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Biology Subject Test (SAT II) > Chapter Six: Classical Genetics > Flashcards

Chapter Six: Classical Genetics Flashcards

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1
Q

Who is the father of modern genetics?

A

Gregor Mendel

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2
Q

How did Mendel study inheritance?

A

He bred garden peas and collected data from hundreds of plants across many generations and applied statistical analysis to his data

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3
Q

What 3 laws did Mendel’s work establish?

A

Law of dominance
Law of segregation
Law of independent assortment

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4
Q

What is probability?

A

The likelihood that a particular event will happen. It cannot predict whether it will actually occur, but if the sample is large enough it can give an average outcome

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5
Q

State the law of dominance

A

When two organisms, homozygous (pure) for two opposing traits are crossed, the offspring will be hybrid (carry two different alleles) but will only exhibit the dominant trait.

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6
Q

State the law of segregation

A

During the formation of gametes, the two traits carried by each parent separate

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7
Q

What is a monohybrid cross?

A

Cross between two organisms that are hybrid for a single trait

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8
Q

What are the phenotype (what it looks like) ratios from a monohybrid cross?

A

75% dominant trait

25% recessive trait

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9
Q

What is the genotype ratio for a monohybrid cross?

A

25% homozygous dominant
50% heterozygous
25% homozygous recessive

1:2:1

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10
Q

If the offspring phenotype ratio is 3:1 what were the parents?

A

They both were hybrid for the trait (monohybrid)

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11
Q

What is a test/back cross

A

Is a way to determine whether an individual organism showing the dominant trait is is homozygous dominant or heterozygous

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12
Q

How is a test cross done?

A

The individual is crossed with a homozygous recessive

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13
Q

Explain the 2 outcomes of a test cross

A
  • If the individual was homozygous dominant all offspring will have hybrid genotype (dominant)
  • If the individual was hybrid 50% or at least one of the offspring will show the recessive trait
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14
Q

What is a gene, and what is an allele?

A

Gene specifies which trait, allele specifies what form the gene takes

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15
Q

State the law of independent assortment

A

During gamete formation when 2 hybrids for 2 traits on separate chromosomes are crossed, the genes for 1 trait are not inherited along with the genes for another.

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16
Q

What is incomplete dominance?

A

It is characterised by blending but one, allele is more noticeable than the other. Unlike in Co dominance where both are expressed equally

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17
Q

How are alleles written incomplete dominance?

A

Different letters, all capitals since neither trait is dominant

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18
Q

What is co dominance?

A

When both traits are fully expressed. (the genotype has both dominant traits)

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19
Q

Most genes in a population often exist in 2 allelic forms. When > 2 its called:

A

Multiple alleles

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20
Q

Humans have 4 blood types. How many different alleles?

A

3

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21
Q

How are homozygous A and hybrid A written? Also state in terms of I

A 
AA= I^A
A(O)= Ai
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22
Q

How is blood type O written?

A

It is recessive

(ii)

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23
Q

What are characteristics controlled by many genes (by blending) called?

A

Polygenic

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24
Q

Which factor determines how alleles are inherited?

A

How the homologous pairs line up on the Metaphase plate during Metaphase 1 of meiosis

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25
Q

What is a dihybrid cross?

A

Cross between individuals that are hybrid for two different traits (Tt Yy × To Yy)

26
Q

What are phenotype ratios for a dihybrid cross?

A

9:3:3:1

recall punnet square for Tt Yy

27
Q

What are traits/genes carried on X chromosome called?

A

Sex-linked

28
Q

Why is it that males suffer sex-linked conditions more than females?

A

If the condition is due to recessive mutation the female can express it only if she inherits 2 mutated genes, if one she’s only a carrier. If a male carries one mutated X-linked gene he will express it

29
Q

2 examples of common recessive sex-linked traits are:

A

Color blindness

Hemophilia

30
Q

In sex-linked inheritance how are daughters and sons affected from parents?

A

Affected (they have to express cannot be carriers, mutated X) fathers pass traits to daughters(carriers)
Fathers cannot pass it on to sons because they only pass on the Y chromosome
Carriers mothers can pass on the trait to sons (50% chance)
Daughters can be affected only if both parents have the trait (2 mutated Xs)

31
Q

Apart from genetic predisposition what can alter the expression of genes?

A

The environment

32
Q

Inheritance can be influenced by sex. What does this mean?

A

This means that a particular traits genotype and phenotype and differ between genders

33
Q

What is a karyotype

A

It is a laboratory procedure that analyses the size, shape and number of chromosomes

34
Q

How is a karyotype done?

