Studied by 5 peopleWhat are chromosomes?
Strands of DNA & proteins inside the nucleus (eukaryotic).
What are histones?
Carriers of genes located on specific portions of chromosomes.
Types of cells
Diploid and Haploid cells.
What are diploid cells?
2 sets of chromosomes; mitosis; homologous; all body/somatic cells.
What are homologous sets?
Chromosomes with the same number and types of genes; one from mom and one from dad.
Haploid cells
1 set of chromosomes; meiosis; reproductive/gamete cells—sperm/egg.
What does meiosis do?
Cuts down the number of chromosomes in a cell; results in four haploid cells; makes sexual reproduction possible.
Two stages of meiosis
Meiosis 1 & 2
Each contain 4 phases—prophase 1 & 2; metaphase 1 & 2; anaphase 1 & 2; Telophase 1 & 2
What occurs during Meiosis 1?
Chromosomes undergo replication prior to 1st phase, which is known as interphase 1; replication only occurs once; replicated chromosomes pair and are attached at the centromere; separation of homologous chromosomes.
What occurs during Prophase 1?
Homologous (mom/dad) chromosomes pair and form tetrads; 4 chromatid each; process called crossing-over occurs as chromosomes pair (ONLY PROPHASE 1); spindle fibers form and attach to tetrads.
What is the process of crossing-over?
Chromatids cross and exchange genes, which increases genetic variation.
What is gene linkage?
Chromosomes are groups of linked genes, and genes located close together on the same chromosome will be inherited together; chromosomes assort independently, not genes.
What occurs during metaphase 1?
Paired homologous chromosomes line up along the equator.
What occurs during anaphase 1?
Spindle fibers pull homologous chromosomes to opposite ends of the cell.
What occurs during telophase 1?
Nuclear membrane forms around each cluster; cytokinesis follows; forms two new daughter cells; each daughter cell contains 2 of each chromosome.
What does Meiosis 2 do?
Neither cell replicates the DNA—NO INTERPHASE; Meiosis 2 separates sister chromatids.
What occurs during prophase 2?
Chromosomes become visible; each chromatid attaches at the centromere; tetrads do not form; there is NO crossing-over since the homologous chromosomes were already separated; spindle fibers form and attach to centromere of each chromosome.
What occurs during Metaphase 2?
Chromosomes line up at the center of each cell.
What occurs during anaphase 2?
Chromatids separate and move to opposite ends of each cells.
What occurs during telophase 2?
Nuclear membranes form around each cluster of chromosomes; cytokinesis occurs after and produces 4 haploid cells, each with 23 chromosomes; the 4 haploid cells have one set of chromosomes each.
What are male gametes called?
Sperm
What is the production of 4 sperm with every round of meiosis 1 & 2 known as?
Spermatogenisis; 4 haploid cells change shape & grow flagella.
What are female gametes called?
Eggs/ova
What is the production of 1 egg with every round of meiosis 1 & 2 called?
Oogenesis; 4 haploid cells that are unequal in size (1 large egg, 3 smaller polar bodies).
What happens to the 3 smaller polar bodies that are produced from the 4 haploid cells?
They do not survive.
What is Fertilization?
The fusion of sperm & egg to create a genetically unique combination of genes; a new cell called a zygote is produced.
What occurs to the zygote that is produced from fertilization?
It undergoes mitosis, repeatedly, to become a new organism.
Key aspects of mitosis.
Doesn’t change chromosome #; produces genetically identical diploid cells; form of asexual reproduction.
Key aspects of meiosis.
Reduces the number of chromosomes; produced genetically unique haploid cells (from crossing-over); step in sexual reproduction.
What is the delivery of characteristics from parent to offspring called?
Heredity
What is the scientific study of heredity?
Genetics
What are genetics key to?
The understanding of what makes each organism unique.
Who is Gregor Mendel?
Austrian monk who studied pea plants and changed biology forever.
What are pea plants known as?
They are known as the “model system.”
Why are pea plants the model system?
Because they are small, easy to grow, and produce hundreds of offspring.
What are the roles of fertilization in pea plants?
Male part of plant makes pollen, which contains plant’s sperm; female part produces eggs
Pea plants reproduce
Asexually, because the sperm and egg are from the same plant; they self pollinate.
What is fertilization?
Male and female reproductive cells joining.
What is “true breeding”?
When the offspring are identical to the parent; means traits of each generation are the same.
What are traits?
Specific characteristics (example-plant height)
How was Mendel able to see how traits are determined?
He cross-pollinated two true-breeding plants; he did this by removing the male part and dusting the female part with pollen from a different plant.
What did cross-pollinating allow Mendel to do?
Breed plants with traits different from those of their parents, which created a cross of parents with different traits. These cross of parents are called hybrids.
How many traits did Mendel study?
He studied 7 different pea plant traits.
What is the P generation?
The original parent generation.
What is the F1 generation?
