is an example of codominance in animals?

A

coat colour in short horn cattle

alleles C^R C^R = red
alleles C^W C^W = white
allleles C^R C^W = roan

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24
Q

Draw a genetic diagram of a roan female and roan male and calculate the phenotypic ratio

A

1 white: 2 roan: 1 red

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25
Q

What is an example of codominance in humans?

A

MN blood groups

gene coding for a particular protein on surface of erythrocytes

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26
Q

Draw a genetic diagram of two individuals with an MN blood group

A

1 MM:2 MN:1NN

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27
Q

What is an example of codominance in plants?(hint: camelias)

A

if red flowered camellias are crossed with white, the offspring will have red and white spotted flowers (P^R and P^W)

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28
Q

What does multiple alleles mean?

A

characteristic for which there are 3 or more alleles in the population’s gene pool

29
Q

Describe multiple alleles in human blood groups. What genotypes make what phenotypes?

A
  • gene encoding isoagglutinogen, I, on surface of erythrocytes
  • I^A and I^B are codominant, I^O is recessive

A is either I^A I^A or I^A I^O
B is either I^B I^B or I^B I^O
AB is I^A I^B
O is I^O I^O

29
Q

Define autosomal linkage

A

gene-loci present on same autosome that are often inherited together

29
Q

How does autosomal linkage with crossing over compare with no crossing over?

A

NO CROSSING: linked genes ALWAYS inherited as one unit -> 2 phenotypes
CROSSING: creates recombinant gametes (the further apart the gene loci on a chromosome, the more likely)
-> 4 phenotypes

29
Q

Cross a purple flowered, long pollen grained plant (homozygous dominant x 2) with a red flowered, short pollen grained plant (homozygous recessive x2).
P or p, L or l. Assume there is autosomal linkage.

Note down the F1 phenotypes and genotypes.

Then cross the F1 generation and note down the phenotype ratio

A

Gametes are PL or pl

All purple flowered, long grains (PpLl)

3:1 ratio of purple flowered, long grain : red flowered, short grain

29
Q

Define epistasis

A

Interaction of non linked gene loci where one masks the expression of the other - reduces genetic variation

29
Q

What 2 main types of epistasis are there?

A

Antagonistic and complementary fashion (genes working to code for 2 enzymes that work in succession catalysing sequential steps of a metabolic pathway

30
Q

Define recessive epistasis, epistatic and hypostatic

A

Homozygous presence of a recessive allele at the first locus prevents the expression of another allele at the 2nd locus

Alleles at first locus EPISTATIC to those at 2nd, which are HYPOSTATIC to those at first locus.

30
Q

If pink variety of Salvia (AAbb) are crossed with white variety (aaBB) what do you expect? aa is epistatic to B/b, B is purple and b is for pink.

A

All AaBb = all purple flowers

31
Q

For recessive epistasis, what would the phenotypic ratio be for the F2 generation of Salvia flowers when all purple flowers from F1 AaBb are bred?

A

9 purple: 3 pink: 4 white

32
Q

Define dominant epistasis

A

When a dominant allele at a locus completely masks the alleles at a second locus

33
Q

Chicken feather colour example:
I allele for I/i epistatic gene prevents formation of colour, even if C allele on hypostatic C/c gene is present ( coding for colored feathers). cc is also white therefore as no pigment is made.

A) what would the phenotype be of F1 if you bred white leghorn (IICC) and white Wyandotte (iicc)
B) if you bred the F1 generation together, what would the phenotypic ratio be? What is an exception?

A

A) all IiCc (white)
B) 13 white:3 coloured

Sometimes ratio is 12:3:1

34
Q

Mice coat colour example:

CC/Cc produces coloured fur
cc = albino- doesn’t matter what A/a
AA/Aa = agouti colour (codes for distribution of pigment)
aa is black

What is the phenotypic ratio when you breed 2 agouti mice (AaCc) together?

A

9 agouti: 3 black : 4 albino

35
Q

Pea plant example:
A/a codes for colourless intermediate (dominant) B/b codes for purple pigment (dominant)

A)
What are the offsprings phenotypes if two white pea plants, AAbb x aaBB are bred?
B) What is the phenotypic ratio when the F1 generation are bred?

A
  • need at least one dominant B and one dominant A to be purple
  • F1: all purple (AaBb)
  • F2: 9:7 ratio of purple: white
36
Q

Chicken combs:
At least one dominant of each is needed for walnut, pp is rose, rr is pea, and pprr is single

If you bred true breeding pea comb chickens with true breeding rose comb chickens, what is the genotype of the offspring

What is the phenotypic ratio of the F2 generation?

A

F1: all PpRr = walnut
F2: 9 walnut: 3 pea: 3 rose : 1 single
Just like Mendez’s dihybrid ratio

37
Q

What are the characteristics of discontinuous variation? (4)

A

-discrete phenotypes
- no or few intermediates
- determined by alleles of single gene usually = monogenic
- bar chart

38
Q

What are some examples of discontinuous variation?

