Test 2 - Meiosis and Genetics Flashcards
- The lifecycle of a multicellular organism is?
a. The sequence of stages leading from adults of one generation to the adults of the next
- Humans are what kind of organism
a. Diploid organism
b. Contains two sets of chromosomes
- Human’s gametes are?
a. Haploid – having only one set of chromosomes
- Sexual life cycle involve an?
a. Alternation of diploid and haploid stages
- What happens in meiosis?
a. Haploid gametes are produced in diploid organisms
b. Two consecutive division occur, meiosis I and meiosis II, preceded by interphase
c. Crossing over
- Meiosis I
a. Homologous chromosomes separate
b. Prophase I – Methaphase I – Anaphase I – Telophase I/Cytokinesis
- Prophase I
a. Homologous chromosomes pair and exchange segments (cross over)
- Metaphase I
a. Tetrads line up
b. Microtubules attached to chromosomes
- Anaphase I
a. Pairs of homologous chromosomes split up
b. Sister chromatids remain attached
- Telophase I/ cytokinesis
a. Two haploid cells form: chromosomes are still double
b. Cleavage furrow develops
- Meiosis II
a. Sister chromatids separate
b. Prophase II – Metaphase II – Anaphase II – Telophase II and cytokinesis
- During another round of cell division (meiosis II), the sister chromatids separate to form?
a. Four haploid daughter cells, containing single chromosomes
- The chromosome theory of inheritance states that?
a. Genes are located on chromosomes
- The behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns which are?
a. 1. Law of segregation
b. 2. Law of independent assortment
- Where are genes located?
a. On chromosomes
- Homologous chromosomes have genes where?
a. At specific loci
- What is genetics
a. Branch of biology that deals with heredity and variation
b. The science that attempts to explain the similarities and differences that occur among related organisms
c. Explains the relationship between genes and traits
- Genetics explains life at the level of?
a. Molecules – Dna -> protein
b. Organisms – brown eyes
c. Populations – heterozygote frequency
- Why study genetics?
a. Genetics is relevant to many aspects of human life and society
b. Diseases
- Who is the father of genetics
a. Gregor mendel – planted pea pods
- Mendelian genetics consists of
a. Principle of dominance
b. Principle of segregation
c. Principle of independent assortment
- What is preformation, one early theory of heredity
a. The idea that an organism contains all of its future descendants, encased in increasingly miniature forms, like Russian nesting dolls
- Inheritance timeline 400 BC
a. Greek philosopher Hippocrates proposes that tiny particles from every part of the body of each parent became blended
- Inheritance timeline 350 bc
a. Aristotle dismisses Hippocrates theory – children do not always resemble parents
b. Theory still centers on mixing of “fluids” from each parent
- Inheritance timeline 1700s
a. Scientific thinking about reproduction is dominated by “preformation”
b. Idea that an organism contains all of its future descendants, encased in increasingly miniature forms, like Russian nesting dolls
- Inheritance timeline 1760s
a. Joseph kolreuter pioneers the scientific study of plant hybrids (a “cross” between parents of different varieites
- Inheritance timeline: 1780
a. English livestock breeder Robert bakewell pioneers the systematic breeding of sheep and cattle to obtain higher quality wool and fatter beef
- Inheritance timeline: 1800s
a. Idea of heredity as a “blending” process continues to dominate scientific thought until the late 1800s
- Inheritance timeline: 1856
a. An inquisitive friar named gregor mendel began conductin experiments that held the answer to the riddle
- In mendel’s time, biologists held to the theory of?
a. Blending inheritance – an offspring was an average of its parents
b. Substance (fluids) blended together to yield unique individual with traits from both parents
i. Green + yellow = lime
- The father of horticultural science?
a. Thomas Andrew knight, president of London horticulture society
- Who are the Two plant breeders that paved the way for mendel’s experiments
a. Thomas Andrew knight
b. John goss – English horticulturalist
c. Both were studying ediple pea, pisum sativum
- Why are edible pea or pisum sativum good study subject?
a. Short generation time
b. Small and easy to grow large numbers
c. Inexpensive
d. Numerous varieties available (easily observable traits)
e. Ability to cross fertilize and self fertilize
- Goss’ observation
a. The ability to make short plants is transmimtted from P to F1 to F2
b. Therefore, the F1 has the hereditary particles (genetic information) to make tall and short plants
- Mendel was the first person to?
a. Analyze patterns of inheritance instead of just guessing how traits were passed down from parent to offspring
- How is genetic information transmitted from one generation to the next
a. Not through blending
b. Passing of discrete heritable factors (genes)
- Gregor mendel deduced the fundamental principles of genetics which is?
a. Parents pass on tot their offspring discrete heritable factors (genes) that are responsible for inherited traits
- What did mendel do differently from goss with his garden pea?
a. Limited the number of variables
b. Quantified results
c. Developed possible models that could be tested
- How did mendel limit the number of variables?
a. Started with true breeding (pure breeding) varieties of plants…pure for a specific gtrait P (parental) generation
- Mendel set up experiments to answer?
a. Why do hybrids revert to parental phenotypes?
b. Can one predict the frequency of specific phenotypes in each generation?
c. Can these model studies provide foundation for explaining all heredity?
