midterm 1 Flashcards
(199 cards)
1
Q
genetics
A
experimental study of heredity/genes
2
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gene
A
fundamental unit of heredity
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genome
A
all the genetic material of a chromosome set
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mutation
A
a change in DNA sequence
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allele
A
an alternative form of a gene (resulting from a mutation)
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genotype
A
the specific allele composition of a cell
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phenotype
A
outward characteristic of a specific genotype
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chromatin
A
the substance of chromosomes; now known to include DNA and chromosomal proteins
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histone
A
a type of basic protein that forms the unit around which DNA is coiled in the nucleosomes of eukaryotic chromosomes
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nucleosome
A
the basic unit of eukaryotic chromosome structure; a ball of eight histone molecules that is wrapped by two coils of DNA
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dominant phenotype
A
the parental phenotype that is expressed in a heterozygote
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dominant allele
A
an allele that expresses its phenotypic effect even when heterozygous with a recessive allele; thus, if A is dominant over a, then A/A and A/a have the same phenotype
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recessive phenotype
A
the parental phenotype that is not expressed in the heterozygote
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recessive allele
A
an allele whose phenotypic effect is not expressed in the heterozygote
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first filial generation (F1)
A
the first generation resulting from a controlled cross between two known parents (P)
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Second filial generation (F2)
A
the second generation resulting from a controlled cross between two known parents (p), generated by selfing/intercrossing the F1 generation
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heterozygous
A
a cell/organism having different alleles at a given gene (A/a)
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homozygous
A
= true breeding
a cell/organism having identical alleles at a given gene (A/A or a/a)
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monohybrid
A
an individual heterozygous at one gene (A/a)
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monohybrid cross
A
a cross between two individuals identically heterozygous at one gene pair (A/a x A/a)
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product rule
A
the probability of two independent events occurring simultaneously is the product of their individual probabilities
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sum rule
A
the probability that one or the other of two mutually exclusive events will occur is the sum of their individual probabilities
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test cross
A
a cross of an individual organism of unknown genotype or a heterozygote with a tester
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tester
A
an individual organism homozygous for one or more recessive alleles
used in a test cross
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gamete
a specialized haploid cell that fuses with a gamete of the opposite sex or mating type to form a diploid zygote
in mammals
an egg or a sperm
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diploid
a cell having one chromosome set or an individual organism having two chromosomes sets in each of its cells
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haploid
a cell having one chromosome set or an organism composed of such cells
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sister chromatids
the juxtaposed pair of chromatids arising from the replication of a chromosome
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homologous chromosomes
chromosomes that pair with each other during meiosis and (usually) have the same genetic loci (may have different alleles)
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meiocyte
a cell in which meiosis takes place
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dyad
a pair of sister chromatids joined at the centromere
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tetrad
(1) four homologous chromatids in a bundle in the first meiotic prophase and metaphase
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chiasma
a cross-shaped structure commonly observed between nonsister chromatids in meiosis
the site of crossing over
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molecular marker
a site of DNA heterozgosity (difference), not necessarily associated with phenotypic variation
used as a tag for a particular chromosomal locus
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sex chromosome
a chromosome whose presence is correlated with the sex of an individual
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autosome
any chromosome that is not a sex chromosome
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homogametic sex
the sex with homomorphic sex chromosomes (XX)
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heterogametic sex
the sex that has heteromorphic sex chromosome (XY)
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hemizygous gene
a gene that is present in only one copy in a diploid organism
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reciprocal crosses
a pair of crosses of the type genotype A (female) x genotype B (male) and B (female) x A (male)
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Sex linkage
The location of a gene on a sex chromosome
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Independent assortment (mendels 2nd law)
-Unlinked or distantly linked segregating gene pairs assort independently at meiosis
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dihybrid
an individual heterozygous at two genes (A/a, B/b)
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dihybrid cross
a cross between two individuals identically heterozygous at two gene pairs (A/a, B/b x A/a, B/b)
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chi-square test
a stat test used to determine the probabilty of obtaining observed proportions by chance, under a specific hypothesis
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null hypothesis
a hypo that proposes no difference between two or more data sets
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recombination
The process that generates a haploid product of meiosis whose genotype is different from either of the two haploid genotypes that constituted the meiotic diploid
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recombinant gamete
any gamete with a genotype that differs from the genotypes of the two haploid parents that fused to form the diploid meiocyte
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parental gamete
any gamete with a genotype identical to one of the haploid parents that fused to form of diploid meiocyte
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maternal inheritance
a type of unparenital inheritance in which all the progeny have the genotype and phenotype of the parent acting as the female
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What is genetics?
the study of heredity proformed using a set of principles and analytical procedures
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What are genes?
