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AP Biology > Heredity > Flashcards

Heredity Flashcards

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AP® Biology flashcards
1
Q

Gregor Mendel

A

● Father of modern genetics

● His theory of genetics is one of particulate inheritance

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2
Q

Particulate inheritance

A

● Inherited characteristics are carried by discrete unis that Mendel called elements
- These elements eventually became known as genes

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3
Q

Probability

A

● THe likelihood htat a particular event will happen
● If an event is an absolute certainty, its probability is 1
● If an event cannot happen, its probability is 0
● Probability cannot predict whether a particular event will actually occur

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4
Q

Law of dominance

A

● States that when two organisms,each homozygous (pure) for two opposing traits are crossed, the offspring will be hybrid but will exhibit only the dominant trait

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5
Q

Hybrid

A

Carry two differnet alleles

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6
Q

Dominant trait

A

The trait that is exhibit in the offspring

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7
Q

Recessive trait

A

THe trait that remains hidden in the offsprin

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8
Q

Law of segregation

A

● States that during the formation of gametes, the two traits carried by each parent separate

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9
Q

Monohybrid cross

A

● A cross between two organisms that are each hybrid fro one trait
● The phenotype ratio from this cross is 3 tall to 1 dwarf plant
● The gentotype ratio is 1 to 2 to 1, given as percentages: 25% homozygous dominant, 50% heterozygous, 25% homozygous recessive

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10
Q

Phenotype

A

Physical characteristics of a gene

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11
Q

Genotype

A

Genetic code that scientists assign to a given gene

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12
Q

Testcross / backcross

A

● A way to determine the genotype of an individual plant or animal showing only the dominant trait
● Involves a cross between real organisms

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13
Q

Law of independnet assortment

A

● Applies to dihybrid cross
● States that during gamete formation, the alleles of a gene for one trait, such as height (Tt), segregate independently from the allels of a gene for another trait such as seed colour (Yy)

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14
Q

Dihybrid cross

A

● when a cross is carried out between two individuals hybrid for two or more traits htat are not on the same chromosome
● Phenotype ratio is 9:3:3:1

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15
Q

Linked genes

A

● When two traits are linked, the genes will not assort independently
● Genes on the same chromosome
● Linked genes tend to be inherited together and do not assort independently unless they are separated by a cross-over event

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16
Q

Incomplete dominance

A

● Characterized by blending

● Ex) A black animal (BB) with a white (WW) animal roduces all grey (BW) animals

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17
Q

Codominance

A

● Both traits show in hybrid genes

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18
Q

Multiple alleles

A

● When there are more than two allelic forms of a gene

● In humans there are four different blood types: A, B, AB, and O

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19
Q

Pleiotropy

A

● Ability of one single gene to affect an organism in several or many ways
● Ex) Autosomal recessive disease cystic fibrosis

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20
Q

Cystic fibrosis

A

● Characterized by an abnormal thickening of mucus that coats certain cells
● Instead of protecting the body, thick mucus builds up in the pancreas, lungs, digestive tract, and other organs leading to multiple, pleiotropic effects, including poor absorption of nutrients in the intestine and chronic bronchitis
● Autosomal recessive disease

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21
Q

Epistasis

A

● Two separate genes control one trait, but one gene masks hte expression of the other gene
● The gene that masks hte expression of hte other gene is epistatic to the gene it masks
● Ex) Coat colour in mice is controled by two genes. If the dominant allele for one of the gene is absent, even if the other gene is present, the coat is colourless (albino)–we say the first gene is epistatic to the second gene

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22
Q

Polygenic inheritance

A

● Result from a blending of several separate genes that vary along a continuum
● Characteristics such as skin colour, hair colour, and height
● Two parents who are short carry more genes for shortness than for tallness
- However, they can have a child who inherits mostly genes for tallness from both parents and who will be taller than the parents

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23
Q

Penetrance

A

● Proportion or percentage of individuals in a group with a given genotype that actually show the expected
● Ex) Many people who inherit a mutant allele for BRCA1 develop breast cancer in their lifetimes
- For reasons that are unknown, some people with the allele do no develop breast cancer

24
Q

Sex-linkage

A

● Traits carried on the X chromosome are called sex-linked

● Few genes are carried on the Y chromosome

25
Q

Autosomal chromosomes

A

● 44 out of 46 chromosomes in human are autosomes

● Do not carry sex iinformation

26
Q

Sex chromosomes

A

● X and Y

● 2 out of 46 chromosomes in human are sex

27
Q

Recessive sex-linked mutation

A

● If a sex-linked trait is due to a recessive mutation, a female will express hte phenotype only if she carries two mutated genes (x/x)
● If a female only carries one mutated X-linked gene, she will be a carrier (X/x)
● Males (XY) inherit only one X-linked gene; if its mutated (xY), then the male is infected
● Much more common than dominant sex-linked traits

28
Q

Dominant sex-linked mutation

A

● A female will express hte phenotype with only one mutated gene (X/x), (X/X)
● Males will express hte gene if its mutated (XY)

29
Q

Map unit

A

● One map unit distance on a chromosome is hte distance within which recombination occurs 1% of the time

30
Q

Linkage map

A

● Can be constructed from infromation about cross-over or recombination frequencies

