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Question 1

Identify starting cells and end product cells involved in meiosis and locate these cells in the human body.

Answer 1

1. GERM CELL and produces gametes.
2. Introduces genetic variation at 3 different stages = no 2 gametes are the same
3. Since cell ÷ occurs 2x during meiosis, 2xn = 4n (eggs or sperm)

Question 2

Relate the human life cycle to meiosis and mitosis

Answer 2

1. In a mature human (2n), eggs (n) are produced by meiosis in the ovary of a woman, or sperm (n) are produced by meiosis in the testis of a man.
2. Fertilization to form a zygote (2n)
3. Zygote divides by mitosis to produce a mature human

Question 3

Identify how and when meiosis decreases the ploidy in gamete production

Answer 3

• After fertilization, 2n number of chromosomes in cells
• During meiosis, the ploidy (number of sets of chromosomes) is reduced from diploid (2n) to haploid (n) in production of eggs and sperm
• With the successful union of egg and sperm, the normal diploid (2n) complement of chromosomes is restored

Question 4

Recognize, and give details for all events in each phase of meiosis, including tetrad formation, chiasmata and crossing over.

Answer 4

Tetrads : two homologous chromosomes, with a total of four sister chromatids held together by a structure named the chiasmata.

Meiosis I
- reduction division (2n → n) in which homologous chromosomes are separated

Prophase 1: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
Metaphase 1: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell
Anaphase 1: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell
Telophase 1: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells

Meiosis II
The second division separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I)

Prophase 2: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
Metaphase 2: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator
Anaphase 2: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles
Telophase 2: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells

https://qph.cf2.quoracdn.net/main-qimg-5bd15bee61f9b92e80becf0badc23493-lq

https://biologydictionary.net/wp-content/uploads/2016/12/Meiosis-Stages.jpg

Question 5

Identify unique features of meiosis; state the fundamental genetic differences between mitosis and meiosis

Answer 5

Mitosis results in two nuclei that are identical to the original nucleus. Meiosis, on the other hand, results in four nuclei, each having half the number of chromosomes of the original cell.

Question 6

Discuss how meiosis introduces genetic variation considering crossing-over, independent assortment and random fertilization.

Answer 6

• During fertilization, 1 gamete from each parent combines to form a zygote.
• each gamete contains a different set of DNA = unique combination of genes in the resulting zygote.
• In MI, crossing-over during P and independent assortment during A creates sets of chromosomes with new combinations of alleles.

Question 7

Identify Mendel’s three principles. Be prepared to support each principle with evidence from Mendel’s use of garden peas

Answer 7

1. Principle of segregation: A parent gives just one allele for a gene to each gamete they produce.
‘Aa’ parent = ‘A’ or ‘a’ gamete

2. Principle of dominance: when one gene hides the expression of the other, the expressed allele is DOMINANT; the hidden allele is RECESSIVE
AA X aa > Aa

3. Principle of independent assortment:
During gamete formation, different pairs of alleles segregate independently of each other.
Two traits A and B on separate chromosomes separate during meiosis will produce AaBb > 9:3:3:1 mixture of traits

Question 8

Demonstrate how Mendel determined each principle using the mono- and dihybrid crosses. Be able to identify the parental and first or second filial generation in any genetic cross. Define reciprocal cross.

Answer 8

1. Supporting evidence for Principle of simple dominance:
F1 has only purple flowers and; F2 sees white return thus white was hidden and not permanently blended or lost

2. Principle of segregation supported because white returned in F2: the purple and white alleles must have been present in the F1 generation (thus they did separate in meiosis)

The F1 (first filial) generation consists of all the offspring from the parents.

The F2 (second filial) generation consists of the offspring from allowing the F1 individuals to interbreed .

Reciprocal Cross: A cross in which the sex of two parents is reversed (not a sex-change operation)

Question 9

Describe the human somatic cells genetic make-up. Differentiate between autosomes and sex chromosomes.

Answer 9

In humans, somatic cells are diploid, meaning they contain two sets of chromosomes, one inherited from each parent.

• autosomes contain genes that are responsible for the determination of somatic characteristics
• sex chromosomes contain genes that determine sex and sex-related characteristics of an organism.