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Principle of inheritance weekly test Flashcards

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1
Q

What type of traits did Mendel study?

A

Traits with distinct alternate forms (e.g., purple or white flowers).

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2
Q

What kind of variation is seen in human height?

A

A range or gradient, not just tall or short.

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3
Q

What is a polygenic trait?

A

A trait controlled by three or more genes.

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4
Q

What influences polygenic inheritance besides genes?

A

The environment.

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5
Q

Give an example of a polygenic trait in humans.

A

Skin colour.

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6
Q

How does each allele contribute in polygenic traits?

A

The effect of each allele is additive.

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7
Q

Which genotype gives the darkest skin colour?

A

AABBCC (all dominant alleles).

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8
Q

Which genotype gives the lightest skin colour?

A

aabbcc (all recessive alleles).

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9
Q

What is pleiotropy?

A

Pleiotropy is when a single gene influences multiple phenotypic traits.

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10
Q

How does pleiotropy usually occur in organisms?

A

Through the effect of a gene on metabolic pathways that affect different traits.

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11
Q

What kind of gene is referred to as pleiotropic?

A

A gene that causes more than one phenotypic effect.

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12
Q

Give one human example of a pleiotropic gene disorder.

A

Phenylketonuria (PKU).

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13
Q

What causes phenylketonuria (PKU)?

A

A mutation in the gene coding for the enzyme phenylalanine hydroxylase.

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14
Q

What are the phenotypic effects of phenylketonuria?

A

Mental retardation and reduced hair and skin pigmentation.

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15
Q

Where did the initial clue about the chromosomal basis of sex determination come from?

A

Experiments carried out in insects.

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16
Q

What led to the development of the concept of chromosomal sex determination?

A

Cytological observations in various insects.

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17
Q

Who discovered a specific nuclear structure during spermatogenesis in insects and when?

A

Henking, in 1891.

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18
Q

What was unusual about the nuclear structure Henking observed?

A

It was received by 50% of the sperm, while the other 50% did not receive it.

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19
Q

What name did Henking give to the nuclear structure he discovered?

A

The X body.

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20
Q

What was later concluded about Henking’s ‘X body’?

A

It was actually a chromosome.

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21
Q

Why was the structure Henking discovered called the X-chromosome?

A

Because it was involved in determining sex and showed up in only some sperm.

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22
Q

What is the XO type of sex determination?

A

In large number of insects all eggs bear an additional X-chromosome. On the other hand, some of the sperms bear the X-chromosome whereas
some do not.

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23
Q

Who proposed the chromosomal theory of inheritance?

A

Sutton and Boveri

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24
Q

What important synthesis did Sutton make?

A

He united chromosomal segregation with Mendelian principles to form the chromosomal theory of inheritance.

