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Biology (NCERT) - Class XII > XII Chap 5 Inheritance & Variation > Flashcards

XII Chap 5 Inheritance & Variation Flashcards

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1
Q

Genetics is a branch of biology that deals with

A

principles of inheritance, its practices and variation of characters from parents to offspring

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2
Q

Define inheritance

A

process by which characteristics are passed from parents to progeny

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3
Q

Define variation

A

Degree by which progeny differ from parents

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4
Q

What is the evidence that early humans knew sexual reproduction was linked to variation

A

selective breeding of plants and animals (e.g. Sahiwal cows)

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5
Q

How early did we (humans) know that sexual reproduction was linked to variation?

A

Early humans (8000-1000 BC)

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6
Q

Who conducted hybridization experiments to determine the laws of inheritance?

A

Mendel

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7
Q

When did Mendel conduct his hybridization experiments?

A

1856-63

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8
Q

What type of plants and how many plants did Mendel use during his experiments?

A

14 true-breeding plants

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9
Q

What are the 7 pairs of traits Mendel tested?

A
  1. Stem height (tall v. short)
  2. Flower color (violet v. white)
  3. Flower position (axial v. terminal)
  4. Pod shape (inflated v. constricted)
  5. Pod color (green v. yellow)
  6. Seed shape (round v. wrinkled)
  7. Seed color (yellow v. green)
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10
Q

What is a true-breeding plant?

A

Continuous self-pollination would show stable trait inheritance and expression for several generations

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11
Q

What is a gene?

A

Unit of inheritance;

contains information to express a trait

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12
Q

Gene was first called a ______ by Mendel

A

Factor

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13
Q

What is an allel?

A

Pair of contrasting trait;

slightly different form of the same gene

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14
Q

What is genotype and phenotype?

A 
Genotype = technical way of writing the gene e.g. TT or tt 
Phenotype =  observable / descriptive characteristic
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15
Q

Heterozygous v. homozygous?

A

Hetero - dissimilar alleles (contrasting traits)

Homo - similar alleles (identical traits)

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16
Q

True breeding plants are heterozygous. T or F?

A

False

Homozygous => identical alleles

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17
Q

The F1 generation of a cross of a true-breeding plant will be heterozygous. True or False?

A

True

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18
Q

What is F1 represent?

A

Filial 1 progeny => first hybrid generation

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19
Q

Define monohybrid

A

Hybrid made from genes controlling for one/single character (flower position)

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20
Q

What is a monohybrid cross?

A

Cross between gene controlling for 1 trait e.g. pod shape

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21
Q

What is a Punnett Square

A

Diagram by British geneticist, Reginald C. Punnett;

calculates probability of all possible genotypes of offspring in a cross

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22
Q

What is a “test cross”?

A

To determine the genotype of a dominant phenotype, crossing it with recessive parent (instead of self-crossing)

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23
Q

What are the principles/laws of inheritance?

A

Law of Dominance - in dissimilar pair, one dominates the other
Law of Segregation - alleles don’t blend, they separate and gamete receives only ONE of two alleles

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24
Q

The law of dominance implies that only one parent’s characteristics are expressed in filial progeny 1. True or False?

A

True

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25
Q

The law of dominance implies that only one parent’s characteristics are expressed in the second generation of hybrid. True or False?

A

False, both are expressed

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26
Q

What are the phenotype and genotype ratios of the second hybrid generation?

A

Phenotype 3:1

Genotype 1:2:1

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27
Q

What are the phenotype and genotype ratios of the first hybrid generation?

A

Phenotype: 4:0
Genotype: 4:0

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28
Q

The genotype of the second hybrid generation can be expressed by which binomial equation?

A

(ax + by) ^2

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29
Q

According to the law of segregation, gamete only receives one of 2 alleles. True or False?

A

True

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30
Q

What is incomplete dominance?

A

An in-between state, neither dominant nor recessive gene but a blending of the two to product a 3rd phenotype

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31
Q

Dogflower is an example of ________________

A

incomplete dominance

Red (RR), Pink (Rr) and White (rr)

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32
Q

What are the phenotype and genotype ratios of a hybrid exhibiting incomplete domination of 1 factor?

