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Biology Unit 4 > 8 - Inheritance > Flashcards

8 - Inheritance Flashcards

1
Q

EXAM QUESTION

Explain what is meant by phenotype (2)

A 
1. Expression / appearance /
characteristic due to genetic
constitution/genotype/allele(s);
2. (Expression / appearance /
characteristic) due to
environment;
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2
Q

EXAM QUESTION

Explain what is meant by a dominant allele (1)

A

Is always expressed/shown (in the

phenotype);

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3
Q

EXAM QUESTION

Explain what is meant by a recessive allele (1)

A

Only expressed/shown (in the phenotype) when homozygous /
two (alleles) are present / when no dominant allele / is not
expressed when heterozygous;

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4
Q

EXAM QUESTION

Explain what is meant by co-dominant alleles (1)

A

Both alleles are expressed/shown (in the phenotype);

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5
Q

EXAM QUESTION (generic)

Use evidence from the diagram to explain that …. is caused by a recessive allele (2)

A

Identify and state unaffected parents
Identify and state affected offspring
Parents must be heterozygous

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6
Q

EXAM QUESTION (generic)

Use evidence from the diagram to explain that …. is caused by a dominant allele (2)

A

Identify and state affected parents
Identify and state unaffected offspring
Parents must be homozygous

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7
Q

EXAM QUESTION (generic)

Use evidence from the diagram to explain that … is caused by a gene on the X chromosome (1)

A

Affected son has unaffected father

Father has recessive allele on X chromosome

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8
Q

EXAM QUESTION (generic)

Use evidence from the diagram to prove that the allele for … is not on the X chromosome (1)

A

Affected daughter has unaffected father

Father does not have recessive allele on X chromosome

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9
Q

EXAM QUESTION

In birds, males are XX and females are XY

Use this information to explain why recessive, sex-linked characteristics are more common in female birds than in male birds. (1)

A

Recessive alleles always expressed in females (XY)

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10
Q

EXAM QUESTION

The allele for normal haemoglobin in red blood cells is HbA. In some parts of Africa
where malaria occurs there is a high frequency in the population of the allele HbC.
Individuals possessing the HbC allele have a lower chance of developing severe
malaria. Severe malaria causes a large number of deaths in Africa.
Explain the high frequency of the HbC allele in areas where malaria occurs. (3)

A
  1. Individuals with the HbC
    (allele) reproduce;
  2. Pass on HbC (allele) which increases in
    frequency;
  3. HbA HbA
    individuals less likely to
    survive/reprod
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11
Q

EXAM QUESTION

A breeder crossed a black male cat with a black female cat on a number of occasions. The female cat produced 8 black kittens and 4 white kittens.

Explain the evidence that the allele for white fur is recessive. (1)

Predict the likely ratio of colours of kittens born to a cross between this black male
and a white female. (1)

A
  1. Parents are heterozygous;
  2. Kittens receive white allele from parents /black cat;

1:1

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12
Q

EXAM QUESTION

The gene controlling coat colour has three alleles. The allele B gives black fur,
the allele b gives chocolate fur and the allele bi gives cinnamon fur.
● Allele B is dominant to both allele b and bi
● Allele b is dominant to allele bi

Complete the table to show the phenotypes of cats with each of the genotypes shown:

B bi = ?

b bi = ?

B b = ?

A

Black
Chocolate
Black

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13
Q

EXAM QUESTION

A chocolate male was crossed several times with a black female.
They produced
● 11 black kittens
● 2 chocolate kittens
● 5 cinnamon kittens.

The breeder had expected equal numbers of chocolate and cinnamon kittens from the
cross between the chocolate male and black female. Explain why the actual numbers
were different from those expected. (1)

The breeder wanted to produce a population of cats that would all have chocolate fur. Is this possible? Explain your answer. (2)

A
  1. Offspring ratios are a probability/not fixed/arise by
    chance/
  2. gametes may not be produced in equal numbers/
  3. fertilisation/fusion of gametes is random/
  4. small sample;
  5. Possible if parents homozygous/ bb;
  6. Don’t know genotype of chocolate cat / chocolate cat
    could be homo- or heterozygous / chocolate cat could be
    bb or bbi
  7. Two chocolate cats could give cinnamon kittens;
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14
Q

EXAM QUESTION

What does the Hardy-Weinberg principle predict about the frequency of the t allele after another 10 generations? (1)

A

The frequency remains the same

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15
Q

EXAM QUESTION

In cats, males are XY and females are XX. A gene on the X chromosome controls fur
colour in cats. The allele G codes for ginger fur and the allele B codes for black fur.
These alleles are codominant. Heterozygous females have ginger and black patches of
fur and their phenotype is described as tortoiseshell.

Male cats with a tortoiseshell phenotype do not usually occur. Explain why. (1)

A

Only possess one allele / Y
chromosome does not carry allele/gene
/ can’t be heterozygous;

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16
Q

EXAM QUESTION

Polydactyly in cats is an inherited condition in which cats have extra toes. The allele for
polydactyly is dominant.

Some cat breeders select for polydactyly. Describe how this would affect the
frequencies of the homozygous genotypes for this gene in their breeding populations
over time. (1)

A

Homozygous dominant increases and

homozygous recessive decreases;

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17
Q

EXAM QUESTION

Tay-Sachs disease is a human inherited disorder. Sufferers of this disease often die
during childhood. The allele for Tay-Sachs disease t, is recessive to allele T, present in
unaffected individuals.

