Inheritance

Question 1

What is a homologous chromosome?

Answer 1

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

Question 2

What are sex chromosomes

Answer 2

X and Y chromosomes

Question 3

What are autosomes

Answer 3

Autosomes are all chromosomes except sex chromosomes

Question 4

What is a gene

Answer 4

A gene is a specific DNA sequence that codes for polypeptide

Question 5

What is a sex-linked genes?

Answer 5

Genes on sex chromosome

Question 6

What is an autosomal linked genes?

Answer 6

Genes on autosomes

Question 7

What are linked genes

Answer 7

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 8

What is an allele

Answer 8

A form of gene➡️result of mutation

Question 9

What is a locus

Answer 9

Locus plural loci is a position of gene on chromosome

Question 10

What is a diploid cell

Answer 10

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

Question 11

What is a haploid cell

Answer 11

Haploid cells have only one set of chromosomes (n)
= only one copy of each gene = 1 allele
* gametes/germ cells
In humans n=23
➡️ result of meiosis

Question 12

When does meiosis occur

Answer 12

Meiosis aka reduction division
Before fertilisation in sexual reproduction

Question 13

What is the importance of meiosis

Answer 13

• To produce gametes/sex cells with half the no. of chromosomes
• Mantain the diploid no. of chromosomes in each generation
• To produce genetic variation in offspring

Question 14

Describe what happens during prophase 1 of meiosis

Answer 14

• Condensation of chromatin/chromosome
• Centrosomes move to opposite poles
• Nuclear 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)
➡️ Results in exchange of genetic material

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

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

Result in:
➡️ Exchange of genetic material (NOT genes)
➡️ Linkage groups broken/ linked genes on same chromosome are separated
➡️ New combination of alleles within each chromosome
➡️ Genetic variation

Question 15

Describe what happens during metaphase 1 of meiosis

Answer 15

• centrosomes reach opposite poles
• spindle fibres are fully formed
  ➡️ attached to chromosomes at centromeres

*Bivalents/ tetrads line up across equator/ metaphase plate
➡️ chromosomes line up in pairs

*Independent assortment of homologous chromosome pair occurs
➡️ Each pair lines up independently of others on equator
➡️ e.g. could be red-blue or blue red
➡️ Results in gametes that are genetically unique

Question 16

Describe what happens during telephase one of meiosis

Answer 16

• chromosomes reach the poles
• chromosomes partially decondenses
• nucleolus reforms
• Nuclear envelope reassembles
• spindle fibres breakdown
• Cytokinesis occur
• number of chromosomes in each daughter cell are now halved
• Two haploid cells formed

Question 17

Describe what happens during cytokinesis in meiosis and animal cell

Answer 17

Cytokinesis is the division of cells cytoplasm

In animal cells:
* cell membrane drawn together
➡️ by contractile ring of microfilaments
➡️ forms a cleavage furrow
➡️ creating a drawstring effect

• cell membrane fuses
• to divide cell into two
• organelles are shared out

Question 18

Describe what happens to cytokinesis in plants during mitosis

Answer 18

In plants:
* Vesicles transported to equator
➡️ to form cell plate at equator
* cell wall laid down

• so cytoplasm divided into two
• Organelles are shared out

Question 19

Brief interphase between meiosis 1 and meiosis 2

Answer 19

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

*Plant cells go straight into meiosis ll
*No reformation of nucleolus and nuclear envelope

Question 20

Describe prophase ll in meiosis

Answer 20

P/S: Meiosis is just like mitosis

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

Question 21

Describe metaphase ll

Answer 21

*’Centrosomes reach opposite poles
* Spindle fibres fully formed

• Chromosomes line up at the metaphase plate/ equator
  *At right angles to first equator

*Chromosomes attached to spindle fibres at centromere/ kinetochore

*Independent assortment of sister chromatids

Question 22

Describe the anaphase ll of meiosis

Answer 22

• Centromere of each chromosome divides
• Sister chromatids split at the centromere

*Spindle microtubules shorten
* Chromatids move to opposite poles
➡️ With centromeres leading towards poles

Question 23

Describe telophase ll and cytokinesis of meiosis

Answer 23

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

*Nucleolus reforms
*Nuclear envelope reassembles
* Spindle fibres break down

*cytokinesis occurs

➡️ 4 haploid cells formed

Question 24

How does meiosis cause genetic variation?

