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Flashcards in Genetics & Evolution Deck (42):
1

Evolution

Eventual changes in the gene pool that bring about phenotypic changes

2

Genes

DNA molecules in a locus of a chromosome carrying inheritable physical and biochemical traits of living organisms and passing them down generations

Have alternative forms that are expressed in variable alleles

3

Alleles

Alternative forms of a gene that are either
1. dominant
2. recessive
3. homozygous
4. heterozygous
5. hemizygous

4

Genotype

Genetic combination possessed by a person

5

Phenotype

The physical expression of genotypes

6

Hemizygous

Gene property when only one allele is present

7

Gene Dominance Patterns

1. Complete Dominance (Full phenotypic expression of one dominant allele entirely masking the expression of the recessive allele for a give gene)
2. CoDominance (Equal phenotypic expression of two dominant alleles of a given gene)
3. Incomplete Dominance (Intermediate phenotypic expression of two homozygous genes)

8

Gene Expression Variables

1. Penetrance
2. Expressivity

9

Penetrance

A population parameter stating the percentage of individuals in a population that express the phenotype for the genotype that they carry

Categorized into:
1. Full penetrance
2. High penetrance
3. Reduced/ low penetrance
4. Nonpenetrant

10

Expressivity

Gene expression variable explored at individual level to discover the phenotype variability of a given genotype.

May be:
1. Constant
2. Variable

11

Mendelian Laws

1. Law of Segregation - [alleles of a gene separate during meiosis and allow each gamete to carry only one allele]
2. Law of Independent Assortment [despite recombination of genes, the inheritance of one gene is independent of that of other genes]

*Both of these laws increase the diversity of an offspring and its survival ability by making it capable of adopting to environmental changes

12

Recombination

Swapping of genes b/w chromatids of homologous chromosomes

13

Tennets of Mendelian Law of Segregation

1. Genes exist in alternative allele forms
2. Each gene has two alleles, one inherited from each parent
3. The two alleles of a given gene are segregated during meiosis, allowing each gamete to carry to incorporate only one allele during fertilization
4. The allele with the greater dominance is expressed

14

3 Strategies for Increasing Bacterial Genetic Variability

1. Transformation
2. Transduction
3. Conjugation

* REVIEW Chap.1 BIO

15

Experiments Performed to Confirm DNA as Inheritable Material of Genes as Opposed to Protein

1. 1920s-Groups of mice were injected with virulent and nonvirulent bacteria-transformation of the nonvirulent bacteria led to mice's death- however when nonvirulent bacteria were treated with DNA-degrading enzymes, transformation failed to occur and mice remained alive

2. 1952-Protein and DNA radio-labeled bacteriophages were created and permitted to infect a sample of non-labeled bacteria. Upon analysis, DNA (and not protein) was confirmed to have entered the bacteria to cause disease. [****Virus's need for entry inside a cell to cause disease was known****]

16

The Difference B/W Meiosis & Mitosis

Meiosis produces haploid gametes through two division cycles whereas mitosis divides diploid somatic cells into diploid daughter cells

17

Steps of Meiosis

1. Meiosis I
1. Interphase-[1. cell grows, 2. genetic material
replicates/duplicates]
2. Prophase-[1. nuclear membrane dissolves, 2.
chromosomes condense, 3. centrosomes
travel to opposite sides of the cell]
[***cross-over/recombination occurs
between homologous chromosomes***]
3. Metaphase-[1. Chromosomes line along the
metaphase plate, 2. microtubules push
centrosomes to the sides of the cell
while pulling chromosomes toward
centrosomes]
4. Anaphase-[homologous chromosomes completely
separate]
5.Telephase-[1.chromosomes unravel, 2. nuclear
membrane redevelops, 3. cytokinesis
occurs, 4. 2 haploid cells result]

2. Meiosis II
1. Prophase II: [1. chromosomes condense, 2. nuclear
envelope dissolves, 3. centrosomes spread to
opposite sides of the cell]
2. Metaphase II: [chromosomes line along the plate]
3. Anaphase II: [Microtubules pull sister chromatids
toward centrosomes]
4. Telephase II: [4 games result after cytokinesis,
redevelopment of the nuclear
envelop, and unraveling of the
chromosomes]

18

Genetic Pool

All of the existent alleles in a species

19

Factors that Induce Genetic Variability

1. Mutation (production of change in DNA sequence)
2. Genetic leakage
3. Genetic Drift

20

Advantage of Genetic Variability

Promotes survival of species by allowing them to adapt to environmental changes in addition to conferring selective advantages such as delivery of viable, genetically diverse offsprings

21

Means for Mutation Inducement

1. Chemical Exposure
2. Radiation
3. Errors made by DNA polymerase in replication of DNA
4. Presence of mutagens
5. Presence of transposons

22

Mutagens

Mutation inducing substances

23

Transposons

Nucleic Acids that insert or remove themselves from gene-coding sequences

24

Types of Mutations

A. Nucleotide-Level Mutations
I. Point Mutations [one nucleotide replaces another]
1. Silent - [No change in final protein]
2. Missense- [Replacement of 1 Amino Acid in the
protein synthesized]
3. Nonsense [Premature stop codon is introduced
into the protein synthesized]
II. Frame-Shift Mutations [one nucleotide is inserted or
removed/impacting the
reading frame/codon of DNA
sequence]
1. Insertion
2. Deletion
B. Chromosomal-Level Mutations -[Involves large DNA
segments]
1. Insertion - [involves insertion of segment from
another DNA molecule]
2. Deletion
3. Inversion- [Involves reversing DNA sequence in a
segment]
4. Translocation - [involves swapping DNA b/w 2
molecules]
5. Duplication

25

Range of Effects of Mutations

Changes in DNA genetic sequence that may bring about either of the following:

1. Positive Selection Advantages - [sickle cell trait
prevents malaria due
to short life span of
sickle cells]
2. Deleterious - [phenylketonuria gives rise to inborn
error metabolites that can cause
cognitive impairments and learning
disabilities]

26

Phenylketonuria (PKU)

A metabolism problem where phenylalanine hydrolase is not present to digest phenylalanine, resulting in toxic metabolite build-up that can cause neurological impairments if not recognized at birth to set limitations on diet.