31
Q

Pedigree

A

● Family tree that indicates the phenotype of one trait being studied for every member of a family
● Geneticists use the pedigree to dtermine how a particular trait is inherited
● Females are represetned by a circle and males by a square
● The carrier state is not always shown–if it is, its half-shaded-in shape
● A shape is completely shaded in if a person exhibits the trait; white shape means hte person is healthy

32
Q

Genetic mosaic

A

● Early int he development of hte embryo of a female mammal, one of hte X chromosomes is inactivated in every somatic cell
● The inactivation occurs randomly–some cell shave one X ainactivated, some cells have the other X inactivated

33
Q

Barr body

A

● The inactivated chromosome condenses into a dark spot of chromatin
● Can be seen at the outer edge of hte nucleus of all somatic cells in the female

34
Q

Mutations

A

● Any changes in the genome
● Can occur in the somatic cells and be responsible for hte sontaneous developmetn of cancer, or they can occur duing gametogenesis and affect future offspring
● Even though radiation and certain chemicals cause mutations, when and where mutations occur is random

35
Q

Gene level mutations

A

● Caused by a change in the DNA sequence
● Common diseases include PKU, cystic fibrosis, hemophilia, colour blindness, sickle cell disease, down syndrome and klinefelter’s syndrome

36
Q

Chromosome level mutations

A

● Inclues four types, deletion, inversion, translocation and polyploidy

37
Q

Karyotype

A

● Shows the size, number, and shape of chromosomes and can reveal the presence of certain abnormalities
● Can be used to scan for chromosomal abormalities in developing fetuses

38
Q

Deletion

A

When a fragment lacking a centromere is lost during cell division

39
Q

Inversion

A

When a chromosomal fragment reattaches to its original chromosome but in the reverse orientation

40
Q

Translocation

A

When a fragment of a chromosome becomes attached to a nonhomologous chromosome

41
Q

Polyploidy

A

● When a cell or organism has extra sets of chromosomes

● Often found in plants

42
Q

Nondisjunction

A

● An error that sometimes occurs during meiosis in which homologous chromosomes fail to separate as they should
● One gamete receives two fo the same type of chromosome and another gamete receives no copy

43
Q

Aneuploidy

A

Any abnormal number of chromosomes

44
Q

Trisomy

A

● If a chromosome is present in triplicate

● People with Down syndrome have an extra chromosome 21–also referred to as trisomy 21

45
Q

Genomic imprinting

A

● Variation in phenotype depending on whether a trait is inherited from the mother or from the father
● Occurs during gamete formation and is caused by the silencing of a particular allele by methylation of DNA
● A zygot expresses only one allele of the imprinted gene
● The imprint is carried to all body cells and passed down from generation to generation
● Located on autosomes

46
Q

Extranuclear genes

A

● Genes located in mitochondria and chloroplasts
● The DNA in these organelles is small, circular, and carries only a small number of genes
● Have been linked to several rare and severe inherited diseases in human
● Mitochondrial DNA is inherited only from the mother because hte father’s mitochondria do not enter hte egg during fertilization

47
Q

How do you find the probability of two independent events happening?

A

● Multiply the chnace of one happening by the chance that the other will happen

48
Q

How do you find hte probablity of evnets when there are more than one arrangement of evnets?

A

● Add the probabilites for each outcome together

49
Q

Describe how testcross work.

A

● The individual in question (B/_) is crossed with a homozygous recessive individual (b/b)
● If the individual being tested is in fact homozygous dominent, all offspring of the testcross will be B/b, and will show the dominant trait
- There can be no offspring shwoing the recessive trait
● If the individual being tested in hybrid (B/b), 1/2 of the offspring can be expected to show the recessive trait
● If any offspring show hte recessive trait,t he parent of unknown genotype must be hybrid

50
Q

How does the environment alter the expression of genes?

A

● In fruit flies, the expression of the mutation for vestigal wings (short, shriveled wings) can be altered by temprature
- WHen raised in a hot environemnt, fruit flies homozygous recessive for vestigial wings can grow wings almost as long as normal wild-type wings
● Many human diseases have a multifactorial basis
- There is an underlying genetic component with a significant environmental influence such as heart disease, diabetes, cancer etc
● THe development of intelligence is hte result of an interaction of genetic predisposition and hte environment or nurture and nature

51
Q

What are common examples of recessive sex-linked traits?

A

● Colour blindness
● Hemophilia
● Duchenne muscular dystrophy

52
Q

What happened to the daughters of affected fathers?

A

All daughters of afected fathers are carriers

53
Q

What happened to the sons of affected parents?

A

● Sons cannot inherit a sex-linked trait from the father because hte son inherits hte Y chromosome from the fateher
● A son has a 50% chance of inheriting a sex-linked trait from a carrier mother

54
Q

What does the distance of genes on a chromosome mean?

A

The farther apart two geens are on one chromosome, the more likely they will be separated from each other during meiosis because a cross-over event will occur between them

55
Q

What does hte rate of cross-over tell us?

A

● It does not give information about the actual distance between genes
● It tells us the order of the linked genes on the chromosome

56
Q

Whats the formula to calculate recombination frequencies?

A

Number of recombinants divided by total number of offspring multiply 100

57
Q

How do you determine if a disease in the pedigree is dominant or recessive?

A

● In order for daughter generation to have dominant disease, at least one of the parents must also be afflicted

AP Biology (15 decks)

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