A
  • plant stem height, gender, seed shape, blood group
39
Q

What are the characteristics of continuous variation? (4)

A
  • many intermediates
  • quantitative traits very by small amounts between each group
  • polygenic
  • histogram
40
Q

What are some examples of continuous variation?

A
  • height, birth mass, hair colour, heart rate, leaf length, mice tail length
41
Q

Environment has a greater effect on expression of which types of traits?

A

greater for polygenic than monogenic

42
Q

What is stabilising selection?

A

environment remains unchanged usually

favours intermediate phenotypes

43
Q

What is directional selection?

A

gradual shift in optimum/mode/mean value -> favours an extreme
artificial selection is an example

44
Q

What is disruptive selection?

A

selection pressure towards extremes creates two modal values, and less intermediates

45
Q

What is genetic drift? Which populations are more at risk?

A
  • random changes in allele frequency in a population that occur even when the habitat doesn’t change
  • small populations -> each individual forms a great proportion of a population
46
Q

What is a genetic bottleneck?

A

Population size shrinks and increases again
Non selective, catastrophic event
Genetic diversity decreases (but might coincidentally be beneficial still)
Sometimes fertility affected -> species become endangered/extinct

47
Q

What is the founder effect?

A
  • new population formed by a very small number of individuals who originate from a large population
  • likely to have a small gene pool if isolated
48
Q

Define population

A

Group of individuals of the same species that can interbreed

49
Q

Define gene pool

A

Total number of alleles present within the population

50
Q

What factors affect allele frequencies and genetic diversity in a gene pool?

A

Population size
Mutation rate
Migration
Natural selection
Genetic drift
Gene flow
Non-random mating

51
Q

What is the p and q in the Hardy Weinberg equation and what is the purpose?

A

Q = recessive allele, P = dominant allele. Determine frequencies of those carrying a recessive allele (heterozygous) for a genetic disorder with recessive inheritance

52
Q

What are the assumptions for Hardy Weinberg?

A

Large population, random mating, no selection, no mutation/migration/ genetic drift

53
Q

1 out of 2000 is a sufferer (bb;q^2) of cystic fibrosis. Use this to calculate number of people that are carriers

A

Q^2 = 0.0005, q= o0.02236
P = 1-q
P = 0.9776

2 x p x q = 0.043
0.043 x 2000 = 87

54
Q

Define speciation

A

Splitting of a genetically similar population into two or more populations that undergo genetic differentiation (accumulation of diff allele frequencies)due to reproductive isolation, leading to evolution of two or more new species.

55
Q

Describe geographical isolation

A
  • geographical features act as gene flow barriers
  • different selection pressures = independent changes to allele frequencies/ chromosome arrangement
  • eventually leads to reproductive isolation

= ALLOPATRIC SPECIATION

56
Q

What are the types of reproductive/sympatric isolation? Give examples

A

Prezygotic: prevent fertilization. E.g.
- temporal (changing foraging behavior, diurnal populations unlikely to mate with crepuscular or nocturnal populations)
- ecological: similar regions but diff habitats
- behavioral: respond to diff courtship patterns
- mechanical: genital differences or plant flower structure differences

Postzygotic: prevents formation of fertile offspring
- hybrid infertility, reduced viability of hybrid zygotes, hybrid breakdown.

57
Q

What is a deletion chromosome mutation?

A

part of gene is lost

58
Q

What is an inversion chromosome mutation? What is the consequence?

A

segment breaks and reattaches in diff orientation on same chromosome

some genes become too far from regulatory sequences

59
Q

What is a translocation chromosome mutation?

A

interferes with gene regulation

pieces of chromosome break off and join a different one

60
Q

What is a duplication chromosome mutation?

A

overexpression of genes can disrupt metabolism

61
Q

For centuries, artificial selection has been used to improve the quality of crop plants used for human consumption. Explain, with reference to selective breeding, why it is important to maintain viable wild populations of crop plant species. (6)

A

genetic variation
 genetic resource / gene bank
 source of useful alleles
 can be cross bred with crop varieties  allows introduction of different traits
 unknown future requirements
 potentially useful in changing climate
 prevention of inbreeding depression
 promotion of hybrid vigour
 prevent dwindling gene pool
 source of replacement if cultivated
population is in danger
 plausible example(s) of any of the above

62
Q

It is thought that the modern cheetah population has low genetic diversity because the population, relatively recently, experienced a genetic bottleneck. Explain why this can lead to low genetic diversity (2)

A

(many) alleles lost (when population dropped)  ora
(modern population) descended from few survivors / AW 

63
Q

Scientists are concerned about genetic drift in the remaining cheetah populations.
Explain why genetic drift is likely to be of particular concern in the population of 100
cheetahs in Iran.

A

idea that one individual or allele has proportionally higher effect
on small population 
(more likely that) alleles will be lost from population 
(population) more vulnerable / likely to become extinct due , to
environmental change / AW 

OCR Biology A Level Module 6 (6 decks)

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