exam 3 (review slides) Flashcards
asexual vs sexual reproduction
asexual reproduction: a single individual passes all of its genes to its offspring without fusion of gametes
asexually reproducing individuals gives rise to clone, offspring that are genetically identical to parent
sexual reproduction: 2 parents give rise to offspring that have unique combinations of genes inherited from 2 parents
offspring vary genetically from their siblings and both parents
each pair of homologous chromosomes includes _______________
1 chromosome from each parents
how many chromosomes in human somatic cells and how many are autosomes? also what chromosomes determine sex of offspring?
- 46 chromosomes in a human somatic cell
- 2 sets of 23: one set from mother, one set from father
- XX is female, XY is male
diploid & haploid cell
diploid cell has 2 copies of each chromosome = 2n (formed by mitosis)
for humans, diploid number is 46
haploid cells contain only copy of each chromosome = n (formed by meiosis)
nonsister chromatids vs sister chromatids
main difference in structure
sister chromatids are two exactly similar copies of a chromatid, with the same genes (only aa or BB)
non-sister chromatids are chromosome couples having the same length, patterns and position of the centromere, but have mixed genes (like a B)
in a cell in which DNA synthesis has occurred, each chromosome is _______________
each __________ chromosome consists of 2 _______________
replicated
replicated
identical sister chromatids
how is the number of daughter cells different in mitosis and meiosis?
mitosis produces 2 daughter cells, whereas meiosis produces 4 daughter cells
explain the difference between meiosis I and meiosis II, which occurs first?
meiosis I occurs first
meiosis I (reductional division): homologous chromosomes pair up and separate, resulting in 2 haploid daughter cells with replicated chromosomes
meiosis II (equational division): sister chromatids separate resulted in 4 haploid cells with unduplicated chromosomes
what are homologous chromosomes? (for your knowledge)
pairs of chromosomes that carry genes for the same traits, with one chromosome inherited from each parent
synapsis
pairing up of homologous chromosomes during meiosis, forming structures called tetrads, where each chromosome aligns with its corresponding partner from the opposite parent before genetic material is exchanged between them (crossing over)
slide says: DNA breaks are repaired, each broken end is joined to corresponding segment of the nonsister chromatid, producing crossovers (nonsister chromatids exchange DNA segments)
when does crossing over occur?
prophase I
what is chiasmata?
plural of chiasma, X-shaped point of attachment where paired homologous chromosomes exchange genetic material
what is a tetrad?
2 pairs of homologous chromosomes next to each other
each pair of chromosomes forms a tetrad, a group of 4 chromatids
- each tetrad usually has 1 or more chiasmata
mitosis _______ the number of chromosome sets, while meiosis _________ the number of chromosomes sets
conserves; reduces
what 3 events are unique to meiosis that all occur in meiosis I?
- synapsis and crossing over in prophase I
- alignment of homologous pairs at the metaphase plate: whereas in mitosis individual chromosomes line up at the metaphase plate
- separation of homologous chromosomes during anaphase I: sister chromatids of each duplicated chromosome remain attached, whereas in mitosis chromatids separate
what are the 3 mechanisms that contribute to genetic variation?
- independent assortment of chromosomes
- crossing over
- random fertilization
how do you carry out a test cross and what is it used for?
- to determine the genotype
testcross: breeding individual of unknown genotype with a homozygous recessive individual
- if any offspring display recessive phenotype, unknown parent must be heterozygous
law of segregation (Mendel)
each individual organism has two alleles for each gene & alleles segregate during the formation of gametes
result: each gamete carries only one allele for each gene, and when fertilization occurs, the offspring inherits one allele from each parent. This process contributes to the variation in traits among offspring.
chat gpt answer ^
how did mendel derive his law of segregation and law of inheritance?
- law of segregation derived by following a single trait
- heterozygous for 1 character (single gene of interest), monohybrid cross
- law of inheritance by following 2 character traits at the same time
- heterozygous for both characters (2 genes of interest)
dihybrid cross: a cross between 2 F1 dihybrids, determines whether 2 characters are transmitted to offspring together as a unit or independently
law of independent assortment (mendel)
- using a dihybrid cross, Mendel developed the law of independent assortment
states that each pair of alleles segregates independently of any other pair of alleles during gamete formation
- applies only to genes on different, nonhomologus chromosomes or those far apart on the same chromosome
- genes located near each other on the same chromosome tend to be inherited together
mendel’s model (thats the name of this slide but really im asking what those 2 important points about genes are but I dont think he discovered this stuff)
- alternative vision of a gene = allele
- different alleles have different DNA sequences at the same locus on a pair of homologous chromosomes
- each gene resides at a specific locus on a specific chromosome
- DNA at locus can vary slightly in its nucleotide sequence, which can affect the function of encoded protein and this an inherited character of organism
describes mendel’s experiments with the white and purple flowers
- Mendel crossed contrasting, true-breeding white-and purple flowered pea plants (P generation) = all F1 hybrids were purple
- Mendel crossed F1 hybrids = many of F2 plants had purple flowers, but some had white
- Mendel discovered a ratio of about 3 purple flowers to 1 white flower in F2 generation (3:1)