Biology > Patterns of Inheritance > Flashcards

Patterns of Inheritance Flashcards

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1
Q

Interspecific variation

A

-Variation between different species.

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2
Q

Intraspecific variation

A

-Variation within individuals of the same species.

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3
Q

Types of genotype

A

-AA, homozygous dominant.
-Aa, heterozygous (dominant expressed).
-aa, homozygous recessive.

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4
Q

Locus

A

-Where on the chromosome the alleles are.

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5
Q

Monogenic inheritance

A

-Inheritance of characteristics controlled by a single gene.

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6
Q

Monohybrid cross

A

-Displays variance in only one phenotype.
-In Mendel’s experiment on pea plants, he compared tall-stemmed vs short stemmed pea plants.
-

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7
Q

Codominance

A

-Both alleles of a gene of a heterozygous individual contribute to the phenotype
-Eg coat colour in cattle. One gene determines colour but it has two alleles (red and white).
-In codominant inheritance both are expressed (roan).
-Different letters are used for both alleles (Cr for red and Cw for white).
-In humans, this can be an IAIB blood type, in which the erythrocytes have both types of protein.

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8
Q

Dihybrid inheritance

A

-Inheritance of two genes
-The parent’s genotype will contain 4 alleles and each gamete will contain 2 alleles.
-Eg AaBb produces four gametes (AB, Ab, aB, ab)

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9
Q

AaBb x aabb

A

-Heterozygous gametes of AB, Ab, aB and ab
-Homozygous gametes of ab.
-Offspring of AaBb, Aabb, aaBb and aabb.
-1:1:1:1 ratio.

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10
Q

Dihybrid cross

A

-Displays the simultaneous inheritance of two characteristics.
-Mendel’s experiments involved the inheritance of seed shape and seed colour.
A fully heterozygous (AaBb) cross will give a 9:3:3:1 ratio.

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11
Q

Multiple alleles

A

-Eg in blood with A, B, AB and O.

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12
Q

Allele combination of A blood type

A

-IaIa or IaIo.

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13
Q

Allele combination of B

A

-IbIb or IbIo.

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14
Q

Allele combination of AB

A

-IAIB.

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15
Q

Allele combination of O

A

-IoIo.
-Since O in recessive and A and B are co-dominant.

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16
Q

Directional selection

A

-Favours individuals that vary one side of the mean.
-Changes the characteristics of a population.
-Change in phenotype, the frequency of the successful allele will increase.

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17
Q

Stabilising selection

A

-Favours individual around the mean.
-Preserves the characteristics of the population.
-Phenotype remains unchanged, reduces extreme allele frequencies.

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18
Q

Disruptive selection

A

-Favours individuals at both extreme ends of the mean.
-Leads to evolutionary change and species.

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19
Q

Genetic bottlenecks

A

-Large numbers of a population die, some alleles are lost.
-The remaining population has highly reduced genetic diversity.

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20
Q

Genetic Drift

A

-Characteristics are passed on by chance rather than due to factors.
-Eg a disaster wipes out members of a population with alleles that neither offered an advantage nor disadvantage to the individual.
-These alleles are lost due to chance, not to selection pressure.

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21
Q

Founder effect

A

-A segment of a population with some alleles are separated and breed.
-Only these alleles are retained, leading to only their presence in the new population.

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22
Q

Reproductive isolation

A

-Populations are isolated from each other and can no longer interbreed.
-This leads to them diverging, and alleles causing genetic separation that leads to speciation.

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23
Q

Reasons why populations can no longer breed

A

-Seasonal changes eg different mating seasons.
-Mechanical changes eg changes in genitalia.
-Behavioural changes eg different courtship rituals.
-Chromosomal changes so hybrids cannot produce homologous pairs.

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24
Q

Allopatric speciation

A

-Where there are geographical barriers to populations mixing.
-Populations are geographically isolated from each other.