A

Phenotype: 1:2:1
Genotype: 1:2:1

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33
Q

The genotype ratio of incomplete dominance is different than that of Mendelian monohybrid cross. T or F?

A

False, same

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34
Q

The phenotype ratio of incomplete dominance is different than that of Mendelian monohybrid cross. T or F?

A

True
Incomplete dominance 1:2:1
Mendelian monohybrid 3:1

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35
Q

What is co-dominance?

A

When traits of BOTH parents are observed e.g. AB blood groups

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36
Q

How many phenotypes and genotypes in human blood groups?

A

4 phenotypes

6 genotypes

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37
Q

What is the gene representation for blood groups in humans? What are the different alleles?

A 
I
3 alleles:
IA
IB
i
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38
Q

How does the plasma membrane of an RBC look based on ‘i’ gene?

A

No sugar - no protuding sugar polymers

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39
Q

How does the plasma membrane of an RBC look based on IA or IB gene?

A

Sugar polymer protruding from the plasma membrane

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40
Q

If a human gene has 3 or more alleles, what is the challenge in studying the variations?

A

Humans are diploid => they’ll possess only 2 of the 3 alleles => can only study such alleles via population studies

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41
Q

Occasionally one gene manifests as 2 effects or phenotypes. T or F?

A

True

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42
Q

How does one interpret dominance when a gene translates to 2 phenotypes? Give an example

A

Depends on the phenotype.
e.g.
Starch synthesis gene in pea seeds;
heterozygous seeds are round => dominance of B allele
heterozygous seeds are intermediate size => incomplete dominance

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43
Q

Dominance is an autonomous feature of a gene. T or F?

A

False, depends on the phenotype being examined

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44
Q

When 2 traits are crossed simultaneously it’s call a _________ cross

A

Dihybrid

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45
Q

What factors did Mendel study when exploring inheritance of 2 genes

A

Round, yellow seed

Wrinkled, green seed

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46
Q

What are the phenotypes and genotypes of Mendel’s dihybrid cross?

A

Phenotypes (16 total) 9:3:3:1

Genotypes (8 total) 1:1:1:1:2:2:2:2:4

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47
Q

What is the law of independent assortment?

A

When 2 pairs of traits combined in hybrid, segregation of 1 pair is independent of other

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48
Q

Who rediscovered Mendel’s experiments in 1900s?

A

deVries, Correns and von Tschermark

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49
Q

Who made the connection that both genes and chromosomes appear in pairs?

A

Sutton and Boveri

50
Q

What is the chromosomal theory of inheritance?

A

Pairing and separation of a pair of chromosomes leads to segregations of a pair of factors (genes)

51
Q

Who is credited with the chromosomal theory of inheritance?

A

Sutton and Boveri

52
Q

What did Morgan & Co contribute?

A

Idea of linkage and recombination; law of independent assortment doesn’t apply when both genes are on the same chromosome, distance between both affects the frequency in progeny

53
Q

Two genes on the same chromosome indicates more parental combinations than non-parental in subsequent generations. T or F?

A

True

54
Q

Define linkage

A

Physical association of genes on same chromosome

55
Q

Recombination

A

generation of non-parental combinations

56
Q

When genes are tightly linked they have ______ recombinations. Example?

A

low (ie. more parental combinations);

white eyes and yellow bodies in Drosophila - 1.3% recombination in F2

57
Q

When genes are ________ linked they have high recombinations

A

Loosely;

white eyes and miniature wing => 37.2 % recombination in Drosophila F2

58
Q

Morgan’s student ________________ is credited with the concept of “genetic maps”

A

Alfred Sturtevant

59
Q

What does it mean to “map the position” of a gene?

A

Use frequency of recombination as a measure of distance between 2 genes

60
Q

Genetic maps is another name for _________

A

mapping positions of genes

61
Q

Genetic maps are used in which large-scale project recently?