Basic units of biological info that transmit traits from parents to offspring
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traits
-any biological, physical, or behavioral characteristic
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What are genes composed of?
Double helical DNA
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mutation
a change in DNA
-caused by errors in replication and proof-reading machinery
-exposure to mutagens (chemicals, UV, x-rays)
creates a new version of gene
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characteristics of organisms that are commonly used in genetic analyses
-small size
-large numbers of progeny
-small genome
-representative
-short generation time
-easily maintained
-diploid
-varieties with varying traits available
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Chapter 1 - summary
-genetics is the study of heredity
-genes are basic units of heritable biological info
-genes are composed of DNA that:
-stores info that can be transformed into cellular structures/functions ( DNA -> RNA -> proteins)
-faithfully replicates
-has the ability to change over time to create raw material for selection and evolution
-study of mutations has model organisms that help uncover molecular to ecological questions
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Packaging of DNA in chromosomes
-the supercoiled packaging of DNA in chromosomes makes this possible
-chromosomes of chromatin consists of DNA and proteins for packaging to control expression of genes
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How is DNA packaged?
chromosomal DNA is wrapped around histones (protein octamer) to form nucleosome
nuleosomes associate with and coil around H1 histone to make a solenoid
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each chromosome is made of-
1 molecule of DNA
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What are the 3 patterns of inheritance
autosomal variation
sex-linked inheritance
cytoplasmic inheritance
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autosomal variation
the phenotypic variation arising from the genes located on regular chromosomes (autosomes)
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sex-linked inheritance
the phenotypic variation arising from the genes located on sex-determining chromosomes
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cytoplasmic inheritance
the phenotypic variation arising from the genes located on organellar chromosomes
-mitochondria and chloroplasts (plants)
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pure-breeding lines/pure lines
lines which do not show variation in a particular phenotype over generation
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crosses:
a cross is a way to introduce traits/genes from one variety or line into a new genetic background
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parental and filial generations:
Parents are parental generation (P)
-first generation that arises from a cross -> first filial generation (F1)
- subsequent generations arising from selfing -> F2 -> F3 -> ....Fn
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Complete dominance
alleles which, when combined in the heterozygote show a phenotype indistinguishable from one of the homozygotes
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haplo-sufficency
one copy of the normal gene is able to confer a normal phenotype
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haplo-insufficiency
one copy of the normal gene is unable to confer the normal phenotype
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codominance
alleles which, when combined in the heterozygote show phenotypic characteristics of both homozygotes
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lethal allele
an allele whose expression results in the death of the individual expressing it
can be ressesive or dominant
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pleiotropic mutation
a mutation that affects several different phenotypic characteristics
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prototroph
an organism that will survive on minimal medium (carbon source, inorganic salts, water)
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auxotroph
an organism that will not survive on minimal medium, but whose growth depends on supplementation of medium with a specific substance
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complementation test
a test for determining whether two mutations are in different genes (they complement) or the same gene (they fail to complement)
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heterokaryon
a cell composed of different nuclear types in a common cytoplasm
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epistasis
the phenotype of a mutant allele at one gene overrides the phenotype as the first mutant
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suppression
a mutation in one gene can cancel the effect of a mutation in a second gene, resulting in a wild type phenotype
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genetic redundancy
-duplicate genes
-two independent genes that produce the same phenotypic effect when present individually or when present together
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penetrance
the proportion of individuals with a specific genotype who show that genotype phenotypically
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expressivity
the degree to which a particular genotype is expressed in the phenotype
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a hereditary factor is
a gene that is responsible for each phenotypic character
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each parent contains-
2 copies (alleles) of each factor
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parental lines =
pure lines
-have 2 identical alleles
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each parent contributes -
1 copy of each factor to offspring with equal frequency (mendels first law of equal segregation)
-gametes are haploid (one allele of each gene) and fuse to form diploid (2 alleles of each gene) offspring
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F1 contributes ____ to F2 ___
1 allele to F2 offspring with equal frequency
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random fusion of gametes results in-
4 equally frequent combinations
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a test cross
a cross between an unknown genotype and homozygous recessive parent for the same locus
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for monohybrid crosses
-if an individual heterozygous for one gene (A/a) is selfed (A/a x A/a), a 3:1 phenotypic ratio and 1 (AA) : 1 (aa) genotypic ratio will result
-if an individual heterozygous for one gene is testcrossed (A/a x a/a), a 1:1 phenotypic and genotypic ratio will result
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probability= product (AND) rule[
the probability of independent events occurring together is equal to the product of their individual probabilities
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if you tossed 2 coins, what is the probability of getting 2 heads?