Answer 24

1. crossing over at prophase one

*Between non sister chromatids of homologous chromosomes at chiasma

➡️ Exchange of genetic material (not genes)
➡️ linkage groups broken/linked genes on same chromosome are separated
➡️ new combination of alleles with an each chromosome so genetic variation

2. Random/ independent assortment of homologous chromosomes @ metaphase l

• each pair lines up independently of other on equator
• Possible combinations= 2^n
  ➡️ results in gametes that are genetically unique

3. Independent assortment of chromatids @ metaphase ll
4. Possible chromosome mutation
   *Faulty meiosis may cause changes to chromosome number or structure ➡️ New alleles

P/S: besides meiosis, fertilisation can also cause genetic variation!
This is due to;
Random mating
Random fusion of gametes

Question 25

Define genotype

Answer 25

Genotype= the alleles possessed by an organism
Gene=a specific DNA sequence that codes for polypeptide
*Represented by same alphabet 9e.g. B and b= same gene, different allele)

Allele=a form of gene ➡️ result of mutation
*Dominant allele represented by capital letter and always placed in front 9e.h. B)
*Recessive allele represented small letter and always places behind (e.g. b)

Question 26

Define phenotype

Answer 26

Phenotype:the observable characteristics of an organism
➡️ Can be influenced by genotype, environment

Question 27

Define homozygous and heterozygous

Answer 27

Diploid cells: 2 sets of chromosomes, so 2 alleles
*Homozygous= have two identical alleles of a gene
*Can be homozygous dominant 9e.g. BB) OR homozygous recessive (e.g. bb)
*Heterozygous= have two different alleles of a gene (e.g. Bb, NEVER bB)

Question 28

Define dominant allele

Answer 28

*Expressed in the phenotype even when only one copy of the allele is present
*Expressed in heterozygotes and homozygote for the allele (e.g. Bb and BB)

Question 29

Define recessive allele

Answer 29

Expressed in the phenotype only when two copies of the allele are present
* Expressed only in a homozygote for the allele (e.g. bb)

Question 30

Describe monohybrid cross

Answer 30

*Trait is controlled by 1 gene
*Mendel crossed a purebred tall pea plant and purebred short pea plant. Both are homozygous
*This is the parental (P) generation

*All resulting offspring in the F1 generation is tall
*Crossed offspring in F1 with each other (self-fertilisation)
*In the resulting F2, he obtained 787 tall and 277 short pea plants
*Aproxx. A ratio of 3:1

We can represent genetic crosses using a genetic diagram

Every genetic diagram must have:
1)Parental phenotypes
2) Parental genotypes
3) Gametes (you must circle gametes)
4) Offspring (F1) genotype and phenotype
You MUST draw a punnet square
R) Probability/ratio
Depends on what the question wants

Question 31

What must every genetic diagram have?

Answer 31

Every genetic diagram must have:
1)Parental phenotypes
2) Parental genotypes
3) Gametes (you must circle gametes)
4) Offspring (F1) genotype and phenotype
You MUST draw a punnet square
R) Probability/ratio
Depends on what the question wants

Question 32

What is a test cross

Answer 32

Test cross= method to determine exact genotype of a dominant phenotype organism
➡️ is it homozygous dominant or heterozygous for the gene?
➡️ cross with individual homozygous recessive for the gene
➡️ also known as a short plant (TT)

If the tall plant is TT:
*TT x TT
➡️ All offspring will be tall (Tt)

If the plant is TT:
*Tt x TT
➡️ offspring can be either tall (TT) or short tt) Escape room

Question 33

Define purebred

Answer 33

A cross of same purebred organisms always produce offspring with the same genotype. Homozygous individuals

Question 34

Define parental (P) generation

Answer 34

Initial generation

Question 35

Define F1 and F2 generation

Answer 35

F1 generation: stands for first filial generation/first set of offspring
Result of crossing w different purebreds (i.e. 2 homozygotes of different phenotypes). F1 offspring are all heterozygotes

F2 generation: offspring result of self pollination of F1 plants OR cross of 2 heterozygotes

Question 36

What is a test cross

Answer 36

Test cross is a method to determine exact genotype of a dominant phenotype organism. Cross with individual homozygous recessive for the gene(s).