Question

Meiosis and Sexual Reproduction 1. What does meiosis ensure? 2. Do you think there is anything wrong with a 94 year old fathering children (I don't mean physically but maybe genetically for the child?): 3. What cells does meiosis happen in? 4. Contrast diploid number and haploid number: 5. What does "homologous chromosomes mean? 6. Look at the karyotype in Figure 10.1 - how many pairs of chromosomes are there in a "normal human? Why are there 2 at each number? What do the X chromosomes represent? 7. What is an allele? 8. What is crossing over? 9. In what phase does this happen? 10. How does this relate to the fact that many siblings look very different from each other? 11. What is independent assortment? 12. Fill out the chart below to compare Mitosis to Meiosis: Mosis Meiosis In what cells? Big Idea of daughter colle? Chromosome number Does crossing over Identical to parent and other daughter cells? 13. What is spermatogenesis? Where does it occur? 14. What is oogenesis? Where does it occur? 15. What are polar bodies?

Answer 1

1.

Meosis ensures that humans have the same number of chromosomes in each generation. It is a two-step process that reduces the chromosome number by half from 46 to 23 to form sperm and egg cells.

• Meiosis is used for just one purpose in the human body: the production of gametes sex cells, or sperm and eggs. Its goal is to make daughter cells with exactly half as many chromosomes as the starting cell.

2.

As seen in case of down syndrome in children with old mothers there is possibility of certain genetic disorders that can occur in children with older fathers also.

3.

Meiosis occurs in diploid cells.

• Meiosis occurs only in sexually reproducing organisms as it produces sex cells where it replicates the diploid cells to haploid cells.

4.

DIPLOID CELL	HAPLOID CELL
Diploid cells have two complete sets of chromosomes 2(23). They reproduce by mitosis.	Haploid cells have only one complete set of chromosomes 1(23). they are formed as aresult of meiosis.
The number of total chromosomes in diploid cell is 46.	The number of total chromosomes in haploid cell is 23.

5.

Homologous chromosomes are made up of chromosome pairs of approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci. One homologous chromosome is inherited from the organism's mother; the other is inherited from the organism's father.

example :The sex chromosomes in both males (X and Y) and females (X and X) are homologs.

6.

• 23 pairs of chromosome in humans.
• Two copies of chromosome 2, one copy inherited from each parent, form one of the pairs
• It represents about 800 protein-coding genes compared to the Y chromosome containing about 70 genes, out of 20,000–25,000 total genes in the human genome. Each person usually has one pair of sex chromosomes in each cell.

7.

An allele is a variant form of a given gene, meaning it is one of two or more versions of a known mutation at the same place on a chromosome.

Function. Genes are responsible for the expression of traits. Alleles are responsible for the variations in which a given trait can be expressed.

Gene Alleles Gene Locus Genk Caleles Homologous Chromosomes

8.

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis, which results in new allelic combinations in the daughter cells.These pairs of chromosomes, each derived from one parent, are called homologous chromosomes.

homologous chromosomes * crossover between non-sister chromatids non-sister chromatids * exchange of DNA between non-sister chromatids

9.

prophase I

Crossing over occurs between prophase I and metaphase I and is the process where two homologous chromosome non-sister chromatids pair up with each other and exchange different segments of genetic material to form two recombinant chromosome sister chromatids.

10.

After all, kids get their genes from the same parents. But brothers and sisters don't look exactly alike because everyone (including parents) actually has two copies of most of their genes. And these copies can be different. Parents pass one of their two copies of each of their genes to their kids. As crossing over occurs between two non-sister chromatids each from two parents that leads to different genes occurance.

11.

The Principle of Independent Assortment describes how different genes independently separate from one another when reproductive cells develop. During meiosis, the pairs of homologous chromosome are divided in half to form haploid cells, and this separation, or assortment, of homologous chromosomes is random.

During meiosis,( metaphase !) the pairs of homologous chromosome are divided in half to form haploid cells, and this separation, or assortment, of homologous chromosomes is random. This means that all of the maternal chromosomes will not be separated into one cell, while the all paternal chromosomes are separated into another. Instead, after meiosis occurs, each haploid cell contains a mixture of genes from the organism's mother and father.Recombination occurs during meiosis and is a process that breaks and recombines pieces of DNA to produce new combinations of genes.

Homologous chromosomes carrying T gene Homologous chromosomes carrying t gene Meiosis Paring of homologous chromosomes Segregation Gamete Gamete

12.

	MITOSIS	MEIOSIS
IN WHAT CELLS	Happens in somatic cells	Happens in Germ(sex) cells
BIG IDEA	The big idea to remember is that mitosis is the simple duplication of a cell and all of its parts.	During meiosis, four daughter cells are produced, each of which are haploid (containing half as many chromosomes as the parent cell).
n of daughter cell	02 daughter cells	04 daughter cells
Chromosome number	In each daughter cell 46	in each daughter cell 23
Does croosing over occur	no	yes
Identical to parent and other daughter cells	yes(as no cross over occurs and only duplicates are formed due to duplication of parent cell)	no(cross over takes place leading to different chromosomes of different genes)

13.

• Spermatogenesis is the process of the production of sperms from the immature germ cells in males.
• It takes place in seminiferous tubules present inside the testes.
• In humans, spermatogenesis takes place in the seminiferous tubules, which are an intricate system of tubules in the testes where spermatogenesis takes place. The seminiferous tubules of an adult human male can sometimes produce over 100 million sperm per day.

14.

Oogenesis, in the human female reproductive system, growth process in which the primary egg cell (or ovum) becomes a mature ovum. ... These cells, known as the primary ova, number around 400,000. The primary ova remain dormant until just prior to ovulation, when an egg is released from the ovary.

Oogenesis occurs in the outermost layers of the ovaries.

15.

Polar bodies form because the egg cell (oocyte) does not divide evenly. The resulting cells have the same DNA, but one is much smaller, called a polar body.This is the type of cell division that results in haploid cells. The cell with more cytoplasm becomes a mature ovum while the polar body usually dissolves.