Genes L9 Notes Flashcards by Jade Benita McLaughlin

What is population genetics?

• Population genetics:

- Study of the gene pool of a population over time

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What is molecular genetics?

• Molecular genetics:

- Study of the molecular structure & function of genes

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Describe factors involved in inheritance & gene function

• Inheritance & gene function:

Transmission of genes
Genotype vs. phenotype
Function of genes in organism

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What can genetics be applied for? Give examples

• Applications of genetics:
- Human genetics
Breast cancer research
- Plant breeding
Genetically modified crops
–>Creation of semi-dwarf (shorter) wheat in India-> less likely blown over -> more likely to grow.
- Analysis of biological processes
Eg. circadian rhythm ->period gene controlling circadian rhythms discovered ->
can modify rhythms of organisms.

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What is a gene?

• What is a gene?
- DNA molecule
Includes transcribed & non-transcribed regions
Includes exons, introns & gene regulatory regions
- Inherited
- Effects phenotype/physical characteristics of organism
- Located on chromosomes

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State the normal amount of haploid & diploid chromosomes in humans

• Humans

N=23 -> 23 haploid chromosomes
2N=46 -> 46 diploid chromosomes

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Distinguish between the two types of cell division

-	Mitosis:
Produce -> 2 genetically identical diploid daughter cells 
1 cell division
Occurs -> All tissues
-	Meiosis:
Produce -> 4 haploid gametes -> from diploid mother cell
2 cell divisions
Occurs -> gonads (ovaries/testes) only.

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What is the cell cycle?

• Cell cycle:

- Period between -> birth of cell -> division -> 2 daughter cells

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Briefly describe Meiosis

•	Meiosis:
-	G2 phase -> S phase cell cycle 
-	Meiosis I:
	Divides pairs of chromosomes
	Reductional division (chromosome no. halved)
	2 haploid (n) daughter cells 
-	Meiosis II:
	Divides sister chromatids
	Equational division
	4 haploid gametes

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Describe the process of meiosis I

 Meiosis I:
&raquo_space; 2n = 6.
&raquo_space;3 bivalents
-> each -> 4 chromatids.

        Prophase I: 
      Chromosomes condense
      Homologous chromosomes -> synapsis -> (pairing)
      Crossing-over -> genetic material -> non-sister chromatids -> each bivalent
        Metaphase I:
      Homologous chromosome pairs -> line up -> equator of cell. 
        Anaphase I:
      Homologous chromosomes -> separate 
           -> opposite poles of cell 
          -->sister chromatids -> still attached 
         Telophase I: 
      One of original pair -> homologous chromosomes 
          -> each pole of cell
         Cytokinesis I:
      Cells divide -> 2 haploid daughter cells 
          ->Each daughter cell -> chromosome -> 2 chromatids

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Describe the process of meiosis II

 Meiosis II:
Prophase II:
Chromosomes -> attach -> spindle
Metaphase II:
Individual chromosomes -> line up -> equator
Anaphase II:
Sister chromatids -> separate -> opposite poles of cell.
Telophase II:
Each haploid daughter cell -> 1 each type chromosome.

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Describe the process of meiosis

 Meiosis I:
&raquo_space; 2n = 6.
&raquo_space;3 bivalents
-> each -> 4 chromatids.

        Prophase I: 
      Chromosomes condense
      Homologous chromosomes -> synapsis -> (pairing)
      Crossing-over -> genetic material -> non-sister chromatids -> each bivalent
        Metaphase I:
      Homologous chromosome pairs -> line up -> equator of cell. 
        Anaphase I:
      Homologous chromosomes -> separate 
           -> opposite poles of cell 
          -->sister chromatids -> still attached 
         Telophase I: 
      One of original pair -> homologous chromosomes 
          -> each pole of cell
         Cytokinesis I:
      Cells divide -> 2 haploid daughter cells 
          ->Each daughter cell -> chromosome -> 2 chromatids

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State the consequences of meiosis

Independent assortment

Crossing over

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Describe independent assortment

 Independent assortment:
- Different arrangement of chromosomes -> lined up at equator of cell -> pulled to diff sides of cell -> metaphase
 Different combinations -> chromosomes -> gametes
2n different gametes -> generated -> independent assortment
->(n=haploid chromosome no.)

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Describe crossing over

Crossing over -> non-sister chromatids -> diff. homologous chromosomes
 New combinations of alleles
Recombinant chromatids -> chromatids which have crossed over during meiosis
Non-recombinant chromatids -> chromatids which have not crossed over during meiosis

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Describe the process of mitosis

•	Mitosis:
-	Prophase:
Chromosomes condense
Mitotic spindle formed -> (composed -> microtubules)
Nuclear envelope -> breaks down 
Chromosomes attach -> mitotic spindle 
-	Metapahse:
Chromsomes line up -> equator of cell
Sister chromatids -> attached -> opposite poles -> mitotic spindle
-	Anaphase:
Microtubules contract -> breaks bonds between sister chromatids
Sister chromatids pulled -> opposite poles of cell
-	Telophase:
Chromosomes spread out 
Nuclear envelope reforms
-	Cytokinesis

What is the centromere?

