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A2 Biology > 6 - ICH - Genetics & Inheritance > Flashcards

6 - ICH - Genetics & Inheritance Flashcards

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1
Q

Define Genotype

A

Genotype = The genetic makeup of an organism and describes the organism in terms of the alleles it contains

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2
Q

Define Phenotype

A

Phenotype = Observable characteristics of an organism. It is the result of the interaction between the genotype and the environment which can modify the organism’s appearance

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3
Q

Define Gene

A

A DNA sequence that codes or a polypeptide

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4
Q

Define Allele

A

Different forms of the same gene

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5
Q

Define Homozygous and Heterozygous

A

Homozygous = Body cells in an organism have 2 identical alleles for a gene and all gametes carry the same allele

Heterozygous = Body cells in an organism have 2 different alleles for a gene and gametes will carry one copy of one of the alleles

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6
Q

Define

Dominant

Recessive

Co dominant/ incomplete dominance

A

Dominant = Allele if present will always be expressed in the phenotype

Recessive = Allele is only expressed in phenotype in the homozygouse state

Co dominant/ incomplete dominance = Both alleles are equally dominant and are both expressed in the phenotype

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7
Q

Define Locus

A

Locus = The specific position of a gene on a DNA molecules/ chromosome

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8
Q

What are genetic diagrams and their purpose?

A

Genetic diagrams show the possible genotypes and phenotypes of the offspring that would be produced if two parents are crossed

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9
Q

What is monohybrid inheritance? + Example

A

Inheritance of a characteristic controlled by a single gene

  • E.g. Tall/ short pea plants
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10
Q

What is another name given to monohybrid inheritance?

A

Monogenic inheritance

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11
Q

If 2 homozygous parents are crossed in a monogenic cross. What is expected of the genotypes of the F1 (first generation offspring)

A

They’ll all be heterozygous

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12
Q

What is a phenotypic ratio?

A

Phenotypic ratio = The ratio of different phenotypes in the offspring

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13
Q

Name 3 different types of genetic cross diagrams you need to know + example of each

A

Monohybrid inheritance - Inheritance of 1 gene

  • Tall/ short pea plants

Dihybrid inheritance - Inheritance of 2 genes

  • Shape and colour of pea plants

Multiple allele inheritance

  • Blood group
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14
Q

Why is blood group expressed as IA, IB and IO

What does the I stand for?

A

Immunoglobin

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15
Q
  1. How many pairs of chromosomes do humans have?
  2. What are autosomes and how many pairs do humans have?
A
  • Humans have 23 pairs of chromosomes
  • Autosomes = pairs of chromosomes that are identical in appearance (humans have 22 pairs)
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16
Q

XY chromosomes for a male and female?

A

Female = XX

Male = XY

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17
Q

Can any gene on a sex chromosomes be sex-linked?

A

Yes

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18
Q

Can alleles be carried on the X and Y chromosome?

What is particular about the alleles expressed and the X chromosome?

A

Y = Carries no alleles

X = Carries a allele ∴ in males often when the allele on X is recessive it will still be expressed since there’s no allele on the Y chromosome

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19
Q

Draw a genetic cross diagram to illustrate the inheritance of sex

A

Monohybrid cross diagram

20
Q

What a gene being called sex-linked mean?

A

Sex-linked = The allele is carried on either the X or Y chromosome but in practise very few is carried on the Y chromosome (we assume none for genetic crosses)

21
Q

If a genetic disease is carried on the X chromosome what sex has a greater predisposition for the disease? Why?

A

Males, because the Y chromosome doesn’t really carry any alleles (assume none in questions) ∴ the allele carried on the X chromosome regardless of whether it is recessive or dominant will be expressed

22
Q

Name 2 diseases that are sex linked

  • Is the faulty allele dominnt or recessive
  • What sex has a greater predisposition for the disease?
A
  • Haemophilia and red/ green colour blindness
  • Alleles responsible for these diseases are recessive
23
Q

What is haemophilia

A

Condition in which the blood does not clot, leading to slow and persistent bleeding, especially into joints

24
Q

What is red green colour blindness?

A

Difficulty distinguishing between red and green.

Gene controlling red green colour vision is located on the X chromosome

25
Q

Question - Sex linkage:

A man, which is red-green colour blind marries a woman who is homozygous for the allele for normal vision. Show by means of a genetic diagram, the possible genotypes and phenotypes of their children

A
26
Q

Question - Sex linkage:

Cross a female carrier of haemophilia with a normal male

A
27
Q

ABO blood group is an exmaple of what? Why?

A

Multiple allele inheritance and codominance.

IA and IB are codominant

Both IA and IB are dominant to IO

28
Q

Name 2 situations that illustrate monogenic inheritance of codominant alleles

A

Sickle cell anaemia

Pink flowers

29
Q

Possible genotypes for blood group:

  1. A
  2. B
  3. O
A

Blood group A = IAIA and IAIO

Blood group B = IBIB and IBIO

Blood group O = IOIO

30
Q

There are 3 alleles for blood groups A,B and O. At any given time can one carry all 3?