- Pattern of inheritance observed for genes located on ?
a. The autosomal chromosomes
- What are autosomal chromosomes?
a. ONLY chromosome 1 – 22 (not sex chromosome)
- By analyzing the pattern of autosomal inheritance mendel was able to?
a. Deduce the very existence of genes and their alternative forms
- Why did mendel chose the garden pea?
a. Available in many variant shapes and colors that could easily be identified and analyzed
b. Peas can either a) self pollinate (pollinate own ovules) or b) cross pollination: transfer pollen from one plant to the ovule of the second plant
- Mendel studied ?
a. 7 traits in the garden peas which had 2 mutually exclusive phenotypes
i. Round or ripe seeds
ii. Yellow or green seed interiors
iii. Purple or white petals
iv. Inflated or pinched ripe pods
v. Green or yellow unripe pods
vi. Axial or terminal flowers
vii. Long or short stems
- Procedure of mendel’s experiments
a. Mendel isolated pure breeding lines (true breeding) identical phenotypes are observed from generation to generation ( P – F1 – F2)
b. 7 pairs of pure lines for 7 characteristics, with each pair differing in only one characteristics…many different phenotypes
- Monohybrid crosses
a. A cross between parent plants that differ in only one trait/characteristics
b. Trait: flower color (purple vs white)
i. Parents: Purple x White
ii. F1 generation: all plants have purple flowers
iii. F2 generation: ¾ of plants have purple flowers, ¼ have white flowers
c. 3:1 ratio
- What we learned from mendel’s monohybrid crosses
a. The existence of genes
b. Genes are in pairs
c. Halving of gene pairs in gametes
d. Equal segregation
e. Random fertilization
- The existence of genes
a. Trait are determined by “discrete heritable factors” genes
- Genes are in pairs
a. Gene may have different forms (alleles) each corresponding to alternative phenotypes of a particular characteristic
b. In adult pea plant, each type of gene is present twice in each cell (gene pair)
c. In different plants, the gene pair can be of the same alleles or of differentn alleles,
- Alleles
a. Can be dominant or recessive (properties of the phenotype)
b. T = dominant
c. t = recessive
- homologous chromosomes
a. have genes at specific loci
b. have alleles of a gene at the same locus
- PP
a. Homozygous for the dominant allele
- pp
a. Homozygous for the recessive alleles
- Pp
a. Heterozygoes
- Halving of gene pairs in gametes
a. Principle of segregation
b. Each gamete carries only one member of each gene pair
c. To prevent the number of genes from doubling every time gametes fused (fertilization), mendel proposed that during gamete formation the gene pair halved
- Equal segregation
a. Principle of segregation
b. The members of the gene pairs segregate (separate) equally into the gametes
c. 50% of the gametes will carry one member of the gene pair, and 50% will cary the other (Tt)
- Random fertilization
a. The union of one gamete from each parent to form the zygote is random
- Principle of segration
a. The two alleles segregate during gamete formation (Aa) then the fusion of gametes at fertilization creates allele pairs again
- Genotype
a. The gentic make-up of an individual (allelic make up)
- Homozygote
a. An individual that carries two identical alleles of a particular gene
b. TT
c. tt
- Heterozygote
a. An individual that carries two different alleles of a particular gene
b. Tt
- Phenotype
a. The physical appearance of an individual as a result of its genotype
- Types of crosses
a. Monohybrid: single trait is being considered
b. Dihyrid: two traits are being considered at same time
- Punnett square
a. Named after british scientist reginald punett
- Phenotypic and genotypic ratios resulting from a monohybrid cross
a. Phenotypic classes: smooth: wrinkled: 3:1
b. Genotypic classes: SS:Ss:ss 1:2:1
- What is used to determine an unknown genotype?
a. A testcross
- Testcross
a. Mating between an individual of unknown genotype and a homozygous recessive individual
b. P_ x pp
- Dihybrid cross
a. Two genes: mating of parental varieties differeing in 2 characteristics
b. 9:3:3:1
c. Independent assortment of each other
d. Should make four types of gametes in equal numbers
- Summary of crosses
a. One trait – monohybrid: 3:1 F2 phenotypic ratio (1:1 test cross phenotypic ratio)
b. Two trait – 9:3:3:1 F2 phenotypic ratio (1:1:1:1 test cross phenotypic ratio)
- A particular trait or phenotypes is determined by?
