AP Bio Exam 3 Flashcards
Heredity
The transmission of traits from one generation to the next
Variation
A different combinations in which genetic traits are passed down
Genetics
Scientific study of heredity and inherited variation
Genes
Hereditary units of coded information
Where is the genetic program encoded in
DNA (polymer of four different nucleotides)
Gametes
Reproductive Cells
Somatic Cells
All cells of the body except gametes
How many chromosomes do humans have
46
Locus
Location of a specific gene’s location along the length of a chromosome
Describe asexual reproduction
A single individual passes copies of all of its genes to its offspring without the fusion of gametes. Creates an exact clone.
Describe sexual reproduction
Two parents give rise to offspring that have unique combos of genes.
What happens to chromosomes during mitosis
They condense, enough to be visible. Thus, we can distinguish them by size, the position of the centromeres, and the pattern of colored bands
The 46 chromosomes of the human body have
Two chromosomes of each 23 types
Karyotype
An ordered display of chromosomes
What do homologous pairs share?
Same length, centromere position, and staining pattern
(Except for X, Y, chromosomes!)
What is an interesting notice about the X, and Y chromosome?
The X is much longer
Sex Chromosomes
The X and Y chromosomes that determine your sex
Autosomes
All other chromosomes outside of sex chromosomes
The number of chromosomes represented by a single set is denoted by the symbol
n
Diploid cell
Any cell with two chromosome sets (2n)
Diploid number for humans
46 = 2n
What do gametes contain?
Haploid cells (n = 23)
Diploid v. Haploid Cells
Haploid: Single set of chromosomes
Diploid: double set of chromosomes
Human Life Cycle
Two haploids (Sperm, n) and (Egg, n) join to make a diploid zygote (2n)
In the human life cycle, chromosome sets are
Halved in meiosis and doubled in fertilization
Somatic v. Gametic
Somatic: Diploid developed in mitosis (23 pairs of chromosomes)
Gametic: Haploid, developed by germ cells (23 chromosomes)
Fertilization
Fusion of nuclei in gametes
Zygote
Diploid made from two unique haploid sets
If gametes aren’t made during mitosis, how are they made?
Develop from germ cells in gonads (ovaries and testes)
Meiosis
Cell division that reduces the number of sets of chromosomes from two to one in gametes
Alternation of generations
Multicellular diploid and haploid stages called sporophyte. Meiosis in the sporophyte produces haploid cells called spores
Differences in sexual life cycles
Look at picture
Meiosis has two steps:
Meiosis I and Meiosis II
Similarities of Meiosis and Mitosis
Preceded by the duplication of chromosomes
During interphase
The way chromosomes segregate
Both the processes occur in the M-phase of the cell cycle.
In both cycles, the typical stages are prophase, metaphase, anaphase and telophase.
In both cycles, synthesis of DNA takes place.
Differences of Meiosis and Mitosis
Meiosis had two cell divisions instead of one
Four daughter cells (meiosis) vs. two (mitosis)
Genetic content
ONLY Meiosis: homologous chromosomes pairing up, crossing over, and lining up along the metaphase plate in tetrads
At anaphase I: it is homologous chromosomes, instead of sister chromatids, that separate
Allele
Different versions of a single gene at a corresponding loci
Prophase I
Prophase I: Chromosomes condense, centrosomes move and from spindles, nuclear envelope breaks down
Crossing over occurs: DNA molecules of nonsister chromatids are broken and rejoined
Chiasmata: X-shaped regions where crossovers have occurred
Metaphase I
Pairs of homologous chromosome arrange at the metaphase plate, one chromosome of each pair facing a pole
Kinetochores attach
What are the three major sources of genetic variation?
Crossing over, independent assortment, and random fertilization
Independent assortments contribution to genetic variation
Random orientation of pairs of homologous chromosome at metaphase of meiosis I.
A 50-50 chance of each pair being flipped one way or the other.
Roughly 8.4 million possible combinations of chromosomes
Separation of the homologous chromosomes in meiosis I ensures that each gamete receives a haploid
(1n) set of chromosomes that comprises both maternal and paternal chromosomes.
Crossing Over contribution to genetic variation
Crossing over makes recombinant chromosomes. Instead of each chromosome being exclusively paternal or maternal, they’re mixed.
During meiosis I, homologous chromatids exchange genetic material
Random Fertilization contribution to genetic variation
Random male and female gamete combinations lead to about 70 trillion types of zygotes.
Who is Gregor Mendel
A monk who studied mechanisms of inheritance in pea plants
Why did Mendel choose peas?
Distinguishable varieties (white vs. purple flowers, etc.)
Short generation times, and large amount of offspring.
Strict control of mating
True Breeding
Offspring only have the same variety of traits as the parent
ex. From purple parent, there is only purple children
Hybridization
Crossing two true breeds (ex. true breed white and true breed purple)
P Generation
True breed parents
(P for parental)
F1 Generation
Offspring when P generations are mixed
(First filial)
F2 Generation
Offspring of either self pollinated or cross pollinated F1 generation
Law of Segregation
Two alleles for a heritable character segregate during gamete formation and end up in different gametes
How did Mendel prove that the blending model is incorrect?
He showed that the F1 generation weren’t all pale purple, but rather either white or purple.
Mendel’s F2 generations almost always had a
3:1 ratio
Four parts of Mendel’s Model
- Alternative versions of genes account for variations in inherited characters
- For each character, an organism inherits two alleles of a genes, one from each parent
- If the two alleles at a locus differ, then one (dominant) determines the appearance, and the recessive does not appear noticeable.