coin 1 = 1/2
coin 2 = 1/2
1/2 x 1/2 = 1/4
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Probability- Sum (OR) Rule
the probabilty of either one OR the other mutually exclusive events occurring is equal to the sum of their individual probabilities
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if you tossed two coins, what is the probability of getting 2 heads and 2 tails
heads on coin 1 and coin 2 = 1/2 x 1/2 = 1/4
tails on coin 1 and coin 2 = 1/2 x 1/2 = 1/4
probability of getting 2 heads OR 2 tails 1/4 + 1/4 = 1/2
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mendel
-each individual has 2 copies of each factor and passes one copy to their offspring with equal frequency
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Muntjac genome
organized into 6 chromosomes
3 homologous pairs
diploid (2n) = 6
haploid (1n) = 3
gene pairs - 1 member on each chromosome 2 allelles of genes A,B, and c on red chromosomes
2 alleles of gene T,P on purple chromosome
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sexual life cycles (involving cell fusion) have to -
reduce the genome from 2n to n prior to fusion event
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cellular division
mitosis (making cell copies)
meiosis (reductional cell division to make gametes)
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cell cycle - S phase
-synthesis phase
DNA synthesis generates identical DNA molecules = sister chromatids
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Key points for S phase
S Phase is for DNA synthesis
DNA content is doubled
Each DNA molecule (chromosome) is copied to make 2 daughter DNA molecules
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Cell cycle- M phase
mitosis and meiosis
Pass my amazing taco, chief
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Mitosis -interphase and prophase
Early stage: chromosomes condense, and shorten
late stage:
sister chromatids joined at the centromere visible
nuclear membrane breaks down, spindle fibres attach to the kinetochore of the centromere
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Meiosis, interphase and prophase 1
Leptotene
zygotene
pachytene
diplotene
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Leptotene
meiosis
chromosomes condense, and shorten
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zygotene
meiosis
chromosomes starts to align with the homologous partner
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pachytene
meiosis
chromosomes are fully synapsed (aligned)
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diplotene
meiosis
crossing over occurs between the non-sister chromatids
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synapsis during meiosis
synaptonemal complex proteins guide pairing of homologous chromosomes based on sequence similarity
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crossing over during meiosis
the exchange of genetic material between the non-sister chromatids to introduces new allelic combination
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separation of chromatids driven by microtubules attached to centromere via kinetochore
-kinetochore is a multiprotein complex that binds to centromere
-site of attachement for microtubles extending from poles
-after anaphase checkpoint (all centromeres attached) microtubules depolymerize at kinetochore, drawing chromatids apart
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a hereditary factor (gene) is responsible for-
each phenotypic character
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haploid phase
for organisms that have a haploid life cycle
is predominant (undergoes mitotic divisions)
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how do alleles result in different phenotypes?