The actual percentage of heterozygotes is likely to be lower in future generations than the answer calculated in Hardy-Weinberg. Explain why. (1)

A 
Affected individuals (usually) do not
reproduce/die during childhood/do not
pass on allele/genetic screening;
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18
Q

EXAM QUESTION

What does the Hardy–Weinberg principle predict? (3)

A

The frequency/proportion of alleles (of a particular gene);

Will stay constant from one generation to the next/over
generations / no genetic change over time;

Providing no mutation/no selection/population large/population
genetically isolated/mating at random/no migration;

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19
Q

EXAM QUESTION

White cats are deaf. Would the Hardy–Weinberg principle hold true for white cats?
Explain your answer. (2)

A

White/deaf cats unlikely to survive/selected against;
Will not pass on allele (for deafness/white fur) (to next
generation)/will reduce frequency of allele;

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20
Q

EXAM QUESTION

What is the evidence that non-agouti and blotched are alleles of different genes? (1)

A

In Paris/London frequencies (of these alleles) add up to more than 1;

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21
Q

Define genotype

A

The genetic composition of an organism, all the alleles that it contains.

22
Q

Define mutation

A

A change to the structure or quantity of the sequence of bases in DNA. (can be inherited if in gamete formation)

23
Q

Define phenotype

A

Expression/appearance due to genotype and environment.

24
Q

Define modification

A

A change to the phenotype that does not affect the genotype (uninheritable).

25
Q

Define gene

A

Section of DNA on a chromosome, codes for a particular polypeptide, determines single characteristic

26
Q

Define locus

A

Position of a gene on a chromosome.

27
Q

Define allele

A

One of the different forms of a gene

28
Q

How many alleles can homologous chromosomes carry? why?

A

2, 2 loci

29
Q

Define heterozygous

A

2 alleles different

30
Q

Define homozygous

A

2 alleles same

31
Q

Define dominant allele

A

Always expressed in the phenotype

32
Q

Define recessive allele

A

Only expressed in the phenotype when homozygous

33
Q

Define monohybrid inheritance

A

The inheritance of a single gene

34
Q

What is the Law of Segregation? (2)

A

In diploid organisms characteristics are determined by alleles that occur in pairs.

Only one of each pair of alleles can be present in a single gamete.

35
Q

How many pairs of chromosomes do humans have?
22 have? 1 pair?
Females = ?
Males = ?
Name 2 differences between Y and X chromosome

A 
23
Identical partners, sex chromosomes
XX
XY
(y is) smaller, different shape
36
Q

Define sex-linked gene

A

Any gene carried on the X or Y chromosome.

37
Q

Explain why recessive, sex-linked characteristics are more common in males (4)

A

Recessive allele always expressed
X chromosome longer
Y chromosome has no equivalent homologous portion
Dominant allele less likely to mask recessive allele

38
Q

What causes haemophilia? what not coded for?

How can haemophilia be treated?

A

Mutation of a recessive allele - clotting protein

Protein can be transplanted

39
Q

Name 2 symptoms of haemophilia

A 
Slow blood clotting 
Internal bleeding (especially in joints)
40
Q

Why do males always inherit the defective haemophilia allele from their mother? (2)

A

Males always inherit defective allele from mother because:
Linked to X chromosome
Males can only inherit Y from father so X comes from mother

41
Q

If the mother is unaffected, she is?

Define carrier

A

heterozygous/carrier

an individual who carries the allele without it being expressed in their phenotype

42
Q

Why can males only pass haemophilia on to their daughters? (2)

A

Linked to X chromosome

They pass on X chromosome.

43
Q

Define co-dominant allele

How can co-dominance present itself? (2)

A

Both alleles are expressed in the phenotype

  • blend of both features
  • both features represented
44
Q

Why do some snapdragon plants produce pink flowers? (3)

A

Heterozygous
1 allele codes for the enzyme that catalyses formation of red pigment, other doesn’t
Sufficient pigment to produce pink flowers

45
Q

Define multiple alleles

How many can be present? why?

A

When a gene has more than 2 allelic forms

2, 2 loci

46
Q

Multiple alleles - ABO blood grouping

What gene has 3 allelic forms?

A allele produces?
B allele produces?
O allele produces?

A and B are?
O is?

A

Immunoglobin gene (gene I)3 alleles linked to

A antigens on RBC
B antigens on RBC
no antigens

A and B co-dominant
O recessive to both

47
Q

Define gene pool

A

All the alleles of all the genes of all the individuals in a population at any one time.

48
Q

Define allelic frequency

A

The number of times an allele occurs within the gene pool.

49
Q

Interesting combinations of ABO blood grouping system

O crossed with AB gives rise to?
A crossed with B can give rise to?

A

A or B offspring

Any blood group

49
Q

Cystic fibrosis:

Results in?
Caused by?

A

Thick, sticky mucus production

Recessive allele

51
Q

State the Hardy-Weinberg principle (3)

Why may the principle not work in nature?

1.0 = ?

A
  1. The frequency of alleles of a particular gene
  2. Will stay constant from one generation to the next
  3. Providing:
    No mutations
    Isolated population - no gene flow
    No selection - alleles equally likely to be passed on
    Large population
    Random mating

These conditions never apply

Total number of alleles of one gene in a population

Biology Unit 4 (29 decks)

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