Chapter 7: Cellular Replication and variation Flashcards
What is meiosis?
A two phase-type of cellular division to form 4 daughter cells
What are sex cells called?
Gametes
What is a locus?
The position a gene occupies in a chromosomes
What are homologous chromosomes?
Two copies of the same gene, not always the exact same
What is an allele?
Small differences in DNA sequence forming a different form from the other homologous chromosome
What is a genotype?
The alleles present in the cell of an organism. (Yy)
What is a karyotype?
Order by length, smallest to largest, display of homologous pairs (sister chromatids, joined at the centromere). One from father and one from mother. Page 141
What are matched sex chromosomes called?
Autosomes
What are females chromosomes and males chromosomes?
Females (XX), Males (Xy)
What is diploid?
Describes an organism comprising of two copies of each chromosome, 2n
What is a haploid?
Describes an organism comprising of one copy of each chromosome, n
What reduces chromosome numbers from (diploid) 2n to (haploid) n?
Meiosis, to produce egg and sperm
What produces chromosome numbers back to 2n from n?
Fertilisation to form a zygote
Where does Meiosis occur in plants?
Female and male parts
Where does Meiosis occur in animals?
Ovaries and testes
What happens at interphase?
DNA replication occurs resulting in sister chromatids attached at the centromere
What is the process of meiosis?
prophase, metaphase, anaphase and telophase
What is the process of prophase I?
Chromatin shortens and thicken, a spindle begins to form and attached to the centromere of each chromosome, homogenous chromosomes lie side by side (synapsis), they may coil around each other (now bivalent (visible)), later they move apart but non-sister chromatids remain in contact (chiasmata) and finally the nuclear membrane breaks now
What happens at metaphase I?
Homologous chromosomes move together to line up, still attached at chiasmata
What happens in anaphase I?
Maternal and paternal chromosomes are pulled towards opposite polls of homologous chromosomes by spindle fibres, sister chromatids remain joined at the centromere and move towards the same poll, the disjunction of each homologous pair happens independently of the others.
What happens in telophase I?
A haploid set of chromosomes can be seen at each poll, each chromosome still having a sister chromatid, the spindle breaks down, the cell starts to split and cytokinesis completes the first stage.
What happens at the end of meiosis I and before meiosis II?
Interphase, but DNA does not replicate
What happens in prophase II?
A new spindle forms
What happens in metaphase II?
Chromosomes move to the equator of the cell
What happens in anaphase II?
Sister chromatids separate and move to polls, chromatids become the chromosomes of daughter cells a
What happens in telophase II?
Spindle disappears, chromosomes de-condense, cytoplasmic division follows resulting in 4 haploid cells. Page 143
Describe the process of crossing over and recombination
During synapsis in prophase 1, the non-sister chromatids become attached at points called chiasmata. They exchange genetic material (crossing over), this recombination scrabbled the genetic material and rearranges the combinations of alleles on each homologous chromosome. This produces new genes and increases the genetic diversity of offspring. Page 144
what is oogenesis?
The process in the ovary that results in the production of female gametes
What is spermatogenesis?
The continuous production of sperm cells in the testis
Differences between oogenesis and spermatogenesis?
In oogenesis, cytokinesis in both meioses is unequal and produced 1 egg. Spermatogenesis produced 4 sperm in contrast. At birth women have all eggs to ever mature, men produce sperm at puberty. Sperm is produced continuously, whereas oogenesis has long breaks that can take more than 40 years between the beginning and end of meiosis I.
What happens at fertilisation?
Haploid cells fuse to create a diploid zygote. n to 2n
What is an independent assortment?
Maternal and paternal chromosomes act independently from homologous pairs during meiosis ensuring a mixture of maternal and paternal DNA
What does independent assortment do?
Increases the number of different combinations of genes, increase variety of children
What is random fertilisation?
Meiosis and fertilisation shuffle existing alleles into different combinations increasing the potential for different genotypes