a. A factor or gene
- What are the two forms of factors or alleles?
a. Dominant or recessive
- What is the principle of dominance?
a. When T and t co-exist in a plant, one observes the T phenotype
b. T: dominant
c. t:recessive
- what is principle of segregation
a. the wo alleles, T and t, separate segregate during gamete formation, then unite at random, one from each parent, at fertilization
- what is principle of independent assortment
a. the alleles of different genes segregate (assort) independently
- what are some complication when mendelian principles are extended to human populations?
a. Most traits are affected by more than one gene and cannot be analyzed using simple medelian genetics
b. Many single gene traits that can be followed cause rare diseases, rather than common phenotypes
- List some reasons why genetics is not straight forward
a. No pure breeding humans
b. Generation tie is long
c. No controlled matings
d. Siblings rarely mate to generate F2
- The rule of multiplication/ of probability
a. The probability of a compound event is the product of the separate probabilities of the independent events
- Mendel’s principles apply to the inheritance of many human traits such as? (there are dominant and recessive alleles)
a. Freckles, no freckles
b. Widows peak, straight hairline
c. Free earlobe, attached earlobe
- What is family pedigrees?
a. Shows the history of a trait in a family
b. Allows researchers to analyze human traits
- What is a carrier
a. A person with one copy of the allele for a recessive disorder and does not exhibit symptoms
- Many human traits show simple inheritance patterns and are controlled by?
a. Genes on autosomes
- What are autosomes
a. Chromosomes other than sex chromosomes X & Y
- Recessive disorders
a. Most human genetic disorder are recessive
b. Predict the probability of affected offspring likely to result from the marriage between two carriers (heterozygotes)
- Example of a dominant disorder
a. (some are caused by dominant alleles)
b. Achondroplasia: form of dwarfism
c. Symptoms: normal development of head and torso, but arms and legs are short
d. 1/25k people, only heterozygotes have the disease
e. Homozygous dominant genotype causes death of embryo
- 99.99% of population are?
a. Homozygous for the normal, recessive allele (aa): proves that dominant allele is not more plentiful in a population than corresponding recessive allele
- What are some patterns of genetic inheritance that are not explained by Mendel’s principles
a. Incomplete dominance
b. Multiple alleles
c. Codominance
d. Pleiotropy
e. Polygenic inheritance
f. Environment
- Incomplete dominance
a. F1 hybrids have an appearance in between the phenotupes of the two pure breeding parents
b. Example snapdragons
c. Phenotypic ratio and genotypic ratio same: 1RR, red:2 RR, Pink 1 R’R’, white)
- Hypercholesterolemia
a. Is a human trait that is incompletely dominant
b. Involves the recessive allele (h), where the condition characterized by dangerously high levels of cholesterol in the blood
- Multiple alleles/ codominance
a. Blood type
b. ABO blood groups in humans are examples of multiple alleles
c. Two of the human blood type alleles exhibit codominance, where both alleles are expressed in the phenotype
- Pleitropy
a. The impact of a single gene on more than one hereditary characteristic
b. Most of our genetic examples have been cases in which each gene specified only one hereditary characteristic
- Polygenic inheritance
a. The additive effects of 2 or more genes on a single phenotype (converse of pleiotropy, where a single gene affects several characteristics)
- Hypotherical example
a. Human skin pigmentation is controlled by 3 genes that are inherited separately
b. Dark skin allele for each gene A, B, C contributes 1 unit of darkness and is incompletely dominant to the other alleles a, b, & c
c. AABBCC = dark
d. Aabbcc = light
e. AaBbCc = intermediate
- Sex chromosomes
a. X and Y determine an individual’s sex
b. XX: female
c. XY: male
- Sex-linked genes
a. Any genes located on a sex chromosome
b. Were first discovered during studies on fruit flies
- Sex-linked disorders in humans
a. Recessive sex linked traits are expressed much more frequently in men than women
b. If a man inherits only one sex-linked recessive allele from his mother, the allele will be expressed
c. With a woman, she needs to inherit 2 alleles to exhibit the trait
d. Red-green color blindness: characterized by a malfunction of light-sensitive cells in the eyes
- Hemophilia
a. A blood clotting disease (failure of the blood to clot)
- The role of environment
a. Some characteristics such as eye color, appear to be almost entirely genetically determined
b. Other human characteristics result from combination of heredity and environment
- Role of environment examples:
a. Skin color, height, heart disease, cancer, alcoholism, etc