The first filial (offspring of P).
What happened every time Mendel crossed the P generation?
A version of a trait seemed to disappear in the F1 generation.
Mendel wanted to know what happened to the version of the trait that was missing, so he
Crossed the F1 generation.
What happened when Mendel crossed the F1 generation?
It resulted in the F2 generation, and the missing trait that was lost before reappeared in 1/4 of F2.
What is a version of a gene called?
An allele.
Example of 2 alleles that determine a plant’s height.
Short & tall.
Some alleles are .. and some alleles are ..
Dominant and recessive.
What is segregation?
During gamete formation alleles or each gene separate from one another.
Conclusion of Mendel’s experiments.
An individual’s characteristics are determined by factors being passed from parent to offspring.
What are factors called
Genes, and different versions of genes are alleles.
What is the Principle of Dominance?
Organism with at least one dominant allele exhibit that trait; organism with recessive allele will only exhibit that trait if dominant is not present.
What are dominant alleles represented with?
Capital letters.
What are recessive alleles represented with?
Lowercase letters.
What is probability?
The likelihood that a particular event will happen.
What are punnet squares used for?
Use of mathematical probability to help predict the outcome of genetic crosses.
Heterozygous genes
Two different alleles for the same traits; Contains a dominant and recessive allele.
Homozygous genes
Two identical alleles for the same trait; can be homozygous dominant or homozygous recessive.
Define genotype.
Genetic make up; inherited from a parent.
Define phenotype
Physical trait; result of environment and inherited genotype.
Even if two organisms have the same phenotype, it doesn’t mean they’ll have the same ..
Genotype
Genotypic ratio
Ratio of genetic makeup present; when writing ratio, dominant alleles go first.
Phenotypic ratio
Ratio of physical characteristics; dominant allele goes first when writing the ratio.
Law of Independent Assortment
The genes of different traits can segregate independently during gamete formation.
How did Mendel test the Law of Independent Assortment theory?
He followed two different genes as they passed from parent to offspring.
Dihybrid cross
Two-factor cross
What did Mendel conclude on the Law of Independent Assortment?
Genes that segregate independently do not influence each other’s inheritance.
What did Mendel’s traits form?
The basis of modern genetics.
Inheritance is determined by genes passed from
Parent to offspring
Most organisms carry .. copies of the gene. Separated from one another during gamete formation and are usually independent of one another.
Two
What can the basic principles of Mendelian genetics be used for?
To study inheritance of human traits & to calculate the probability of certain traits appearing in the next generation.
Exceptions to Mendel’s Principles
Some alleles are neither dominant nor recessive because many exist in several forms and have multiple alleles, which causes incomplete dominance, co-dominance, multiple alleles.
Many traits are produced by interaction of several genes, which causes
Polygenic traits
What can Mendel’s principles NOT predict?
Traits controlled by multiple alleles or multiple genes.
What is incomplete dominance?
When neither allele is dominant; one allele is not completely dominant over the other.
Where does the heterozygous phenotype lie in incomplete dominance?
Somewhere between two homozygous phenotypes.
What is codominance?
When phenotypes produced by both alleles are clearly expressed.
Erminette
When black feathered chickens crossed with white feathered chickens produce speckled chickens with white and black feathers.
What are multiple alleles?
Genes with more than two alleles (example- human gene for blood).
Polygenic traits
Traits controlled by two of more genes; show a wider range of phenotypes.
Why are characteristics not determined solely by genotype?
Because genotype only provides a “blue print.”
Phenotype is partly determined by
Environment.
Where is an organism’s full set of genetic information carried?
In its DNA
Study of .. starts with chromosomes.
Genomes
What do biologists use to study genomes?
Karyotypes
What are karyotypes?
A picture that shows a complete diploid set of chromosomes; grouped in homologous pairs; arranged in order of decreasing size.
Cells are photographed in mitosis when chromosomes are fully ..
Condensed.
Two of the 46 chromosomes are known as ..
Sex chromosomes
Male sex chromosomes.
One X and one Y; determine the sec of the organism; half sperm carry X and half carry Y; ensures 1/2 zygotes will be male and 1/2 will be female.
Female sex chromosomes.
Two X chromosomes; ova only carry X
How many genes are found on the X chromosome?
More than 1200.
How many genes are found on the Y chromosome?
Only about 140; most associated with male sex determination and sperm development.
Aside from the two sex chromosomes, what are the remaining 44 chromosomes called?
Autosomes
Genes located on Y chromosome are found only in males, meaning they are ..
Passed directly from father to son.
Genes located on X chromosome are found in both sexes. Since males have only one X chromosome, recessive phenotypes tend to be ..
More common in male (example-color blindness).
In females, most genes on one X chromosome is randomly switched
Off, which forms a dense region in nucleus called Barr body.
Dense region in nucleus called Barr body is generally not found in males. Why?
Their one X chromosome is always active.
Note
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