27

Genetic Leakage

Flow of genes from one species to another through mating between members of the hybrids to produce hybrids

* Most hybrids cannot reproduce due to odd number of chromosomes (Ex: mule) but some can (like beefalo) and promote genetic flow

28

Genetic Drift

Gene pool changes in small populations due to

1. chance
2. bottleneck effect - factors that drastically reduce the
size of a population (decrease
genetic diversity/promote disease)
3. founder effect - isolation of a small population due to
physical barriers and natural
catastrophies (decrease
genetic diversity/promote disease)
4. inbreeding - mating of genetically related individuals
due to bottlenecks and founder effects
(lead to inbreeding depression due to
loss of genetic variability and fitness)
& 5. out-breeding or out-crossing (increases genetic
diversity by introducing unrelated
individuals into a breeding group)

29

Biometric Techniques

Statistical analysis strategies in biology such as
1. punnett square [predict phenotypic and genotypic traits of an offspring resulting from breeding of two individuals]
2. Genetic Mapping
3. Hardy-Weinberg Equilibrium

30

Punnet-Square Notations

1. Parental or P-generation
2. Filial or F-generation (F1 & F2)

***genetic diversity increases in F2 generation****

31

Types of Punnet-Square Crosses

1. Monohybrid cross [studies one type of trait]
2. Test cross/back cross [uses offspring phenotype to
predict parent genotype; crosses one known with
one unknown genotype]
3. Dihybrid cross [studies two traits in a 4x4 Punnet-Sq]
4. Sex-linked cross- [uses X & Y symbols to indicate X &
Y chromosomes-***males hemizygous for a
disease-promoting gene are often carriers even if the
genetic allele they carry is recessive]

32

Genetic Mapping

Determining the linear order of genes on a chromosome using recombination frequencies

33

Recombination Frequency

The probability of two genes separating during prophase I of meiosis given their distance from each other

****Takes 2nd Mendelian Law of Independent Assortment into consideration****

34

Allele Frequency

The likelihood of finding a given allele in a gene pool

***Changes in the allele/gene frequency as a result of inbreeding, outbreeding, migration, bottleneck effect, founder effect, etc. give rise to evolution and better organism fitness.

35

Hardy-Weinberg Equilibrium

An equilibrium in which evolution does not occur because the change in gene frequency is 0 due to

1. lack of migration
2. large size of population (no genetic drift)
3. random mating
4. absence of mutations
5. reproductive success of all gene types

MMMRS
(Mutation-Migration-Mating-Reproductive Success-Size of Population)

36

Hardy-Weinberg Equilibrium Equations

p+q=1 [provides allele frequency]
p^2+2pq+q^2=1 [provides phenotype/genotype
frequency]

*p: defined as allele frequency of the dominant alle
**q: defined as alle frequency of the recessive alle

37

Theories Explaining Evolution

1. Natural Selection [proposed by Charles Darwin 1859
states that possession of certain traits makes some
individuals more fit to survive and to reproduce
offsprings]
2. Neo-Darwinism [proposed by post-Darwinists, states
that changes in gene frequency induced by
mutations, depending on their deleterious or
favorable nature and depending on their ability to
increase the fitness and reproductive ability of a
population, give rise to evolution, either increasing or
decreasing the frequency of the mutated gene in the
gene pool. [***This is known as differential
reproduction****]
3. Inclusive Fitness [states that success of an individual
in a population depends on traits that contribute to
its success/long standing]
4. Punctuated Equilibrium [proposes that in some
populations, change occurs in rapid bursts rather than
evenly over time]**************************REVIEW

38

Modes of Natural Selection

1. Stabilizing-maintains phenotypes in a given range
and selects against extremes
2. Directing-gives rise to emergence & dominance of
an extreme phenotype
3. Disruptive-selection of extreme phenotypes over
the norm.

39

Speciation

The rise of a new species as a result of evolution.

40

Types of Isolations b/w 2 Populations Preventing Interbreeding

A. Prezygotic
1. Temporal [breeding occurs at different times]
2. Ecological [geographical niches varry]
3. Behavioral [courtship behaviors varry]
4. Reproductive [reproductive anatomies are
incompatible]
5. Gametic [gametes fail to fertilize each other]
B. Postzygotic
1. Hybrid inviability [zygote cannot be developed to
term]
2.Hybrid sterility [hybrid cannot reproduce]
3. Hybrid breakdown [hybrid's offspring is
infertile/sterile]

41

Patterns of Evolution Based on Similarities Shared by Species


***Similarities could be due to genes or environment***

1. Divergent - [development of dissimilar traits in lineages of a common ancestor]
2. Parallel - [development of similar traits in genetically related species due to similar environmental factors]
3. Convergent - [development of similar characteristics in lineages with an unrelated ancestor due to similar environmental pressures]

42

Molecular Clock Model

A model that determines the approximate time of evolution between two species based on their genomic similarities.