- Law of segregation
Homozygote
Has a pair of identical alleles for a gene (PP or pp)
Heterozygote
Has two different alleles for a gene (Pp)
Phenotype
Observable traits
Genotype
Genetic Makeup
Character
Category in which there is distinguishable traits
(ex. hair color)
Trait
The varying types within a character
(ex. blonde, brunette, ginger)
Monohybrid
Heterozygous in one character ex. Yy
Monohybrid Cross
Crossing monohybrids (bro be fr)
Dihybrids
Heterozygous in two different characters
ex. YyRr (crossing them is a Dihybrid cross)
Dihybrid cross usually lead to a
9:3:3:1 ratio
Law of Independent Assortment
Two or more genes assort independently. Each pair of alleles segregates independently of any other pair of alleles during gamete formation
Multiplication Rule
To determine the probability (that two or more independent events will occur together) we multiple the probability of one event by the other event
P(A and B) = P(A) * P(B)
Addition Rule
The probability that any one of two or more exclusive events will occur is calculated by adding their individual probabilities.
P(A or B) = P(A) + P(B)
Complete Dominance
Phenotypes of heterozygote and dominant homozygotes are indistinguishable
Incomplete Dominance
Neither allele is completley dominant
Codominance
Both alleles affect the phenotype in separate, distinguishable ways
Pheiotropy
Most genes have multiple phenotypic effects
Epistasis
The phenotypic expression of a gene at one locus alters that of a gene at a second locus
ex. Lab fur color having black or brown pigments, but the gene to have the pigment distributed is different.
Quantitative characters
Instead of discrete traits in characters, they vary by gradient
Quantitative characters usually indicate
polygenetic inheritance
Polygenetic inheritance
An additive effect of two or more genes on a single phenotypic character (ex. skin color).
ex. AABBCC (very dark skin) aabbcc (very light), AaBbcC (middleish)
Carrier
Someone who carries a gene that is not expressed in them, but could be in offspring
Chromosome theory of inheritance
Mendelian genes have specific loci along chromosomes, which undergo segregation and independent assortment
Thomas Morgan
Studied fruit flies
Wild type
Most commonly observed phenotype for a species (red eyes for fruit flies)
Mutation phenotypes
Phenotypes that differ the normal wild types
Distribution of X and Y chromosomes in human gametes
All eggs carry one X, while half of sperm have X and half have Y
SRY
Sex-determining region of Y
Sex-linked gene
A gene located on either sex chromosome
X-linked genes
~1100 genes linked to the X chromosome
Y-linked genes
~78 genes linked to the Y chromosome
Barr body
The inactive X in each cell of a female that condenses into a compact object which lies on the inside of the nuclear envelope
ex. Discolored patches of tortoiseshell cats, and patches of lacking sweat gland skin in women who are heterozygous
Barr body example: cats
The early embryo carries an allele for orange fur and an allele for black fur. As cells divide, areas deactivate the black or orange allele, leading to spots of one or the other.
Linked Genes
Genes located near each other tend to be inherited together
Genetic Recombination
The production of offspring with combinations of traits that differ from those found in either P generation parent
Parental Types
Offspring that match either of the phenotypes of the parents
Recombinant Types
Offspring that make new combinational phenotypes of parents
Where can recombination occur?
The independent assortment of chromosomes give independent allele combos
Crossing over creates different allele locations from the original parents
Nondisjunction
Members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II
Aneuploidy
If either of an aberrant gametes unites with a normal one in fertilization, the zygote will have an abnormal number of a particular chromosome.
Monosomic
An aneuploid zygote that has no copy of a particular chromosome
(2n - 1)
Trisomic
A chromosome present in a triplicate in the zygote (2n + 1)
ex. down syndrome
Meiosis I nondisjunction leads to
n+1, n+1, n-1, n-1 daughters
Meiosis II nondisjunction leads to
n+1, n-1, n, n daughters
Polyploidy
More than two complete chromosome sets in all somatic cells. Common in plant kingdom (3n, 4n, 8n, etc.)
Deletion
Chromosomal fragments are lost
Duplication
A Chromosomal fragment attaches to a sister or non sister chromatid
Inversion
A chromosomal fragment may reattach to the original chromosome but in the reverse orientation
Translocation
A chromosomal fragment joins a nonhomologous chromosome
Where does breakage of a chromosome come from?
Errors in meiosis or damaging agents such as radiation
What does meiosis result in?
Daughter cells with half the number of chromosomes of the parent cell.
Are the X and the Y chromosomes homologous chromosomes?
No, they don’t carry the same type of genetic information
What “fundamental result” is shared by all life cycles regardless of type?
Genetic variation among offspring
What introduces novel (completely brand new) variation into a gene pool?
Mutation
How many unique gametes can be produced from independent assortment of chromosomes?
2^n
(humans, 2^23)
Outcome of Meiosis I
Two haploid daughter cells
Outcome of Meiosis II
Four haploid daughter cells
Anaphase I
Homologous chromosome of each pair separate
Telophase I and Cytokinesis
Two haploid cells form
When do tetrads occur
Prophase I
When do these occur in Meiosis?
synapsis
crossing over independent assortment
haploid
diploid
Synapsis: Prophase I
Crossing Over: Prophase I
Independent Assortment: Metaphase I
Haploid: After Cytokinesis in Meiosis I
Diploid: Meiosis I
Three Important Details of Mendel’s experiments
Controlling Plant Reproduction: Mendel could always ensure parentage of new seeds
Tracking “either-or” traits: Allowed for clear observation of results
Beginning with true-breeding plants: Ensured he knew what he was starting with
