3.3 Meiosis Flashcards
What is meiosis and its significance in sexual reproduction?
Meiosis is a form of nuclear division that produces four haploid nuclei from one diploid nucleus, allowing for sexual reproduction where two diploid individuals each contribute half of their DNA to produce offspring with a new and unique combination of alleles.
What are the two cycles of division in meiosis?
The two cycles of division in meiosis are meiosis I and meiosis II, each divided into four phases: prophase, metaphase, anaphase, and telophase.
How does prophase I in meiosis contribute to genetic variation?
In prophase I of meiosis, homologous chromosomes pair up and form tetrads, undergoing crossing over where non-sister chromatids exchange equivalent segments of DNA, contributing to genetic variation.
What occurs during metaphase I and how does it promote genetic variation?
During metaphase I, homologous pairs move along the metaphase plate, showing random orientation towards the poles, which contributes to genetic variation by allowing for a random assortment of chromosomes to be distributed to each daughter cell.
Describe the process and significance of crossing over in meiosis.
Crossing over is a process during prophase I of meiosis where non-sister chromatids of homologous chromosomes exchange DNA segments at points called chiasmata, creating new combinations of alleles and contributing significantly to genetic variation.
What is non-disjunction and when can it occur?
Non-disjunction is an error during meiosis where homologous chromosomes or sister chromatids fail to separate properly, leading to gametes with an abnormal number of chromosomes, which can result in conditions like Down syndrome.
How do amniocentesis and chorionic villus sampling (CVS) differ?
Amniocentesis, performed between weeks 14 and 20, uses a needle to withdraw amniotic fluid for fetal cell karyotyping, while CVS, performed during weeks 10-13, extracts fetal cells from the chorion, both with varying miscarriage risks.
Explain the impact of maternal and paternal age on the incidence of chromosomal anomalies.
Studies show a positive correlation between the age of the mother during pregnancy and the incidence of chromosomal anomalies, with risks increasing sharply after age 30-34. A similar but less clear correlation exists with paternal age, particularly for conditions like Down syndrome.
Explain the pairing of homologous chromosomes during prophase I of meiosis.
During prophase I of meiosis, homologous chromosomes pair up, forming tetrads or bivalents. This pairing is essential for the process of crossing over, where non-sister chromatids exchange DNA segments, significantly contributing to genetic variation among offspring.
How does the fusion of gametes from different parents promote genetic variation?
The fusion of gametes from different parents combines two distinct sets of genetic information, introducing a new combination of alleles into the zygote. This process promotes genetic variation by mixing genetic material from both parents, ensuring offspring have a unique genetic identity.
Analyze the impact of parental age on the chances of non-disjunction and chromosomal abnormalities.
Studies have shown that the risk of non-disjunction and chromosomal abnormalities increases with parental age, particularly in mothers older than 35 years. This increased risk is attributed to the aging of reproductive cells, which may lead to errors in chromosome separation during meiosis, resulting in conditions like Down syndrome.
Why is DNA replicated before meiosis?
DNA is replicated before meiosis to ensure that each chromosome consists of two identical strands, known as sister chromatids. This replication is crucial as it prepares the cell for the complex process of meiosis, where these chromatids will be essential for the crossing over and segregation phases that ensure genetic diversity among the gametes produced.
What is the significance of each chromosome consisting of two sister chromatids in meiosis?
The presence of two sister chromatids in each chromosome during meiosis is significant for genetic diversity. It allows for the exchange of genetic material during the crossing over process in prophase I. This exchange leads to gametes with a unique combination of DNA, contributing to the genetic variation essential for evolution and adaptation.