alleles are variants of the genes sequence resulting from mutation
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a gene may have many different variants or alleles, depending on-
the nature of the mutation, an allele may or may not be associated with a phenotype
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null allele
no functional gene product formed
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leaky allele
some functional gene product
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silent allele
no change in gene product function
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mutant alleles may be-
recessive (more common) or dominant (less common)
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haplosufficient
one wild type gene copy is sufficient to confer the wild type phenotype
-loss of funtion mutations of haplosufficient genes are recessive
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wild type alleles make ____ units, ___ are required for normal function for haplosufficient
12 units
10
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haploinsufficient
one wild type gene copy is not enough to confer the wild type phenotype
-loss of function mutations of haploinsufficient genes may be dominant
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wild type alleles make ___ units, ___ are required for normal function for haploinsufficent
12 units
20
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wild type alleles are indicated either by -
uppercase letters or by +
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Sex chromosomes
special chromosomes
-determine the sex of the individual
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sex of an individual is correlated with-
presence/absence of these chromosomes
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non-sex chromosomes are called-
autosomes (A)
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human females and males have ____chromosomes
females = 2 X chromosomes
44AA + XX = 46 chromosomes
44AA + XY = 46 chromosomes
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pseudoautosomal region
sequence similarity allows pairing between X and Y chromosomes during meiosis in male cells
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Differential regions of X and Y chromosomes
regions that have different sequence
this region accounts for sex linkage
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phenotypes associated with the genes on the-
sex chromosomes (usually x)
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characteristics controlled by sex linked genes show different-
phenotypic ratios in males than in females
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how to identify sex-linkage of a phenotype
monohybrid crosses, reciprocal crosses yeilded identical results
in the case of red and white eyes files, reciprocal crosses yielded different results (diagnostic for sex linkage)
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phenotype is correlated with-
SEX
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indications of sex linkage
reciprocal crosses show different results
phenotype is correlated with sex
-different sexes have different phenotypic ratios
(overall males more commonly show recessive traits)
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Square shape meaning
male
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circle shape meaning
female
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dimonad shape meaning
unknown gender
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coloured in shape meaning
affected individual
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a line between shapes meaning
mating between individuals
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pedigree symbols
the shape to show gender and trees and such jazz
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characteristics of autosomal recessive traits
-the phenotype appears in progeny of unaffected parents
-affected progeny includes both male and female
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characteristics of autosomal dominant traits
-the phenotype appears in each generation
-affected parents can have affected and unaffected kids
-affected progeny includes both male and female
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pedigree analysis for an autosomal dominant phenotype
-if the trait is dominant, all unaffevcted individuals must be homozygous recessive
-affected individuals must have dominant allele
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many human diseases are caused by -
mutations in single genes
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inconsistent inheritance patterns
expressivity
penetrance
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expressivity
-the degree to which trait expression differs among individuals
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penetrance
proportion of genotypes that show expected phenotypes is called penetrance
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sympols for a dot inside of shape
carrier of sex-linked recessive
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symbols for a line across shape
death
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shapes with have filled in
heterozygotes for autosomal recessive
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a small filled in circle with a line on top
abortion or still birth
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filled in shape with arrow
propositus
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shapes with two lines connected to it
consanguineous marriage
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shapes with numbers in it
the number of kids of the sex indicated
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shapes with a trangle type lines connected to eachother
dizygotic (nonidentical twins)
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shapes with a trangle type lines (full)
monozygotic (identical twins)
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X chromosome inactivation
permanent inactivation of one of the 2 X-chromosomes in all cells, except the egg cells
(calico cats)
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mendels first law of equal segregation
-during gamete formation, members of a gene pair segregate equally
-monohybrid self-cross- Yy x Yy results in 3:1 phenotypic ratio
-monohybrid test cross - Yy x yy results in 1:1 phenotypic ratio
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Mendels second law of independent assortment
-during gamete formation, the segregation of alleles of one gene is independent of the segregation of the alleles of another gene
