Genetics- Mendel and Meiosis Flashcards
State the Composition of Eukaryotic chromosomes
DNA coiled and condensed around proteins called histones
Define karyotyping
arrangement of chromosomes into homologous pairs
Distinguish between autosomes and sex chromosomes
autosome: chromosome that is not a sex chromosome (#1 to #22)
sex chromosome: chromosome that originates from productive organs (#23)
Describe the reduction division in terms of diploid and haploid numbers of chromosomes in meiosis
At the beginning of meiosis, the cell starts with a diploid, and at the end, 4 daughter cells are produced containing one haploid each
define homologous chromosomes
a pair of chromosomes that have the same size, centromere position, and staining position
Outline the process of meiosis
-Preceded by replication of chromosomes
-Single replication followed by two divisions
-Four daughter cells
-Each has HALF the chromosomes
Explain the steps of meiosis
- Interphase I: chromosomes replicate and two sister chromatids are attached at the centromere
- Prophase I: Chromosomes condense, synapsis occurs (homologous chromosomes come together), tetrad (complex of four sister chromatids), chiasmata (where non-sister chromatids are linked)
- Metaphase I: Tetrads align at the metaphase
- Anaphase I: Homologous separate but Sister chromatids stay connected
-Telophase I and Cytokinesis: Chromosomes reach opposite poles, cleavage furrows or cell plates divide the cell, and NO DNA replication occurs - Prophase II: Spindle apparatus forms, chromosomes move toward the equator
- Metaphase II: Chromosomes align at the metaphase
- Anaphase II: Centromeres of sister chromatids separate
Telophase II and Cytokinesis: Nuclei form at opposite ends of the cell, Cytokinesis occurs and produces 4 haploid daughter cells
Explain how meiosis results in effectively infinite genetic variety in gametes through crossing over in prophase I, independent Assortment, and Random fertilization (FRQ)
- crossing over: the exchange of genetic material between homologous occurs during prophase of meiosis I. Two homologous portions of two non-sister chromatids trade places at chiasmata. Produces chromosomes w/ genes from both parents
-independent Assortment: In metaphase I, the alignment of the homologous pair of chromosomes is random. 2^n possible combinations of chromosomes in gametes (n is haploid #)
-Random Fertilization: Sperm has 1 in 8 mill. Possible combos.Totals zygote with 1 in 64 trillion possible diploid combos.
Define gene, allele, and genome
-gene: units of hereditary info, made of DNA, on chromosomes
-allele: alternate forms of a gene
-genome: complete set of DNA (genetic material) in Organisms
Define gene mutation
mutation: changes in genetic material
a new mutation in the gene may have an effect on some or all traits simultaneously
What is a human pedigree?
-human pedigree: a family tree that shows the relationship among parents and children across generations
women: squares dominant: shaded
men: circles recessive: non-shaded
State Mendel’s Law of Segregation
Mendel’s Law of Segregation: allele pairs separate during gamete formation, one from each parent is passed on to offspring
Explain the relationship between Mendel’s Law of Segregation and Meiosis
The basis of Mendel’s Law of Segregation is the first division of meiosis (meiosis I) in which homologous chromosomes are separated
Define genotype
genotype: an organism’s genetic makeup. (Ex. Tt or TT or tt)
Define Phenotype
Phenotype : an organism’s expressed traits (Ex. tall or short)
Define dominant allele
Dominant allele: an allele that will be expressed if it is present (represented by capital letters)
Recessive allele
Recessive allele: an allele that will only expressed in the absence of a dominant allele (represented by lower-case letters)
Define codominant alleles
Codominant alleles: Inheritance characterized by full expression of both alleles in heterozygote
Define locus
Locus: specific location on a chromosome that contains a gene
Define homozygous
Homozygous: two identical alleles for a trait (TT or tt)
Define heterozygous
Heterozygous: two different alleles for a trait (Tt)
Define carrier
Carrier: heterozygous that carry the recessive allele
Describe the concept of incomplete dominance, multiple alleles, pleiotropy, and epistasis
-incomplete dominance: Dominant phenotype is not fully expressed, leading to intermediate dominance;
Does NOT support the blending theory
-multiple alleles: More than just two alternate forms of a gene (Ex. ABO blood group)
- pleiotropy: The ability of a single gene to have multiple phenotypic effects. Consequently, a new mutation in the gene may have an effect on some or all traits simultaneously
-epistasis: Interaction between two nonallelic genes in which one modifies the phenotypic expression of the other. These genes are sometimes called modifier genes.
Define polygenic inheritance and give two examples of such inheritance
polygenic inheritance: Mode of inheritance in which the additive effect of two or more genes determines a single phenotypic character
Ex. Skin color, hair color