A

Chromosomes are prepared and photographs during metaphase of mitosis

35
Q

Differentiate the 2 types of the 46 chromosomes

A 
44 autosomes (22 pairs) 
2 sex chromosomes (1 pair)
36
Q

What is a pedigree and how does it work?

A 
It is a family tree uses to study how a phenotype of a trait is inherited for every member of a family. 
Females=circle
Males=sqaure
Carrier=half shaded (not often shown) 
Affected=full shaded
37
Q

Recall autosomal dominant, autosomal recessive, sex linked dominant, sex linked recessive traits

A

Okay lol

38
Q

What is a mutation?

A

Abnormalilty in the genome

39
Q

What is a gene mutation?

A

Caused by a change in DNA sequence

40
Q

What is a chromosome mutation?

A

A chromosome may sustain an addition or deletion, or a cell may even have a new chromosome, which results from nondisjunction

41
Q

What are homologous chromosomes?

A

A couple ofhomologs are a set of 1 maternal and 1 paternalchromosomethat pair up duringfertilization. Homologs have the samegenesin the samelociwhere they provide points along each chromosome which enable a pair of chromosomes to align correctly before separating during meiosis

42
Q

What is nondisjunction?

A

An error that sometimes happen during meiosis in which homologous chromosomes fail to separate

43
Q

How can nondisjunction affect a zygote?

A

When nondisjunction happens 1 gamete received 2 homologues while the other receives none. When one of these gametes are paired with a normal gamete the zygote chromosome number is abnormal

44
Q

What is an abnormal chromosome condition called?

A

Aneuploidy

45
Q

What is a condition called when chromosome is present in triplicate?

A

Trisomy

46
Q

An organism with cells with an extra set of chromosomes is called?

A

A triploid (3n)

47
Q

An organism with more than 3 sets of chromosomes?

A

Polypoid

48
Q

What is deletion?

A

A fragment lacking a centromere is lost during cell division

49
Q

What is inversion?

A

A chromosomal fragment reattaches to it’s original chromosome but in the reverse orientation

50
Q

Which mutations are visible under microscope

A

Chromosomal

51
Q

What is translocation (in terms of chromosomal aberrations)

A

A fragment of a chromosome becomes attached to a non homologous chromosome

52
Q

What is polyploidy?

A

Having extra sets of chromosomes

53
Q

State what type of disorder Phenylketonuria is, it’s pattern of inheritance, and describe it

A
  • genetic
  • autosomal recessive
  • inability to break down the amino acid phenylalanine. Intake of it in diet results in mental retardation
54
Q

State what type of disorder Cystic Fibrosis is, it’s pattern of inheritance, and describe it

A
  • genetic
  • autosomal recessive
  • buildup of extracellular fluid in the lungs, digestive tract etc
55
Q

State what type of disorder Tay-Sachs disease is, it’s pattern of inheritance, and describe it

A
  • genetic
  • autosomal recessive
  • onset in early life, caused by lack of enzyme to break down lipids essential for normal brain function, seizures blindness and early death
56
Q

State what type of disorder Huntingtons disease is, it’s pattern of inheritance, and describe it

A
  • genetic
  • autosomal dominant
  • onset in middle age, disease of the nervous system, certain early death
57
Q

State what type of disorder Hemophilia is, it’s pattern of inheritance, and describe it

A
  • genetic
  • sex-linked recessive
  • caused by the absence of 1/more proteins necessary for normal blood clotting
58
Q

State what type of disorder Color blindness is, it’s pattern of inheritance, and describe it

A
  • genetic
  • sex-linked recessive
  • being red-green colourblind is rarely more than inconvenience
59
Q

State what type of disorder Downs syndrome is, it’s pattern of inheritance, and describe it

A
  • chromosomal
  • 47 chromosomes with trisomy-21 = an extra #21 chromosome
  • characteristic facial features, mental retardation, prone to developing Alzheimer’s and leukaemia
60
Q

State what type of disorder Klinefelters syndrome is, it’s pattern of inheritance, and describe it

A
  • chromosomal
  • XXY 47 chromosomes = male with extra X chromosome
  • male genitals, but testes are abnormally small and men are sterile
61
Q

What are the genotypic ratios for the monohybrid cross?

A

1 Homozygous dominant: 2 Hybrid: 1 Homozygous recessive

62
Q

What are the phenotypic ratios for the monohybrid cross?

A

3 dominant: 1 recessive

Biology Subject Test (SAT II) (10 decks)

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