ex- Allele Y has equal probability of combining with R or r
-4 possible gametes (YR, Yr, yR and yr) in equal frequency
-dihybrid self-cross results in a 9:3:3:1 phenotypic ratio
-digybrid test cross- results in 1:1:1:1 phenotypic ratio
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chi-square (X2) test
-allows us to determine if progeny fit expected ratios
-a statistical test to determine if the observed results are significantly different from the expected
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1st step in X2 test
develop a null hypothesis (H0)
-genes Y and R are independently assorting and the dihybrid cross progeny DO NOT significantly deviate from the expected 9:3:3:1 ratio
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2nd step for X2 test
calculate the X2 value
X2 = E (observed - expected)2 / expected
= E (O-E)2/ E
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3rd step for X2 test
determine the degrees of freedom (df)
df = n - 1
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4th step for X2 test
determine the probability (p)
compare the caluclated chi-squared value to the critical value from the table
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5th step for X2 test
evaluate the null hypothesis
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if X2 is smaller than critcial value then p =
is bigger than 0.05 so we fail to reject the null hypothesis
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if X2 is bigger than critcial value then p =
is smaller than 0.05 so we reject the null hypothesis
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recombinants are-
meiotic output different from meiotic input
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parentals- meiotic output-
identical to meiotic input
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polygenic inheritance
traits that show continous variation quantitative phenotypes, distribution in a pop is bell-shaped
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as number of genes contributing to the polygenic trait increases, the histogram approaches -
continuous variation
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cytoplasmic inheritance
inheritance of traits associated with non-nuclear genome
phenotype of offspring depends on genotype of maternal (egg) cytoplasm (white, green, variegated depending on pop. in flower/megaspore)
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cytoplasmic segregation
cells can have hundreds of organelles, each carrying multiple copies of the genome
-accumulation of mutatinos in organellar genome gives to cytohets or heteroplasmons
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mendels findings
one gene controls a single phenotype (character)
one gene has two alleles
one allele is dominant to the other
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mendels gene interactions : monhybrid
selfed:
3:1 (1:2:1)
test-crossed
1:1
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mendels gene interactions : dihybrid
-where two genes are independently assoring (A/a; B/b)
selfed: 9:3:3:1
test-crossed: 1:1:1:1
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polygenic inheritance
more than one gene may control a single characteristic
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polyploid organisms
a gene may have multiple alleles, sometimes resulting in different phenotypes
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pleiotropic genes
a gene may control more than one characteristic
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Case I:
MOST COMMON
wild-type allele is fully dominant to the mutant allele
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haplosufficiency
one wild type allele is sufficient to show phenotype in heterozygous state.
-mutated alleles are recessive
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what case is haplosufficeny from?
case I
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what case is haploinsufficency from?
case II
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Case II
mutant allele is fully dominant to the wild type allele
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Explanation I for case II
haploinsufficiency
-one dose of the wild type allele is not enough to show wild type phenotype
-muatated (null) allele is DOMINANT
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explanation II for Case II
the mutant allele (dominant negative) makes the wild-type allele non-functional
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mutation confers a new function to the gene
neomorphic alleles
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cases where one allele is not completely dominant over the other
-incomplete dominance
-Co-dominance
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if the heterozygote has a phenotype distinct from either homozygote, the phenotypic ratio will be-
the same as the genotypic ratio
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what does a heterozygous individual have between the phenotype of two homozygous individuals?
a phenotype intermediate
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two wild type allele 'doses' produce the -
largest amount of gene product
-largest amount of functional protein product
-large amount of pigment (red flowers)
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a single wild type allele dose produces-
only half gene product
-less functional product
-less pigment (pink flowers)
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codominant allele
heterozygous individual has a phenotype showing characteristics of both homozygous individuals
ex: blood groups
-blood grouping involves interaction between antigen (on the red blood cell surface) and antibody (in plasma)
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complete dominance
the heterozygous individual is indistinguishable from the homozygous dominant individual
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incomplete dominance
the heterozygous individual has a distinct phenotype from either homozygous individual
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codominance
the heterozygous individual has phenotypic characteristics of both homozygous individual
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conditional alleles
phenotype expressed under one condition (restrictive), but not in another condition (permissive)
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penetrance
the % of individuals with a given genotype who exhibit the phenotype associated with that genotype
% expression of a phenotype is allelic combination carrying pop.
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