A

Human Genome Sequencing Project

62
Q

What are polygenic traits? (aka polygenic inheritance)

A

3 or more genes have an additive effect; phenotype is on a gradient, shows influence of each gene
e.eg. human skin color, height

63
Q

Polygenic inheritance takes into account genes and what other factor?

A

Environmental influence

64
Q

What is a pleiotropic gene?

A

One gene, multiple phenotype;
gene effects metabolic pathway

e.g. gene that codes enzyme phenyl alanine hydroxylase, incorrect coding of which results in phenulketonuria (genetic disorder)

65
Q

Henking in 1891 discovered what?

A

“X body”, specific nuclear structure that only 50% of sperms receive

66
Q

Sex determination in insects is of type _____

A

XO
Eggs have additional X
Sperms may or may not

e.g. grasshopper

67
Q

Grasshopper sperms which have an “X” chromosome will produce __________

A

Females

68
Q

Grasshopper sperms which lack an “X” chromosome will produce __________

A

Males

69
Q

Humans, mammals and some insects have _____ type sex determination

A

XY

70
Q

Drosophila have XO type of sex determination. T or F?

A

False, XY (like humans)

71
Q

Humans and birds exhibit male heterogamety. T or F?

A

Humans - male heterogamety

Birds - female heterogamety

72
Q

What is male/female heterogamety?

A

Display pair of different sex chromosomes e.g. XY in human males, ZW in female birds

73
Q

Birds and humans both have same number of chromosomes in male and females. T or F?

A

True

74
Q

There is equal probability that an ovum will fertilize with an X-sperm or a Y-sperm. T or F?

A

True

75
Q

Honeybees have a _______________ system of sex determination

A

Haplodiploid

76
Q

How does sex determination work in honey bees?

A

Sperm + Egg = Female (queen or worker)

Unfertilized Egg = Male

77
Q

Honey bees have both diploid males and haploid females. T or F?

A

False, diploid females and haploid males

78
Q

How many chromosomes in a male v. female honeybee?

A 
Male = 16
Female = 32
79
Q

Why is it that male honeybees can neither have sons or fathers but can have grandfathers or grandsons?

A

Males are result of unfertilized egg => that egg has no father

Male sperms can fertilize an ovum to produce a female who may then produce an egg that is fertilized by another sperm => can be grandfathers / have grandsons

80
Q

Honeybee eggs become males through process of ___________

A

Parthenogenesis

81
Q

How do male honeybees produce sperms?

A

Mitosis

82
Q

Define mutation

A

Alteration in DNA sequence / genetic material => causes change in genotype and phenotype

e.g. cancer, sickle-cell anemia

83
Q

Both recombination and mutation ____________

A

alter DNA

84
Q

What is DNA?

A

Helix that runs continuously from one end to another, highly coiled

85
Q

__________ are chemical and physical factors responsible for mutations

A

Mutagens e.g. UV radiation

86
Q

What is pedigree analysis?

A

Since crosses can’t be performed on humans, we analyze traits in several generations of family

87
Q

What are the 2 categories of genetic disorders?

A

Mendelian

Chromosomal

88
Q

What are Mendelian disorders

A

Alteration in a single gene
Principle of inheritance
Pedigree analysis

89
Q

What are the Mendelian disorders covered in this chapter?

A 
Color blindness
Haemophilia
Sickle-cell anemia
Phenylketonuria
Thalassemia
90
Q

Mendelian disorders could be linked to a dominant or recessive gene, X-chromosome or autosome. T or F?

A

True

91
Q

Main points about color-blindness

A

X-linked, recessive
defect in red/green cone of eye
affects 8% males and only 0.4% females

92
Q

Daughter will be color-blind only if _________

A

Father is color-blind and mother is carrier (or color blind)

93
Q

Main points about haemophilia

A

X-linked, recessive;
single protein in cascade involved in blood clotting affected => non-stop bleeding
possibility of daughter having haemophilia is rare because father being haemophilic in later stages of life is unlikely as survival rate is low

94
Q

Daughter will be haemophilic only if _________

A

Mother is carrier and Father is haemophilic (highly unlikely due to low survival)
Queen Victoria is a famous carrier!