• Centromere
Assembles kinetochore
—>Attaches to microtubules

What is the telomere?

• Telomere

Stabilise ends of chromosomes

What are recombinant chromatids?

Recombinant chromatids -> chromatids which have crossed over during meiosis

What are non-recombinant chromatids?

Non-recombinant chromatids -> chromatids which have not crossed over during meiosis

What are the characteristics of a monohybrid cross?

•	Monohybrid crosses:
	1 gene loci 
2 alleles of gene 
Eg. Gene -> eye colour 
     -> Blue eyes (b) / brown eyes (B)
>>Inheritance -> 1 trait

What are the characteristics of a dihybrid cross?

•	Di-hibrid crosses:
-	2 different gene loci 
 2 alleles of each gene. 
Eg. Gene -> eye colour 
       -> Blue eyes (b) / brown eyes (B)
       Gene -> eye size 
       -> Small eyes (w) / Wide eyes (W)
>>Inheritance -> 2 traits

Phenotypic ratio of F2 generation offspring in monohybrid cross

3:1

Phenotypic ratio of F2 generation offspring in dihybrid cross

9:3:3:1

Offspring Genotypic % ratio -> homozygous parents (RR x rr)

100% heterozygous | -> All -> same genotype (Rr)

% of offspring genotypes & phenotypes -> homozygous parents (BB x bb)

100% Bb genotype | 100% Brown eyes phenotype

% of offspring genotypes & phenotypes -> homozygous parents (BBpp x bbPP)

100% BbPp genotype | 100% Brown eyes & Tanned skin genotype

What would the phenotypic & genotypic results of offspring be for these combinations of genotype. Explain why this is the case. (BBpp x bbPP) (BBPP) x (bbpp)

Phenotype: Both combinations -> 100% BbPp offspring Both combinations -> heterozygous offspring Both combinations -> Same physical characteristics

Homozygous mono & di-hybrid crosses will always result in -> 100% heterozygous offspring -> 100% offspring of same gentotype & phenotype Eg. RR x rr--> 100% Rr Eg. RRbb x rrBB -> 100% RrBb RRBB x rrbb -> 100% RrBb

What is the multiplication rule -> Mendel's theory of inheritance

>>Rules: Multiplication rule: - Random fertilisation - Independent events -> Probability -> event -> occurs in specific way Eg. Heterozygote -> Rr >>P(Heterozygote) = P(R) x P(r)

What is the addition rule -> Mendel's theory of inheritance

Addition rule: - Random fertilisation - Mutual event -> Probability -> event -> can occur in more than one way Eg. Dominant phenotype -> RR / Rr >> P(Dominant phenotype) = P(RR) + P(Rr)

What is Mendel's 1st law?

• Mendel’s 1st law: Principle of Segregation: Alleles of single gene equally segregate -> gametes

What is Mendel's 2nd law?

• Mendel’s 2nd law: Principle of independent assortment Alleles of different genes segregate independently into gametes

Outline the genotypes and phenotypes of offspring from generations 1 & 2 as a result of homozygous monohybrid cross

• Mating -> two homozygous individuals -> one dominant & one recessive  1st generation: YY & yy 4 x Yy genotypes -> 100% heterozygous Yy F1 (First filial) offspring -> same genotype (Yy) & phenotype (yellow) F1 -> first-selfed / self fertilised  2nd generation: Yy & Yy 1 x YY ; 2 x Yy ; 1 x yy F2 (Second filial) offspring -> 3 different genotypes -> 1:2:1 -> 2 different phenotypes -> 3:1 >>> 3:1 phenotypic ratio -> 2 alleles -> same gene.

Outline the genotypes and phenotypes of offspring from generations 1 & 2 as a result of homozygous dihybrid cross

• Mating -> two homozygous individuals -> one dominant & one recessive  1st generation:  RRyy & rrYY  100% RrYy genotype  100% Round, yellow phenotype F1 (First filial) offspring -> same genotype (RrYy) & phenotype (Right-handed & yellow) 2nd generation:  RrYy x RrYy >> 9:3:3:1 phenotypic ratio  9 Round yellow / 3 round green / 3 wrinkled yellow / 1 wrinkled green

Outline the genotypes and phenotypes of offspring from generations 1 & 2 as a result of homozygous monohybrid cross & homozygous dihybrid cross

``` Mono: 1st generation: YY & yy 4 x Yy genotypes -> 100% heterozygous Yy genotype -> 100% yellow phenotype 2nd generation: Yy & Yy -> 2 different phenotypes > 3:1 phenotypic ratio Di: 1st generation: RRyy & rrYY  100% Heterozygous RrYy genotype  100% Round, yellow phenotype 2nd generation:  RrYy x RrYy -> 4 phenotypes >> 9:3:3:1 phenotypic ratio ```