A

No

31
Q

Blood groups are composed of 3 sections. What are they?

A
  • ABO
    • A and B are co-dominant
    • A and B are both dominant to O
  • MN co-domidance
    • M = MM
    • N = NN
    • MN = MN
  • Rhesus factor
    • Positive or negative
32
Q

Question:

A sex-linked, dominant allele, barred (feather pattern) can be used to sex newly hatched chicks, the offspring of a barred hen mated with a non-barred rooster.

Note! In birds, the female is the heterogametic sex (XY) and the male the homogametic sex (XX).

  1. Construct a genetic cross diagram of this cross.
  2. What is the genotype of the female chicks?
A
33
Q

Question:

A mother with blood group A, whose father was blood group O, marries a man with blood group AB.

What is the probability that their first child will be a girl with blood group B?

A
34
Q

What happens when there’s more than 3 alleles for a particular gene?

A

The allelesa re arranged in a hierarchy with each allele being dominant to the ones below it and recessive to thoese above it.

They will give you the order of dominance

35
Q

when does dihybrid inheritance occur?

A

When 2 characteristics are controlled by 2 genes on seperate chromosomes

36
Q

For dihybrid crosses what is the most common phenotypic ratio along with the parental genotype?

A

9 : 3 : 3 : 1

Both parents are heterozygous e.g. RrYy x RrYy

37
Q

What do you do when after drawing the genetic diagrams to predict the phenotypes of F1 individuals, the expected and observed phenotypes are significantly different what do you do?

A

Chi-Squared

38
Q

Define:

Linkage

Autosomal linkage

Sex linkage

A

Linkage = When 2 or more genes are located on the same chromosome

Autosomal linkage = Linked genes which are non-sex chromosomes

Sex linkage = Linked genes are on sex chromosomes

39
Q

Define Epistasis

A

Epistasis (interactions between gene loci) = Interaction of non-linked genes where one masks the expression of the other

40
Q

What can epistasis result in?

A
  • Genes working against each other (antagonistically) ∴ results in masking
  • Genes working together in a complementary fashion
41
Q

Relationship between the epistatic gene and the hypostatic gene

A
  • Epistatic gene at one locus alters or inhibits the expression of a second locus, the hypostatic gene.
  • Epistatic gene produced a protein which influences or controls the expression of the hypostatic gene
42
Q

How does epistasis allow genes to work antagonistically?

A
  • Homozygous presence of a recessive allele may prevent the expression of another allele at a second locus
  • Alleles at the first locus = epistatic
  • Alleles at the second locus = hypostatic

Epistasis is not inherited, it is an interaction between 2 gene loci. It reduces phenotypic variation

43
Q

What does epistasis reduce?

A

Phenotypic variation

44
Q

Explain the concept of recessive epistasis + example

A

Occurs when recessive alleles at one locus stop the expression of alleles at a second locus

  • E.g. Flower colour in Salvia
  • 2 genes on different chromosomes control flower colour A/a and B/b (2 loci)
  • B = purple flowers, b = pink flowers, but if another gene is recessive aa, then no colour can be made (white flowers are produced regardless of what is on B/b gene)
45
Q

Explain the concept of dominant epistasis + example

A

Occurs when a dominant allele at one locus stops the expression of the alleles at a second locus

  • E.g. inheritance of feather colour in some breeds of chickens
    • I/i and C/c are 2 gene loci that control feather colour
    • C = coloured feathers, c = white feathers
    • I = white feathers even if they have the dominant allele C
    • cc = alsp produce white feathers regardless of what is on I/i gene

So if you cross 2 chickens IICC x iiCC

  • All of F1 = IiCc ∴ all white feathers

If F1 interbreeds IiCc x IiCc

  • F2: white feathered : coloured feathered in ratio 13:3
46
Q

How does epistasis allow genes to work complementary with each other? + example

A

Works like a general metabolic pathway:

  • 2 genes affect the colour of sweet pea flowers, Allele A and Allele B
  • Colourless precursor moelcule is the base of what you start with
  • If allele A is present, it produces enzyme A ∴ reaction can continue to second step etc..
  • Purple flowers = A and B is present
  • Red flowers = A must be present but B is absent
  • If A is absent then flowers are white
47
Q

Equation for Chi-squared = ?

When do you reject Ho and accept Ho?

A

To test for whether the difference between observed and expected values are significant or by chance

  • Probability level = 5% = 0.05 (unless stated otherwise)
  • Degree of freedom = n - 1

Xcritical > Chi calculated - Accept Ho

Xcritical ≤ Chi calculated - Reject Ho

A2 Biology (26 decks)

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