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25
Why was Drosophila melanogaster suitable for genetic studies? (List any 3 reasons)
*Grows on simple synthetic medium *Short life cycle (~2 weeks) *Produces large number of progeny *Sexes are easily distinguishable *Shows many hereditary variations visible under low-power microscopes
26
In XO type, what determines whether the offspring is male or female?
Fertilisation by sperm with X produces females; without X produces males.
27
Are the chromosome numbers equal in males and females in XO type?
No, males have one X while females have two X-chromosomes.
28
What are sex chromosomes and autosomes?
Sex chromosomes determine sex; all other chromosomes are autosomes.
29
Give an example of an organism with XO type of sex determination.
Grasshopper.
30
What is the XY type of sex determination? A: Males have XY and females have XX, with equal total chromosome number.
Males have XY and females have XX, with equal total chromosome number.
31
What is male heterogamety?
A system where males produce two types of gametes: with X or Y (or with or without X in XO).
32
What is female heterogamety?
A system where females produce two types of gametes differing in sex chromosomes.
33
What sex chromosomes are found in birds?
Females: ZW; Males: ZZ.
34
How many chromosome pairs are the same in both males and females in humans?
22 pairs (autosomes).
35
What types of gametes are produced during spermatogenesis in males?
50% carry X-chromosome and 50% carry Y-chromosome.
36
What type of gametes do females produce?
Only one type — all ova carry an X-chromosome.
37
What determines the sex of the child in humans?
The genetic makeup of the sperm (X or Y chromosome).
38
What results in a female and male child during fertilisation?
Fertilisation of the ovum by a sperm carrying an X-chromosome and fertilisation of the ovum by a sperm carrying a Y-chromosome.
39
What is mutation?
A phenomenon that results in alteration of DNA sequences, causing changes in genotype and phenotype.
40
Besides recombination, what is another cause of genetic variation?
Mutation.
41
What happens when there is a loss or gain of a DNA segment?
It leads to chromosomal alterations.
42
Where are genes located, and why do chromosomal alterations affect phenotype?
Genes are located on chromosomes; their alteration results in abnormalities.
43
In which condition are chromosomal aberrations commonly observed?
Cancer cells.
44
What is a point mutation?
A mutation caused by a change in a single base pair of DNA.
45
What is a classical example of a point mutation?
Sickle cell anemia.
46
What type of mutation is caused by insertions or deletions of base pairs?
Frame-shift mutations.
47
What are mutagens?
Chemical or physical factors that induce mutations.
48
Give an example of a physical mutagen.
UV radiation.
49
What is pedigree analysis?
It is the study of inheritance patterns of traits in several generations of a family using a family tree.
50
Why can't controlled crosses be performed in humans?
Ethical and practical reasons make it impossible to do controlled crosses in humans.
51
What is the purpose of pedigree analysis in human genetics?
To trace the inheritance of a specific trait, abnormality, or disease across generations.
52
What carries genetic information from one generation to another?
DNA.
53
What is a mutation?
A change or alteration in the genetic material (DNA or chromosomes).
54
What is the connection between mutations and disorders?
Many human disorders are linked to inherited mutated genes or chromosomal alterations.
55
What kind of crosses did Morgan carry out in Drosophila?
Dihybrid crosses involving sex-linked genes
56
Which cross did Morgan perform to study linkage in Drosophila?
Yellow-bodied, white-eyed females × Brown-bodied, red-eyed males
57
What did Morgan observe in the F2 generation of his dihybrid cross?
The F2 ratio deviated significantly from the expected 9:3:3:1 ratio
58
What conclusion did Morgan draw from the deviation in F2 ratios?
The genes did not segregate independently and were likely located on the same chromosome
59
What term did Morgan coin for the physical association of genes on the same chromosome?
Linkage
60
What term did Morgan use to describe the formation of new gene combinations?
Recombination
61
What was observed when genes were on the same chromosome?
Parental gene combinations were more frequent than non-parental ones
62
What is the difference between tightly linked and loosely linked genes?
Tightly linked genes show low recombination; loosely linked genes show higher recombination
63
Give an example of tightly linked genes discovered by Morgan.
White and yellow genes (1.3% recombination)
64
Give an example of loosely linked genes discovered by Morgan.
White and miniature wing genes (37.2% recombination)
65
Who developed the idea of genetic mapping based on recombination frequency?
Alfred Sturtevant, Morgan’s student
66
What did Alfred Sturtevant use recombination frequency for?
To map the position of genes on a chromosome
67
What are the two broad categories of genetic disorders?
Mendelian disorders and Chromosomal disorders
67
What causes Mendelian disorders?
Alteration or mutation in a single gene
68
How are Mendelian disorders inherited?
They follow Mendelian inheritance patterns and can be traced using pedigree analysis
69
Are Mendelian disorders dominant, recessive, or both?
They can be either dominant or recessive
70
What type of disorder is Colour Blindness?
Sex-linked recessive disorder
71
What causes Colour Blindness?
Defect in either red or green cone cells of the eye due to mutation in genes on X chromosome
72
Who is more likely to be colour blind, and why?
Males, because they have only one X chromosome
73
What are the chances of a son being colour blind if the mother is a carrier?
0.5
74
What type of disorder is Haemophilia?
Sex-linked recessive disorder
75
What is affected in Haemophilia?
A single protein involved in blood clotting
76
How is Haemophilia transmitted?
From unaffected carrier female to some male progeny
77
Why is female haemophilia rare?
Mother must be a carrier and father must be haemophilic
78
Which royal family is known to have Haemophilia in their lineage?
Queen Victoria’s family
79
What type of disorder is Sickle-cell Anaemia?
Autosomal recessive disorder
80
What causes Sickle-cell Anaemia?
Substitution of Glutamic acid with Valine at the sixth position of beta globin chain due to a base change from GAG to GUG
81
What are the genotypes for sickle-cell disease and trait?
HbSHbS = diseased, HbAHbS = carrier
82
What change occurs in RBCs in Sickle-cell Anaemia?
RBCs change from biconcave disc to sickle shape under low oxygen
83
What type of disorder is Phenylketonuria?
Autosomal recessive disorder
84
What enzyme is lacking in Phenylketonuria?
Enzyme that converts phenylalanine to tyrosine
85
What are the effects of Phenylketonuria?
Accumulation of phenylpyruvic acid causes mental retardation and is excreted in urine
86
What type of disorder is Thalassemia?
Autosomal recessive blood disorder
87
What causes Thalassemia?
Mutation or deletion reducing synthesis of alpha or beta globin chains of haemoglobin
88
What is affected in α-Thalassemia?
Production of α globin chain (genes HBA1 and HBA2 on chromosome 16)
89
What is affected in β-Thalassemia?
Production of β globin chain (gene HBB on chromosome 11)
90
How does Thalassemia differ from Sickle-cell Anaemia?
Thalassemia is a quantitative defect (less globin); Sickle-cell is a qualitative defect (abnormal globin)
91
What causes chromosomal disorders?
Absence, excess, or abnormal arrangement of chromosomes
92
What is aneuploidy?
Gain or loss of a chromosome due to failed chromatid segregation
93
What is polyploidy?
Increase in a whole set of chromosomes due to failed cytokinesis
94
What causes Down’s Syndrome?
Trisomy of chromosome 21
95
What are symptoms of Down’s Syndrome?
Short stature, round head, furrowed tongue, broad palm with crease, mental retardation
96
What causes Klinefelter’s Syndrome?
Presence of an extra X chromosome (47, XXY)
97
What are features of Klinefelter’s Syndrome?
Masculine development with feminine features (Gynaecomastia), sterile
98
What causes Turner’s Syndrome?
Absence of one X chromosome (45, XO)
99
What are features of Turner’s Syndrome?
Sterile females with rudimentary ovaries and lack of secondary sexual characters

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