95
Q

Main points about sickle-cell anemia

A

Autosome-linked, recessive;
causes RBC to be elongated, sickle-shape => not enough healthy blood cells to carry oxygen in body

Hbs Hbs (homozygous for Hb^s) are affected

Substitution of valine for glutamic acid at 6th position in beta globin chain of haemoglobin; mutation GAG to GUG

96
Q

Main points about phenylketonuria

A

Autosome-linked, recessive;
gene that codes for enzyme phenyl alanine hydroxylase;
lacks enzyme to convert phenylalanine to tyrosine, so it converts to phenylpyruvic acid which accumulates in the brain => causes mental retardation + loss of hair + skin pigmentation

97
Q

Main points about thalassemia

A

Autosome-linked, recessive
blood disease;
transmitted if both are unaffected carriers (or heterozygous)

98
Q

Is thalassemia due to mutation or deletion of gene?

A

Could be either,

alpha - mutation or deletion
beta - mutation

99
Q

What is alpha thalessemia?

A

HBA1 and HBA2 gene are closely linked on chromosome 16 of each parent. If any of the 4 genes are mutated or deleted => alpha thalessemia

The more the number of genes affected => the lesser the alpha globin molecules produced

100
Q

What is beta thalassemia?

A

Single gene on HBB on chromosome 11, if one or both mutate

101
Q

__________ is a quantitative problem of synthesizing too few globin molecules and _________ is a qualitative problem of incorrectly functioning globin molecules

A

Thalessemia - quantitative

Sickle-cell anemia - qualitative

102
Q

What is aneuploidy?

A

Failure of segregation of chromatids during cell divisions => gain or loss of chromosome e.g. Down’s syndrome

103
Q

What is polyploidy?

A

Increase in whole set of chromosomes because or failure of cytokinesis after telophase stage of cell division

e.g. often in plants

104
Q

What is trisomy?

A

Extra or third chromosome

e.g. Down’s Syndrome

105
Q

Down’s syndrome was discovered by Langdon Down in ______

A

1866

106
Q

What is monosomy?

A

only 1 chromosome (where there should be 2)

e.g. Turner’s syndrome

107
Q

Characteristics of Down Syndrome?

A

Short, flat back of head, small/round head, furrowed tongue, open mouth, palm crease,
physical, psychomotor and mental retardation

108
Q

What is Klinefeller’s syndrome?

A

XXY => Extra copy of X chromosome, 47 karyotype

overall masculine development (tall) + breast (gynaecomastia)

109
Q

What is Turner’s Syndrome?

A

XO => one less X => 45 karyotype;

rudimentary ovaries, short stature, underdeveloped female character

110
Q

People with Turner’s syndrome and Klinefeller’s syndrome are both __________

A

Sterile;

have a mutation of the X chromosome

111
Q

What is difference in Mendelian and Chromosomal disorders?

A

Mendelian - alteration of a single gene, follows principle of inheritance so can be traced by pedigree analysis
Chromosomal - absence/excess/abnormal arrangement of chromosome(s), cannot be traced

112
Q

Recessive genes are only expressed in homozygous conditions. T or F?

A

True

113
Q

Mendel’s law of independent assortment is not valid for _________

A

linked genes (genes on same chromosomes)

114
Q

Closely linked genes are assorted together. T or F?

A

True

115
Q 
Which of these is the ultimate source of allelic variation is?
Recombination
Natural selection
Mutation
Drift
A

Mutation

116
Q 
Sickle cell anemia results from which of these? 
Chromosomal aberration
Non disjunction of autosome
A point mutation
Blood transfusion reaction
A

A point mutation

117
Q

Two alleles of a gene pair are located on ________ sites of ________ chromosomes

Homologous / heterologous

A

Homologous sites on homologous chromosomes

118
Q

What Mendelian disorders are connected to the X-gene?

A

Color blindness

Haemophilia

119
Q

George Mendel was born in

A

19th century (1800s)

120
Q

Who was the first to use statistical analysis and mathematical logic to solve biology problems?

A

Gregor Mendel

Biology (NCERT) - Class XII (18 decks)

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