Inheritance 2

Question 1

Define homologous chromosomes

Answer 1

A pair of chromosomes in diploid cells. One inherited from mother, one from father. Same size, same genes in the same position but may have different alleles.

Question 2

What are the sex chromosomes

Answer 2

X and Y

Question 3

What are autosomes

Answer 3

All chromosomes except sex chromosomes

Question 4

What is a gene and what are the different types?

Answer 4

A gene is a specific DNA sequence that codes for a polypeptide
*Sex linked genes=genes on sex chromosomes
*Autosomal-linked genes=genes on autosomes
*Linked genes=all genes on the same chromosome. They are in a linkage group. Likely to be inherited together. (Not the same with sex/autosomal linked genes)

Question 5

What is an allele

Answer 5

An allele is a form of gene➡️ result of mutation

Question 6

What is a locus (plural loci)

Answer 6

Locus (plural: loci)=position of gene on chromosome

Question 7

Describe diploid cells

Answer 7

Diploid cells have two sets of chromosomes (2n) =2 copies of each gene = 2 alleles
*1 maternal and 1 paternal
* Somatic cells=all cells except for gametes
*In humans: 2n=46
➡️ Result of mitosis

Question 8

Describe haploid cells

Answer 8

Haploid cells have only one set of chromosomes (n) = Only one copy of each gene = 1 allele
*Gametes/germ cells except
*In humans: n=23
➡️ Result of meiosis

Question 9

When does meiosis occur and what is its importance?

Answer 9

Meiosis also known as reduction division occurs before fertilisation in sexual reproduction

Importance:
*To produce gametes/sex cells with half the no. Of chromosomes
*Maintain the diploid no. Of chromosomes in each generation
To produce genetic variation in offspring

Question 10

Describe what happens during prophase I of meiosis

Answer 10

• Condensation of chromatin/chromosome
  *Centrosomes move to opposite poles
• Nucleur envelope breaks down
  *Nucleolus disappears
• Spindle fibres form
  ➡️ Start attaching to centromere and pull

*synapsis occurs
➡️Process where homologous chromosomes pair up
➡️ Each pair is called a bivalent/tetrad

*Crossing over takes place between non-sister chromatids
➡️At chiasmata (singular: chiasma)

Question 11

What does crossing over mean

Answer 11

During synapsis; homologous chromosomes coil around each other intimately
*Remain in contact at chiasmata
*Site of crossing over: chiasma

*Part of chromatids break
*Reconnect to another non-sister chromatid

Result in:
➡️ Exchange of genetic material [NOT genes]
➡️ Linkage groups broken/linked genes on same chromosome are separated
➡️ Genetic variation

Question 12

Describe what happens during metaphase I of meiosis

Answer 12

*Centrosomes reach opposite poles
* Spindle fibres are fully formed
➡️ Attached to chromosomes at centromeres

*Bivalent/tetrads line up across equator/metaphase plate
➡️Chromosomes line up in pairs

*Independent assortment of homologous chromosome pairs occurs
➡️Each pair lines up independently of others on equator
➡️Results in gametes that are genetically unique

Question 13

Describe what happens during Anaphase I duringmeiosis

Answer 13

• spindle microtubules shorten
• homologous chromosomes separate
  ➡️ with central mirrors leading towards poles

*Centromeres DO NOT divide

Question 14

Describe what happens during telophase I and cytokinesis of meiosis

Answer 14

*Chromosomes reach the poles
*Chromosomes partially decondenses
*Nucleolus reforms
*Nucleur envelope reassembles
*Spindle fibres breaks down
*Cytokinesis occurs

*Number of chromosomes in each daughter cell are now halved
➡️2 haploid cells formed

Question 15

Describe cytokinesis in animal cells

Answer 15

In animals cells:
*Cell membrane drawn together
➡️By contractile ring of micro filaments
➡️Forms a cleavage furrow
➡️ Creating a drawstring effect

*Cell membrane fuses
*To divide cell into two
*Organelles are shared out

Question 16

Describe cytokinesis in plants

Answer 16

*Vesicles transported to equator
➡️ To form cell plate at equator
*Cell wall laid out

*Did cytoplasm divided into two

Question 17

Describe the brief interphase between meiosis I and meiosis II

Answer 17

*Called interphase II/interkinesis
* Growth
*Synthesis of protein and other substances
*No DNA replication

Plant cells go straight into meiosis II
*No reformation of nucleolus and Nucleur envelope

Question 18

Describe what happens during prophase II

Answer 18

*Condensation of chromatin
*Spindle fibres form
➡️ Start attaching to centromere
*Centrosomes move to opposite poles
*Nuclear envelope breaks down
*Nucleolus breaks down

Question 19

Describe what happens during metaphase II during meiosis

Answer 19

*Centrosomes reach opposite poles
* Spindle fibres are fully formed

*Chromosomes line up at the metaphase plate/ equator
*At right angles to first equator (right angle to first metaphase)

*Chromosomes attached to spindle fibres at centromere/Kinetochore

*Independent assortment of sister chromatids occurs

Question 20

Describe anaphase II

Answer 20

*Centromere of each chromosome divides
*Sister chromatids split at the centromere
*Spindle microtubules shorten
*Chromatids pulled to opposite poles
➡️With centromeres leading towards poles

Question 21

Describe telophase II and cytokinesis of meiosis

Answer 21

*Chromatids reach the poles
*Chromosomes decondense
➡️ Become long and thin

*Nucleolus reforms
*Nucleur envelope reassembles
*Spindle fibres breaks down

*Cytokinesis occurs

➡️ 4 haploid cells formed

Question 22

How does meiosis cause genetic variation?

Answer 22

1. Crossing over @ Prophase I
2. Random/Independent assortment of homologous chromosomes @ Metaphase I

*Each pair lines up independently of others on equator
*Possible combinations = 2^n
➡️Results in gametes that are genetically unique

3. Independent assortment of chromatids @ Metaphase II
4. Possible chromosome mutation