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25
Sympatric speciation
-Reproductive isolation caused by factors other than geography. -Eg different populations developing different behaviours. -Can be due to random mutations. -Rare in nature.
26
Artificial selection
-A human-directed process. -Individuals with desirable traits are selected to enhance or diminish characteristics over generations.
27
Process of artificial selection
-Individuals with desired features are chosen for breeding. -Some alleles with these features are passed on to their offspring. -The same selection occurs with the offspring. -This is repeated over many generations to increase the allele frequency of the chosen feature.
28
Characteristics in selective breeding for cows
-Milk quality. -Lactation period. -Large udders. -Resistance to inflammation called mastasis. -Calm temperament.
29
Ethical and biological considerations of artificial selection
-Discomfort or health problems in individuals. -Reduction of genetic diversity can limit the resilience and adaptability of species and ecosystems. -Ethical implications such as the manipulation of species for human benefit. -Inbreeding leads to increased risk of genetic disorders and vulnerabilities.
30
Continuous variation
-No distinct categories. -Usually quantitative. -Eg height, weight, heart rate, length. -Represented by line graph. -Controlled by many genes (polygenic), and environment. -Range of phenotypes.
31
Discontinuous variation
-Distinct categories. -Tends to be qualitative. -Eg tongue rolling, finger prints, eye colour, blood groups. -Represented by bar graphs. -Usually determined by the alleles of a single locus (monogenic), limited number of phenotypes.
32
Quantitative genetics
-The study of alleles that have an additive (each gene contributes a small amount to the phenotype) effect. -The phenotypic categories vary in a quantitative way.
33
Sex linkage
-X and Y chromosomes are not fully homologous: The Y chromosome is shorter. -For sex linked traits, alleles are found on a sex chromosome. -Sex linked genes are usually those found on X chromosomes, but not the Y chromosome. -Abnormal alleles on the X chromosome can be masked in females by a functional allele on the other X chromosome, but not in males. If the male has an abnormal allele on the X chromosome it cannot be masked as there is no allele on the Y.
34
Sex linked genetic disorders
-Haemophilia A. -Colour blindness. -Duchenne muscular dystrophy. -Sex-linked defects are most common in males.
35
Carriers
-People (females) without symptoms of a genetic disease, but who have an abnormal allele on one of their X chromosomes. -Their offspring are more likely to experience the genetic disease, particularly if they are male.
36
Sex linkage in cats
-One of the genes for coat colour in cats is sex-linked. -It is on the non-homologous region of the X chromosome. -The alleles of this gene are codominant, if both are expressed the cat is tortoiseshell. This can only occur in female cats.
37
Autosome
-A chromosome that is not a sex chromosome.
38
Autosomal linkage
-Genes that are linked are those with loci on the same chromosome. -They do not undergo independent assortment during meiosis, and can only be separated by crossing over. -Therefore, they are more likely to be expressed together. -In Mendel's investigation, the genes for flower colour and pollen grain shape were on the same chromosome.
39
Epistasis
-Where the expression of one gene is affected by the expression of one or more independently inherited genes. -This happens between non-linked genes and only happens when both genes encode proteins that affect the same phenotype. -This often reduces the number of phenotypes produced in the F2 generation of dihybrid crosses. -Therefore genetic variation is reduced.
40
Null mutation
-Means gene is not expressed. -Occurs in epistasis. If either locus is homozygous for a null mutation, none of that enzyme will be made and the phenotype will not be expressed.
41
Epistatic gene
-Masks the effect of another gene.
42
Hypostatic gene
-Recessive. -Expression masked by an epistatic gene.
43
Recessive epistasis
-Where a recessive allele (bb) masks the expression of another gene. -Eg if (Bb) codes for flower pigment and (Aa) for the colour of that pigment, then any genotype with a 'bb' allele will produce white flowers irrespective of the A gene. -This is indicated by a 9:3:4 ratio.
44
Complimentary epistasis
-The presence of a particular allele at two loci is required for a particular phenotype to be expressed. -Eg if 'cc' results in no pigment being produced, and 'aa' results in a deviation from the dominant colour (black from agouti), then only aaCC or aaCc can produce a black mouse. -Any genotype with cc will produce a white mouse. -9:7 or 9:3:4 ratio.
45
Dominant epistasis
-When a dominant allele limits the expression of another. -Eg if (Ii) codes for feather pigment and (Cc) codes for colour, then II or Ii will produce a white feathered bird. -Birds with the genotype with cc also will be white as pigment will not be made. -13:3 or 12:3:1 ratio.
46
Chi-squared test
-Measures the size of difference between observed and expected results. -Allows us to determine if there is a significant difference between observed and expected.
47
When a chi-squared test is used
-Data is in categories and is non-continuous. -Large sample size. -Raw counts (not percentages) -No 0 count. -Tests the null hypothesis (of no significant difference).
48
Steps of chi-squared
-Complete table of observed and expected values. ((O-E)2/E). -Find degrees of freedom (number of categories - 1) -Critical value of X2 in a distribution table. -Accept or reject null hypothesis (if X2 is smaller than critical value then reject).
49
Hardy-Weinberg principle
-Predicts the proportion of dominant and recessive alleles in a population. -Assumes that no mutations arrive and there is no selection or migration in or out of the population. -Assumes that mating is random within the population.
50
P+Q=1
-P=frequency of dominant allele. -Q=frequency of recessive allele. -So frequency of both combined will always be 1.
51
P^2 + 2PQ + Q^2=1
-P^2=amount of dominant homozygous. -Q^2=amount of recessive homozygous. -PQ=amount of heterozygous.
52
Calculation of Hardy-Weinberg
-Q^2=proportion of the recessive phenotype. -So Q is the route of Q2. -P can be found using P+Q=1. -So P^2 and 2PQ can be found.
53
Mutagens
-Physical and chemical agents that increase the rate of mutation. -Persistent, can be transmitted through many generations. -Random, not directed by a need on part of the organism.
54
Physical mutagens
-X-Rays. -Gamma rays. -UV light.
55
Chemical mutagens
-Benzopyrene (in tobacco). -Mustard gas. -Nitrous acid. -Aromatic amines in dyes.
56
Biological agents
-Some viruses. -Food contaminants such as mycotoxins from fungi. -Transposons (jumping genes, remnants of viral nucleic acid that become incorporated into genomes).
57
Inversion mutation
-A section of a chromosome breaks off, turn 180 degrees and then join again. -Genes are still present, but may be too far away from their regulatory nucleotide sequences to be properly expressed.
58
Translocation mutation
-A piece of one chromosome breaks off and then becomes attached to another chromosome. -May interfere with regulation of genes on the translocated chromosome.
59
Duplication
-Piece of the chromosome may be duplicated. -Overexpression of the gene can lead to certain proteins or gene-regulating nucleic acids disrupting metabolism.
60
Non-disjunction mutation
-One pair of chromosomes/chromatids fails to separate, leaving one gamete with an extra chromosome. -When fertilised, the zygote has one extra chromosome. -This causes Down syndrome.
61
Aneuploidy
-Chromosome number is not an exact multiple of the haploid number. -Eg chromosomes or chromatids fail to separate during meiosis.
62
Polyploidy
-If a diploid gamete is fertilised by a haploid gamete, the resulting zygote will be triploid (three sets of chromosomes) -The fusion of two diploid gametes can make a tetraploid zygote. -Many cultivated plants are polyploid (two sets of chromosomes).
63
Recombinant gametes
-Linked genes separated by crossing over during meiosis. -Lead to a change from the 1:2:1 ratio.
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